Dies in gear when throttle applied

[1990Z71Swede]

Are there any precautions that must be taken when testing electrical at the ECU?

E.g. battery ground connected vs not? Or, risk of static electricity etc?

Well Normaly, any device is more ESD sensitive when not installed and/or connected. So from that standpoint I think there is really no need to be overly concerned until you disconnect your ECU from the car. I would leave the battery connected.

Working on more modern Cars is most likely another story though.

You need to be a little bit careful though. If I for some reason were measuring a large connector with lots of pins with ignition/power on I would not just showe my probe in there hoping not to short any of the other pins out.

Soo, be careful. You do not wan't to end up sticking your probe in the wrong place.. and if you do... always front to back... NOT the other way around

 

[92GMCK2500]

Ok, rookie mechanic here so excuse the questions...

I just ran a voltage test with the truck running, same 3.7v reading at the CTS. I back probed the yellow wire. Interesting, everytime I grounded the wire to a goodnkmown ground & Batt negative, the truck would idle higher. Jumping from approx 800 to 1200rpm.

Any clues of what this could be indicative of?

 

[1990Z71Swede]

I'm guessing, but I think it knows when it is open circuit, so it disregards the input and would probably turn the CES light on after a while. When you ground it through the meter it just thinks the engine is cold, and goes into high idle.

Totally normal, I think.

 

[92GMCK2500]

Makes sense.

I swapped in a good battery, charged to 13.2v. The truck started right away. Ran it for 15 mins while I tested stuff.

Went to restart, no go. Won't start, cranked for a while to build oil pressure, still no go. Thought I'd mention this.

Looks like I am diving into the ECU next

 

[1990Z71Swede]

Next time it does not start like that, verify if it is fuel or ignition that is the culprit, either pull a sparkplug to see if it's wet or give it a shot of fuel through the trottle body and see if that helps.

 

[92GMCK2500]

Next time it does not start like that, verify if it is fuel or ignition that is the culprit, either pull a sparkplug to see if it's wet or give it a shot of fuel through the trottle body and see if that helps.

Yeah, thanks. Ignition is all pretty new but you never know these days.

Fuel system is new too. I need to check fuel pump voltage & amps whilst running. I went to start again to test and that's when it stopped! Haha

 

[92GMCK2500]

Here's my game plan.

1. Test V & amps at fuel pump connector to eliminate any electrical issues associated w' fuel pump circuit. Relay V matches battery, already verified this.
2. Test TPS - as this is on the same circuit as CTS.
3. Test for 12V at ECU.
4. Test for 5V at pin C10 (CTS yellow wire)
5. Test ECU ground.
6. Test 5V reference and 5V sensor signal at ECU.
7. Inspect wiring between ECU and CTS.
8. Eliminate any EGR issues. Follow code 32 diagnostics flow chart.

Hopefully I am on the right track.

 

[Schurkey]

Here's my game plan.

1. Test V & amps at fuel pump connector to eliminate any electrical issues associated w' fuel pump circuit.

Very worthwhile, as long as we agree that the "fuel pump connector" is the most rearward one before the harness goes up 'n' over the tank. In a perfect world, you'd be testing the connector INSIDE the tank, but that's just not practical. It is, however, the reason I replace the in-tank wire harness when I shove in a new fuel pump.

2. Test TPS - as this is on the same circuit as CTS.
3. Test for 12V at ECU.
4. Test for 5V at pin C10 (CTS yellow wire)
5. Test ECU ground.
6. Test 5V reference and 5V sensor signal at ECU.
7. Inspect wiring between ECU and CTS.

Or connect a scan tool, verify EVERY sensor in 1/6 the time it would take to do all these manual tests, AND likely have better results. What matters is the accuracy of the sensor signals. Verifying 5-volt references and grounds is the long-way of finding problems IF they exist. If the sensor signal is reasonable, there's no need to play with reference voltages or grounds.

8. Eliminate any EGR issues. Follow code 32 diagnostics flow chart.

Again, very reasonable.

 

[92GMCK2500]

Alright, alright, I'll dive into my old scanner over the weekend and see what I can do. Never used one before so I am learning on the job. I get it though, much faster diagnostics!

Update from tonight...

Tested TPS. It's getting the 5v supply ok, 4.98V on the DVM, at KOEO, connector unplugged. However, when testing TPS signal at KOEO, connector plugged in, I am getting only 0.37v at throttle fully closed and gradually & steadily increases to 2.72v at WOT. According to FSM, I should be 0.6v & 4.5v. No code 22 set, well not yet anyways.

I checked for codes again at the end of the night. I am now getting Code 54 - Fuel pump relay low voltage. First test tomorrow will be V & amps at the FP connector at fuel tank exterior harness plug.

Then that bloody scanner is getting plugged in to this pig.

I definitely have multiple things going on... one repair at a time I guess.

I need this thing moving under its own power before end of month

 

[92GMCK2500]

The TPS & CTS ECU grounds (5v return) are tied together, could a sh1tty ground at the ECU pin be the cause of all this?

I have issues with both sensors.