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Discussion Starter #1 (Edited)
I was driving today and smelled a burnt plastic smell like my RFI module burned out again... and a/c went warm. Cooling fans turned off.

Now when I start the car, the fans run for about 5 seconds then turn back off even with a/c on. Getting really sick of this issue. RFI module doesn't look melted like before. Fans seem to work but won't stay on.

I'm most likely going to have to wire them to the battery directly. If no one has any ideas otherwise, I'd like some tips on how to do that, without a toggle switch for now.

The coolant temp sensor is new and working, rad fans are only a few months old, fuse looked good, I swapped the relays with the wipers and no change. Fans run for 5-15 seconds after starting then they just turn off with a/c on. Only other thing I can think of is the ECM. I don't think it's a wiring short because the fans do turn on for some seconds. When my RFI module was busted, the fans would not turn on at all.

Any ideas?
 

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Discussion Starter #2
Since the fans do turn on, I'm wondering now if it could just be a/c related. Don't think car was at a high enough temp to run the fans with a/c off/broke so they might work, will test later.
 

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Discussion Starter #3
I jiggled the cooling fan harness and the a/c transducer and now it is working again... nothing seemed loose so don't know if that 'fixed' it or what. Old cars I tell you.
 

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Wonder if you have an A/C Transducer that's starting to go out. Causes problems in the 2nd gen LH cars also.
 

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Discussion Starter #5
I think it is possible. But this is very similar to what happened before my RFI module shorted out. My fans would just shut off and car would begin to overheat, then they would work again. I'd feel much better if I could find a Mopar fan assembly, but things are working today... so far.
 

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Discussion Starter #6
It is doing it again. Just going to have to take it into a shop I guess. I don't have a clue what it is this time.
 

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Discussion Starter #7
I'm trying to logically think through this issue.

* Fans work immediately after starting vehicle for 5-10 seconds every time, then turn off. I feel this rules out an electrical issue at the fans themselves.
* The issue 'fixed' itself some how. I drove yesterday and half of today with no problems. Fans shut off mid-drive today.
* Coolant temperature sensor works normally, I just replaced it a few months ago as well.
* I don't think the a/c pressure transducer faulting would cause both fans to stop working.
* a/c compressor clutch engages when starting vehicle, blows cold air for a few seconds until fans turn off.
* Heat works and there does not appear to be any air in the system. Coolant level stays constant between drives.
* No CEL
* Looking at wiring diagram, the only logical thing I can think of is a shorted connection to the PCM, or the PCM itself is faulty.
 

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Discussion Starter #8
The car has cooled off and now the fans seem to be working again. It's a very weird issue. I'm wondering if the relays could be failing or overheating. But I've swapped them around once and the issue arose again which leads me to believe it is not related to the relays.

I also don't think the PCM would be affected by engine temperature. It also doesn't make sense since with the a/c on, the fans should come on as well regardless of engine temp. And why would they work on start up only to not work seconds later even with a/c on or engine over 220F...?

It seems there is at least one thing ruling out each component.
 

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Get your multimeter out and start probing voltages when it starts acting up.
 
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Get your multimeter out and start probing voltages when it starts acting up.
:thumbsup:

...It also doesn't make sense since with the a/c on, the fans should come on as well regardless of engine temp. And why would they work on start up only to not work seconds later even with a/c on or engine over 220F...?...
Here’s something to consider (assuming the fans work like on 2nd gen. LHs):
The fans operate on two speeds. There are two relays that control that. Fans off is with both relays de-energized. Low speed is with one of the relays energized. High speed is with both relays energized.

If the low speed relay is not working for whatever reason (bad relay, bad wire, bad PCM), the fans will stay off when they should be running at low speed, and when high speed is called for, they will operate at a lower speed (probably very close the the normal low speed).

So - if normally, high speed is commanded at startup, the fans will run at something similar to low speed instead, and then they’ll turn off. Then, as the engine heats up, the fans will not turn on at all until the engine gets hot enough to call for high fan speed, at which time they will run at the pseudo-low speed, and will never run at true high speed no matter how hot it gets.

So, it’s a long shot, but, again, consider that as a possible explanation.

If the normal startup run speed is low speed, then you can dismiss my suggestion.
 

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When in Doubt Whip It Out..........












The Multimeter that is!

Think you have a wiring or PCM issue but I'm no expert in 1st Gen cars. Possible brittle wiring harness or connector/connector pin issues.
 

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* a/c compressor clutch engages when starting vehicle, blows cold air for a few seconds until fans turn off.

Possible Control issue. The fans should come on when the A/C engages. PCM? PCMs have to be cheap and plentiful for the 1st Gens?

It seems you're reluctant to take Voltage readings for some reason and so far have just been "Throwing" parts at the problem in a Shotgun approach.

The fans turning on at startup indicates most if not all of the circuit is working. After that it's a control issue. The PCM is ultimately going to control the Cooling Fans.

Have you carefully checked all the ground wires at the PCM and to the Engine Block?

What does the Temp Gauge reading show when all this happens. Is it correct? Showing high temp when the A/C cuts out or the cooling fans stop?
 

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Discussion Starter #13
:thumbsup:

Here’s something to consider (assuming the fans work like on 2nd gen. LHs):
The fans operate on two speeds. There are two relays that control that. Fans off is with both relays de-energized. Low speed is with one of the relays energized. High speed is with both relays energized.

If the low speed relay is not working for whatever reason (bad relay, bad wire, bad PCM), the fans will stay off when they should be running at low speed, and when high speed is called for, they will operate at a lower speed (probably very close the the normal low speed).

So - if normally, high speed is commanded at startup, the fans will run at something similar to low speed instead, and then they’ll turn off. Then, as the engine heats up, the fans will not turn on at all until the engine gets hot enough to call for high fan speed, at which time they will run at the pseudo-low speed, and will never run at true high speed no matter how hot it gets.

So, it’s a long shot, but, again, consider that as a possible explanation.

If the normal startup run speed is low speed, then you can dismiss my suggestion.
I did consider something like this. I have swapped the relays again with the fuel pump and auto shutdown. Before I swapped with the wipers. Everything is working normally for all the other relayed components as well.

Before my RFI module shorted out, the symptoms were very similar. After it shorted out, only my a/c fan was working but before that, sometimes the fans would turn off as they do now. Both fans working when starting the car is what is throwing me off. The RFI module doesn't have the ability to start/stop the fans so it's ruled out.

The fans are getting voltage normally from the PCM and through the relays, then the PCM decides they don't need to be on via the coolant temp sensor's voltage _AND_ the a/c system. There must be a hub where those two components go to that has failed since neither of their signals are influencing the PCM, and the only one I know of is the PCM itself. If one component, either the coolant temp sensor or a/c compressor turned the fans on, the solution is easier. But since both have no effect on the fans, I'd figure either relays or PCM and based on what I've seen, the relays are fine.

If so, my only question would be could the PCM intermittently do this or should it be more of a binary failure; like it either works or it doesn't anymore? Unfortunately, the only way to know is to swap out the PCM for another in which case I'll have to hunt one down.
 

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Discussion Starter #14
* a/c compressor clutch engages when starting vehicle, blows cold air for a few seconds until fans turn off.

Possible Control issue. The fans should come on when the A/C engages. PCM? PCMs have to be cheap and plentiful for the 1st Gens?

It seems you're reluctant to take Voltage readings for some reason and so far have just been "Throwing" parts at the problem in a Shotgun approach.

The fans turning on at startup indicates most if not all of the circuit is working. After that it's a control issue. The PCM is ultimately going to control the Cooling Fans.

Have you carefully checked all the ground wires at the PCM and to the Engine Block?

What does the Temp Gauge reading show when all this happens. Is it correct? Showing high temp when the A/C cuts out or the cooling fans stop?
I haven't thrown any parts at it yet and the only reason I haven't taken voltage readings is because as you said, the circuit is working each time I start the car. So I agree it must be some kind of control issue. I'm sure I can find a cheap one.

When the fans cut out, the engine temp is normal. I notice the a/c goes warm and that's how I know the fans have cut out. From there I turn the heat on and pull over, sure enough fans are off even as the engine temp has risen to the point they should come on. Then I start the car again, fans kick on for 5 seconds and then go off even with a/c on and engine temp in the range the low speed fans should turn on. Just doesn't seem wiring related to me if the circuit works each time.

Looks like I'll be getting a PCM.
 

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When I say a wiring issue....it can be a bad/intermittent connection somewhere in the wiring harness. By that I specifically mean in the area of the PCM.

Maybe try disconnecting the PCM and clean the connectors with Contact Cleaner, etc. And again...carefully check the ground connections. Ground straps, ground wires, etc.
 

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Discussion Starter #16
When I say a wiring issue....it can be a bad/intermittent connection somewhere in the wiring harness. By that I specifically mean in the area of the PCM.

Maybe try disconnecting the PCM and clean the connectors with Contact Cleaner, etc. And again...carefully check the ground connections. Ground straps, ground wires, etc.
Will do.
 

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Just Sayin' !
 

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Discussion Starter #18
Just Sayin' !
It's just a confusing issue. As of now, it is 'fixed' again. It seems to 'fix' itself after the car has cooled down then runs just fine, a/c and all.

I'll check the FSM tomorrow for a ground connection diagram.
 

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It's not uncommon for Thermal Changes/Temperature Changes to cause connection issues. When things "Cool Down" they work, etc.

Possibly Demating/Mating the PCM connections will solve the problem by itself. Wiping any corrosion on pins etc. It doesn't cost anything.

And a can of spray Contact Cleaner/Lube is under $10.
 

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Discussion Starter #20
I have some CRC 5103 around here some where. I'll try it out.
 
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