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Old 04-14-2019, 10:04 PM   #1 (permalink)
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Question Rain stalls engine... but why?

1994 3000GT Base w/ 5-spd and about 320k miles.

Here's the story. Imagine you have a distributor in your car, you get moisture under the cap, and the car barely starts, idles poorly, won't rev past 1,500 RPM, and the backfiring engine sounds like Al Capone's Chicago typewriter when he's avoiding the IRS.

Here's the problem: DIS... no distributor and no rotor. This only happens when it rains, and typically was only an issue if I hit a puddle that would send a wave higher than the front fenders (so I avoided puddles). Now, it rained last Saturday night after I parked my car, and Sunday afternoon my car wouldn't start at all. I took Wednesday and Thursday off work to go trailer my car home to fix it, but she fired right up and pulled herself on the trailer as if nothing was wrong (hadn't rained since Saturday). I drove her 100 miles round trip on Friday without issue. It rained again yesterday here in Texas, but I didn't drive my car yesterday at all - I climb in to head to work, she ran perfect... for about 2 miles. The water has dried up on the roads, so there were no puddle incidents. Go back to the water under cap story above, that's where we are again. I got the car turned around, and though it sounded like a war zone all the way back to my house, I managed to limp her into the driveway. It would frequently die, so I had to cycle the key off and back on and then hold the clutch in and floor it to get the car to fire back up for a quick jerk of aucustic acceleration, just for it to die again and coast a little further.

Now for the messed up part, since it hasn't rained today, when I go out to start it tomorrow, everything will be just fine. How do you fix a problem that you cannot recreate (even with a water hose, I've tried)? I have put dielectric grease in every connector and both ends of the plug wires (only the coil end for the rear bank for obvious reasons). I know that it will not be a waste of money to replace any and all sensors on this high mileage car, but I'd rather focus on the likely culprits first. Any ideas???

EDIT: The car is 100% stock and complete.

Last edited by EJKustoms; 04-14-2019 at 10:06 PM. Reason: EDIT: The car is 100% stock and complete.
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Old 04-14-2019, 11:00 PM   #2 (permalink)
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Default Re: Rain stalls engine... but why?

My guess is that you have a crack in one or more of your coils. It could also be a bad wire.
The next time it happens wait until dark then pop the hood, and look (and listen) for the dancing spark fairies....
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Old 04-14-2019, 11:10 PM   #3 (permalink)
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Default Re: Rain stalls engine... but why?

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My guess is that you have a crack in one or more of your coils. It could also be a bad wire.
The next time it happens wait until dark then pop the hood, and look (and listen) for the dancing spark fairies....
At least we think alike. That was the first place I looked. The second place was to make sure water hadn't pooled up around the spark plugs. No fireworks under the hood. All three coils are less than a year old, same with the plugs and wires (all 6...who designed that intake plenum anyway?) as well as the ECU and ignition module (if that's what the plate the coils mount to is still called). The kid I got the car from was having trouble with the 2-4 coil pack melting down, I resolved that issue with repairing a broken ground wire in the harness.

An old timer I was talking to said something about the plastics that were used in the 90's for sensors are known to attract moisture as they begin to deteriorate, which makes sense. If this were an OBD-II car, I could just plug in a scanner and have a look around, but it's not.

I'm leaning towards a crank sensor to start with, but wanted to get some other input as well. I am hoping I don't have to trace the engine harness wire by wire again. Mine cannot be the first 3000GT to exhibit these symptoms. And with my research, I am thinking of changing out the IAC just for kicks.

My biggest issue is repair verification - if I cannot reliably recreate the issue when it's still broke, I have no idea how to verify the repair after changing parts.
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Old 04-14-2019, 11:50 PM   #4 (permalink)
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Default Re: Rain stalls engine... but why?

I don't know about the plastics absorbing moisture but if it looks like this https://www.3si.org/forum/f1/causes-...sensor-630953/
I'd be comfortable calling it fixed....
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Old 04-15-2019, 02:03 PM   #5 (permalink)
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Default Re: Rain stalls engine... but why?

Well, as predicted, 48 miles to work today without the slightest hint that anything is wrong.

I thought the factory rev limiter was set at 6500 RPM? I was curious if it would cut out after hitting the rev limiter after it warmed up, but I backed off the thottle at about 7100 RPM in 2nd gear when I was getting in the interstate. If the rev limiter isn't working right, what signals does it rely on?

As for a troubleshooting step, I think if I go through an automatic car wash that sprays the underbelly, I might be able to simulate driving in the rain to see if the issue pops up. If it does, then I should have a semi reliable means if repair verification.

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Old 04-15-2019, 02:54 PM   #6 (permalink)
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Default Re: Rain stalls engine... but why?

Also, does anyone have section 16 to Vol. 1 of the service manual (ignition system)? The PDF from 3sx jumps from 15-41 to 17-1.

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Old 04-15-2019, 03:05 PM   #7 (permalink)
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Default Re: Rain stalls engine... but why?

My printed manual does the same thing ('91 Stealth service manual, skips from section 14 to section 16). The ignition system is covered in Vol. II.
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Old 04-15-2019, 03:30 PM   #8 (permalink)
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Default Re: Rain stalls engine... but why?

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My printed manual does the same thing ('91 Stealth service manual, skips from section 14 to section 16). The ignition system is covered in Vol. II.
Thanks. I'll dig in some more on Vol. II.

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Old 04-17-2019, 02:27 PM   #9 (permalink)
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Default Re: Rain stalls engine... but why?

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Originally Posted by EJKustoms View Post
......Mine cannot be the first 3000GT to exhibit these symptoms........
No yours is not first to exhibit those kind of symptoms. Those symptoms sound just like beginning stages of capacitor failure in ECU, but that is not normally associated with rain or water spray under car. Could water issue just be coincidental?
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Old 04-17-2019, 03:03 PM   #10 (permalink)
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Default Re: Rain stalls engine... but why?

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No yours is not first to exhibit those kind of symptoms. Those symptoms sound just like beginning stages of capacitor failure in ECU, but that is not normally associated with rain or water spray under car. Could water issue just be coincidental?
I wish it were just a coincidence, but it's now dependably predictable - if it rains, it will stall out until the engine bay completely dries out... unless the increased humidity in the air is somehow shorting out the sensor that is leading to capacitor failure.

I'm ordering a cam sensor, a crank sensor, and an IAC. I know it's not a good way to pinpoint the issue, but at over 300k miles on the clock, all of these likely need changed now or soon.

If the issue persists after those are changed, I have two ECU's on the shelf.

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