I've been told that possibly my coolant temperature sensor is bad giving the computer a false reading thus making my car run rich. So I'm thinking it wouldn't hurt to replace it. But I'm not sure which one it is. I think my car has 2 of them. I have an 89 L89 350. I think there is one down low next to the starter and one that hooks into the front of the lower intake manifold just under the throttle body. So which one feeds the computer? Also, does my temp gauge feed off the same one the computer is seeing? If so, then maybe that's not the problem because that gauge seems to work fine so if the computer sees the same thing, then that's not the problem. However, if they are different sensors, then maybe it is the problem.

 

The one by the starter is the knock sensor. The temp. gauge sender is on the driver's side head between the front 2 exhaust ports. The CTS is the 2-wire one on the front of the lower intake. Wires should be yellow and black IIRC.

 

Thanks!

 

It seems that there are actually 2 sensors on the passenger side by the starter. Which one is the knock sensor, and what is the other one? One is low in the block and the other one is higher next to the head.

 

The one at the bottom near the oilpan is the knock sensor. The one in the head between the back 2 exhaust ports is the fan switch.

 

Wow, so let me see here... There is a fan switch, a coolant temperature switch and a temperature gauge sender?? Man, why so many temp related sensors? Couldn't they just have a single sensor which sends the temp to the computer which in turn then controls the fans and the temp gauge??

Also, as I mentioned before, the knock sensor and what I now know to be the fan switch have the same type of connector on them. How do I know that the people who put in my new motor didn't switch those connectors? Could that explain why my fan doesn't come on and my car runs like crap? Maybe the computer is getting the knock info from the fan switch and the fan is getting the info from the knock sensor?? Why didn't Chevy use different connectors there? They come from the same wire harness so it's very easy to swap the 2. Maybe I can do a trace back to the ECU to determine the correct wires. Do you know which teminal they should connect to at the computer?

 

Easiest way to check that is to switch them around and clear the codes and see if it runs better. It's strange that they would have the same connector....GM doesn't generally do things that way. You might try peeling the loom and tape back a few inches and see if one of the connectors isn't original.

As for the ECM pinouts...you can probably find it here. You can use an ohmmeter to check continuity on the wiring, just make sure you unhook it first.

 

I just checked and they do seem to be wired correctly. The temperature switch connector was spliced into the wire harness I can tell. But going off pictures of temperature switches and knock sensors, they do appear to have the same exact connector on them. Pretty strange that they would do that IMO. Or, is this incorrect? Can someone take a look at their 89 IROC 350 and see if the knock sensor and temperature switch on the passgenger side have the same connectors?