55 belair with 4.8 fan problem
10-03-2016, 06:28 PM
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55 belair with 4.8 fan problem I have a 1955 belair with a 4.8L with a turbo setup on it which has been like this for several years never having a problem till yesterday. I started getting hot so I shut it off and started checking things and noticed the electric fan was not working. I pulled the 30amp fan fuse and it was blown replaced it and still nothing. So I went to the laptop and used hptuners to command the fan on and it turned right on and about 3 seconds later shut of. I manged to get home as long as I stay on the interstate and no stop and start traffic the car runs 190 or less. So tonight I started checking things. I know the ecu supplies a negative signal to the relay to complete the wiring to make the fan run on my 85 terminal of the fan. I am only running one relay and a single 16" electric fan. So I unplugged the relay and took my test light and put one end on power and the other end on my ground wire coming from ecu. Using hptuners again commanded the fan on and my test light light up and 3 seconds later test light went out. I am not sure what is causing the ecu to stop sending the ground signal. I could sure use some help Thanks in advance.
10-03-2016, 08:16 PM
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Had the same problem with my RCSB. After completely ripping the harness out and almost disassembling it, found out the green wire pin had pushed out of the PCM. Re-pinned it and the problem went away.
Very irritating. The fan would run just long enough to make me think I had found the problem.
Very irritating. The fan would run just long enough to make me think I had found the problem.
10-04-2016, 06:49 AM
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Okay well Of course that didnt fix my problem but sure would ob been nice and easy that way. I just went out and removed the 42 pin from blue connector and clipped it back in and nothing same thing it only sends the ground for like 3 seconds and then stops.
10-04-2016, 11:49 AM
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Someone else just went through this EXACT same thing. Pulled his hair out over it. Reflashed the tune back onto the ECU and it fixed it. I went through a similar issue with my MAP sensor a month or so ago.
10-04-2016, 12:12 PM
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I have switched it with several other good relays and I can get the fan to run for 3 seconds when I command it with hptuners. If I use jumper wire across the relay terminals the fan will run and run no problems. The only thing that leaves the relay is the ground from the ecu when it turns back off. I also have tried to re flash another tune to the car and I also tried to even do a write entire to try to make this work and neither has worked I have tried at least 3 other tunes.
Last edited by 55_chev; 10-04-2016 at 12:27 PM.
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10-04-2016, 12:16 PM
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I have switched it with several other good relays and I can get the an to run for 3 seconds when I command it with hptuners and then it stops which after checking all wires and everything the ecu is what is causing it to stop. I also have tried to reflash another tune to the car and I also tried to even do a write entire to try to make this work.
I had this happen on a vehicle. When we manually hot wired the fan, it would run for a few seconds and shut off. We finally found the motor was bad. But not after a full engine rebuild and a set of head gaskets...
10-04-2016, 01:14 PM
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I dont think that is the issue because If I remove the relay and in the relay socket I insert one end of a test light on pin 85 and the other end into 86 and use hptuners to command the electric fan on the test light comes on for 3 seconds then it turns back off because of the ground. I just removed the wire from blue connector on pin 42 and pinned a new wire in a foot long and clipped to one end of test light and put other end of test light to power and when I command the fan on light comes one for 3 seconds then goes out. So figured that pretty much narrows it down to only being the tune or driver in the ecu
Last edited by 55_chev; 10-04-2016 at 01:50 PM.
10-04-2016, 08:49 PM
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Okay well I am even more confused know I drove a hour to go over to my dads tonight that I did a ls swap in his 63 nova a couple years ago to see how his fan acts. I commanded his on using hptuners and it only ran for 3 seconds also then shut off. I know year or two ago it used to run till I would turn it off so I am not sure if new version they have changed something. So then I started his car and once it got up to temperature his fan came on and ran no problem. So I am going to unhook my fan tomorrow from relay and install 194 light bulb in its place and see if it comes on when reach temperature and works right or not.
10-07-2016, 05:59 AM
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Well for a update I guess I dont have a ecu problem that I thought I did comes to find out in the vcm scanner if you go to command the fan on it only runs for 3 seconds then shuts off. So something in the new version is different than it used to be in previous version. So I am going to look at buying the new spal 3000cfm fan to help make sure it dont get hot on me.
