Richboy1969

I just rebuilt my 3.1 Engine in my 1991 Firebird. While the engine was out I cleaned under the hood and replaced all the wireing harness covers. While I was replacing the split tubing covers I noticed there was a Blue set of wires that wasn't connected on the right back side of the engine bay. The wires apeared to be taped to the wireing harness with black duct tape. The end of the wire(s) were held together with a loop connector that would be bolted to the firewall for a ground. Not realizing what the wires were for, when I put the enging back in I grounded the wire(s). My Bad. Well I have the Pontiac Service Manual for the car and I had read in the manual that if the car didn't have AC that circut 732 would be grounded. Well my car has AC and I grounded circut 732. Big mistake.
Everything worked on the car before I took the engine out but now the cooling fan will not come on nor will the AC compressor engage. Reading the diagnostic section of the service manual I went through all the steps it described. I took the blue wire(s) loose. The final step said that either circut 732 was grounded or a faulty ECM. So my question is did I mess the ECM up?

1991 Pontiac Firebird
3.1V6, Auto, AC, PW, PD.

Richboy1969

Come on somebody. Is there a way of checking it and when I buy another one other than plugging the PROM in to it does it have to be programed?

gorbilax

Circuit 732 on a vehicle with A/C just connects to a switch, which then connects to ground. By grounding the blue wire, you basically just told the ECU to run the radiator fan to draw air over the A/C condenser. It won't hurt the ECU any. Have you checked the Fan fuse in the fuse box (left side of driver foot well)? Also, have you checked the connection to the pressure switch on the AC line? That's where those blue harness wires lead.

That said, if you do choose to swap ECUs, there will be a little access cover on the top that you can unscrew. Then just swap chips with the new ECU. Just make sure it's the same service number ECU.

EDIT: I should mention that the attached wiring diagram is for an '89. Don't know if anything changed.
If the AC compressor does not engage, there will be no pressure in the line, and therefore the switch will not close and the fan will not come on. I think you need to diagnose the AC compressor clutch circuit before the fan circuit. Does the fan still come on when the engine gets above 250 degrees?

gorbilax

Also make sure that your HTR-AC fuse isn't blown, your AC relay is connected and working (I believe that's mounted next to the brake booster and can be swapped with the fuel pump relay for testing). There are also several pressure cut out switches plumbed into the AC lines that require electrical connections and two electrical connections on the compressor itself on my 89 bird. I haven't looked at my 92 bird, which has your engine.

EDIT: Does your blower motor come on when switched to heat and do the other climate control functions operate normally? When you said "cooling fan" earlier, I assumed you meant the engine/radiator fan, but do you mean the blower motor fan for the interior climate controls?

Richboy1969

I did check the fan fuse and it was good. I did check the connection at the AC-pressure line and AC Compressor to make sure no bent pins. Yes the inside blower motor works with heater switch. All functions work inside the car with the AC Selector switch. No the outside radiator fan doesn't come on when the temp reaches 250. Yes I swaped the AC relay with the Fuel relay and then the other relay to make sure all three relays were good on left side of car. If car wouldn't start I would have had a bad relay. I did the diagnostic for the system by Jumping the ALDA (a)(b) and turn key switch on and radiator fan did come on. Now here is more information, When I rebuilt engine I replaced every electronic switch connected to engine. Temp sensor on front intake manifold, Temp switch on left front of head, Knock sensor on lower right engine block, Oil pressure sensor on lower left engine block. That being said is there a way of checking the two coolant sensors, switches with a OHM meter. What should the ohm meter read? When I bought the sensors the one on the left head was button type conection and all I could get was a blade type conection. Advance said it was the same but would that make a differance? I also check the Fusable link on right front side of engine bay, Ground on left rear head, Ground on right rear head. I will check on HTR/AC fuse I didn't check that. I also didn't check for refregerant pressure. I'll pick up a can with a guage on it for the purpose of just checking the pressure.

gorbilax

Let me know what you come up with on the fuse. If it comes on when you jump the diagnostic pins, then your relay is getting power on the coil side and the contact side so all of that is fine, the ECU just isn't feeding power to the relay to turn it on, so there isn't anything wrong with your fusible link or your ground.

The button or blade thing shouldn't make a difference as long as they're electrically compatible, but I'm pretty sure all that does is feed the dash gauge anyway. The other one, the two wire coolant temp sensor on the manifold, is the one that feeds the ECU so that should be the only one that comes into play here.

If you test the two pin coolant temp sensor with an ohm meter, it will range anywhere from 100,700 ohms (-40 degrees) to 185 ohms (210 degrees). If it wasn't working though, it should throw a CEL. You should also check the voltage of the harness going to the sensor.

Also, unless you've done an R-134 conversion on your AC system, those cans with the gauges on them aren't going to help you because they won't fit the connections on your car. Your car uses R-12 refrigerant from the factory.

Maverick H1L

iTrader: (8)

1. The starter enable relay is under the dash, not out in the engine bay. If you looked in the FSM you would know this.
2. The temp SENDER in the cylinder head is ONLY for the temp gauge, PERIOD. Blade type connection or the old screwy button style makes no difference to the ECM because that sender doesn't have anything to do with the ECM.
3. There are more than just the 3 fusible links up by the headlights, the others being at the starter.
4. The HTR/AC fuse has NOTHING to do with the radiator fan, which is on the FP/FAN fuse. The HTR/AC fuse is only for the HVAC system, PERIOD.
5. Swapping the A/C compressor relay with the FP and fan relays will do NOTHING for the radiator fan since the compressor relay is only for the compressor clutch on the front of the compressor.
6. Disconnect the battery for a moment and reset the ECM... May be confused.
7. Remove the connector from the A/C hard line that runs along the passenger's side frame rail close to the coolant bottle. If the radiator fan runs then, everything's fine.
8. Check to make sure you didn't miss any grounds on the back of each cylinder head except the one with the blue wires on it (which I would tape over and stick back into the harness loom). Also make sure you didn't pinch any wires anywhere on the engine (valve covers, etc).

gorbilax

Richboy, are you sure you're actually reaching the correct engine temp for the fan to kick on? If you're going by the dash gauge, maybe it's telling you the wrong temp, and there's actually nothing wrong.

Richboy1969

I checked the HtR/AC fuse and it's good.
Got a Refrigerant can with gauge from Wal-Mart and checked for pressure on A/C System and it was empty.
System had been converted from R12 - R134. I only bought one can and it wasn't enough to hardly charge the system. AC Compressor clutch did start to quick cycle every 2 seconds but Radiator Fan never did come on.
I did disconect the High Pressure switch from the small A/C hard line closest to the antifreeze recovery tank and the radiator fan didn't come on.
I checked the High Pressure switch and with no pressure in A/C system, electrical plug unpluged, there was continuity between switch pins.
I checked Low Pressure switch at A/C Drier with no pressure in A/C system and there was no continuity. After charging A/C system there was continuity.
I'm not sure if the Temp Gauge is correct. I'm going to pick up a Temp Gauge and Sending unit from auto parts place and check that next. I always thought that when inside selector was set for A/C the Radiator fan run all the time. If i'm wrong correct me. I have my douts about the inside temp gauge being correct.
I'm going to jump the Low Pressure A/C switch to keep the A/C compressor kicked in to see if radiator fan comes on. I won't run it very long. Didn't have time today, had church.
I'll post on here as I get more info. If anyone has more ideas or troubleshooting tips just post them here.

For information purpose. This is my project car. I'm restoring this car to the best of my ability for car shows and road trip's. I just want to get all the bugs out of it first. It is not my daily driver.

Maverick H1L

iTrader: (8)

Did you:

1. Reset the ECM by disconnecting the battery?

2. Unplug the A/C pressure switch connector in the hard line on the frame rail to see if the fan will come on? If so, and there was still continuity between the pins, that part of the circuit is shorted and the fan will NEVER come on until the short is fixed because the ECM thinks that the switch hasn't opened. Only if the switch opens with refrigerant pressure will the ECM turn the fan on. This is the ONLY switch you need to worry about as the rest are pressure switches for the compressor clutch.

The radiator fan will only run with the A/C on when the pressure switches signal the ECM to turn the fan on. The fan cycles on and off just like the compressor clutch.

http://www.austinthirdgen.org/mkport...al_V6_vinT.jpg

http://www.austinthirdgen.org/mkport...an_V6_vinT.jpg

Those should get you started... You have the wiring diagrams and troubleshooting charts in the FSM... Use them.

Richboy1969

Well I went through all the trouble shooting and sometimes the most obvious and simplest is the answer. The temp gauge is the problem. I have a mechanical one to use for now. Is there a way to recalibrate the original one?