Cincinnati Kid

so a new green wire solved the no spark problem. engine turned over, and after a few seconds it started. it ran for a few seconds and quit. started it again-same thing. after third time, it turned over but did not fire. checked for spark and had plenty. fuel pump is working. fuel is getting up to the fuel rails. sprayed choke cleaner down plenum and it fired immediately. as soon as the choke cleaner spraying stopped, the engine quit. sprayed choke cleaner for 30 seconds and engine idled (albeit roughly) for 30 seconds until the spraying stopped and engine quit. a couple of odd things: when the engine would quit, it would not restart on its own, but after about five minutes, it would start on its own but quit a second or so later and not restart. secondly, as soon as i touched the gas pedal, it quit running. third, when the was idling with the choke cleaner, when i touched the gas pedal, it backfired. i am at a loss as to what to do next. any advice is appreciated.-

j.kenzie@sbcglobal.net

What kind of car?

Cincinnati Kid

oops- my bad 1982 928

j.kenzie@sbcglobal.net

Hi,
I sounds like you have spark, but may be running on the cold start injector only without the main injectors firing. There function depends on good grounds which are located on the passenger side valve cover near the Porsche lettering. A good cleaning might help.
Good luck,
Dave

Cincinnati Kid

thanks dave, i'll have a look and clean the area. i hope this not a stupid question, but is there only one ground on the right valve cover? what else could keep the injectors from firing?
i appreciate your help...
john

Mrmerlin

there are 2 of them look under the air tube

j.kenzie@sbcglobal.net

Grounds in general are important on these cars. There's lots on posts about cleaning them in the FAQ section. The engine ground strap on the bottom rear of the engine passenger side to chassis is also vulnerable.
Good luck,
Dave

Cincinnati Kid

thanks so much, guys . i'll take another swing at it tomorrow and update...

john

rjtw

Replace the fuel injection relay too. Relay, relay, relay!

Cincinnati Kid

will do. thanks...

The Forgotten On

Sounds like the L jet computer is either not getting power (ground or positive) or a signal. The signal to fire the injectors comes from the ignition computer from a hall sensor in the distributor via the green wire.

The power comes from the fuel injection relay. The pump relay is activated by the ignition system oddly enough via the same hall signal as the l jet, so your car is definitely running off of the cold start injector.

Here is a pinout of the L jet that could help:

Cincinnati Kid

thanks blake- the L jet is located in the right footwell, correct? all other things being equal, if the L jet is ok, and the f i relay is bad, the injectors would not fire, correct?
im going to start with cleaning the ground connectors on the cam covers, move to the f i relay and then the computer. apologies if any questions seem silly, but i am in uncharted territory
with my 928...

john

j.kenzie@sbcglobal.net

Blake gave a good explanation of a complicated system. Sometimes I think I understand it. Others not. The injectors won't fire unless the L-jet brain receives a signal from the ignition brain, that a certain RPM is present (can't remember what RPM, like 300?). Anyway they have to communicate, so you have signal to ignition brain via green wire ,two brains, two connectors and one wire that might not be good. The fuel pump also has a similar safety interlock. Somewhere there are normal values for the 35-pin connector in various non-running states.
Good luck,
Dave

Landseer

The mission critical ground near back of passenger cam cover is hidden under an airpump emissions valve.
Don't waste time trying to clean it without first removing the that valve.
It is easier to remove than it appears.

The fuel injection relay is a special one. Get a new one from one of the parts suppliers here, not from local parts place.
It is possible to bypass it for a test by making a three-ended wire and bridging 30 to 87 to 87 (or 87a if labeled that way)
Careful, 30 is hot to battery. If you do test it, don't leave it in place when you walk away, unplug it.

Injectors batch fire on switched ground (the computer does the switching), so again those two cam cover grounds are important because thats where the computer grounds to.

If any of the little injector harness plugs are twisted to the point that they short, it shorts-out all the injectors.

There is some relatively simple troubleshooting to determine this. I know Rich 928 has posted it up many times before.

I think that each injector, unplugged and tested in situ individually is 2.7ohms. There are a couple ways to test the harness itself for shorts.

But if its just a ground or that relay, as could easily be the case, you don't want to be digging through all that stuff. Should be able to find out quick Congrats on hearing it run, that's a relief.

Cincinnati Kid

thanks so much for the additional info. so this morning i decided to check the injectors. there are 12 volts to the injectors. i used a noid light on one injector and it blinked as it should. that would suggest that everything is working as it should- correct? when i go to start the car it does exactly the same thing as before- starts immediately and then quits. knowing that the car had been sitting for several years, how likely is it that all the injectors are clogged? any help is appreciated...