I bought a set of injector plugs WITH tails from 928SRUS and soldered in the new plugs to the existing wiring with some heat shrink tubing to protect. Took a few hours but realized most of my existing wiring was just about toast. Also did the MAF and CPS plugs while I was there. Should get a new wiring loom but that seems a bit too much at this point.

 

I had a similar issue with the '89 soon after I got it.

Strangely, it seemed to happen more often on left turns - car would die mid-turn, then I could restart as soon as I straightened up, and coasted to a halt.

I re-seated the LH relay (XXV on an '89, I believe it's the same on an '88), along with a dab of De-oxit on each terminal, and haven't had the problem since.

 

Have you checked the CPS to make sure it isn't crumbling and making intermittent contact? It is at the rear of the engine beneath the airbox. It does play a vital role in spark and fuel.

 

Tracy, I agree the CPS is simple enough to eyeball and replace that I will do that jut to eliminate that variable. I have not yet laid eyes on it but will do so tonight.

 

Steve, I replaced all critical 53B relays including the LH. The pulled relays were very clean and upon bench testing them all triggered closed at 7.9-8.1 volts and did not release until voltage was just below 4 volts. The 30-87 contact resistance was under 0.1 ohms.

 

This failure mode interests me. With the incredible amount of these cars I see, I amazed I have not seen this problem.
Interestingly enough, aside from an occasional "injectors clicking with the key turned to the on position" LH failure, I replace virtually zero LH units for other problems. (I've had one LH that had no output signal to the idle stabilizer, because the idle stabilizer shorted out...and that's the only one with a "different" failure mode.


Perhaps most of the LH units have already been rebuilt and uodated, out here, and there just aren't any high mileage units...

I'll add this to my mental list of possible problems.

Thanks.
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Luis, I've had the pleasure to experience 3 separate issues from normal running -with similar symptoms as yours:

1.) Bad alternator... all warning lights would light up as car dies. Restarts in a few minutes, only to die again after a few more miles.
2.) Bad Final Stage module... began running very rough, like trying to stall. Sitting at a light while keeping gas pedal going to keep running, it started smoking from under car. Pulled over to 'cool down' & it restarted & ran fine after about 20 minutes. Happened again & more often. Local 928 expert correctly diagnosed the rare 'limp-home mode' (running on half cylinders) issue.
3.) Prelude to total computer failure... (not mine) rough running & dies while at idle. With steady gas, ran fine at highway speeds without issue. Slowing with traffic would lead to stumbling and dying approaching idle speeds. Started right back up and giving gas kept running -as long as you didn't have to stop. Bridging the positive & negative battery CABLES ONLY (while disconnected!!!) seemed to reset the computer. Told it was a common BOSCH issue among various automobile makes. Replace computers anyway.

Hope this helps!

 

Hi Barry, thanks for your reply! The behavior with my failure, unlike the 3 failure modes you describe, is that when my car runs, it runs *beautifully* well; no irregular idling, no roughness, no constantly trying to die, no weirdness at all. I can drive it for a while (I'm not venturing too far right now) without issue, and it will always restart after 2-4 attempts.

Unless the 928 alternator is different than every other alternator I know (and that would not surprise me at this point, the way these cars are over-engineered...), I would think the charging voltage would be irregular, either too low or too high and the corresponding alternator light would come on. If the alternator completely dies so severely as to shut down the car, I don't think it would restart again like mine does. The car would still run on the battery (with alternator warning on) until the battery dies... so that failure mode is a bit of a mystery to me...

 

Hi Greg,

I can completely understand, it's just from 2 different experience pools. I have personally seen and diagnosed dozens of LH failures in my experience. I am sure the same as you have had many other 928 issues that I haven't seen. That is why the combined knowledge of places like this forum can be so helpful to all the 928ers. No one person can experience it all.

In regards to this thread, all I said was his symptoms seem to mirror a few experiences I have had and it rang a bell with me. FWIW, Never meant to imply these symptoms could not be anything else. It could be water running back and forth on the block from changes in angle, and shorting out the cracked CPS connector when it flows rearward, seen that a bunch of times also. Of course it could be the wiring harness and a myriad of other possibilities, but I do know that the guys here combined will do their best to try and help the Luis figure it out, as always.

Another reason you many not see as many, maybe I have helped diagnose and fix em all, LOL Seriously though, I don't hear of it as often as 10 years ago, so probably most have been updated, that is a good thing!!

Cheers,

Dave

 

Information from trusted sources is always a good thing. I'm convinced that different climates around the country affect things differently. I keep several rebuilt LH units in stock. (I send them to England to have them rebuilt, so there is quite a bit of "lead time"....I have to keep inventory.) We just don't replace very many.

There's no doubt that the OP's problem is a bit unique. The fact that his car "stumbles" and quits is pretty unique and eliminates a bunch of possibilities/components. Most of the components (like the crank trigger) would cut out both the LH and the EZK....and there would be no stumble......just a total "shut off". (It would be interesting to know if the tach drops to zero or if it keeps working while this stumble is going on.)

Edit:

I just went back and reread the OP's first post. It sounds like he is/was having two separate issues. One that stumbled and now one that shuts off everything. I'd guess that the first problem was fuel pump related....just about the only thing that will allow these cars to stumble and still run. The current problem certainly could be the CPS.

 

Hi Greg,

I agree with you about he climate issues, just thinking for example the difference in climates like the dry air out west vs the wet humid air in the deep south.

The point you made about sloppy fuel event, then sharp ignition event is exactly how it went down for me, twice within 1-2 years (89-120K,88- 140K). Each time happened on a 10 hour + Interstate Drives(stopping only for gas and munchies) and they could get spirited on occasion, but it was an interstate. So lots and lots of heat soak. My experiences both mimic closely Luis issues, but of course happening at high interstate speeds over the course of 4-5 hours?? until it was a dead on the road situation.

So basically what I experienced was in real time, on the road time, a failing LH that then failed and exhibited the classic symptoms. Thank goodness I suggested the we do the Frenzy that year at Autothority! Their team and I quickly confirmed the LH was dead and then we spent a lot of time looking at all the circuitry under a microscope....and started seeing cracks. I think the rest is history, but it documented here and the other normal 928 sites. In a nutshell when things that aren't supposed to be "cracked" in electronics (or anything) start cracking on a microscopic level, you can get all sorts of odd behaviors(doubt they could ever all be the same) as components heat cycle and continue to degrade.

I would like to give a special mention to Brian Robinson, he set the bar for 928ers helping others early on back then. During the Frenzy Sat Night party he drove 2 hours home in his 928, pulled his Computers, hopped in his BMW, came back to the Frenzy and gave me his computers to get back home with in Atlanta. Thanks again dude!! Forgot to add, that was the first time we had met!

Oh, and that 89 performed flawlessly again for years as it always had, so in those situations the LH was the only problem.

I hope for Luis sake it is something like the CPS, etc,. it is just his description rang a bell with me and thought I would share.

Hope that helps,

Dave

 

Had an L-Jetronic do that. Flawless running, then dead stop for no apparent reason.

Took us several years of headscratching to actually solve it.

 

Long shot, but is there any chance that a socket terminal was pushed out of place when the new relay was inserted?

In thinking about it afterwards, my intermittent cut-out issue developed after a *spirited* run over some of Australia's famous corrugated roads.
I am hypothesising that the vibration shook the relay loose.

 

OK guys, here's the latest. Last night, it started it several times on the driveway with no issue. Took the fuel rail covers off and jostled the injector wires a bit, without unplugging them and that didn't cause anything, keeps idling fine. Played with the key in the ignition, pushing up, down, left, right and in. Nothing, runs fine. Decided to take it around the block and about 3-4 minutes into my short drive it suddenly died and did not start after maybe 10 tries to start. This is good! I can now hopefully reliably diagnose what is causing it.

Pushed it home the block and a half (heavy car!) and ascertained there is no current going to fuel pump. Forgot to see if I had tach bounce while cranking... Took off airbox at this point. Installed the fuel pressure gauge at the right rail and then jumpered 87 and 30 on the fuel pump. Pump runs and pressure is around 60 PSI (within spec for car/engine at "standstill") but it still won't start. Removed a spark plug wire from each side (one at a time) and installed a fresh plug, cranked and I do see spark while cranking. See attached video. I'd like someone to tell me if the clicking noise that you can hear in the video when the key goes to ON, just before I crank, if that is the injectors clicking or is there another normal source of clicking in the engine compartment that would normally make this noise. I have a noid light but didn't attach it.

So knowing I have spark and fuel pressure (by jumpering 30-87 at the FP relay) I try to start it and it runs but very roughly if I play with the accelerator but doesn't stay running; very rough and wants to die. I removed the MAF and in the process the right side knock sensor connector crumbles as I remove it to access the MAF's hose clamp screw. I can see the CPS connector but can't easily access it until I remove more stuff. So I am thinking my next step is to remove the intake so I can remove the CPS and its connector and replace it. It looks pretty hard without removing the intake. I have a noid light but didn't attach it. Should I do that before removing the intake?

And also the knock sensors since they are original it doesn't make sense to just re-do the connectors, plus all the plastic insulation on the knock sensor cracked off and the shield is exposed.

Thoughts...??

 

You don't need to remove the intake (overkill) to remove the CPS. Just remove the MAF and you should have enough room but it may not be easy if it is stuck in there. Do a search specifically for CPS R&R. Also someone may chime in with links. Also that clicking is probably the LH failure sound but I have not heard it firsthand. On second thought you probably need to do a full intake R&R since your knock sensors need replacement. Good Luck