Luis A.

Hi guys,

Long-time Rennlister, first time 928 forum poster. I recently picked up a very nice '88 S4 from another Rennlister. Having been in long-term ownership it is very well preserved and not abused. I have replaced the WP and TB, fixed the odometer and then proceeded to drive around 400 trouble-free miles, mostly trips of 20-45 minutes.

A few weeks ago leaving work, it died about 5 minutes after starting the car. It stumbled a bit and then died. After several start attempts over the course of 5 minutes it started again and ran for another 10-15 minutes and died again. Same thing, restarted after several tries. Since then it was driven for a few 15 minute trips with no problems. After that it died again 30 seconds after starting, but starts again... You get the idea. When it's running it runs *perfectly*; no irregular idle, no running on 4 cylinders --zero weirdness. On one of the stalling episodes I replaced the FP relay with a new relay, it started and I thought: "Aha, I found it!", but placed the "bad" relay back in and it started and ran just fine.

Have read up every thread I could find about this. I have replaced all 53B relays except the horn, reverse lights and starter. All the relays that came out had pristine contacts. I opened the FP relay and it looked beautifully clean inside. I can hear the FP humming but not horribly. The CE panel has never seen humidity or water judging from the look of those relays and the wiring and grounds clean and pristine condition. I removed and cleaned the battery terminals and the eye connectors on the positive terminal extension. They were very clean except for some old protective grease.I placed a current monitor on the FP relay and the current is normal, around 7.4to 8.2 Amps once the O2 sensor warms up; it is round 9.something for the first few minutes. I left the current monitor on to see what the FP current supply does when it dies.

Then today it died pulling out of the driveway after about 1 minute of running. The episodes are now sudden and complete; the FP current went to zero but I didn't feel like the first stalling episode when I was driving and it started stalling gradually over the course of 10 seconds. I have no clicking of the injectors when turning the ignition on prior to starting (bad LH symptom). I did not remember to see if the tach was bouncing when trying to restart to see if the CPS is sending a signal. Can the CPS act like this? Start and then just die randomly? And kill the engine absolutely and suddenly?

At this point I am stumped. It does not seem to be related to temperature. It has done it mostly shortly after satrting but not always. And it can start and run without trouble 10 times and then do this... I really love this car but I can't live with this unpredictable behaviour.. Help!

docmirror

Plenty of potentials. The car needs three things to run. Compression, fuel in ratio, and a properly timed spark. Unlikely that you are having a compression event, so lets focus on fuel and spark. Since it stumbles a bit then dies, I'm thinking start with the fuel. If can find a pressure gauge that will fit on the end of the fuel rail runner, that will give you an indication of the pressure at the injectors. Most auto parts stores will sell a pressure gauge, but you need the right fitting and ball end to put on the rail. Once you find the setup, and have it installed, try to drive the car. Make sure it doesn't leak. Fuel pumps are a high failure item with the Ethanol, but until you KNOW about the pressure at the injector rail, replacement is on hold.

Lots of people will be along shortly advising you to start replacing parts. Lots, and lots of parts, like relays, etc. Maybe diagnose first and replace after you know something? Just a thought.

Luis A.

Mrmerlin

first place I would start is the battery ,
make sure to clean every contact on the positive + terminal,
Also clean the the chassis ground.

NOTE if the ground strap is original it would be wise to cut open the sheathing to examine the braid for corrosion.
NOTE make sure the Positive terminal has the cover on it so it cant short out on the battery box cover

Luis A.

Hi Mr. Merlin (name??), Thanks for your suggestion. I cleaned the battery terminals , which were not gunky at all but rather clean, and the accessory red wires connected to the positive terminal. The one thing I have not done is take the cover off the ground strap to inspect the strap itself. I will do that but it is exceedingly clean on both ends and it feels consistent throughout its length. I sanded the end of the strap that connects the body with 600 grit and it’s perfectly flat and making very good contact with the body flat area which is also very clean. Thanks for your suggestion.

Could this be an LH issue? Or the ignition module (EZK?)

FredR

A friend of mine had very similar symptoms to those you describe- we fitted my spare LH and the problem disappeared. He had his LH rebuilt by John Speake and problem solved. That does not mean this is your problem and the obvious thing is to try your LH in another car or vice versa. Good if you can find a local owner to test the LH. You can also send the LH unit off for testing- try John's website for details http://jdsporsche.com

The other common failure is the CPS and that could conceivably cause similar symptoms

DR

Hi Guys,

I am leaning towards the LH also. Ever since I first read Luis post it has nagged me that my first LH failure (89S4) had symptoms just like that. As a matter of fact it was on the way to Frenzy 2 or 3, and it died 3 times on the way there, getting worse each time, until finally that was it. Had to tow it rest of way to Frenzy and it became the 1st confirmed S4 LH Tile failure,.. so it has been a while. In a nutshell it had multiple symptoms like above until it failed completely and only then showed the classic symptoms I reported that became the standard for LH failure diagnosis.

Can't say for sure that is what is going on here, but it sounds really familiar to me.

Hope that helps,

Dave

vanster

I would bet on the LH. When I first bought my 86.5 the seller had a similar problem and gave up. I bought the car and took the LH and the MAF out and sent both the Rich Andrade in AZ. He had them on his bench for a few days and they appeared to be good. Then a few days later the LH failed and the MAF had a bad wire. Repaired both and it solved the issue

Luis A.

GregBBRD

I guess I'm just lucky, however, I have never seen an LH failure that would manifest itself like this.

And if this is what is failing, why would it restart every time?

DR

Hi Greg,

Hope you are well, and occasionally taking some time away from all this 928 stuff! We need to get you into daily driving a 928 more!! I bet if you did that with a 100k+ mile S4 with an original computer your luck might change!! LOL

Not sure what is so unusual about an intermittent electronic device failure that eventually fails. Happened to every TV I have owned in the last decade..first they start turning off, then it gets harder to get it to come back on...that rate increases for a few months...and it is dead.

All the best,

Dave

solidude

Chased that same problem for over a year. Car dies anytime,anywhere,may restart right away,may not till battery is almost flat but never left me stranded. I discovered the warning lights in the dash were not working on restart attempts and cycled the key until they did,then it would usually start. Bad ignition switch. Just my two cents

bogdann

May not be your issue but a quick test is start the car and then move each individual lead to the injectors and see if the engine cuts out. Chased down a very similar problem with sudden or juddering stalls. Did a lot of testing of MAF, EZF, LH, new CPS, new O2, new ground cables and cleaning only to discover by accident poor injector wiring.
Its a quick and easy test.

Luis A.

Luis A.