wierd 3.2 problem

john walker's workshop · 02-12-2002, 06:57 PM

here's a wierd problem for you all. 86 carrera won't start. pull off any one injector plug and it runs. i ran into this problem years ago but i can't remember what fixed it. a customer called me on the phone about it, so i thought i would post it, and maybe when i come in tomorrow morning, someone who had the same problem will have enlightened me. thanks.

Joeaksa · 02-12-2002, 07:05 PM

John,

This is not good. If one of the head "guru's" on the list does not know the answer, then we mere mortals would have a rough time with it!

Possibly a grounding or electrical problem that taking one injector plug out of the loop would make it work? How would taking one injector out of the loop interface with the DME computer and could this be part of the problem? Does it matter which injector you pull off? Wiring harness?

Just an idea...

Joe

Doug Zielke · 02-12-2002, 07:06 PM

I'll take a look in my Bentley for ya, John

orbmedia · 02-12-2002, 08:25 PM

Maybe a bad ground on the injector harness. Doesn't the ground point bolt onto the manifold?

Joeaksa · 02-12-2002, 08:40 PM

Why would interrupting the circut on a injector make any difference? Wonder if a diode has gone bad and is backfeeding a relay with power or the like and taking the lead off makes it work? Taking the injector lead off could effect a ground on the DME computer?

This one is weird... but challenging.

JA

Mike the mechanic · 02-12-2002, 08:47 PM

DME problem. Tell the guy to check for dampness in the dme area. Sounds like too much combined resistance for the computer, and by unplugging any injector, you bring down the total injector resistance to the dme unit. but.. Is it a pulse to the injector that is missing upon no start or 12v?

Mike
86 Carrera t

ChrisBennet · ChrisBennet's Garage

John,
I don't know if this will help but it seemed relevant:

Don Istook posted this in Aug 1999 about 944's:

Quote:

"For no injector pulse problems, I usually find that the DME relay is at fault or the fuel pressure relay is bad. I disconnect an injector and crank the engine...if I then have injector pulse (ticking) out of the three remaining injectors, then the fuel pressure regulator is defective. If I still get no injector pulse, I check the relay. Again, I have found cracks in the solder joints of the relays and sticking contacts, but I usually just replace the relay since they are not very expensive."

Martin (porsche@globe.net.nz) posted this in May of 2000:

Quote:

Subject: Re: HELP! car wont start and i gotta see mother-in-law!
Try unplugging one injector and see if it starts, your reading across the coil is correct, the DME drives one side low for a fraction of a second to generate spark. if it starts with one injector unplugged you have a dead FPR, if not you may have a faulty crank sensor, give the wires a wiggle, Best of luck
Martin

john walker's workshop · 02-13-2002, 07:27 AM

this car isn't in the shop so i can't check it out. it's a ferry ride away in bremerton, so i'm trying to help the guy over the phone. he has replaced the DME relay, the grounds are tight on the manifold, the sensor plugs are clean and tight, the car has been stored inside for 6 months, so the computer didn't get wet, and it ran ok before. i suggested he check for a pulse at the injector plug, and that's when the car started for him. so it must not have much, if any pulse with them all plugged in, and sufficient pulse with one unplugged to run the rest. i suspect the computer, and it would be easy to plug in my test unit IF the car was here. guess he'll have to tow it in. keep thinking though.