Well, it's been a few weeks since I posted my problem with both of the fans turning on and staying on whenever the engine is running. After much troubleshooting I'm here to report: they're still on.

I've pulled about every sensor that is even remotely related to the fans; to no avail. Zyla Race came over with his Diacom and confirmed that the ECM is requesting the fans on (thanks ZR!). Can anyone give me a clue as to why Mr. ECM wants those fans on???

What I've done:
Pulled AC pressure switch connectors (no change)
Pulled CTS (Coolant temprature sensor) connector. Set the SES light but no change.
Removed negative power cable from battery to reset ECM, no change.
Sacrificed a Buffalo Chicken Sandwich at Hooters, felt better, no change in the car.

All guages are within range, car never gets over 210* now (keep in mind the fans come on as soon as the engine starts). I can't see this is a bad thing except for all the crap those fans are sucking into the radiator.

Well, what do you think?? :confused: :confused: :confused:


Update:
Well, after scanning the ECM into the ground, I decided to bite the bullett and get another ECM. I had searched around for a used one but no luck. $145 ($325 core charge! :eek:) later from http://www.tld-corvette.com I'm good to go! No more fantom fans! I don't know why I didn't just listen to what the shop manual said (three steps, Ignition on not running, fans on? No --> Start engine, A/C off, fans running? --> Yes. Bad ECM.) :lol:


[Modified by 92Shawnster, 12:45 PM 10/15/2002]

 

Hmmm... a dozen views and still notta huh? Ok, I'm giving you guys one more chance here... :lol:

 

You said that your SES light does in fact work right?

I know that any time your SES light comes on your fans will come on, so if the bulb was blown in your SES light and it was setting a oode that you didn't know about it would make your fans come on. However I doubt that's it because you said you pulled the sensor and it set an SES, and you have the diacom software as well.

Which coolant sensor did you pull? There are two, one in the passenger side head which pretty much feeds the analog gauge, the other one in the water pump housing goes to the ECM.

Do the fans come on with the key ON or only when it is actually running?

 

Yup, the SES light definately works, I can get it to come on by pulling the sensor on the front of the water pump. I also pulled the codes by flashing it.

The fans only come on when the car is started. Get in, turn the key to on, dash lights up, fuel pump energizes, no fans. Start car... turns over, comes to idle and whirrrrrrrr... fans start and never stop until I turn the car off. The ECM wants the fans on, but it won't tell me why! :confused:

 

Ok, Diacom will data log won't it? I would connect it to the car and get a snapshot while it's not running, then start it up and take another snapshot.

Look over every value with a microscope until you figure out what's doing it. Something has to be triggering the car to turn on the fans on. If you can post the values for everything maybe somebody will see something you're not.

 

If the fans are both coming on at start up, it's because the PCM thinks a sensor has failed and it puts the engine control into protect mode. I'll bet your engine is running rich too (the PCM does everything it can to prevent detenation, richer A/F, fans on hard). Everytime my Vette does this, it's because the coolant sensor on the front of the H2O pump is not giving a correct reading. If you can scan your car's PCM, before a cold start (sitting overnight) look at the ECT reading and compare it to the IAT reading, they should be very close. Also monitor the ECT as the engine warms up and make sure the reading is rising steady until the t-stat opens up. I would also wiggle the connector and see if the reading is intermittant.

BTW, the PCM doesn't always set a code if the ECT sensor's reading is jumping around from an intermittant connection.

Eric

 

Hmmm...interesting theory. If memory serves me though, doesn't the car go into open loop when the ECM goes into limp mode? I watched the readings rise slowly until the computer went into closed loop. I'm going to take your advice though and scan it on cold start.

 

It's not limp mode, and my 96 will go into closed loop mode when the ECT is giving bad readings, that's how it sets the A/F ratio so low. In any case, it's worth a try, good luck.
Eric

 

Ok, I'll set up the Diacom again and log it to death.

Hey, ZylaRace, mind if I borrow the cable for a day or two?

 

Well, after scanning the ECM into the ground, I decided to bite the bullett and get another ECM. I had searched around for a used one but no luck. $145 ($325 core charge! :eek:) later from http://www.tld-corvette.com I'm good to go! No more fantom fans! I don't know why I didn't just listen to what the shop manual said (three steps, Ignition on not running, fans on? No --> Start engine, A/C off, fans running? --> Yes. Bad ECM.) :lol: