So, the other day I'm driving home from work, and my truck starts acting like it's flooding down.....losing rpm and power really fast, until it dies.
Only way it would restart is to floor the gas pedal to shut off the injectors and let the cylinders clean out, then it would fire off, blowing clouds of black smoke. It died on my four times on the 18 mile drive from my rig to the bunkhouse, so needless to say, we took another vehicle the next day.
Tuesday evening (end of my work week), I prepare to try and get it home, check the fluids under the hood, oil is good, but the coolant was down almost a half gallon. Top it off, and the truck doesn't skip a beat on the 50+ miles to the house.
Yesterday, I hooked up my laptop and ran WinALDL and TunerPro RT to see what was happening.
Let me interrupt myself and say that from time to time, I get a SES light, which I attributed to the fact that don't have my EGR hooked up with this Vortec 350 and the 4 barrel intake/TBI adapter setup. When it ran so rich it was dying, the SES light came on and stayed on......."Well, that's new" I said to myself.
Anyway, yesterday, after getting everything connected to check data, I started the engine and let it warm up....even with a warm engine, the CTS was showing a reading of -37degrees F! Guess that kinda explains in part the excessively rich fuel condition.
Before I just go out and replace the cheapo Autozone CTS, I want to check voltages....is the reference voltage to the CTS 5 volts?
I really should stop procrastinating and install the '95 TBI PCM I picked up last fall while I'm at it, just not sure that (other than repinning the PCM connectors) it will be plug-n-play and run.
Any thoughts?

 

I can't help you out with any questions on your PCM swap, but a few years ago I had the same thing happen with my '91 RS. The symptoms you describe match my scenario exactly. I checked the SES codes, and it gave me a code for CTS failure (code 15 i believe). Picked up a new CTS at autozone, swapped it out on the side of the road in five minutes, and the car was back up and running. I haven't had a problem since. Just remember to bring some thread sealant or teflon tape with you when you go to swap it out so you don't get any coolant leaks. This was the easiest fix I've ever done on a vehicle. I hope yours goes just as well!

 

Thanks.........I went and checked and have 4.94 volts at the CTS connector, so I kinda think it is the actual sensor itself and not in the wiring.
Think while I'm at it I will replumb the hoses from the heater core......I hooked them up the way the previous owner had them, but rather than going from the heater core to the passenger side radiator tank, I am gonna plug the fitting on the tank and go to the water pump bypass hole. I noticed some time back that at no time did the ECM see a coolant temp of >173 degrees, and I have a 195 degree thermostat in it. I'm not sure the system is ever going into closed loop.
I'm hoping Fast355 will chime in or PM me with comments about the PCM swap.
Thanks!

 

Tie40

The CTS sensor should have two wires black and yellow (although black could be some other color). The black wire is a ground reference and yellow is input line to CTS. Internally ECM has a resistor which pulls yellow line to + 5 volt reference supply. CTS and internal pull resistor form a voltage divider network where ECM measures (A/D input) voltage drop across CTS sensor. If CTS is open (or its ground is missing ) the ECM will see maximum voltage which corresponds to very low temperatures (-40C) and will add fuel.
To measured CTS voltage correctly, CTS should be plugged in and carefully back probe the connector with your DVM test leads. Depending on coolant temperature your voltage should be between 1 to 2.5 Vdc.
Alternatively, you can disconnect CTS connector and measure sensor resistance directly. At room temperature (25C) it should be around 2.7 k and lower as temperature increases. With connector disconnected verify that ground pin of the CTS connector is grounded. Measure resistances between black wire pin and ground - it should be close to 0 Ohms. Anything else check your harness and ground lugs. CTS usually fail as open circuit - very high resistance. As BigEz said it is a very simple R&R job.

//RF