JustDSM

iTrader: (1)

Hello all! I just picked myself up a '93 Trans Am 6spd hardtop car a few days ago and now that I've got it home I'm trying to sort some issues I seem to be having with the cooling fans. The is unmolested and mildly neglected with maintanence related things so I'm trying to go through the car and get it 100% before I sink any money into go-fast bits.

Here's what I've got..

I've tested the fans, relays (both of them), fuses, coolant temp sensor was just replaced along with the water pump. I'm able to get the fans to come on my pulling the "AIR pump" fuse which gets both fans going. With that fuse replaced, I can also get just the primary fan to turn on by using the A/C. So I know the cooling fan circuit and fans themselves are good to go.

I checked the resistance of the coolant temp sensor and the resistances are within spec. The black wire at the coolant temp sensor has no more than 1ohm restance between it and a random ground on the body. With the car warmed up, and the connector plugged into the coolant temp sensor I see approx 2.6-2.3 volts. With the connector unplugged I see 5 volts on the yellow wire. So I dug up some pinouts of the PCM and located the wire at the PCM and I get matching voltages at Pin A13 to what is being seen at the sensor. Thats good to know at least the wiring is OK between the PCM and the sensor.. But the cooling fans are not comming on without "help" from a SES light or the A/C.

From what I am seeing everything seems to be checking out but I'm likely missing something since I've only been a F-Body owner for a few days.. Any suggestions/tips/tricks?

JustDSM

iTrader: (1)

Hmm.. PCM taking a dump? I'm at a loss here guys.

FAD2BLK93

U realize the 93 fans are a little different than the rest? IIRC the fans com on 1 then 2 but no high low...just on and off. The fans are set to come on like in the 220+ range. The guage on the dash can read quite high. Goto Shbox.com and read up...lots of info there!!!!

shbox

Good suggestion.

Read:

http://shbox.com/1/4th_gen_tech2.html#cooling

bufmatmuslepants

iTrader: (3)

Just wire the fans to run all the time when the ignition is turned on. Thats what mine does, never had a problem, runs at 185 degrees constantly

JustDSM

iTrader: (1)

Thank you guys for the suggestions on checking out shbox. I did that.. I completed all the trouble shooting steps on his page, and everything checks out. Which is why I was asking if you guys thought there was a possibility for the PCM to be faulty.

I also realize from the research troubleshooting this problem that the fans don't come on until some pretty high temps. I'll remind you that I did bring the car up until it was right at the "red zone". And before anyone tells me to check the sender on the head, I checked that too, along with the wiring. Everything is within spec.

Sound like the PCM?

shbox

You can't say PCM until you have observed the temp it is getting, seeing if the fans are commanded on and then observing if the ground signal to the relay(s) is being output.

As far as wiring the fans to run all the time, that is a big waste and not needed with a properly functioning system, IMHO.

JustDSM

iTrader: (1)

Agreed.. I'll say I've done all I can without having a cable. Wasn't intending to purchase one just yet, but looks like I'll have to ammend those plans.

Thanks again!

JustDSM

iTrader: (1)

I decided to try one more test as it's been eating me alive worried my PCM is suspect. I keep getting reminded how warm these engines need to be before the fans kick on, and I reassure them that I've done the diagnostics on the two sending units, the wiring, the relays and the fuses. Everything checked out.. So why wasn't my PCM turning the fans on when things got hot I constantly asked myself these last few days..

Well I woke up this morning and decided I'd try to just force the fans on by using a potentiometer to slowly walk the resistance down to where the fans would kick on. Basically mymicing the sending unit warming up. Interestingly enough the fans did come on.. But it was because I had to drop the resistance in the potentiometer so low that it triggered a Service Engine Soon light for sky high coolant temp. Basically indicating to me that the PCM is not turning on the fans regardless of the temperature unless the SES light is on, or the A/C is on.

So I'm confident that the issue lies in the PCM. I've still got my cable on order, but this was a conclusive test that clearly shows the PCM is at fault here. Just thought I'd follow up here for others that may be having the same issue.

jaycenk

iTrader: (1)

Have you verified that the wires and plug are not causing resistance? Any added resistance in the wire or plug will cause the PCM to think the engine is cooler than it actually is.

JustDSM

iTrader: (1)

Yes sir. I checked resistance at the sensor itself, and about 4" from the pigtail, as well as at the ECU and they were all within 1ohm of each other.

shbox

IMHO, you still need to know what temp the PCM sees and know what the fan temp programming is set to. It appears you have done everything you can besides "looking" into the PCM.