Fabio421

I bought an 89 S4 5 speed. It has a problem where the car will randomly stall out. It does this both idling as well as while you are driving at speed. When driving, because it's a 5 speed, the car usually immediately restarts and it feels like a hiccup. The strangest thing about this issue is that the problem is quite a bit worse when the weather is warmer. The problem almost disappears during the winter. (Florida winter is anything below 55 degrees F )

So far the following has been done.

Replaced LH
Replaced EZK
Rebuilt MAF
Replaced Temp II Switch
Replaced Fuel Injectors
Replaced Crank Position Sensor
Replaced Ignition Switch
Checked and cleaned Ground Points at back of engine, behind/above CE panel, and at front of the engine bay by headlight bar.
Replaced all relays that pertain to fuel injection or ignition


There is a fuel gauge on the fuel rail. When the car stalls the fuel pressure stays steady and doesn't drop or leak down. I believe that this would rule out a "vapor lock" situation or a bad fuel pump.

The engine wiring harness looks to be in great shape and I don't see any issues with it.


Can anyone give me any advice regarding what I should check next? I'm at a loss.

Thanks in advance

Speedtoys

So..how's that 14-pin harness plug doin?

SeanR

Do the RPM's drop low before it stalls? Faulty wiring for the ISV can cause this.

Bilal928S4

What about the ignition switch? Just a WAG.

OTR18WHEELER

The ambient air temp clue leads me to think it could be a bad wire critical of ignition, expanding and breaking contact as it gets warm, or a loose coil wire. Check the coils and the ignition.

Speedtoys

BOTH coils failing at the same time...


Ive had this at the side of the road before..

14-pin connector corrosion and age.

jeff spahn

Yep. rebuild the 14 pin connector with parts from Roger. Did this right after I got my car.

James Bailey

How about the big relay for the ignition monitoring/ head temp sensors ? It has the ability to cut off injection to 1/2 the cylinders if it senses too much difference but obviously can also shut down all of them.....it is a fancy relay and we KNOW that a relay can go bad
Plus the location of the sensor on the heads was changed for 1990 due to poor readings on the 89....

Hilton

I can't see the throttle switch on the list of things checked/replaced.

Your fault could also be a problem with the idle contact on it (a microswitch).

Simple test using a multi-meter at the LH harness connector.

edit: just re-read the OP and I see it does it at speed too.. which means not the idle switch (altho' worth testing that too).

edit2: Have you checked the connection on the small red wires at the battery? They include the LH so making sure they're clean and not loose is a good idea too.

soontobered84

Check and clean engine grounds at the back of the Vee,(saw that you did that already) the coil grounds, and remove clean and replace the main engine ground under the car on the passenger side. When the computers find a ground, the car will run great, when they don't find a ground, the engine will shut off just like you turned a key off. The car will crank just fine, but not start until the computer happens to find a ground, then it happens all over again. No rhyme or reason as to when the computer finds that ground.
This problem happened exactly like this on my '89. Cleaned the main engine ground and have not had an issue since.

SQLGuy

I would start with the engine idling and the hood open, and poke around with a dowel to try to aggravate the problem. One area to poke would be the cam position hall sensor and its harness. I would also poke around the ISV harness, and knock sensors/harnesses/connectors.

I hate shotgunning... though it probably doesn't hurt to replace the items you've replaced, if you don't know the history of the car, you may be replacing stuff that was replaced not too long ago anyway.

I wonder if a Durametric or Sharktuner could tell more about the "hiccup."

I would also try tapping and shaking things in the CE area and in the connectors for the two ECUs.

The fact that it hiccups quickly, does sound more like an ignition related problem than a fuel related problem, but that still leaves plenty of possibilities.

Randy V

My WAG is you didn't read the OP closely.



I was going to suggest the LH computer as mine had similar symptoms, but he already replaced that too.

Bilal928S4

Randy,
You are totally correct. I just glazed over that entry.

Koenig-Specials 928

When mine did the same thing it was a coil gone bad.
I replaced it with an MSD coil and that was 3 years ago.

GregBBRD

The most common cause of this is high resistance in one of the spark plug wires....and this includes the coil wires.

This can be "green corrosion", burned up resistors, burned up ends into the caps, not completely pushed in coil wires at the coil, the wrong coil wires at the coil, and a poor brand of spark plug wires.

ANY spark jump or very high resistance (corrosion) will force the spark to "jump" around the rubber boot and short to the actual coil primary terminals. The car will instantly die, but will restart....exactly like you describe.

There's a supplier of spark plug wires, out there, that has ends that go into the distributor caps that make a 90 degree bend, but the actual wire can pull out of that 90 degree piece. The wire will stay inside the "boot", but will be completely disconnected, allowing a spark jump and "coil flame out".

There's two completely different designs of coil wires that go into the actual coils....and two completely different kinds of coils. (A genuine Beru set of spark plug wires includes both kinds of coil wires.) There is a style that had a "pin" inside the coil (just like at the distributor cap end.) This needs a female style end to connect over that internal pin (just like the connector at the distributor cap end.) The other style is a traditional "American style" coil with a male end that connects to the brass contact inside. Many times we will find the wrong style coil wire at the coil end, which forces a "spark jump" situation.

The other common problem is the plastic rain caps that are on the coils. The coil wire MUST go over the top of the inner edge of these rain caps, in order to make a good connection at the coil. The rubber must go over the top of this plastic by about 4mm. There are poor quality coil wires out there that are too small and will not go over this inner edge....they butt up to the plastic and stop. When this happens, the coil wires are generally not be connected internally and, once again, the spark will have to jump.