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Discussion Starter #1
Howdy all,

Hoping to get some help in regards to my 04 WJ with a 4.7HO. So back story, about a year ago bought it non running and knew it needed to have the engine rebuilt for a dropped valve seat. Did that with a bunch of other things. December rolls around driving fine go inside to Costco come out, jeep runs like crap. Well it dropped the valve seat again. Head ended up being bad. So engine is getting rebuilt again. So now engine is rebuilt fires up but the cooling fan will not kick on. Did a bit of trouble shooting but not having a lot of luck. Took off the ECT sensor and it goes into airplane mode, put a scanner on to see if the PCM is sending the signal and it is. No codes are popping up. Fan spins by hand with little resistance. Cooling system is all new. Any ideas? Only other thought was the solenoid is bad.
 

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The beast from Brazil
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8,285 Posts
Even with a bad solenoid the fan should spin with 400-500 rpm as soon as the engine runs. But since it goes into take-off mode with the ECT sensor disconnected, the solenoid is working ok. Power steering fluid level is ok?
 

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Discussion Starter #3
Thanks for the reply. Yep fluid is good. Was reading some more last night was suggested to, "Put a external 12v on the connector going to the solenoid will reveal your next step. If it still doesn't spin faster its hyd fan unit, if it sounds like a airplane its PCM or wiring between the two. Some have indicated that disconnecting the engine coolant temp sensor (no engine temp info going to the PCM) will cause the fan to run at full speed. That seems reasonable because for engine safety reasons the PCM probably would default to a steady 5V signal allowing 12V to be applied to the solenoid continuously causing the solenoid valve open to the full speed position. However, if the wire to pin 2 is faulty or if the PCM is faulty, I don't believe the fan will run full speed because there won't be a 5V control signal from the PCM."

So that's where I am at
 

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The beast from Brazil
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But you did remove the connector from the ECT sensor and it did go to high speed. So that means that the PCM lost the temperature input and it send the solenoid into the high speed mode. So the solenoid and the PCM must be ok.
The hydraulic motor should run at its idle speed (400-500 rpm) when the engine runs. If it doesn't,there seems to be a failure inside the hydraulic motor control circuit. Was the fan running at its idle speed before the problem with the engine?
 

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Discussion Starter #5
But you did remove the connector from the ECT sensor and it did go to high speed. So that means that the PCM lost the temperature input and it send the solenoid into the high speed mode. So the solenoid and the PCM must be ok.
The hydraulic motor should run at its idle speed (400-500 rpm) when the engine runs. If it doesn't,there seems to be a failure inside the hydraulic motor control circuit. Was the fan running at its idle speed before the problem with the engine?
Correct, removed the ECT and went to airplane mode. Yes fan will idle at low speed. Just doesn't kick on once the temp start getting over 220*
 

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The beast from Brazil
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Ok, understood you wrongly. Thought it wouldn't spin at idle speed. It probably has to go a bit higher in temperature before the PCM will ramp up the speed. I live in Brazil with quite high temperatures, but never ever heard the fan speeding up.
 

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Discussion Starter #7
Got it, thanks for the info. Just hesitant to let it get above 220. Would having the AC on force it to ramp up quicker?
 

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The beast from Brazil
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The AC can make it spin faster, but on my WJ i don't recall to have seen it going any faster with the AC on. The PCM gets an input from the AC pressure (not the temperature) and will speed up the fan when the pressure increases over a certain limit.
There are in fact 4 inputs which the PCM receives which have influence on the fan speed: besides the coolant temp and AC press it also monitors the transmission temp and the battery temp.
When i'm not wrong the fan will only speed up at coolant temperatures between 220-225.
 

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Discussion Starter #9
Great, thanks for your replies. WJ is currenlty at the mechanic and they can't figure it out but there's a slight part of me that thinks they just want it out of there. Going to grab it next weekend and will troubleshoot myself if there is infact a problem.
 

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03 WJ, 4.Slow, 3" IRO
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Not sure if this helps, but... My WJ had, somewhat, similar issues. It had been in a front-end collusion that took out the radiator and fan. After which, it would always stay in low speed mode causing it to over heat constantly. We could never get it sorted out correctly. I ended up removing all the hydraulics and installing an electric fan and a clutch fan (I live in Phoenix where 118 degrees is not uncommon). Installing an after-market electric fan it's not difficult and relatively inexpensive.
 

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Discussion Starter #11
So just to close this out, it was user error from the shop. Been driving on the Jeep for about 2 months now. My actual dash gauge will only read 210, but the trail dash plugged into the OBDII will register 220+. It has got up to 224 a few times with uphill climbs at slow speeds but then cools back down. Guess moral is don't trust dash gauges......
 
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