1990 S4 Surging - Barely Running
 

Hi All,
Spent a few hours yesterday using "search" and didn't come up with anyone that had my specific problem (I may be being too picky here though). So, Saturday morning I take the car out to grab some groceries and etc., and the first stop, no problem everything working just fine. Second stop, car warmed up but not heat soaked, stopped for maybe 10 minutes, and when restarted, surged a couple times and stalled. Car can be kept running a bit longer with feathering the throttle, but, no revs and no power. Flat bedded it home, let it go back to stone cold, started and no change. Disconnected the battery for half an hour, reconnected after checking that things were charged, and no change. There is a strong smell of gas at the rear of the car when it runs. Top end refresh was done about six - seven years back IIRC, with new TPS, CPS and Hall Sensor included. MAF may be original, I don't know. Same with the computers.

Suggestions on the likely culprit or where to start checking?

TIA!

First suspects to eliminate from your investigation invariably are the LH, the MAF and the CPS If you are getting a strong smell of fuel from the rear that may suggest the fuel pump is running- you can easily check for that by listening from underneath the fuel tank. You should also check to ensure there is no leak at the rear but unlikely i would think. The TPS and Hall sensor are not suspects based on your description.

If you can, swap out the MAF and the LH for known good ones [or try yours in a running 928 S4/GT/GTS].

At the moment my prime suspicion would be the MAF or the wiring inside the connector but...?.

Thanks Fred! Yes, I'm quite sure the fuel Pump is doing it's thing. I have a spare MAF to try out on the shelf (Rebuild acquired with some other parts). I'll go there first and report back.

Running on 4 cylinders? Fuel smell could be unburned fuel from the exhaust?

Rich

Doesn't seem to be. There's no lights flashing on the relay and the last time (was a left / right temperature differential) the car ran a lot better on four than it's doing right now.

Update:
Just went out and tried it again. No surging now. Fires right up as usual and immediately dies. Giving gas helps, but hardly noticeable.

Just had a thought. Although it doesn't explain the fuel smell, I wonder if the fuel pump relay hasn't packed it in......hmmmmmm.
Going to try that next.
If it works, I'm really going to feel like an idiot.

What about a fuel pressure regulator?

All redone with new Bosch bits a couple years ago. I haven't checked the vac lines for fuel though.

Failed LH is my guess. When mine died the symptoms were similar. That’s if all your relays and dampers check out.

Start the diagnosis wih relay-relay-relay. Injection, fuel pump, ignition.

Clean the battery positive termainal connections. These include the feeders for the fuel pump and the injection system.

Your symptoms mathch a failing LH controller. Test yours in another car to verify its function. Known-good rebuilders add labels to the case. If yours has no rebuilder label, it's an even bigger suspect.


There's a great document from Wally Plumley titled "Annual Electrical Maintenance Protocol" that' an esssential read (and execute) for 928 owners. Many owners operate in "reactive mode" and only look for problems when the symptoms appear. A huge number of annoyances are avoided proactively by doing stupid-simple things like cleaning ALL the grounds, cleaning battery terminals, looking for hot relays and fuses, cleaning door switches. I hate getting stranded by Stupid Stuff, and firmly believe that the cars can be very reliable drivers with just a few hours of prophylactic efforts each year. Good connections and a good battery and alternator work wonders.

Rob, you can bring your LH to me and I can test it. Unless you can find someone closer. I’m in Burlington. :)

I've seen it happen when fuel dampers and/or FPR diaphragms are no longer holding and fuel is being fed into the vacuum line. Too much fuel dumped into system. Check with a Mightyvac to see if they hold vacuum.

Thanks! Improbable there's someone closer Adam. Just have to find the time to run out there assuming the other items check. How long does it take?

15 minutes max to test it.