[FIXED] 1990 Camaro Iroc 5.0L ECT circuit

ECT sensor was replaced by another shop. Scan data shows ECT in Degrees Fahrenheit, only. Voltage at the sensor with a Some-what warm engine was 1.24v. ECT pid was a fixed 104. ECT code stored. I assumed 104 was a substituted value, due to the ECT code. I cleared the code and rechecked. I bounce around the shop like popcorn, so after the code was cleared enough time had passed that the engine was cold. No code, cold engine, ECT pid 75. Signal wire voltage check 2.5v. I let it warm up and the scan data temperature never increased beyond 104. IR thermometer indicated 165 degrees with voltage at .4v (400mv). I disconnected the temp sensor and, as expected, the reading dropped to -38. 5v. With a test light to ground, I shorted the signal wire expecting to 260+. The value was 104. At this point, I started blaming the ECM. Backprobed at the ECM, same result.

Before I replace the ECM ,...Am I missing something? With a test light to ground, shouldn't I be able to get the data to indicate MORE than 104 degrees?

High ressistance would produce exactly those symptoms -- it could of course be a high resistance soldered joint within the ECU or the ECU connector
I would look for green crusties

Thanks for the reply, Andy.MacFadyen!

Andy.MacFadyen wrote: I would look for green crusties

Bypassing resistance problems is why I backprobed the ECM. I would expect to see much higher than 104 degrees.

Do you have access to a variable resistor? Wondering if being able to manipulate the circuit while looking at the scan data might be the easier way to test this. i.e. if you can make the voltage PID show the whole range, but the ECT PID never plays along.

IR thermometer indicated 165 degrees with voltage at .4v (400mv).

This sounds abnormally low to me? I dunno what the temperature/voltage chart looks like for this sensor, but .4V is closer to 185/195 on most. This may be nothing. :lol:

No code, cold engine, ECT pid 75. Signal wire voltage check 2.5v. I let it warm up and the scan data temperature never increased beyond 104.

This part really makes me believe in a PCM problem. Perhaps try a battery disconnect before pulling the trigger on a replacement?

I was confident enough that I ordered the ECM a couple days ago. It came in this morning. I installed it. I shorted the signal to ground with a test light and the PID indicated 300 degrees. Engine running, Temp PID reads as it should.

Nice. Just curious, what was the original complaint? I mean, before this other shop replaced the ECT. Fueling issue due to the inaccurate ECT?

Tyler wrote: Nice. Just curious, what was the original complaint? I mean, before this other shop replaced the ECT. Fueling issue due to the inaccurate ECT?

The story is, for whatever reason, this thing has been sitting for 5 years. It drove in...barely. Running like crap, one of the first things I checked was fuel pressure. Fuel pressure was 35 psi, down to 10, back up to 35.....I scoped the fuel pump an it looked terrible, to a flat-line, and back to terrible. New fuel pump installed...steady 45 psi. Releasing the pressure on the fuel gauge, I notice the color was a little dark. Fuel is VERY tarnished. Tank not very full, so I added 10 gallons of good gas.(I know I should have drained the tank, but there was a pre-cut hole in the trunk. So, the tank was never dropped:dry: ) Still runs like crap (and probably will until the bad gas get ran through). Won't idle. Ignition parade showed a fixed 4kv on ALL spark lines. Cap and rotor were very crusty. New Cap, Rotor, Plugs, and wires. Getting better, but it still doesn't run well. It's much better, though, and idles on it's own, at least. THIS is where I, myself, start looking at the temp sensor...you know this part, so I'll skip over it. After the New ECM was installed, if fired right up. Idled, nicely. Warmed up. The exhaust is no longer noxious (did I mention that it was? Smokey.) Tried to rev it a little and it's backfiring out the exhaust. Shut it off. Try to start it 5 minutes later, NO-START. I just shook my head and walked away. Floated back to it a couple times through the day and turned the key. No Start. I still have it. I'll get back to it, tomorrow.

pole71 wrote: The story is, for whatever reason, this thing has been sitting for 5 years. It drove in...barely...

Oh, it's one of THOSE cars. No matter what you do, at the end of the day, it's still broken! :silly:

Tyler wrote:

pole71 wrote: The story is, for whatever reason, this thing has been sitting for 5 years. It drove in...barely...

Oh, it's one of THOSE cars. No matter what you do, at the end of the day, it's still broken! :silly:

Yep. In the last episode of the Saga, we left it with a no-start. I had, previously, stated that I had put 10 gallons of gas in it. That wasn't totally accurate. I had asked my helper to put the gas in. Turns out, no gas was put in. The no-start was, simply, no-fuel. :whistle:

Fuel added, it idles fine. Fully warmed up, the O2 signal is stuck in the 600-700mv range. Neither vacuum leak, nor added fuel would change it. Single circuit test good. New O2 sensor. O2 activity restored. I, finally, think I'm ready to test drive! Didn't make it half way down the block before I turned around and came back. Lots of misfiring. Ramped bank 1 and bank 2 injector control from the ECM.
Going in, individually, Bank1 has 1 shorted injector and Bank 2 has 3 shorted injectors.:woohoo:

To be continued.....