sorry guys this topic has been beat to death im sure. i just cant find an answer. i bought a 1989 Trans am GTA with a 5.7. i was told it was completely rebuilt and restored. when we started the car it idle high and had a miss. I noticed the temp gauge wasnt moving and few other items didnt work so i offered the guy a price accordingly. It seem to drive ok and run ok but the more i drove it i noticed the temp gauge not working. the car then started loosing power and seem to be in limp mode and wouldn't go over 15mph had the car towed home checked the temp sending wire it had power put the wire to ground and the gauge did not move still at 0. i jump the relay and fan kicked on. My question is would a non working gauge cause the car to go in limp mode? and is it common for the gauge to go bad? i also check for power at the injectors and all had power. When touching the injectors i could feel the pulse on all but one so i am changing injectors now. Im a carb guy so this electronic stuff is over my head.

 

Check basics, the gauge sender is in the drivers side head. Ecm coolant temperature sensor is front of intake yellow and blk wires. Check fuel pressure ohm injectors cold and hot. Could even be a exhaust restriction or low fuel pressure all should be checked.

 

There are three coolant measurements taken.

1. Sending unit for the temperature gauge. This sensor is on the driver's side of the engine.
2. ECM sensor for the fuel management and cooling system control (primary fan). This sensor is on the front side of the engine.
3. Switch on the passenger side of the engine for the secondary fan

When you turn the ignition switch to Start, the temperature gauge should quickly swing to the hot side. This is because the ignition switch provides a "bulb test" ground, via the Start position, to the gauge and makes it move to the highest point. So if the gauge does not move when the engine is being started during Start position, and doesn't move when the engine is warm, the suspect would be the gauge because the ground paths between the previously mentioned conditions are different.

So whatever the gauge is or isn't doing will have no direct result on the EFI as the ECM has its own coolant sensor that it monitors. However, of course, it does matter what the engine's actual coolant temperature is.

 

I have power at the temp switch on the drivers head when I ground it shouldn’t the gauge move to full hot? The gauge does sweep when the key is turned on but doesn’t move again. And what is the switch Called at the front of the intake? I have 40 psi fuel pressure while running. And I went ahead and am replacing injectors now just cause they are cheap and not a big job. I went with the 22# from south bay

 

Are the injectors multec and ohm low ? Just wondering the reason for replacing.
the ecm uses coolant temperature sensor same sensor as manifold temperature sensor different location and function. The green wire on the gauge sender should peg full hot when grounded koeo.

 

The coolant temperature gauge should peg to Hot if you ground the dark green wire that goes to the cooling sending unit on the driver's side of the engine with the key On. If that does not happen but the coolant temperature gauge does peg to Hot in the Start/Crank ignition position, then that means the gauge itself is working. In that case, the wire between the sending unit and the cluster may have a break.

 

My thoughts to but the green wire has power

 

I'm not an EE but maybe you're seeing some sort of feed through the gauge. The gauge requires a hot and ground to operate, plus the signal wire that gets a resistance value to ground through the coolant sending unit in the block. Measuring for voltage is not part of the standard troubleshooting on that type of circuit.

I guess I'd make sure you're on the right wire.

Lastly, the car is 34 years old and you said "restored". We don't know what the previous owners did and didn't do that may have caused this issue.

 

New injectors fixed my problem. Now i need to figure out why my temp gauge isnt working.

 

No
Very possible on old car! The temp gauge on my '89 IROC was replaced after 1 year under warranty

 

I'm having issues in my 88 GTA (5.7L) with the engine running rough, running rich, and an idle that goes low and dies once in closed loop. I've been going down the list of usual suspects. Today I noticed that the fan wasn't coming on as I'd expect, and started to read up on fan issues. Anyways, I just wanted to clarify with you if I'm understanding point #2 correctly. Is the ECM temp sensor in the front of the engine also involved in fuel management? That's not something I was expecting. I was looking at it just because of my fan not turning on as it had previously, but now I'm wondering if it might have anything to do with the car running rich, and idle issues? Thanks!

 

Yes

Going from memory:
For crank fuel delivery
For open loop AFR
For idle rpm
For closed loop threshold engine temp
For SA
For a bunch of other stuff also

Bottom line, make sure it’s working properly

 

SbFormula, thanks very much for the reply. I had no idea at all that the CTS was involved in any aspect of the EFI. At least I now have something to check and rule out.

 

OP:

Did you do the simple basic test yet and see if it goes to full Hot when you ground the connector?