As previously posted, the main fan hasn't been coming on. Messed with the relays tonite and found the following:
1-When the engine gets hot (245*+) no fans come on
2-When I turned on the A/C, both fans came on full force.
3-If I switch the relays, the secondary fan comes on when I start the car, even when cold.
4-Oil temp never got over 125-130* even at 245* +
5-When I turn on the key, amp gauge dropped to 6-8 amps; started, the amp gauge reads 14-15 until I turn on the air, then it drops to 12.5 or so. Turning on the lights didn't seem to change anything, although turn signals made the amp needle move.
I am pretty good at mechanical things, but this electrical stuff confuses the s**t out me sometimes.
Any suggestions, hints, ideas, HELP
Thanks

Subman

 

Thats not an amp gauge on your dash, its a voltmeter and 6-8 volts engine off , shows a badly discharged battery and you couldn't possibly start your car with a battery that only has 6-8 volts. If the relays aren't identical, then swapping them can't be done for diagnosis. Your ECM turns on the fans from temp info from the sensor on the front of the engine under the MAF. You would have stored codes if the sensor was defective. Check for stored codes.
At 245, the fans would be on, so the sensor is suspect. Your battery cable connections or alternator are suspect too because the battery voltage should not drop 2 volts with the a/c turned on. Remove battery cables (neg first) clean lugs and battery terminals and replace (neg last). Have your alternator checked.

 

The temerature gauge is connected to the sensor in the right head. The ecm works from the sensor under the front of the intake maniflod. The sensor in the left head turns on Aux. fan at 235 since both fans fail to run at 245 sounds like a relay because it is not likely that both sensors failed at once. On my 89 all three sensors are the same which relays did you check. their is one on the radiator shrould and two near the battery. Since they run with ac on the fans are OK and that relay is good so it is one of the others. I had a new spal fan throw a blade less than one hour on it and they refused to honor their warranty saying it was improperly mounted but they didn't even know how it was mounted. When the fan threw the blade and locked up it burned up a relay and burned out a fusible link. I replaced the link and fans didn't run thats when I checked the relays and found that I had fried one. Dam P.O.S. Spal fans are over priced and they won't stand behind them. So I feel your pain just when throught the same problem with mine. Have you checked the relay at the radiator that runs the main fan.

 

Both relays are on the rad shroud. I checked the connection for the temp sensor on the right side of the block. The plactic cover has broken off but the connection seems to be ok. Checked for power with 12 volt tester and it had juice. Will also check for a 2nd sensor on the left. I did replace the temp sensor under the TB on the front of the engine when I replaced the injectors. I will double check the battery cables and connections tonite.
Anything else that might be wrong? Thanks for the help.

 

Getting a hold of a factory service manual may provide the answer to your question. Without one, it's a guessing game. The FSM provides step by step instructions to isolate the problem including voltage, resistance, and by-passing various circuits and relays. If you don't find your problem soon, e-mail me and I'll print out a few pages of the FSM and fax it to you. I know how frustrating this stuff can be. As mentioned, your fans and at least a relay is working since the AC is turning them on. But I believe the AC signal is seen by the computer to actuate the fans. During normal operation the computer is sensing the coolant temp and when it reaches a certain point like 230 degress on a stock motor it turns the fans on via a relay. If the sensor or the ECM (computer) has a problem another sensor on the engine block over-rides everything and turns the fans on. If the ECM is in limp mode, it relys on the sensor that turns on the fans at the higher temp because the ECM is failing to monitor the circuit. I would expect a CEL if the ECM was bad, but not one if one or more of the sensors is bad. Even if the sensors and relays prove good an open circuit to the ECM is a possibility but is remote, but I guess it could happen. :chevy

 

The relay for the main fan should have a blk/red wire on terminal A
The relay for the aux. fan should be blk/pnk on terminal A
Find the main relay and place a jumper wire from terminal A to E if fan runs replace that relay. Oh YEA be SURE THE KEY IS ON Since you say you have voltage at the relay this would be the next thing to check if that don't solve your problem let us know and I will tell you how to check to see if the priblem is the ECM :cheers:

 

Just FYI, both relays on the 94 should be the same.

 

blk bart - replaced both relays tonite - same prob. same solution to cool. turn on the A/C and both fans come on. I'm willing to try to understand whatever you have in mind re: the ecm. Please type slow for I may have a hard time hearing you.
Just to add to all the confusion, looking tonite to see how hard it would be to change the O2 sensors and discovers the plastic cable covering going to the starter has melted all over the pre-cat below it. Suggests maybe the wiring to the starter may have some problems as well.
Thanks for the help.
Subman


[Modified by subman, 10:18 PM 8/21/2003]

 

subman,
:rant:I gotta jump in here just for a sec and I'll be off. If you want accurate help to your problems you really need to put the year of you Corvette somewhere in your post. Most of these guys that are trying to help have pre '90 Corvettes that have a different fan configuration than your '91. For example, one member mentions a sensor in the passenger side head for the Aux Fan; you won't the sensor or an Aux Fan, so you'd be wasting your time. You have what are commonly referred to as a primary and secondary fan that are mounted side by side in the engine bay. You'll get more accurate info if the members know that their experiences will be the same for you.

 

Ray - Now that makes sense! Thanks. To the posters, sorry 'bout that. Mine is a 91, stock with the following mods: 21# Ford injectors, APR, no frizbee, Flowmasters, K&N filter w/cut lid and 112000 on the clock. Battery replaced 18 mos ago, alt replaced 3 years ago.

 

[QUOTE]blk bart - replaced both relays tonite - same prob. same solution to cool. turn on the A/C and both fans come on. I'm willing to try to understand whatever you have in mind re: the ecm. Please type slow for I may have a hard time hearing you.
Just to add to all the confusion, looking tonite to see how hard it would be to change the O2 sensors and discovers the plastic cable covering going to the starter has melted all over the pre-cat below it. Suggests maybe the wiring to the starter may have some problems as well.
Thanks for the help.
Subman


[Modified by subman, 10:18 PM 8/21/2003][

/QUOTE] Dam I hate it that you bought new relays that is why I gave you the instructions on how to test them so you wouln't just throw parts at it in hopes of fixing it. I have a GM shop manual for my 89 is has info for 89 only but I also have a Haynes manual it is corvette 84 through 96 and it has wiring diagrams plus several pages on cooling fans. I would not be able to describe the diagrams where you could follow me. I suggest you go to a Place like Auto Zone and pick up one of these manuals. They only cost about $15.00 it could help for problems that you may have in the future also. By looking at these wiring diagrams you can see which terminals to check for voltage and determine where the problem is. It shows that you have a temperature switch on the right side behind the oil dipstick have you checked it that could be your problem.

 

Bart - Fortuantely, the relays were cheap. Have the manual and will try to understand it tonite - the sensor behind the dipstick has 12 volts to it. the wire that attaches to it has a broken plastic cap, however the wire connection seems to be tight. If I understand these sensors correctly, when the engine temp reaches xxx*, the sensors grounds to the block and sends a signal to turn the fan on. How would I ground the sensor? It would seem to me that the "nut" to screw it in is already grounded at the block. If I attach a ground to the wire that is already got 12 volts, I will short. I know this should be elementary, but electronics has always confused the s**t out of me.
Thanks for the help.

 

Subman Remove the wire from the sensor behind the dipstick and ground it if the fan runs replace the sensor if it don't run problem is something else.
The ecm sends a low voltage signal to the sensor how did you get 12 volts was you using a test light or did you put a voltmeter on it.

 

Used a test light. Will ground first thing in the morning. Let you know. Thanks

 

OK I thought that was what you did because the ecm only puts out about 0.5 volts If you need to drive the car you can ground the green/white wire at the relay and the fan will run all the time. Lets hope the sensor is the problem lot easier and cheaper than replacing the ecm. If I had that thing here in my shop I could fix it but kinda hard to do it over the internet.

 

Indiana is a long way from soCal. I really appreciate the help. This stuff has always made me crazy. Have never figured out why the engineers put seemingly unrelated items on the same circuits. You know, brake lights with the left seat and cigar lighter. Anyway, will try at 1st light. Thanks again.

 

Okay - grounded the sensor to the block (also took the grond to the battery) no go - checked the voltage on wire to the sensor - .5 volts. So are we talking ECM now? And how do I check it? Boy, I hate this kind of stuff, but I guess it's all part of owning a Vette.

 

Ok I assume you had the key on when you grounded it so go to the ALDL it is under the dash on right side of the steering wheel. Remove the rubber and with a fused jumper connect terminal A to B that is the two on the upper right. Turn the key on and both cooling fans should be running. If one or both fans are inoperative locate fan relays mounted on the radiator shrould and with key on ground the inoperative cooling fan relay connector terminal F If the fan operates the problem is in the ECM control circuit. Check the wire for opens shorts and grounds. If the wiring appears to be OK then the problem may be in the ECM at that point take it to a professional to get the ECM diagnosed :banghead:

 

Yep - grounded w/key on. ALDL turns on both fans and I have replaced both fan relays. Will check terminal F and look for broken/bad wires as soon as I can get son-in-laws trans fininshed. Is there a possibility that the fusible links could be bad? I really appreciate the time.
Subman

P.S. - Took a look at you site - absolutely awesome!!! What you have done with your Vette is beautiful. It looks like your monster truck could be a load of fun too.

 

You have two fusible links one for each fan but if both fans ran the link is OK.
Also their is a fuse in the fuse panel labeled ECM but if you use your test light on terminal D on the fan relay and it lights up then it is OK. Better to check like that than to check the fuse because if you have voltage at D then you know that not only is the fuse good but the wiring is also.
Thanks for the comments on my vette going to take her out tommorow and exercise it. :steering: Maybe I will fry some horsemeat. :D