Porsche 928 cranks but wont start

dorsche · 04-13-2009, 02:47 PM

Hello ,

I am hoping someone here would be able to help with this issue. The car was running fine last year on august. Since then it was parked outside . In mean time i did interior resto, carpet, dash, cluster ,seats,center console , all those items were removed and recently reinstalled. Anyway no other work beside interior were done and car just took a big no no , and refuse to start.
84 928 s
First day during the attempt to start engine start for about 2 seconds. I guess it was the cold start ,but it would not stay running.
Checked the folowing:
pump relay,
injector relay,
visually inspected the green wire( not sure what should be the reading)
Spark is ok .
fuses are ok
Belts are ok
Then next day we pushed the car into garage and now it wont even stay on for 1 second.
It will run with starting fluid.
I dont hear the injectors , and the sparks looks dry.
The pump is working , injector relay even jumped makes no difference. Seams like there is no injector pulse or possible bad 8 injectors?Jetronic?
The Tach on the dash is not moving during the crank?
The car acts like it would like to start .... but it wont .

Any input would be greatly appreciated here.

Thank you
Dan

928 Bro · 928 Bro's Garage

Have you checked you fuel pressure? It sounds like a fuel problem.

dorsche · 04-13-2009, 06:44 PM

Im gonna check it in the morning with the gauge( i loosen the fitting few days ago just see if there is any pressure but not checked with the gauge. What is should be at 40 psi , 46psi?
Anyway im gonna check it and post it here.

Thanks for the tip Bro!!

Dan

Danglerb · 04-13-2009, 08:25 PM

Green wire?

dorsche · 04-13-2009, 08:51 PM

Quote:

Originally Posted by Danglerb

Green wire?

Well you know the green shielded wire that pops out of distributor housing wire coil.
Is this the ignition signal? I mean how does the dme is receiving information such as : timing, crank position or whatever it is , in order to time injector impulse? Is there a sensor anywhere ?!! I can t find it ...This is 84. I was thinking the magnetic coil wound inside the distributor was acting as a reference for injection.
I guess i should start digging for some shop manuals

guys sorry for my bad English, im trying to described it best i can , but have a hard time to remember correct English terminology. Joust hope you guys can understand me.

Thanks
Dan

BTW, is the green wire shield act as an isolated ground? is it wired straight to bosch computer?

Danglerb · 04-13-2009, 09:24 PM

84 US model? If so then its a Ljet and the green wire goes from dist to ignition box on the passenger fender. I don't know the electrical characteristics of the green wire, but its a bright green and nothing happens if its bad.

Trouble shooting does not start, best to stick the basics, spark, fuel, and compression.

I like to check the spark with an inductive timing light, so timing can also be checked.

If you you have spark, then using a noid light to check for injector pulses is a good second test. If the noid light pulses, check plugs for fuel.

If you have spark and fuel, do a compression check.

SolReaver · 04-14-2009, 08:54 AM

It runs on starting fluid. Thinking Ignition OK. Not likely that all 8 injectors go at once. No tach signal probably no signal to FI system. If no fuel pressure... I suggest Really basic stuff. Check all FI connections, relays, fuses, Grounds, Green wire and position sensor.

Danglerb · 04-14-2009, 10:06 AM

Quote:

Originally Posted by SolReaver

It runs on starting fluid. Thinking Ignition OK. Not likely that all 8 injectors go at once. No tach signal probably no signal to FI system. If no fuel pressure... I suggest Really basic stuff. Check all FI connections, relays, fuses, Grounds, Green wire and position sensor.

Actually I saw a car a few months ago that had all 8 injectors frozen from sitting with old fuel or something. A single short will also take out all 8 injectors.

SolReaver · 04-14-2009, 12:02 PM

Yes Dangerleb, All 8 CAN go. It is just not "likely" or "as likely" as the FI system not getting signal or the Short to ground thing. I think they all have a common ground...Yes? Or are they paired as in the 944s? I will check when I get a chance. A noid would tell you if the injectors are getting signal. It is said that the injectors are not clicking...so I am leaning towards no signal. Actually a bad ground would explain it as well. The only time I see all the injectors go teats up at the same time was when the fuel was compromised. Lets wait to see if Dorsche has fuel pressure. If so, the next step would be the noid to check 4 signal. Because of the no tach thing...I am thinking that we will confirm a no signal...Rats! where is that crystal ball? It sure would come in handy right now.

Isn't there a diagnostic mode for the FI brain...the one that cycles the injectors..Damn, I remember using it on Saab buckets all the time.

Dean_Fuller · 04-14-2009, 02:30 PM

With having ALL the interior out...what about the alarm system ?

Eep · 04-14-2009, 02:36 PM

Quote:

Originally Posted by Danglerb

Actually I saw a car a few months ago that had all 8 injectors frozen from sitting with old fuel or something. A single short will also take out all 8 injectors.

I myself dealt with a 1982 that behaved similarly and eventually responded (long past the point where I thought there was any hope) to a tank full of fresh gas and injector cleaner. That one had sat for a looooong time, though, and it wasn't an issue where the condition deteriorated over time.

Actually this also sounds similar to the issue I've brought up in a couple threads. Dan have you tried starting the car with the fuel relay jumpered AND just a little gas? That's about as far as I've gotten on the diagnosis on a 1990 928 I'm working on: it will start with the fuel relay jumpered and just the right amount of gas. Wish that meant I could help, but at the least it might indicate that we're working on similar problems.

dorsche · 04-22-2009, 04:43 PM

Thanks for all the suggestion guys,

Well here is where im right now with this nightmare

heheh
I did go over the points you guys posted above and after checking , looks like fuel injectors are not getting any pulse. The harness seams to be dead. I did check the relay like 10 times hahah.
Whats wired the tach is not registering any crank rotation durring the start attempts. How does jetronic system receive information on when and duration of the impulse for injectors?I cant find any reference sensor or something similar...

Danglerb, its 84 and thanks for the info on the green wire and rest of the info.

SolReaver , Checked the stuff except the position sensor. Could someone point me on location of it? Sorry i just could not find it anywhere around front or back. Is it by trans housing on the rear?

Eep, i was hoping for the bad gas or something simple as this. 5 gal of fresh gas and we played with the throttle for quiet a bit and no luck. This was before we checked the injector pulse.

thanks

Dan

SolReaver · 04-22-2009, 06:51 PM

the cps is located under the air cleaner. in the back of the block on top just as the engine meets the bell housing. K?

BB500 · 04-22-2009, 06:59 PM

It sounds like the engine is COMPLETELY SHOT! Haven't you been dreaming of the day you could upgrade to an S4? Stop what your doing immediately, and come buy my beautiful S4 engine!
(just kidding...

Danglerb · 04-22-2009, 07:01 PM

Quote:

Originally Posted by Danglerb

Green wire?

^^^^^^^^^^^
++++++++++++
++++++++++++

Sounds like the green wire, which takes the impulse from the distributor and tells the fuel injection its ok to fire the injectors.

SolReaver · 04-22-2009, 09:10 PM

Green wire ^2

check connections both at the dist and to the brain on the fender wall just forward of the pass cam cover. a lot of times the old connector at the brain end gets brittle and breaks. Carefully take it apart and make sure that it is all clean and contacting.

You really should try a noid. They are cheap ya know.

BB: very funny, but hold onto that engine...you may need it. I wish I had something to put it in....Maybe a mustang?

dorsche · 04-22-2009, 09:59 PM

Danglerb, SolReaver , i will check the damn green happy wire again. The connector and the connector at the ignition box , or whatever is this thing called.
hehe u know that engine got to run again !!! S..t i might face the divorce if that stupid thing wont fire up in the right way !!!

And whats funny , when i was younger , my uncle was always telling be (mostly when working on his damn 944) don't u ever waste your money on those cars ...
well i had few of the watercoolers and they all got me seriously worry at some point of their lives with me .But it was love i could not reject... right. I hope this lovely 928 will just fire up tomorrow morning like nothing ever happen, maybe i should call Copperfield or something , just to make sure ....

Well we gonna try again in the morning ...

and thanks on the info on crank sensor, i will check it again, hahaha. I guess some things just want to stay invisible for me .

BB500 , u must like to start fire!!! Man that "Completely Shot" <- thingy you wrote got my blood pleasure rolling quiet well Mr!! HAHA (i might have to steal your S4 !!!!) You know ,I am having nightmares about early Porsche achievements, that some Hanz Frunkner purposely switched the blue prints of 928 like a day before setting up production... so everyone will get this magical "i won't start" surprise some day. Well i think that's exactly what happen.

Thanks for all the help, at least i still have some spirit left to try more TS

THANKS!!

dorsche · 04-22-2009, 10:03 PM

just in case if some kid is reading it : Hanz Frunkner did not work for Porsche , and we dont need to sue them for early cars sabotage.I still love Porsche, and not planing to drop ls1, i rather get bold and watch weeds taking ownership.

SolReaver · 04-22-2009, 10:40 PM

Dorsche: Don't worry Bout BB: he is just having fun. He is putting a Ford Truck engine in a 928.. I would like to talk him out of it.....but you know...KIDS.

Trigger pulse comes from dist...Goes through green wire to brain. Brain give impulse to FI brain and the FI brain also gets signal from CPS to figure what injector to fire.

If your wire and CPS check out...we will have to get tricky. We are just clearing out the easy stuff. Don't stress it. It is just a car.

dorsche · 04-23-2009, 11:29 AM

Well im gonna try to trace the green wire to the jetronic computer, and see if there is continuity. I checked the short guy between dist and the 2 pin connector, the shield showed grounded.

I did check the ground points today, it took forever.
I still cant find the Reference sensor???No where around housing near flywheel, i cant see even any harness going that way. I mean nothing from under, nothing on the top . The cps must be really sabotaged on this car!!!

btw , how often the jetronic box takes a dump?