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Old 06-06-2021, 06:17 PM   #1
DavePolyakov
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Default 1990 740 sputters then dies in rain

Im on a camp trip and its the first time I’ve ever drove this car in the rain. After a few minutes the car started to miss and then it turned off and made a popping sound. It started after about 20 minutes, then the same thing happened again. It will not hold an idle and will keep shutting off in the rain. The dizzy is dry, I checked fuel pressure by loosening the connection on the fuel rail and testing if fuel would come out. What should I check? Please help me make it home
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Old 06-06-2021, 06:45 PM   #2
dl242gt
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The most common problem with rain driving issues are bad spark plug wires. They may be cross firing and shorting to each other or shorting to the valve cover. You could try insulating them from each other and from the valve cover. Also check the coil wire for shorting to something nearby like an a/c line. If the top of the coil is very dirty that can also short out the spark.

Another location that may be a problem is the ignition amp. That is the module near the battery on the left inner fender and the connector can get corroded which may be worsened in the rain. Also make sure none of the air intake hoses are cracked or split.

Last edited by dl242gt; 06-06-2021 at 06:45 PM.. Reason: spelling correction
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Old 06-06-2021, 07:32 PM   #3
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Checked everything you said, haven’t found the issue yet. The ignition amp is totally dry. Spark plug wites aren’t new, but in fine shape, not bad condition at all. Could I use blue tape on the spark plug wires to insute them? I feel like they’re fine but im not sure, maybe the blue tape would melt. I do not have the metal heat isolators on the plugs.
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Old 06-06-2021, 08:04 PM   #4
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Would grease on the spark plug wires help covering any cracks?
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Old 06-06-2021, 09:31 PM   #5
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^ Might be worth a try. I'd use dielectric grease, as I don't know the flammability of anything else at high temperatures such as the plugs experience combined with the possibility of rogue sparks. Same goes with tapes, glues, etc. Be safe when working on the ignition system.
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Old 06-07-2021, 11:03 AM   #6
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You can test the plug wires with a squirt bottle of water and see if that makes the car stall. Plug wires can look fine but still leak spark.
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Old 06-07-2021, 12:00 PM   #7
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I did make it home. After stalling about every 15 minutes and waiting for 20 minutes before it would start again, it then drove for an hour in a half with no issues in very rainy weather. I almost made it home, then decided to do a 2nd gear pull at about 10 lbs of boost. It broke up and stalled again. I eventually limped it home.

So, because I replaced my dizzy a few weeks ago it's probably a good idea to replace the wires and plugs anyways. I also am not sure if the stalling is 100% correlated to the rain, but I think it is.
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Old 06-07-2021, 10:28 PM   #8
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Is your firewall/hood seal dangling?
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Old 06-08-2021, 01:12 AM   #9
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Probably half of the clips are gone, but it's still there. The dizzy didn't look wet from it leaking, it doesn't even really look like it is leaking.

Last edited by DavePolyakov; 06-08-2021 at 01:18 AM..
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Old 06-08-2021, 01:13 AM   #10
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Wiggle test the crank sensor while it's running.
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Old 06-08-2021, 05:59 AM   #11
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Is this an LH2.4 turbo? If so, check the connector for the RPM sensor, it may be getting wet/coming loose or the wiring may be shorting together, replace it if in doubt

Another thing to look at is the fuel pump relay
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Old 06-08-2021, 05:47 PM   #12
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Quote:
Originally Posted by ZVOLV View Post
Is your firewall/hood seal dangling?
Can you get the little clips separately?
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Old 06-08-2021, 09:32 PM   #13
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I don't know where to get them right now. I am going to look into upgrading to the later model version that I think rivets in.


Things I would check:

-Corrosion, fretting, oxidation, etc at the ignition coil connectors.

- Poor grounds at the intake manifold

- Poor connection/terminals at the powerstage

- Open insulation for the crank sensor (or just a dying sensor)

- King lead (coil to dist) shorting to ground

- Moisture in the cap. Due to a failed hood seal
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Old 06-10-2021, 01:19 PM   #14
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- Moisture in the cap. Due to a failed hood seal

I've had this problem on several 740s

Its takes very little water in there for it to not want to run at all.
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Old 06-11-2021, 01:01 AM   #15
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Ok. I'll use a little bit of silicone to reinforce it to the firewall.
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- Moisture in the cap. Due to a failed hood seal

I've had this problem on several 740s

Its takes very little water in there for it to not want to run at all.
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Old 06-12-2021, 05:42 PM   #16
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Ok, my crank sensor was ripped completely at the base. Maybe this was why my car occasionally stalls and breaks up in boost? I replaced it with a good condition used one I had laying around. I tried reinforcing the hood seal with silicone but I think I'll have to completely remove it and all the plastic clips and use only the silicone if I want to do it properly.
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Old 06-12-2021, 08:33 PM   #17
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Yep, that lets moisture right into the sensor and it will affect the sensors operation. Good find!
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Old 06-12-2021, 08:43 PM   #18
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My 15-minute test drive went smoothly. However, I don't think I'll know for sure until I can test it in the rain but I'm hoping this was the only cause of the issue.

Edit: Just went for a drive and I was parked for about two hours. When I went back to start the car it took three tries before it fired up. Maybe not related but probably it is. Guessing the problem isn't fixed.

Last edited by DavePolyakov; 06-13-2021 at 01:00 AM..
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Old 06-18-2021, 01:06 AM   #19
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Quote:
Originally Posted by dl242gt View Post
You can test the plug wires with a squirt bottle of water and see if that makes the car stall. Plug wires can look fine but still leak spark.
^^


I had a problem with an internally cracked dizz cap that acted up only in wet weather.


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Old 06-18-2021, 02:54 AM   #20
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Quote:
Originally Posted by Otto Mattik View Post
^^


I had a problem with an internally cracked dizz cap that acted up only in wet weather.


Bonus points if you can do it in a really dark area so you can see the sparks.
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Old 06-27-2021, 09:28 AM   #21
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if you had this leaking issue between paravan and hood it is a good idea to take the dizzy cap off completely and clean/dry it inside and outside. Both the red cap and the black cap that sits over it. There might be residual moisture between the caps causing intermittent leaking of HT-energy leading to missfires
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Old 06-27-2021, 10:59 AM   #22
DavePolyakov
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They were both brand new before I had this issue. Less than a week since I installed them. It's now been three weeks since I installed the new CPS and I've not had the issue persist. My only concerns are an intermittent long crank time and the car intermittently breaks up when I'm boosting over 10psi.
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Old 06-27-2021, 12:20 PM   #23
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Quote:
Originally Posted by DavePolyakov View Post
My only concerns are an intermittent long crank time and the car intermittently breaks up when I'm boosting over 10psi.
if the check valve on the main pump won't hold pressure it will take a longer time cranking to start
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Old 06-27-2021, 02:22 PM   #24
dl242gt
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If your spark plug gap is too large. That can cause misfires under boost. Try using .028" gap.
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Old 06-27-2021, 02:45 PM   #25
DavePolyakov
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Will pull my plugs and check the gap. Thanks for the advice
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If your spark plug gap is too large. That can cause misfires under boost. Try using .028" gap.
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