neilschelly

I have been having an issue for some time now with my relatively-new-to-me 1989 944 S2 with ~215k miles. The car was undriveable didn't run at 208k when I acquired the car, so a lot has been refreshed, and it runs great on dry days now. When it's wet out, I have the following symptoms, and I'd love the community help troubleshooting.

* The car will lose power suddenly when driving. It won't happen right away, but it will happen during a rainy drive within 20-25 minutes. It will also linger with the car the next day for a bit, even if it's sunny and warm.
* .It can stall out, but I can usually save it if I clutch in and slam on the accelerator to rev the motor. It will also generally always start right up, and it will idle fine. The power only really cuts out when the engine is under load. Sometimes that happens immediately if you haven't revved the engine high enough before lifting the clutch pedal. When I've had to get home and not be stuck, I've come home with a burnt clutch smell because clutch drops are reliable ways to get going again.
* It will be less likely to happen when the the tachometer is kept higher, like dropping a gear to keep the tach over 4-5k, but that is not a given.
* I have the Focus9 DME relay with the diagnostic LEDs and the pre-prime fuel pump timer. That might explain why it always starts up right away because fuel is always available at startup.
* I have witnessed the Focus9 DME relay lights when this is happening. The lights for fuel pump power and fuel pump control signal from the ECU blink when the engine hesitates.
* I have replaced the DME relay with a jumper to force the fuel pump to stay on. This keeps the car from stalling out, but it will still hesitate. occasionally. If I just keep my foot on the gas, it will continue again.

Things I'm confident of...
* I have reliable power at 14V everywhere I can test.
* I have cleaned every ground I can find, including the ones behind the headlights, the ones all around the engine, the ones back by the fuel pump, the ones near the fuse box (above and below), near the battery, etc.
* The cam position sensor is new, as well as the connector that disintegrated when I first touched it.
* All ignition wires, distributor, the ignition coil, and the "other ignition coil" that is behind the left headlight are new/good.
* All fuel lines and filters (outside and inside the tank) and the pump are recently replaced.
* The battery is good and reasonably new.
* All the ignition components under the hood are staying dry, even when I drive without the engine trays installed. The same for the cam position sensor, engine reference sensor, and the fuel injector harnesses.
* I idled the car in my driveway for 30-40 minutes and just sprayed everything under the hood with a hose for that hole time. It never hesitated or skipped or anything. Every connector and ground connection got a straight blast of hose water jetted at it with no impact, but it wouldn't drive well after that. Whatever water had gotten _somewhere_ needed to be gone before the car drove well enough again.
* The dashboard under the driver's side is staying dry. There's no water getting into the wiring under the fuse box, and the driver's side floor is staying dry (except for whatever comes from my shoes). The floor and ECU under the passenger side is also staying dry.
* The distributor is staying dry. The S2 doesn't have that extra seal behind it that could allow water in.

Top Theories:
* Water is getting _somewhere_. It sounds obvious, but that explains why it doesn't happen right away, and it would explain why the issue may continue the next day with nice weather for a little while.
* When it happens, the ECU is interrupted. That would explain the ECU signal for the fuel pump cutting out. That would explain the engine still hesitating when the fuel pump jumper is forcing the fuel pump on permanently.
* The tray under the windshield over the HVAC fans has a few cracks in it. Maybe water is getting under that tray and grounding something out?
* Either the engine reference sensor or the cam position sensor (or the signal from them) is getting interrupted. That would cause the ECU (probably?) to cut the fuel pump signal and ignition.

I'm running out of ideas. Has anyone else ever run into anything like this?

goblues38

check the air filter...is it wet?

to me it sounds like the air fuel is getting messed up during rain. is the air box sealed, is the intake set up correct?

neilschelly

The airbox is stock, and I cannot imagine how water could get into the S2 airbox hidden inside the nose piece, but that's worth a look. I know the path from the airbox, through the MAF, and into the engine i intake manifold s all dry at least. I wish the filter was something I could quickly access next time this happens. Hopefully, I'll have some time to kill afterwards!

Dan Martinic

Perhaps it's not water but moisture (ie. dampness or humidity). On a rainy day, when problem begins, get out and spray WD40 on anything electrical incl. fuse box & see if changes

Since jumping the DME relay changes the behaviour, I'd put a stock relay in for now

jhowell371

This is coming from left field but you may be experiencing icing in the throttle body. Just as piston powered airplanes experience carburetor icing and have "carb heat" available to help prevent it the S2 throttle body is heated with engine coolant to prevent the same. Check your car's TB hose when it's warmed up to see if it's hot.

neilschelly

I don't think it's just moisture-related. Humid days don't cause a problem. Light rain/drizzle doesn't cause a problem. It needs to be reasonably heavy and consistent for 10-15 minutes of driving before water gets to wherever it is getting to.

I'm unfamiliar your technique of \spraying WD40 on anything electrical. I strongly suspect it won't affect anything, because the stumbling doesn't happen while idling in place. What would you be trying to learn by doing this?

As for the DME relay, I'm confident it's not causing the issue. I have a functional stock one, and this behavior was occurring before I got the Focus9 one. The F9 one just provided the additional benefit that I could see the ECU signal for the fuel pump cutting out. I think that jumpering it just causes the fuel pump to stay on (and thus the fuel system pressurized) even when it stumbles. Normally, whatever causes it to stumble seems to convince the ECU to kill the fuel pump, and that exacerbates the problem.
-N

neilschelly

That's not a theory I've considered. I do know that coolant flows through there, but could it really ice up in summer heat temperatures? And why would that happen only in the rain?
-N

T&T Racing

I am a 944 8V owner. Are there electrical diagrams available for all the wiring input to the ECU? If so, lists all the symptoms observed, all individual in tabular form. Then, list the individual inputs to the DME that might cause that symptom. See what are common threads.
An observation: only happens under load at Xxxx rpm and not at idle. Is the oxygen sensor circuit a possibility?

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Dan Martinic

As you know, WD40 stands for "Water Displacement"... In my youth, I would wash engines then wonder at all the stumbling / poor running afterwards... then I started spraying WD40 before & after and problems stopped. You could wait until the issue starts then get out and spray something and see if goes away. Though by the sounds of it, this issue involves a buildup of water rather than simply moisture and in this case, you got to look where water would accumulate.

Maybe you have some blocked drains or something

Take a hose and see if the drains under the cowl are clear. Is it possible you got a problem in back with the fuel pump? Spray some there. Tough one man

jhowell371

Icing occurs most during high humidity and can occur during summer temps. I luckily never experienced carb icing in the plane but I used carb as recommended. I did have visible frost form once on the throttle body of a Carter Thermoquad mounted on my 396 Chevrolet over 50 years ago. YMMV

neilschelly

There are electrical diagrams, but they are somewhat difficult to trust. The docs for the S2 are less accurate from what I've seen, and there were two different S2 ECUs to make it even more confusing. I have tried brainstorming all the possible causes by this logic, but I always come to a point where I don't entirely know what the ECU would do in a given circumstance.

I would say the symptoms appear while under load, but not predictably at any specific speed. I might be able to drive fine for 1000' and then have it stall out on me 3 times in the next 100'. And as it gets wetter, it will be more persistent.

I have not inspected or replaced the oxygen sensor. I wonder what the behavior would be if that were to get a short. Could I run "okay" with it disconnected I wonder? If so, maybe I can at least run reliably "okay" and know that's the culprit. I like this line of thinking because it's one I haven't considered before. I'll do some closer inspection on that next time I'm under there.
-N

neilschelly

Today I learned what WD stands for. That is literally news to me. I could definitely spray it around a few theoretical problem spots and see if that magically fixes it. That test might have to wait for the dry day when it's misbehaving after getting soaked the day before.

I should have mentioned in the first post. All drains are cleared. (4x sunroof drains and the battery/fuse-box drains)

curtisr

You said that the distributor is new. I presume you mean the cap. However, if you don't I'd check the cap for cracks.
BTW: the 40 (in WD - 40) is in reference to the number of formulations tried before getting it right.

neilschelly

The cap and rotor are new within the last few thousand miles. There are no cracks i can see in the cap. Also, the distributor always seems dry when I poop the hood after getting a lot of stumbling.

This behavior matches behavior I've seen described with 8v engines where the seal behind the cap is missing or failing. It seems like the belts can get wet and splatter water up into the back of the cap, but the design on the 16v cars is different. There's no way for water to get in there I can find.
-N

walfreyydo

You might also want to check the harness connection at the DME under the passenger footwell.

I do have a spare S2 DME (note: not the relay, the dme) available if you need it, this could be your issue.

Have you tested the AFM and retracked the contacts? Ive found this can cause all sorts or weird stuttering issues, "cutting out" and so forth.


Lets make sure we are using the correct terminology here. DME = engine ECU computer, DME relay = the fuel pump relay (F9tech solid state relay in your case). I am seeing you use these terms interchangably and its important to distinguish these as separate and different parts that do different things to avoid confusion. In both of the above quotes you are referencing the DME RELAY, not the DME.

You may also want to test/inspect your ignition switch, as the signal from that switch will activate/deactivate the DME relay (causing the lights to go off/on). So check your ignition switch - that may be the cause of the car randomly shutting off.