Just to re-capp, I bought this car, an '86 FB 2.8L w/ MPFI for $300. My strategy is to make all the minor repairs, paint it, enjoy it for a time, and then sell it to some German for an exhorbitant amount.

I've managed to fix everything but for two things. Engine code 34 and the cooling fan. This essay pertains to the cooling fan but both are related.

When I bought the car, the fan was wired in pure ghetto fashion, straight to the ignition switch -- with speaker wire! I wired it back up, bridged the fan relay terminals and the fan came on.

I have tried warming up the engine to see if perhaps the system still works but of course, this car has only idiot lights so there's no easy way to determine when the fan should be kicking in. I'm afraid to run the engine too long for fear of overheating it.

I measured the voltage at the relay and came back with some funky readings, though. The other thing I noticed was that the wires going into the relay were bare, leaving about 1/4 inch of each wire totally exposed. It almost looked like they had overheated at one time. Confused, I moved on to troubleshoot the code 34.

I had checked the codes using the jumper wire on the diagnostic plug many times before. But this time, when I jumped the terminals............ the fan came on?!?!?!? I find this to be very strange.

Questions.

1. Has anybody ever experienced this phenomena?

2. The fan relay can be closed by way of either the temperature switch or the ECM... Why both? Is this some kind of built-in redundancy in the event that one fails?

3. Where is the temp switch located on my make of car? I think it's on the front left cyllinder head just above the exh manifold.

Pat

 

Im not sure about your problem but Im pretty sure that the relay is ECM controlled. there should be 4 wires going to it. one is the one that has constant power and should be a larger wire. then there is a wire that goes to the fan itself which should also be a larger wire. then there is a wire that should be on when the key is on . Finally the last wire will be the wire that goes to the ecm which is put to ground by it. What is supposed to happen is that the computer watches the coolant temp and when it reaches around 220 or so it will then ground that terminal on the relay, which turns the fan on. I hope that helps out some

 

Yes sir, you are correct. Except that there are actually five wires going into four connections. The ECM terminal has two wires -- one to the ECM and one to the sensor. I tried again yesterday to get the fan to come on by idling the engine but it would not. The relay works, though because I grounded the ECM terminal and the fan came on. I really need to find this temp switch so that I can test it.

 

Whenever you jump the ALDL service pins to retrieve codes the ECM will activate the electric fan as a self test. This tells you that the relay and the fan and the ECM are all working as they should. My wiring diagram shows only the coolant temp sensor, they do not show a redundant separate fan switch as the V8 models have. If Chilton is correct you should have one heavy red, one heavy blk/red, one dk.grn/wht and one brown wire. First two are high current lines for fan, last 2 are relay coil power and relay control(it gets grounded from ECM). Since you corrected the wiring it is in fact working as it should. My fuel pump relay has the wires stripped a little too much and it has never been touched. Any possibility that you may have them confused? Keep us posted, Dan

 

Actually, when you jump pins A & B it energizes ALL of the circuts for the engine, every relay will energize (except fuel pump). You should hear lots of clicking and such in the engine compartment when the aldl is jumped.

 

Good to know that everything seems to be in order, however there are definitely two wires going into the same connector. When I ground these two wires, the relay trips and the fan comes on so I'm pretty sure it's the fan relay. I am going by the electrical schematic on this site for the 2.6L V6, engine code S. The relay is mounted on the far top right of the fire wall as you face the rear of the car. As my car is not equipped with gauges, how long does it normally take to get the fan to kick in?