Fr8trplt

I have been battling this for over a year. I apologize for the lengthy post. 1985 US 928S model with a performance chip. Car would quit anytime, hot cold, did not matter. Right before it quit, tach needle went nuts. Turn key all the way off and it would then start and run fine until the next episode, which might happen in 5 mins or two weeks.

I replaced crank sensor, temp II sensor, cleaned all ground points and added second ground strap from frame to engine. Removed and cleaned entire fuse relay panel. New battery.

Car will still quit for no apparent reason. Now, when I restart, it starts and then immediately stalls. It won't stay running, but it fires up every time and then quits. I am getting good spark. I checked ohms on coils and they seem fine. Plugs and wires are fairly new (2yrs).

I replaced all intake tube sleaves and checked vacuum lines under MAF are okay. Relays have been swapped, ohm checked, etc. more times that I can remember. Jumper across LH relay and fuel relay from 30 to 87 has no affect. I walk away and come back and it may or may not start.

Any ideas or new avenues to explore would be greatly appreciated. I am at my wits end here. As much as I enjoy hanging out in my garage, this is getting old fast.

Mako 928

Two things come to mind,
MAF, ignition switch.
Do you have the factory alarm? Long ignition key.

tilac999

Try another crank sensor.

John Speake

Did you replace the CPS with a genuine Bosch unit ? 3 pin harness connector OK ? From what you say it is much worse since you replaced the CPS.

To simplify fault finding, put back the stock chips. The EZ-F ECU is quite tricky on getting synchronisation with the flywheel gap, so it can produce lots of spraks, but not at the correct time :-( and this is the usual failure mode with them.

So get the car back to stock. See where you are then. Let us know.....

Landseer

+1 on back to stock!!! What a PITA to troubleshoot otherwise!

And get-to-know your 85 wiring diagram.

Ideas mostly involve the harness area behind the engine, running out to the injectors. This includes valley grounds and the integrity of every wire in the harness and under every rubber boot. Also, replace the battery groundstrap (corrodes beneath the plastic).

Here's a video that I shot a couple weeks ago. Should have stripped the harness to find the issue, but ashamedly, I manipulated the harness till the pain stopped and have driven it 2000 miles since:

http://www.youtube.com/user/Landseer86?feature=mhsn

PorKen

If the 'performance chip' is AutoThority (or an eBay copy), it's not really a performance chip, anyway.


My new-to-me '86.5 has random cutouts at all different rpms at part throttle. 5 mins to 15 mins. I can hear the idle control valve cycle, then a relay clicks, then it shuts off for a brief second.

All sensors have been replaced, computers swapped, relays, the whole shebang.

The wire loom was misrouted after an intake refresh, so I figure it's an in-harness issue, or an injector plug wiring problem.

rad_951

Check the injector wiring. All of them are in series; if one shorts, none of the injectors open. The wire breaks under the boot at the injector. The ones near the air cleaner are the worst because they get abused when removing the air cleaner.

John Speake

They're all wired in parallel..... same result with a short though :-)

Fr8trplt

Thanks to all. CPS is indeed a Bosch unit. Injector idea sounds interesting. Here in Memphis it is 100 degrees in summer, so I find that lots of stuff such as elec wires and vacuum lines get baked and brittle. I was told that LH computer almost never fails. Is this a fact?

John Speake

For the 85/86 cars, yes they are very reliable.

Fr8trplt

It was indeed the ignition switch. Considering how easy it was to install, as well as the relatively inexpensive purchase price, I wish I would have found this earlier. However, I do have some new parts now and a lot of knowledge from all of you here at the forum. Thanks. So far, 2 months and it has not quit once. Nice to have her back again.

dizzle28

i'm glad you got that resolved. i wish i had a driveway like you to work on my car. but i'm hoping you guys can help me, because i'm pretty much having the same problem. lol. i also have an '85 928S, automatic. had it since 2008. it amazed me that it's for the most part, a strong, attractive, and (for its age) reliable car. this is the first "major" problem i've encountered.

the car has never shut down on me, but when i left work one night months ago, it wouldn't start up. it kept trying to, but no dice. no performance mods. i took it to two mechanics. neither them nor the person that towed me home had any idea what was wrong. the most it would do is start up for a second, then idle down to where it's completely off. even if you give it gas to keep it from turning off, it will ignore you.

the Porsche dealer won't take a look at the car because it's older than 1996 and I don't see as many seasoned European car mechanics around, like i used to back in the 90's when my Dad had his 944. the problem was resolved for 2 weeks a while back. the first mechanic didn't know what he did to get it to work. he said all he did was just jiggle some wires near the engine, problem solved, and i went home. reading what you guys have posted, i'm wondering if this is related to injector wiring or something to that effect?? i mean the spark plugs and air filter are way overdue for a change.. but i had a new battery put in, the starter replaced, the fuel pump checked, and diagnostic on the fuel relay. still no luck...

dr bob

Basic diagnosis:

Is there spark?

Is there fuel?

Is there compression?


Kinda narrows down the troubleshooting process when you can limit work to one search area.



We always supect that there's some exotic cause for our 928 ills since it is an exotic car. Sometimes that's true, but for the most part the problems are relay, relay, and relay, then connections, fuel pump, out of gas (it's happened...), stuff like that. Start with the easy stuff instead of assuming something exotic.

tilac999

The only failure I've ever had was a no start due to a melted fuel pump fuse. White powdery corrosion, increased resistance, didn't blow but melted. Luckily in my driveway. a Good CE panel cleaning is cheap insurance.

PC-85-928S

anyone have a good pic of the "valley grounds"
85?