neilschelly

The harness connection at the DME is solid. I have removed it for inspection and replaced it with no change in behavior.

A spare S2 DME is tempting. This one was a replacement from long before I got the car, and I don't know what was wrong with the original one. I may PM you to see if it can better survive a drive in the rain, but I struggle to see how the rain can so easily affect it if it's not getting wet.

I have tested the AFM. I did clean it, but I didn't see any gaps in its connectivity as the flapper moved.

And yes, I will be more careful to distinguish the DME from the DME relay. I fixed the typos in my posts.
-N

walfreyydo

See my edit related to the ignition switch - something to look into

neilschelly

One of the lights on the F9 DME relay is for ignition power, and that one is never wavering. I also can't imagine why the ignition switch wouldn't work only when wet since I have the roof in when it rains.
-N

neilschelly

I found my oil pressure sender was disconnected from both wires. One wire broke from it's ring terminal, and the other one just pulled itself off the spade connector. I'm not sure if those were supposed to be two different connection mechanisms originally or if that's been repaired before. Either way, both wires are connected again. I really doubt that this is the electrical ground issue I'm looking for because I don't see how either of these could have been causing issues only when wet, but it's fixed now.

I also found the oxygen sensor wire wasn't properly supported. The metal clip wasn't attached to the stud over the torque tube, but it is now. Again, that isn't necessarily a source of the problem, but it does suggest I should take a closer inspection at the cable to the O2 sensor when I get a chance. It's clearly been replaced before, and it's got a lot of wiring splices along its path wrapped in just electrical tape. Again, no obvious culprits, but it certainly doesn't look great.

I have another theory to investigate too. I have the alarm control unit near the DME (928.637.104.05). I don't have specific reasons to suspect this, but I'm pretty sure interrupting the voltage signal to the DME relay is the way this implements it's immobilizer. Again, this unit has stayed dry when this problem is occurring, but I don't really know all the things it's connected to. I wonder if something is convincing the alarm unit to cut power to the DME relay.
-N

Dan Martinic

I understand it's common to disconnect / disable the alarm due to issues...

neilschelly

I have heard that too, but mine appears to work fine (assuming it's not the culprit here). I'd rather diagnose it before assuming it's dead and bypassing it. I'll need to learn more about how it works so I can maybe diagnose it during the next rainy drive.
-N

jhowell371

Read this before doing alarm work:
https://rennlist.com/forums/944-turb...989-951-a.html

neilschelly

That tells me that I'm one of the '89 cars with the late alarm, but it certainly sounds like mine works. I've never had issues with central locking, opening the hatch, locking/unlocking doors, etc. I'll have to do more research into exactly what circumstances would trigger the immobilizer and what it would do if the immobilizer was triggered while driving.
-N

951Tom

[QUOTE=I also found the oxygen sensor wire wasn't properly supported. The metal clip wasn't attached to the stud over the torque tube, but it is now. Again, that isn't necessarily a source of the problem, but it does suggest I should take a closer inspection at the cable to the O2 sensor when I get a chance. It's clearly been replaced before, and it's got a lot of wiring splices along its path wrapped in just electrical tape. Again, no obvious culprits, but it certainly doesn't look great.
-N[/QUOTE]

Are these suspect repairs/splices on the O2 sensor side of the plug or the DME side? I'd definitely look into this more closely as a bad O2 signal can affect fuel mixtures once warmed up. You mentioned it doesn't do it when the motor is cold and the O2 sensor signal isn't looked at until the engine reaches a certain temp. My car is a turbo, but way back in the beginning I had some poor running issues (bucking/hesitated) and I remember a new O2 sensor corrected them. Try disconnecting the O2 sensor and see if your problem goes away. Get the correct S2 genuine Bosch sensor not the universal one.

Tom
'87 951

Breakaway944

I have a '91 that I put a turbo engine in. One of the differences is that on the S2 there is a connector behind the left headlight that connects to an igniter (?) to fire the coil. I have been chasing a miss and I checked this connector because it can get wet as water gets in from around the headlight. If this gets wet it will cause a miss or even a no run. Sounds like you have a weak ignition when car gets wet, this would do it, or the wiring of it going to the coil - totally exposed.
I do not fully understand the functioning of the FTech9 relay. You are thinking the relay is indicating no ignition power when acting up. The only thing I can think of that would cause that (and could get wet) would be a major battery cable. If it was going out getting wet could be enough to cut car off. Does not seem to fit your symptoms though.

neilschelly

Near the O2 sensor, there are at least 3 different colors of electrical tape wrapped around the wiring, so it's been spliced in a few times at least. The sensor itself looks new enough, but I'm pretty sure I haven't replaced it. I imagine it's very possible that water seeps into those splices causing at least some inaccurate readings from the O2 sensor. I haven't had a chance yet to pull off all the tape and clean it up.
-N

neilschelly

I have replaced the igniter behind the left headlight when having weak ignition issues in the past. It does not seem like it's the culprit at least.

The FTech9 DME relay with the diagnostic LEDs has 4 LEDs on it. One is 12V ignition power which goes on when you turn the ignition to on. One is fuel injector power which turns on when the DME relay is turning on the circuit for the fuel injectors. One is fuel pump power which turns on when the DME relay is turning on the circuit for the fuel pump. The last one is the signal wire from the DME itself to turn on the fuel pump. When I've had this issue, I've seen that the last two lights are off. The DME stops sending the signal to the relay to turn on the fuel pump, so the relay turns off the fuel pump.

Anyway, I can't be sure it's not an ignition cut, but it doesn't _feel_ like an ignition cut to me. It feels like a fuel pressure cut, and the DME relay LEDs definitely support that.
-N

Jfrahm

Probably time to send the DME out for testing/repair, or get a replacement. I have a 1991 S2 DME laying around but they might not be compatible. At least I recall it's a 1991. Came with a 91 engine I bought at one point and later sold.

neilschelly

I pulled the O2 sensor, and I decided it was worth replacing after seeing it too. There was definitely some peeling electrical tape from at least two spots on the wiring. Now, I'm just waiting for some rain to really test it.

I _did_ go for a drive-thru car wash, which has definitely triggered this before. There were no issues. There's no rain in the forecast for at least the next week, and I've already turned off the hoses outside for winter, so I was impatient. I'm hesitant to call victory yet, but I'm cautiously optimistic.
-N

neilschelly

Finally, some rain...

It's literally been this long since I had an opportunity to drive in the rain. Today, I was out in heavy-ish, consistent rain, on back roads and highways, with stop and go driving, restarting after parking for a bit, etc. There wasn't a single hesitation or misfire, and this weather definitely would have caused a problem every time before.

The O2 sensor was it! Woohoo! Thanks all for your help/ideas!
-N