Which System?
Do-it-yourself fuel injection usually involves transferring the
necessary parts from an injected version of the same or very similar
engine. Although I haven’t done it, updating a Chevrolet small block
with throttle body or tuned port injection should be a fairly
straightforward project, since most of the engineering is already in
place.
The 18RGU engine has no fuel-injected successor. Whatever system
selected would require lots of fitting and serious tuning. Pulsed,
computer-driven systems seemed uninviting, since the old man has only
a hearsay knowledge of digital electronics. What you don’t know, you
have to buy. A programmable CPU – the electronic equivalent of
changing carburetor jets and centrifugal advance springs -- costs
$2000.
I opted for a Bosch mechanical system, generally known as the CIS
(continuous injection system). "Continuous" means that the
injectors emit a constant stream of fuel, once past pop-off pressure.
The earliest, or K-Jetronic, versions of the system were purely
mechanical. The one selected includes a small computer to meet
emissions requirements and improve cold running. Omitting the computer
has no serious consequences on driveability.
Hot and cold idle rpm and, to some degree, mixture strength are
manually adjustable. Hardware modifications can provide additonal
mixture control.
Major components – fuel distributor, throttle body, auxiliary air
device, injectors, thermal/time sensor and warm-up regulator – came
a from 1984 VW 1.7-liter sohc Rabbit. In retrospect, a Volvo or Saab
CIS would have been a far better choice for the fuel-hungry 1.8-liter,
dohc Toyota with oversized valves, hemispheric combustion chambers and
pop-up pistons.
The conversion described here is not very elegant. The exercise was a
learning project with fixes tried, abandoned and sometimes retained
with the aim of achieving an acceptably rich mixture at all speeds and
loads. The 18RG was never an economical engine and oversized valves
installed during the recent overhaul have made it less so. I knew that
an extremely rich mixture, registering something on the order of 900
millivolts on the oxygen sensor, was required to stabilize the idle.
What flexible, responsive cruising might take was a matter of
conjecture, but it would be far more than the 0.500 volt described in
the literature as chemically perfect.
CIS Pros and Cons
The CIS is a reliable and fairly inexpensive system to work with --
the high pressure pump rarely fails, if protected by a filter on the
suction side and supplied with clean, water-free fuel. Running the
pump dry will quickly fry it. Injectors appear to be quite reliable
and, to some minor extent, respond to cleaning with laquer thinner.
New ones list at around $38 apiece, or about a third as much as you
would pay for more modern examples. The fuel distributor is the most
expensive part, with $500 or so asked for rebuilt examples. But
millions of functional distributors reside in junkyards.
Because it is mechanical, the CIS is tweakable to some degree,
although serious modifications are easier to talk about than to make.
Bosch provides adjustments for idle and low-speed mixture control.
Adapting components from different applications allows room for
maneuver, especially as experience is developed with the system.
On the debit side, the learning curve is fairly steep. Few
professional mechanics understood the technology when it was new, and
fewer still can cope with the problems of transplants. Nor will you
encounter much by way of shade-tree wisdom. You're pretty much on your
own.
CIS occupies a great deal of underhood space, making for a busy engine
compartment. First priority is to rout lines clear of the exhaust
manifold and armored OEM lines clear of coil terminals and other
voltage sources. The fuel filter should be accessible and, if under
the car, adequately shielded. Tie down the heavy fuel distributor with
removable brackets so that changing out the air filter does not become
a major project. Mate the throttle body to the fuel distributor with
any of the various OEM rubber sleeves. Couple these parts as close
together as possible for good throttle response. You should, for the
sake of the engine, install an oxygen sensor close by the exhaust
manifold, whether or not you run a computer with the KE. When you're
done and all the parts are in place, it would be nice to be able to
see the ignition distributor and reach the oil filter.
To my way of thinking, the worst aspect of CIS is its potential for
fire. Most of the plumbing, including the feed line running the length
of the car from the tank to the engine bay, contains gasoline under
high pressure. OEM plastic fuel lines fail if crimped or merely as a
function of age and handling. There is no automatic shutdown when
pressure is lost: the pump will run until the engine stops.
Like modern technology generally, fuel injection improves reliability
while introducing a small, but real, potential for catastropic
outcomes. The price is vigilance: fuel lines must be routed safety,
made up to the appropriate connections, armored against abrasion with
plastic sheathing, and routinely inspected.
Information Sources
The basic documentation – theory of operation and
troubleshooting/repair procedures – can be had from any of a dozen
sources. But one would have to resort to industrial espionage to
obtain engineering data for this or any other fuel injection system.
- Automotive Electric/Electronic Systems,
Robert Bosch GmbH,
1988, licensed to the Society of Automotive Engineers, Inc., ISBN
0-89883-509-7. This book gives a general overview of the systems and,
read carefully, reveals some of the design concerns.
- How to Tune & Modify Bosch Fuel Injection,
Ben Watson, MBI
Publishing, I992, ISBN 0-87938-570-7. The author provides pressure
data for all applications and, while skimpy on modifications,
incorporates tips and shortcuts developed by working mechanics
- ALLDATA. This subscription-only database is intended for
technicians, but similar information on the CIS can be found in shop
manuals of the 1970s and 80s.
- http://www/Google.com. This
metasearch engine currently lists 2400 entries for CIS, mostly
dealing with theory of operation and troubleshooting.
- Miller Fuel Injection
adapts CIS to air-cooled VW engines on a commercial basis. Gary
Miller probably has more experience with CIS transplants than anyone
in the country and is more than happy to share what he has learned.
- Do-It-Yourself Electronic Fuel
Injection hosts the EFI332 mailing list. Most contributors are
interested, obcessed, with GM electronic units, but discussions of
CIS and other mechanical systems are included. Bosch
Manifold is a nice website with a beautifully crafted adaptation
of a Volvo CIS to a Type IV VW engine. The author maintains a file
on CIS conversions.
Notes on Components
Fuel Distributor Assembly. This component consists of the fuel
distributor (the part that mounts the cylinder injector, warm-up
regulator, cold-start injector, inlet and tank-return lines),the
air-flow sensor ("flap valve") and air filter element.
All distributors have a central horizontal port in the head for fuel
delivery to the warm-up regulator and four vertical injector ports.
The central port also functions as a test port for delivery and
control pressure readings. Gary Miller identifies three generations of
K-series fuel distributors by the pattern of connections on the sides
of the units. As I understand it, the view is looking down on the
distributor with the center outlet in the head at the 12 o'clock
position.
- First Generation -- fuel filter inlet at 10 o'clock, feed to
cold-start injector taken at the same port; return to tank and
return from warm-up regulator share the port at 1 o'clock.
- Second Generation -- fuel filter inlet at 11 o'clock; return to
tank at 8 o'clock; return from regulator at 9 o'clock; cold-start
injector feed at 7 o'clock.
- Third Generation (computer)-- fuel filter inlet at 11 o'clock;
return to tank at 8 o'clock; return from warm-up regulator at 9
o'clock;cold-start injector feed at 7 o'clock. These units, which
Gary modifies, have a blocked oxygen-sensor port at 4 o'clock.
Injectors.
Bosch has a special tool for removing injectors, but a large, flat-bladded
screwdriver works about as well. Exercise care why prying injectors out
of junkyard vehicles. Rust and heat-hardened o-rings make it easy to
inadvently bend the injector barrel.
The injectors should howl audibly and produce a flat, fan-shaped
pattern; an offset pattern can be tolerated, so long as the fuel does
not congeal into a stream. Injector delivery volume is critical. The
Bosch test requires a container graduated in cc's and a timed pump run.
For a quick test, you can use baby food jars as catch pans, run the pump
for a few seconds, and line up the jars on a flat working surface to
compare the fluid levels.
Injector dribble under reduced pressure makes for difficult hot starts,
never a CIS strong point. Most of the hot-start problem appears to be
the result of percolation, which can be helped, but not cured, by
mounting the injectors in the threaded plastic sleeves used by
Volkswagen.
According to Bosch, the o-rings should be installed dry and rolled over
the injector barrels. Silicone may help, since new o-rings fail upon
repeated removal and installation. Normally, o-rings come out with
injectors. Green (nitrile) aftermarket o-rings appear to give better
service than the OEM black rings.
Fuel Filters. Some type of filter, preferably incorporating a water
trap, should be installed upstream of the pump. The OEM filter should be
on the discharge line and mounted where it will be accessible. Some CIS
applications include a check valve, intergral with the banjo-connection
bolt, on the discharge side of the filter. Although the 10-mm bolt and
valve assembly can thread into the inlet connection at the fuel
distributor, to mount it there results in erratic performance. For the
check valve to function properly, gasoline must enter the center hole in
the bolt and exit through the radial holes.
Auxiliary Air Device. The open-loop, K-Jetronic version of this device
employs thermostatically controlled air vent which automatically opens
when the engine is cold. The surplus air, taken from some point between
air vane and throttle plate, increases idle speed. As the engine warms,
the combined effects of an electric heating element and engine heat
cause the vent to close.
For the device to work properly, it should mounted on the intake
manifold where it will be warmed and with the port adjacent to the
connection feeding air into the engine. The line from the remaining port
connects to a port at the rubber sleeve or at the throttle body, above
the throttle plates. Connection pins are ungrounded, which means that
you can use either of the two leads can for B+.
Warm-Up Regulator. The warm-up regulator reduces regulating fuel
pressure to enrichen the mixture during cold operation. It normally
bolts to the engine block at some position well clear of the exhaust
manifold. One may also mount it remotely and provide heat by connecting
heater hoses to the mounting fixure. The regulator also incorporates one
or more electrical heating elements, which accelerate warm-up period.
Merely disconnecting the heaters has no long-term effect upon mixture
strength, since engine heat finally determines pressure. Should you
disable the engine-heat sensing diaphragm, the regulator will lose its
"memory" and enrichen the mixture during hot starts.
Regulators that I have seen include a vacuum port, which is almost
always a dummy. A tiny minority use the port in conjunction with a
barometric pressure sensor to lean the mixture at high altitudes.
Thermal-Time Switch.
This heat sensor mounts in the coolant, preferably upstream of the
thermostat. It controls the bimetallic heater strips in the auxiliary
air device and in the warm-up regulator. Contacts on the thermal-time
switch are normally closed and open under the dual effects of an
internal heating element and coolant heat. The switch is grounded when
cold and contacts are closed. Switches I have looked at have one
connector pin dead grounded to the switch body and the other reading
0.038 ohms to ground. This figure represents heater resistance, which
should rise to infinity when the switch is warm.
Bosch uses sophisticated time and ignition-pulse sensitive relays in
conjunction with the thermal-time switch to control cold-start injector
on time, idle-air port area and enrichment developed by the warm-up
regulator.
In the best of all possible worlds, one would transfer the whole CIS
system, wiring and all, to the receiving vehicle. Not doing that means
that some other provision must be made for cold mixture control. The
thermal-time switch can be wired in series with the warm-up regulator
and fast-idle device, if the hot wire to the thermal-time switch is
connected to the switch heater and not to the permanently grounded pin.
A relay, energized by the ignition switch, provides power. As mentioned
earlier, low manifold vacuum normally trips the cold-start injector in
my particular application. Dashboard switches enable the injector to be
pulsed or completely turned off.
In passing it should be noted that a bent awl 
of the kind sold by Mac Tools makes quick work of the spring
locks on Bosch electrical connectors.
High Pressure Lines. Gary Miller can supply the proper replacement hoses
and fittings. His Aeroquip blue hose carries a 250 psi rating. The
application described here uses Gates fuel injector hoses with homemade
fittings (the original Bosch fittings do not mate securely with rubber
hose). As mentioned earlier, Gates hose works for now, but I have
reservations about its durability and the integrity of the screw-type
clamp connections. You would be better advised to use Miller's hose.
Stage 1
A machine shop in Knoxville drilled and tapped 22-mm threads in the
homemade manifold-to-block adapter plate to accept VW injector mounts.
The rest of the conversion was accomplished with hand tools.
The CIS fuel pump and accumulator were mounted in the trunk of the
car, next to the fuel tank and forward of the battery that had lived
there since replacing the original R20 engine. A relay energizes the
pump during cranking and after starting when the engine develops oil
pressure. A plastic Celica filter was installed between the suction
side of the pump and the fuel tank. A Volkswagen CSI filter was
mounted in the engine bay, just upstream of the fuel distributor.
Braided rubber fuel injection hose was used after a call to the vender
established that the hose has a burst strength of 900 psi. The high
pressure side of the Bosch system runs at around 70 psi. The ends of
the steel fuel lines were bulged slightly with a double-upset flaring
tool for hose purchase. Connections were secured with ordinary
stainless steel screw clamps. So far, there have been no fuel leaks,
although I would sleep better if proper high pressure hoses and
connectors had been used.
The Toyota quarter-inch steel fuel delivery and return lines were not
changed. That may have been a mistake, since the VW, a smaller car,
used a 5/16 in. delivery line from the rear mounted pump to engine
bay.
A plate was fabricated to mount the throttle body on the manifold
where the carburetor had been.  A
throttle
body with a large primary was initially used.
A rubber elbow, salvaged from some unknown vehicle, and a short length of
3" exhaust pipe connect the throttle body with the fuel distributor.
Vacuum hose connections on the pipe supply air to the PCV and a
Volkswagen device that boosts idle rpm in cold weather. The warmup
regulator was mounted low on the side of the block where a mechanical
fuel pump had been originally fitted. A green R-6 O-ring, intended for
R-134a AC systems, seals the dipstick and prevents false air entry.
The exhaust manifold was already threaded for an oxygen sensor.
The overall arrangement can be seen by clicking here
.
The experimental, evolving state of the project meant that automatic
controls were eliminated or fitted with manual overrides. Dashboard
toggle switches control the fuel pump, enabling it to be turned off
during starting (to prevent flooding)or to run without starting the
engine (for injector and pressure tests). The cold-start injector can
be switched off or energized manually with a push button switch. Phono
jacks allow oxygen sensor voltage to be monitored with a digital
voltmeter. Indicator lamps monitor voltage to the pump, cold-start
injector and MSD ignition system.
Stage 1 Results
The engine ran, but was lean under acceleration and at speed. As a
short-term fix, the VW cold-start injector was mounted on the throttle
body adapter plate and connected to an adjustable vacuum switch,
contributed by another Volkswagen. The switch, acting through a Toyota
normally-off relay, energizes the injector under low manifold vacuum.
Press on the accelerator, a lamp on the dash lights, and the injector
squirts. A dash-mounted pushbutton switch gives manual control over
the injector, which may be useful this winter. Another switch enables
the fuel pump to be turned off momentarily during hot starts to
prevent flooding. A better solution would be to devise a means of
disabling the injector during cranking. But I needed to get home to
Texas.
The installation gave no problems on the 1000-mile trip, although lean
steady-state mixtures punctuated by bursts of power from the
cold-start injector became annoying. But the car would move out,
easily hitting 90 mph during passing on two-lane East Texas roads.
Fuel consumption hovered around 29 mpg. The new stainless steel valves
survived the abuse without warping.
Stage 2
A digital voltmeter connected to the oxygen sensor tracked the lean
condition, which began at about 2000 rpm. The mixture adjustment (via
a three millimeter Allen screw that raises the air vane on its pivot)
had little effect at this speed. Under heavy acceleration, the
cold-start injector produced a roughly stoichiometric mixture.
Transitions were abrupt, but no worse that had been experienced with
the Weber carburetor. The mixture went rich during coast down.
Fuel delivery and control pressures were within specification,
although fuel quantity measured at the return line tank connection was
550 cc in 30 seconds. Bosch calls for 750 cc/30 sec for the VW
application. Since filters had been replaced and pump appeared almost
new, the quarter-inch fuel lines might be responsible for the reduced
flow. But what effect could reduced delivery have when fuel pressure
at the forward distribution point appeared normal? If someone has the
answer, I would appreciate the information.
The CIS regulates fuel delivery by the displacement of a
counter-weighted air vane. Incoming air lifts the vane and causes more
fuel to pass through the injectors. Thanks to inertia, the vane should
over swing during accelerating, richening the mixture even more.
I suspected that the moving the throttle body adjacent to the air vane
might richen the mixture. Close coupling should lift the vane higher
at any given throttle angle and encourage over-swing during
acceleration. Either that or tie a string to it.
A manifold adapter
was machined from 1-inch-thick aluminum plate. I bored the plate for a
press fit to 3 in. diameter exhaust pipe and undercut the lower ¼ in.
of the bore to conform to primary and secondary ports on the intake
manifold.
The plan was to run 3" exhaust pipe from the plate to a 90 deg ell,
with the vertical leg of the ell shortened for hood clearance and
reduced the plenum volume. Cutting the ell near its apex left an
oval-shaped cross-section that was welded and filled to accommodate
the round pipe. The open end of the stub pipe was then press fitted
into the 1-inch-thick manifold adapter plate. Epoxy secured the
connection.
In hope of better low-speed torque, I substituted a throttle
body from a later model Volkswagen, which has a smaller primary
than the throttle body originally used. The new throttle body mounts
to an adapter consisting of a ¼" steel plate welded to a length of 3"
exhaust pipe, with the bore of the pipe biased slightly toward the
primary throttle. The open end of the pipe was mated with the ell and
welded. 
A larger photograph showing better detail can be accessed by clicking
here. A VW boot bridges the gap between the air horn and the fuel
distributor. Eighth-inch-thick neoprene gaskets were installed at each
of the two plate connections.
The engine receives PCV air from a port on the side of the throttle
body. At some point, I will tee-in the cold idle hose to this line.
The VW throttle cable turned out to be just barely long enough to
reach the relocated throttle body.
Stage 2 Results
The lean condition has mollified somewhat, but persists at constant
throttle angles beyond 2300 rpm and during fourth and fifth-gear
acceleration. There is yet work to be done. On the plus side, the
abrupt transitions between part and full throttle have disappeared.
The engine feels happier: it runs smoother and, lean condition aside,
seems to track small changes in throttle angle more precisely. Power
has increased a bit. And I was glad to get rid of that stupid rubber
elbow.
Stage 3
Efforts made during this stage of development were aimed at increasing
fuel delivery at higher speeds and during acceleration.
I disassembled the fuel distributor far enough to extract the
piston. Parts were cleaned with lacquer thinner and lightly oiled.
The piston showed bright wear marks, but no evidence of abrasive
scoring. A severely worn piston should leak fuel into the space above
the air filter and send the engine rich. That was not my problem.
The o-ring that seals the interface between the upper (iron on the VW)
and lower aluminum fuel-distributor castings was replaced with the
homemade gasket show in the photo above. This lowered the fuel
ports a few thousandths of an inch relative to the piston, but the
difference in height had no noticeable effect upon the mixture. Nor
should it, when you consider that total piston travel is on the order
of 5/8". These devices are more loosely set up than the literature
suggests.
The next step was to disassemble the warm-up regulator, mounted on the
block where the mechanical fuel pump had lived. The regulator came
apart in spring-loaded pieces, which took some thought to reassemble
in the correct sequence. Other than a white film of corrosion on the
aluminum castings, the device with its engine heat sensor and two
electrically heated bimetallic strips appeared functional. Before
disassembly, it developed a hot control pressure of 55 psi, within VW
specifications.
I installed a .020" gasket as a shim between the two
regulator castings to reduce control pressure by increasing the distance
between the thermostatically controlled push rod and regulator
diaphragm.  A test drive showed that the modification resulted in a
marginally richer mixture, but nothing to write home about. At 2500
rpm in fifth gear, oxygen sensor voltage hovered around .20V. One
needs something on the order of .45V under these conditions.
Several vendors sell an adjustable fuel pressure regulator, intended
(I think) for a direct hookup to Ford injector fuel rails. One vendor
said the regulator would drop pressure as low as 30 psi. A vacuum
diaphragm boosts pressure under low manifold vacuum to richen the
mixture during acceleration. Unfortunately, CIS control pressure is a
mirror image of injector pressure. For better acceleration, you would
want to reduce, not increase, control pressure. Bosch supposedly made
vacuum-assisted warm-up regulators, but I have yet to see one.
I made several attempts to incorporate manual pressure adjustment into
the existing warm-up regulator. The regulator was removed from the
side of the engine and relocated near the intake manifold, in hopes
that a linkage could be constructed to adjust pressure from inside of
the car.
The heat-sensing bellows was replaced with a 1/2-inch-thick aluminum
disc, pressed into the regulator housing and threaded for a 5/16"
socket-head adjustment screw. Various methods of translating screw
movement to the regulator were tried, and some allowed a degree of
adjustment. In an attempt to increase the range of adjustment, I
eliminated the coil spring originally fitted. A brass extension on the
screw bore directly against the pressure controlling diaphragm.
Control pressure dropped to around 5 psi, regardless of how tight the
screw was turned against the diaphragm. Disassembly revealed that the
stainless steel diaphragm had crumpled from the abuse. So much for the
warm-up regulator.
The next step was fabricate a restrictor plate from a 1/2-inch
diameter steel bar. The bar was drilled through from end to end, and
the ends tapped to accommodate the banjo-type bolts originally used to
make up the fuel lines to the warm-up regulator. A 1/8-inch diameter
brass rod, pressed and soldered into the end smaller (8-mm) bolt,
functioned as a plug to block fuel entry. The idea was to drill out
the plug with progressively larger bits until control pressure dropped
to a value that would provide sufficient fuel at high rpm.
With the plug blanked off, control pressure was 72 psi, or the same as
fuel delivery pressure. Then the plug was drilled through a No. 60
(.040-inch-diameter) bit. Control pressure dropped to 7 psi, resulting
in a mixture too rich to fire. I replaced original plug was replaced
with another, this time drilled with a jeweller's bit about the
diameter of a human hair. Control pressure remained at 7 psi.
I'm not sure why a nearly invisible vent would bleed down all control
pressure. It probably has to do with the small volume of essentially
incompressible fluid in the circuit. Bosch regulates control pressure
with a stainless steel disc subject to fuel delivery pressure and one
face and spring force on the other. As best I can figure, the disc
oscillates, opening under initial pressure and closing when the fuel
vents and pressure dissipates.
I discovered that the valve on the CIS test gauge could function as a
pressure reducer. With a light touch -- just breathing on the valve --
control pressure could be varied across the range from zero to 70 psi.
Stage 3 Results
At 40 psi the engine ran rich at idle with oxygen-sensor readings of
more than 0.9 volts at speeds below 2500 rpm. As before, the mixture
went lean at higher speeds and especially during fifth-gear passing
maneouvers. Throttling the valve down to 15 psi resulted in black
smoke rings at idle and flooding during hot starts. But the mixture
was almost perfect at highway speeds. After much experimentation, 33
psi was settled on as the best compromise between an overly rich idle
and power. The vacuum-actuated cold-start valve was still needed
during acceleration at wide throttle angles. Manual control over the
fuel pump and cold-start injector made starting the engine possible,
but not pleasant, on cold mornings.
To summarize the lesson learned in Stage 3: do not eat at a cafe
called Mom's, play cards with a man named Doc, or attempt to adjust
CIS fuel delivery by making gross changes in control pressure.
Stage 4
One of Gary Miller's "100-hp" fuel distributors was ordered,
together with another warm-up regulator. With UPS delivery charges,
the cost for these parts came to $160, which seemed quite reasonable.
The parts arrived in good shape and appear to have been bead-blasted.
The fuel distributor is a standard (non-computer) K-Jetronic unit,
modified with the addition of a wedge
in the air cone. The wedge functions as a partial shroud to reduce
slippage between the airstream and the flap valve. Gary said that
arriving at the right shape took a lot of dyno time.
As installed, the mixture was extremely rich, registering 0.980 volts
and higher on the highway. Tweaking the 3-mm adjustment as lean as
idle would tolerate dropped cruise voltage by about one point to 0.875
volts. But it was nice to have the thing running rich for a change.
This was the first real breakthrough in the whole experiment.
Advised of the problem, Gary replied that "the critical thing is
the area of wedge vs height." He said that he "narrowed them
at bottom to a point for lean at cruise" and that a good starting
place would be to go for "50% of current width at bottom and
taper from 1/2 height." Okay.
The plan was to machine a wedge from aluminum, nylon or PVC. Almost
anything would work. But examination of the part with its complex
angles and turned tapers meant that one would have to begin with a
thick-walled tube with an ID the size of a fuel distributor air horn.
That sort of thing is not easy to find. I'm not certain, but it looks
like Gary used a fuel distributor as the raw material. The OD was
turned and wedges sliced out with radial saw cuts.
Sacrificing a distributor for a single part hardly made sense, so the
existing wedge would have to be modified. After thinking about the
problem, I decided make initial cuts parallel to lean the mixture
across the whole rpm band. If necessary, the wedge would be then
tapered, leaning out the low end and preserving wedge area near the
upper limit of air vane travel. In this way, richness could be held in
reserve until needed by less restrictive K&N air filter and other
dreamed-about engine mods. Cuts were made very gingerly, 0.020"
or so at a time, and the oxygen-sensor voltage logged on the same
stretch of highway.
As supplied, the rectangular wedge was 0.790" wide. In its final
form the wedge measured 0.492" at the base, tapering to
0.552" at the mounting-screw hole. The taper stopped at
mid-height, leaving the upper half of the wedge with parallel sides
for a width of .0610".
Stage 4 Results
A 100-mile trip over the flat coastal plain that rings Houston gave
oxygen-sensor voltage readings of about 0.810 volt, which sounds rich.
But the engine purred and responded to the lightest touch on the
accelerator. A patch of new blacktop with a rough, pebbled texture
produced enough rolling resistance to pull down the output by 0.015
volt. Turning on the headlamps cost another 0.025 volt. Fuel mileage,
nearly all of it on I-10, came out to 25.53 mpg. A few thousandths
more off the wedge might boost that figure to 26 or 27 mpg. But I'm
going to leave the calibration stand, at least for now. As the
Russians say, "The best is the enemy of the good."
Stage 5
Tickled pink with the progress, I emailed a photo of the system to
Gary Miller. He replied that "it is interesting to see what will
run." Okay, Gary, so a carburetor manifold cobbled up a fuel
distributor looks a little weird, but it works. Sort of.
Although the engine felt healthy at 85 mph, high speed acceleration
was nothing to write home about. The tiny ports on the Corolla
manifold, none of which indexed accurately with the head ports, acted
like a NASCAR restrictor plate. Nor did it help that incoming air had
to make three right turns and branch into a candlebra before reaching
the engine.
About all I could learn about intake manifold design was that runners
should be of equal length, as long as possible for flat torque and as
straight as possible for volumetric efficiency. Ideally runner
diameter should be a few thousandths less than port diameter: the step
helps prevent reversion, or flow reversals when the intake valve
closes. Plenum volume should be no smaller than half and no greater
than three-quarters of engine capacity. Space constraints made tuning
the manifold for peak torque at a particular rpm impractical.
What material to use? Scott Frazer constructed the manifold for his Volkwagen
project from semi-flexible electrical conduit, which makes sense
considering the complex bends involved in plumbing a flat four.
Another approach, favored by some race-car builders, is to TIG weld
manifolds together from light-gauge aluminum sheeting, sort of like
the way a tailor would make a pair of trousers. A few brave souls have
cast manifolds in alumium or plastic. After much thought, I decided to
use exhaust tubing after the example of the aircraft manifold shown at
Simple Digital Systems website.
The stuff is cheap, welds easily and can be mandrel bent.
Weeks of dither followed before I settled on the design pictured
here.
The four 1/2" tubing runners make up to a 3" OD plenum,
whose volume amounts to 43% of the engine capacity. Each pair of tubes
terminates into an adapter plate, secured to the engine with 1/8"
thick neophrene gaskets. The neophrene should offer some heat
insulation. In retrospect, I should have used 4" exhaust tubing
for the plenun, which would have matched the spread of the throttle
blades. Three-inch tubing does not quite accommodate the spread of the
throttle-body bores, which means that the secondary throttle is
partially masked when wide open. The cold start injector mounts to the
back of the plenum and the cylinder injectors plug into 3/4" bar
stock stubs,
machined to match the the ID of the plastic Volkwagen injector holders
used in previous configurations.  >
Mounts angle at 38 deg, a figure than
was dictated by the swivel limit of my milling-machine vise. Backyard
manifolds sure ain't rocket science.
In order to simplify construction, the rubber elbow on top the fuel
distributor was positioned at engine intake port height. Because of
vertical space limitations, the plan was to remove the air filter box
from under the fuel distributor, seal the bottom of the distributor
with an aluminum plate, and mount the air filter remotely. PVC elbows
and piping would connect the filter to a hole the aluminum plate
directly under the distributor flap valve.
Once the manifold was installed, there was no room left in the engine
bay for the filter and its awkward plastic plumbing. So much for the
plans of mice and men. Flexible ducting would have simplified the
hookup, but the stuff available locally is paper-thin and leaks at the
connectors.
For want of a better idea, I trimmed 1" off of the bottom of the
original filter housing. That lowered the distributor enough so that
the rubber elbow could make up to the throttle body. About half of the
filter pleats are exposed now, which probably will make for a noisy
intake.
Stage 5 Results
Success
at last! El carro es mas fuerte, smooth as baby's bottom and, while
the 1 1/2" runners should have cost some low-speed torque,
improved volumteric efficiency more than compensates. The only problem
is that the mixture is richer than before, registering 0.80v at 70 mph
cruise. I suppose that lower pumping losses in the new manifold
translate as greater lift on the fuel-distributor flap valve at any
given rpm. A few thousandths shaved from the Gary Miller's wedge
should bring the mixture back to around 0.75v, at which the engine
seems happiest.
And while we're on the subject of oxygen sensors, there are published
charts that purport to cross-reference O2 voltage readings with
air/fuel ratios. But this data is highly suspect: commercial O2
sensors do not have this sensitivity. GM TPI systems read anything
less than 0.45v as lean, and anything more than 0.55 as richer than
stoichiometric. The condition of the spark plugs are a far more
precise indication of mixture strength.
Except for a few housekeeping details, the project is finished, and
the question arises whether the exercise was meaningful. Performance
has improved: the old Toyota runs better today than it ever has. Parts
that were dying in a junkyard have been utilized, which is a good
feeling, a kind of victory against entropy. On the other hand,
conversion to fuel injection was not easy and there were times than I
would have dropped the whole project had a useable carburetor been
within easy reach. What has come out of it is knowledge of a kind that
difficult to quantify but which seems valuable. One can learn about
the Bosch CIS and induction systems by reading about them, but the
knowledge attained by actually working on and modifying these systems
is deeper and more immediate than the knowledge one gets at second
hand. We have to do in order to learn.
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