Mr Earbrass

I have a 1987 928 S4 automatic. It has been mine for 15 years and has 150,000 miles on the clock. The car starts easily and runs fine, but lately it has taken to just shutting down - sometimes at a traffic light, sometimes while gliding down I-79 at 80 MPH, never in the driveway (not yet anyway). I shut the key off and it will start up and run as if nothing happened. This makes it a bit hard to diagnose as it is running fine and starting every time without hesitation. Any suggestions? Thanks in advance.

SMTCapeCod

maybe ignition switch?

docmirror

Another vote for ign switch. Not a hard job. Contact Roger at 928srus.com and he'll have one on the way to you.

davek9

Might be easier to just replace the three main relays (LH, EZK, FP) and check Fuses for corrosion first.
The Ignition switch requires pod removal, the two Phillips head screws are a bitch to get out

Mrmerlin

I vote for relay swap and deoxit 100 spray the fuses
Chase the easy stuff first

worf928

Without knowing the history of the car and what's new - if anything - Internet diagnosis is simply a list of possibilities:

As above: ignition switch, relays (fuel pump, LH, EZK).
Engine ground strap
Battery ground strap
Symptom of pending failure of original unrebuilt LH.
Crank position sensor or wiring from CPS to main LH wiring harness.

9two8

As has been mentioned check your Battery ground strap, strip back the outer sheath and look for corrosion / burn marks etc. I replaced mine recently after uncovering it and finding those issues. It would idle and drive just fine, and then randomely cut out, and restart itself..., since i fitted a new one, the issue went away.

safulop

Yeah, CPS wiring is a culprit, mine did this and that was the problem. New CPS fixed it.

sendarius

When mine did this, it was after a run over a rough road.

Take Stan's advice - relay, relay, relay. For me it was the fuel pump relay had been shaken a little loose, and was going intermittent.

Deoxit, reseat, and fixed.

Mrmerlin

as Safulop suggested if the relays/ fuse isnt the issue, replace the crank position sensor

outbackgeorgia

So, go through all the diagnostics, and when you are done, if you haven't replaced the LH computer with a rebuilt one, do so. If everything else checks out, it is the LH. They WILL fail, there is a hybrid chip inside that fails due to age/humidity. Fix it now or fix it later, possibly on the side of the road, your choice.
Just one of the fun things about the S4 series.
Dave

Fogey1

And please remember to post when you do get it fixed!

Carl Fausett

Being a 1987 - this is a good candidate for the relay on the LH-Jet that shuts off the car if the exhaust temp sensors identify one bank is cooler than the other. A safety feature meant to help prevent engine fires.

928 International has a euro-type relay that will make the computer happy and circumvent that system.

Randy V

Sounds similar to an issue I had awhile ago:

https://rennlist.com/forums/928-foru...ermittent.html

worf928

Except for the fact that system doesn't appear until MY'89.