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-   -   1990 740 sputters then dies in rain (https://forums.turbobricks.com/showthread.php?t=360652)

DavePolyakov 06-06-2021 06:17 PM

1990 740 sputters then dies in rain
 
Im on a camp trip and its the first time Iíve 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

dl242gt 06-06-2021 06:45 PM

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.

DavePolyakov 06-06-2021 07:32 PM

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.

dalek 06-06-2021 08:04 PM

Would grease on the spark plug wires help covering any cracks?

daniels740 06-06-2021 09:31 PM

^ 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.

dl242gt 06-07-2021 11:03 AM

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.

DavePolyakov 06-07-2021 12:00 PM

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.

ZVOLV 06-07-2021 10:28 PM

Is your firewall/hood seal dangling?

DavePolyakov 06-08-2021 01:12 AM

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.

ZVOLV 06-08-2021 01:13 AM

Wiggle test the crank sensor while it's running.

hessam69 06-08-2021 05:59 AM

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

dalek 06-08-2021 05:47 PM

Quote:

Originally Posted by ZVOLV (Post 6191431)
Is your firewall/hood seal dangling?

Can you get the little clips separately?

ZVOLV 06-08-2021 09:32 PM

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

Tonyte619 06-10-2021 01:19 PM

- 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.

DavePolyakov 06-11-2021 01:01 AM

Ok. I'll use a little bit of silicone to reinforce it to the firewall.
Quote:

Originally Posted by Tonyte619 (Post 6192125)
- 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.


DavePolyakov 06-12-2021 05:42 PM

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.
https://i.postimg.cc/W3brHTSD/IMG-2300.jpg

dl242gt 06-12-2021 08:33 PM

Yep, that lets moisture right into the sensor and it will affect the sensors operation. Good find!

DavePolyakov 06-12-2021 08:43 PM

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.

Otto Mattik 06-18-2021 01:06 AM

Quote:

Originally Posted by dl242gt (Post 6191187)
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.

^^ :nod:


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


:-P

Khrrck 06-18-2021 02:54 AM

Quote:

Originally Posted by Otto Mattik (Post 6193971)
^^ :nod:


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


:-P

Bonus points if you can do it in a really dark area so you can see the sparks.

Janspeed 06-27-2021 09:28 AM

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

DavePolyakov 06-27-2021 10:59 AM

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.

philski o'flood 06-27-2021 12:20 PM

Quote:

Originally Posted by DavePolyakov (Post 6195874)
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

dl242gt 06-27-2021 02:22 PM

If your spark plug gap is too large. That can cause misfires under boost. Try using .028" gap.

DavePolyakov 06-27-2021 02:45 PM

Will pull my plugs and check the gap. Thanks for the advice
Quote:

Originally Posted by dl242gt (Post 6195901)
If your spark plug gap is too large. That can cause misfires under boost. Try using .028" gap.



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