Fuel Injection Conversion !

Well this is a long story. Fuel Injection. Sure. Let's do a conversion !

Years ago I wanted a Ferrari 308 GT4 & couldn't afford one. I tricked out an X1/9 as my cost effective substitute. At one junction I converted it to Bosch L-Jetronic injection from a later model car. Had to swap the gas tank & wiring harness, cut holes, curse, learn new things & swore I'd never do it again.

Later on I finally got a GT4 & learned that for the tight hilly roads I live on, the X1/9 was a better car, Huh. By then I had sold the X  to an unappreciative owner to raise some cash & he beat it into the ground, A sad story. I spent three years tuning that GT4 to try to make it sing as well as that modified X1/9. I learned how to bore out the Weber carb body air correction  circuits on a Bridgeport milling machine to get rid of the transistion hesitations, ( it would have been too easy if they made that part a changeable jet... ) & figured out that if you made a huge rear sway bar it would finally start to turn in, ( Carefull in the rain ! )  Alas, It threw 2 connecting rods through the side of the block when I was driving in a hill climb in Nevada...........   Oh dear.  That was a bother.  The tow bill home was more money than I had alloted for the weekend, & to pull a 308 motor the transaxle comes out with it. I think the factory book time is 14.5 hours for removal, & that is when they were new with no rust & a couple guys with factory tools. That project took forever. I fell out of my chair when I got the parts quotes. I think a factory gasket set was $1250 & aftermarket was around $800. Ow.  It got worse from there. Ran great when I was done, but the tariff was devilish........

Back to the fuel injection plot:

A year or two ago I converted a Citroen I bought in France to a throttle body fuel injection setup. It was mainly to prove that all things really have a common denominator. I tried to take parts from as many different countries as possible. A Peugeot fuel pump, German temperature senders, A Suzuki throttle body, Italian relays, a computer from a 3 cylinder GEO Metro, ( Just to prove you can run a 4 cylnder car on a three cylynder black box, )  & hacked into the computer with a soldering iron & an attitude.  I figured out how to generally fine tune the mixture, & used a tone pot from a Gibson les Paul with a big fat weighted knob from an old Tube Macintosh stereo amp to dial it in.  Put that knob in the dash where the choke used to be, & what a difference ! The hill I drive home used to require  2nd gear, & it now climbs up in third.  The power used to die off by 4000 rpm, & now it wakes up at 3850 & pulls off the tach. It also gets better mileage. Wow !

Of course I was so wrapped up in building it between customer projects I never fully documented it.

Darn it.

For the next conversion I'll try to keep some photos.

How about multi port injection this time ?

For a pancake motor like this Citroen GS it will probably have improved cold running & throttle response as the injectors will be right on top of each inlet valve instead of having one central injector on top of long runners.


Here goes................

Hey, Look at that nice late model inlet manifold. Let's use it as a donor.........

OK, Time to whip up some injector holders.

The lathe saves the day

Coming along, but we need to bevel the holders to match the inlet tubes. Now the mill comes in handy,.......

Look at that: Closer to glory

Check out the cool bevel I got on the injector holders:

OK, a few holes in the inlet manifold

Solder, braze, weld or TIG ?

 I decided to braze, & pre tinned ( buttered ?) both sides first with flux & brass. Heat the metal before you apply the flux for better results.)

Taking a break to bang on an old les Paul like the one I stole that tone pot out of for the mixture controll knob.

Hey, look at that ! The manifold is coming along.

Uh oh. need some inlet tubes for the fuel supply.

I bent & flared brake line, & then silver soldered the junctions. I pressure tested with compressed air through a regulator & it all looks pretty good.

Will it ever end ? How about an O2 sensor in the exhaust manifold.........

Had to drill a big hole, find a threaded bung, & braze that thing in with some brass & flux.

Once again I am trying to use parts from as many different sources as possible to prove that al of this stuff is compatible as it is simply physics.

All of these pieces can communicate together as electron flow & computer pulses share the common language of logic.

This Oxygen sensor came out of a Husqvarna from Sweden. Chain Saw or Motorcycle ?   ( I  don't know, I just found it on Ebay........)

The fuel pump ? Jaguar ! Some Porsche sensors, an American computer, Japanese injectors...........

Need to get a hunk of aluminum to adapt the throttle body. That 52mm hole was difficult to make. ( 4 jaw chuck in a lathe.)

Swiss cheese that thing. Here's the measuring process to adapt a computer controlled Idle air valve stepper motor. ( Got the stepper motor from a Jeep. Support American industry...)

How cool will it be if it fires up & idles at 1250 cold without ever touching th gas pedal ?

Coming together

OK, reflect on this chart for a minute.

The interior comes out to install a wiring harness for the computer.

Here's the overview in the driveway

Learning how to run a computer controlled ignition I needed a spark generator on the test bench. This is an old bevel drive Ducati coil with time period correct
braided ignition wire I found at the Padova swap meet. If you ever get a chance, the meet is late October or early November every year & it will melt your neurons
if you like Italian cars.  Biggest swap meet of the year in Italy. I recommend a Google search to get you fired up.

Computer testing & programming

Gibson the cat reflecting on it all in the back of a Flaminia.


So here's an interesting thought:

If you have contemplated an injection conversion, it becomes obvious that a high pressure fuel system ( maybe 40  psi injected, vs 4 psi carburetted ) usually
has a return to the fuel tank. If an early carburettor system has no tank return , plumbing one in can be an event, ( I never liked welding on gas tanks reeking of petrol fumes with a torch anyway....)
Several options:  Remove the fuel gauge sending unit & silver solder in a u bend & return line, solder or braze a return line into a metal fuel filler line ( Sounds dangerous to me, I wouldn't do it without removing & flushing everything first, ) or try this idea I came up with:

Keep the original mechanical fuel pump. Starting with the line out introduce high pressure fuel line. Regular 5/16 carburettor fuel line is cheaper, but will blow out 2 years down the road & burn your car to the ground. You must get fuel line for injection purposes !

Run this line into a 3 way T junction & feed an injection fuel pump.  Feed all the injectors, & end up in a regulator ( I used a Subaru one. All this stuff is pretty much interchangeable. There's warning labels & cautions everywhere as we are a fear based society, but from a point of physics & mathematics, close works pretty well most every time. ) run the regulator overflow back to the T junction & feed the EFI pump.

In a previous experiment in the driveway I know that if you block off an injection pump with a pressure gauge it will peg the gauge at 80 psi, blow the line off & spray gasoline everywhere.

Cautiously for this installation I used compressed air ( necked down with the regulator from a leak down gauge to 10 psi ) to check for leaks & functionality.  A squirt bottle of soapy water showed no leaks, but as I wound up the regulator to 60 PSI the pressure was the same in all circuits. A bother to rig up all those gauges, but better than catching a car on fire later.

Huh. So much for my great idea. I know my regulator blows off at 38 psi, but with an air loop there is no regulation.

Let's try it with pumps hooked up & gasoline. Will the loop run at 100 psi ?  Will it blow off the hoses and cover everything in gasoline ? Get a fire extinguisher just in case, & let's find out.

Nah. It works great. The injector lines hold a steady 38 psi, & the injector loop circulates at 0 psi. Cool ! When you stop the electrical pump, the residual 38 psi stays on the injectors, & the pressure in he T junction climbs to the 5 psi the mechanical pump would normally hold.

How about that !

What a time saver.

If you lived in a hot area & had vapor lock concerns this may not be an optimum solution, but it sure beats pulling out & welding a gas tank.

Remember ( as my lawyers tell me ) this is all just information, not advice. I don't recommend that you try any of these ideas, & if you do, carry 2 fire extinguishers & don't blame me for any surprises.

As Jon Norman once said, you always have fun, sometimes it just not the type of fun you thought you would have............

But how cool is it that the loop will cycle at basically 0 psi with the pump running full time. I feel safer already.

OK: Starting to assemble pieces on the car instead of on the test mule motor.

Looks like I'm going to need some fuses. Time to make some way to organize them

Alright. That worked out OK

Hey: the car is outside. That must mean it runs, as I can't get it off the lift if the hydraulic suspension has deflated.
It fired up instantly & settled into a perfect idle.

Yeah !

Open the throttle & it  bogs though.


A bit of sleuthing & I discovered that inside the throttle position sensor ( TPS)  there are only two switches instead of a rheostat.

Bosch L-jetronic systems, licensed around the world use that system. Later model injection systems almost universally use a rheostat.
It never occured to me that my late model Subaru Turbo TPS was the early type.

Of course I never checked into that before I spent all those hours machining brackets, adapters,  & linkage bits..............

Oh well. Time to find one that will fit. Off to visit the local car shops & a wrecking yard.

Of course none of them fit. All the rheostat style TPS modules have a different drive mechanism.

Darn it. I'll have to fabricate a converter. I'm ready to drive this car, not keep making stuff for it. Not to mention the customers want their cars worked on.

Somehow it's already Thursday morning & I thought I'd be done with this project by  last Sunday night.....

OK. Get to it. First finish that Lancia Flavia PF coupe that's on the lift.

Back again.

I now discover all the modules that fit my needs turn counter clock wise & the setup I have turns clockwise.

If I mount a new one it will have to go on the other side of the butterfly, and that means it will run into the oil filter & the spare tire mount.

All that working machining the manifold & the car actually runs ( at idle) but I have hit another brick wall.

This is not a problem, it's an opportunity.

I wonder how I'll solve it..........

Next day:

OK: I figured it out.

Remachining a new pedestal for another throttle body, & building a new linkage seems like too much work. All of the variable resistor TPS I find turn the wrong way. If I mount them on the other side of the shaft so they turn properly, at the very least my spare tire won't fit anymore. There must be a simple solution.

Heck, the darn thing is just a variable resistor carrying a 5 volt signal with no amperage of consequence to a computer.

I'll just make something that will fit on the correct side of the shaft. How hard could it be ?

What about that Gibsone Firebird in the studio? I changed out the volume potentiometer on that guitar to get a different tone.

I just rustled around the electronics workbench at home, found the old volume pot, whipped up a bracket, made a little connector shaft on the lathe & bolted it on.

Works pefectly.

Wow !

I've now got fuel injection !

What could possibly go wrong next ?


Uh oh.  What's this? :

Hmmm.. It seems that my idea for the fuel return loop wasn't so hot.

Actually it was too hot.

The fuel pump was warm to the touch, & then it went to 120 degrees while running. Then the car stalled due to vapor lock.

Darn it !

Now I have to rig up a return line to the gas tank.

Above is a picture of the fuel gauge sending unit I found lurking in the trunk.

Maybe I could somehow put a return line in there so I won't have to remove the gas tank.

Not much room for another pipe though.

It's also held in with an unobtanium clip that looks like a one use only job.

What happens if I break it ?


Will it come out ?

Let's take a break.

I'm starting a new business to sell things  I design & manufacture called Scuderia Zombie. There's going to be lots of cool stuff coming out ( when I find the spare time.....)

Flavia wheel bearing wrenches perhaps ? I've prototyped a delicious 5 channel datalogger for vibration analysis that uses modern technology from several different fields, hopefully smoothly integrated.............. Another good one on the bench is the Zombie Love Box, a Cool guitar amplifier gizmo that has some good looking architecture & great tone.

Anyway, got to build the brand & all that. I came up with this design for a rear window water transfer decal.

The undead thing is about bringing old mechanical things back to life.

I'm building a website for the project with lots of cool photos of old things in fields & dark garages too.

More on that soon.

Back to the task at hand.

I got the fuel sender out with no destruction.

Here it is with a return line made from 1/4 inch brake line that I bent & was getting ready silver soldered on.

The solder wouldn't stick, that nice amber brown fuel sender caught fire & burned like movie film.

Aw shucks.

After I took it apart ,remanufactured  it, & calibrated the gauge, the piece was now too big to fit back in the gas tank.

Oh come on. I just want to drive it.

Back to the drawing board, I took it all apart again & re-engineered it.

Works fine, no leaks, no more time in the day.

Off to dinner.

Here's the return pipe running underneath the chassis. ( It's the shiny new one.

It actually turned out to be a fairly clean solution.)


So how's it run ?

Darn great actually. Just took it out on the freeway tonight while I tried to dial in a fuel map.

Pulls hard, idles really well, starts instantly when you reach in the window & twist the key without having to touch the gas pedal.

I programmed that little stepper motor to open up a bit for 6 seconds & then ramp down to a nice smooth idle.

That's exciting.

Just like a real car.

Overall I'm thrilled with the improvement.

Time to put away the tools, make some notes, fine tune it a bit & then..............

Work on a Flaminia Zagato that's coming in this week. Light green metalic mist.

I always like it when the cars arrive in interesting colors.

Cool !

See ya.