chevyboy07 91

hey all, trying to get this car right before storing her again for my next trip to the desert!!!

A month or so ago, I was cruising and lost both fans. Looked at the realys, swapped some around, etc.....no changes, still no fans. BTW I never had any wires hooked up to the fan switch (pass. head)....they are both "on" from the tuning in the chip. Never had the wire grounded, etc. Anyway, I eventually just pulled the fan fuse and ran a wire from the fuse box to fans and they both run now when IGN is forward...not the fix I wanted to resort to, but it works. I tried running a fusible link in line between the fuse box and the fans but NOTHING will last in there. Keeps popping fuses.....hmm, maybe this can lead to an answer of what really went wrong?

Well, after that fiasco I noticed that my voltage is lower than normal. OK, check battery, it was good, but weak so I replaced it. Same problem. OK, check alternator....it was good but replaced it anyway (all warranty stuff). Car runs at about 12 volts idle or at speed. It used to run at about 13.25 Volts or so and I know 12 flat is bad. With the car off, the battery will recover to about 12.50 volts which is normal by itself. So, there is a drain when running somewhere and I cant find it!

All grounds looked good. Leads from battery are in good shape. Ground straps from back of engine, etc are in place and snug. What the heck is going on here? There is a large 4 pin connector pack type deal that lays near the pass frame rail by some metal hoses that deal with the A/C and cooling system...what is that? leads from the battery go into that also.

I'm sure my issues are related to the same problem I just cant figure it out.

Please help if you can!!! thanks

edit: the voltage issue still remains even after unplugging power to the fans

Cobra289

Hi chevyboy,

I would check the next wire, because perhaps it is broke or loose the connection somewhere.
The wire starts at the alternator connector (BRN = Brown) at th "F" point, that goes to the "FP FAN fuse" but also give the +12v to the Coolant FAN relay, it is also connected to the Heavy Duty FAN relay with the same function.

The FP FAN fuse is connected to the ign. key via an ORN = Orange wire at the C1 connector of the switch.
Check this one too, but first check the "FP FAN Fuse" that is a 20Amp.

I hope this help.
Regards,
Cobra289

Vader

With the engine running, measure the voltage from an engine ground to the output stud on the alternator.

_____ V

If the alternator voltage is higher than the battery voltage, measure voltage between the output stud and battery positive.

_____ V

In other words, if there is a difference, start looking for voltage drop at connections.

chevyboy07 91

Cobra, I'll try that tonight. Might need clarification though. Is that connector at the ALT supposed to be sending power OUT via both wires? Meaning, one runs power to the fuse box and the other to the fan relay? I am thinking that power goes from the fuse box to the connector, (not vice versa) and then from the connector to the relay


Vader, they're the same.

thanks for the replies...keep ideas coming plz

Cobra289

The power +12v goes from the Ign. Switch to the "FP FAN Fuse" and than it goes to the Alternator and the Relays, so the alternator gets +12v via this cable.

The relays will be activated via the ECM that pass the earth and the above mentioned +12v wire.

Sorry if I did explain in a bad way.

But if your fuses pop every time, it means that you have a short +12v and earth together.

I have take some bad pictures of a 87 service manual I hope this help to trace the problem

Regards,
Cobra289

Vader

If the alternator output voltage is only 12.0, there is either a weak alternator or excessive load. Until you can get the charging system operating properly, the rest is secondary. Determinimg why the charging system cannot sustain 13.8V or more may solve the fan problem as well.

You might begin by disconnecting several of the larger loads at the fusible links or wherever it is convenient. If disconnecting one of those loads allows the alternator to sustain a reasonable charge voltage, you may find a problem in that circuit.

chevyboy07 91

ok, sorry its been a while. Busy doing the Army thing.

Here is some more info. With the fans "hard wired" from fuse box to fans, the voltage drops and stays down. When I disconnected the hard wire and threw the fuse back in the car is at 13.5+ volts which is great. So the "charging problem" is nothing more than the fuse being where its supposed to be. What is really weird is that if I take the fuse out, a(and have nothing hard wired) the voltage problem will show again. There has to be a fuse in there for the car to charge properly! Still no fans though. So, in summary, when the fans died, i tried messing around with stuff, never figured it out. So, I automatically threw the hard wired rig together in order to have the fans and then noticed the "charging problem" which is nothng more than the fans drawing too much from the box.

Now, I went from the battery itself, to the fans, via a switch. I interrupted the "hot" wire with the switch but now am thinking that i should pull the switch from there and put it /use it as a ground interrupt instead. Dumb move by me but was in a big hurry yesterday and needed the car.

So, now I'm charging at least.