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Old 11-23-2021, 11:00 PM   #1
Jyromefedx
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Join Date: Oct 2015
Location: Saskatchewan,Canada
Default Para-limpic 740 Looking for advise.

Hello and good day Brickers

I have a fantastic 1989 740 (LH2.4), her existence started with me as a 400.00 field car and six years later has been a true tough beast.

Please let me know what you think, I will try to be descriptive as I can.

As long as I have had the car when the roads are wet enough to dampen the underside of it, she may start running rough and trying to stall out at low throttle. This is what I though the case was recently, we had a harsh rain before snow this winter and on that rain day she got wet in the wrong spot and I had to drive her home in Limp mode. We have had some nicer days and it only usually takes a couple to dry her out and function %100 again. Not this time.

Here is what I know:
On a cold start she runs great as ever, give it 10 or so minutes and as the heat starts building it progressively runs worse until the rpms get dippy to a point where it can stall.

Unplugging the MAF or IAC putting it in limp home mode works great, RPMs steady at 1000.

I have swapped out the Maf with a spare to no difference, I have swapped the IAC with a spare to no difference.

Unplugging the Coolant temp sensor does not seem to make it worse or better as it chugs.

I have checked all my grounds and have even added a new one to no benefit.

I have not found any vacuum leaks but I am not completely certain there wouldn't be a small one.

My bougicord plugs are all pushed on and in.

I have sprayed WD-40 on most of the relevant wiring harness to displace any moisture that might have still been in there.

Can this all be an issue from a faulty 02 sensor signal? I have only found people saying with LH2.4 that 02 doesn't matter too much.

Does this sound like a bad Coolant Temp Sensor?

Thank you all.
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Old 11-23-2021, 11:10 PM   #2
Cwazywazy
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Having 2 bad mafs isn't impossible. Checking the coolant and o2 sensors is worthwhile, but I'd think if you're not getting an engine light the o2 is probably not your issue. (Are you getting an engine light?)

Have you ever looked in the distributor cap for water?
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Old 11-24-2021, 12:48 AM   #3
ZVOLV
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Crank sensor
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Old 11-24-2021, 09:32 AM   #4
Jyromefedx
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Quote:
Originally Posted by Cwazywazy View Post
Having 2 bad mafs isn't impossible. Checking the coolant and o2 sensors is worthwhile, but I'd think if you're not getting an engine light the o2 is probably not your issue. (Are you getting an engine light?)

Have you ever looked in the distributor cap for water?

I hadn't looked in the distributor cap, can add that to the list even if they are hard to get to on the 740.

I haven't had any engine light when it is driving


Quote:
Originally Posted by ZVOLV View Post
Crank sensor
Crank sensor has been replaced with a new one a couple years ago, I can check the connection. If its the CPS does it make sense that it only starts running rough when the engine is building temp?

Thank you for the replies so far.
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Old 11-24-2021, 11:29 AM   #5
ZVOLV
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Default Crank sensor and powerstage

Sure, any component can fail with engine heat. Crank sensors are known to be bad right out of the box.

Consider swapping in a new powerstage and put the right grease on the backplate.

Moisture in the Dist cap is common. Is your seal dangling/missing at the firewall?
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Old 11-29-2021, 08:28 AM   #6
Jyromefedx
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Well verdict is in.
After more warm weather the car fixed it's self again. Which is unfortunate for a reliability standpoint, it means I still can't go through car washes.

I did the powerstage a couple years ago as well, with new thermal paste on the heatsink.
The Firewall seal is drooping but only in one spot that doesn't have anything important for it to land on should water come down, Driver side shock tower.
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