codes and grounds
Thread Starter
Heel & Toe
Joined: Jul 2017
Posts: 22
Likes: 0
From: silver creek,ny
codes and grounds
Hello again, thanks for the help on my first post, but here we go again, first let me say that the car does run ok, but some minor issues we are tracing. Here goes it may be long but I will try and be correct as possible as my son is doing the checking.
ECM: Sees .5v at idle for TPS but only sees 1.3v at WOT
At sensor .5v at idle for TPS but goes to 3.7v at WOT with volt meter. we are changing TPS
All wiring from 3 sensors to ECM are at .6 to .9 ohms
ECM ground pins D1,D3,D10, were at 11 ohms to ground after cleaning all now at .6-.9 ohms
ECM reads ECT coolant temp, 104 degrees cold and MAT temp corresponds have already changed coolant sensor
but after about 2 minutes of run time, ECT spikes to approx. 230degrees and actual temp is still low 140ish.
Ref voltage @ECT is approx. 3.8v should be 5v, checked ref volts @ ECT to ground at frame and TPS ground is 3.8v.
TPS ref voltage is 5v
mat ref voltage is 5v
Now here is the screwy part,
MAT: wiring, tan wire at Mat has continuity to ECM ground @ D2, but no continuity @ C12 signal wire at pin
But when checking tan and black wires, they show reversed. black(ground) is showing at D2,should be tan wire
Tan (signal) showing at C12 at ECM and black at sensor.
So to get meter to read you put one end at sensor on black,but you have to probe tan wire for response. and visa-versa, there is no connection between the two when disconnected from ECM.
I hope I explained everything correct.
We have cleaned all known grounds, maybe the computer is causing all of this, just don't know, you would think car won't move but it runs fine except for a code now and then, took it about 100 miles last night with no issues but want to clear up the small things so wife is secure.
Thanks again for all your help, This is for a 1988 c-4 coupe
ECM: Sees .5v at idle for TPS but only sees 1.3v at WOT
At sensor .5v at idle for TPS but goes to 3.7v at WOT with volt meter. we are changing TPS
All wiring from 3 sensors to ECM are at .6 to .9 ohms
ECM ground pins D1,D3,D10, were at 11 ohms to ground after cleaning all now at .6-.9 ohms
ECM reads ECT coolant temp, 104 degrees cold and MAT temp corresponds have already changed coolant sensor
but after about 2 minutes of run time, ECT spikes to approx. 230degrees and actual temp is still low 140ish.
Ref voltage @ECT is approx. 3.8v should be 5v, checked ref volts @ ECT to ground at frame and TPS ground is 3.8v.
TPS ref voltage is 5v
mat ref voltage is 5v
Now here is the screwy part,
MAT: wiring, tan wire at Mat has continuity to ECM ground @ D2, but no continuity @ C12 signal wire at pin
But when checking tan and black wires, they show reversed. black(ground) is showing at D2,should be tan wire
Tan (signal) showing at C12 at ECM and black at sensor.
So to get meter to read you put one end at sensor on black,but you have to probe tan wire for response. and visa-versa, there is no connection between the two when disconnected from ECM.
I hope I explained everything correct.
We have cleaned all known grounds, maybe the computer is causing all of this, just don't know, you would think car won't move but it runs fine except for a code now and then, took it about 100 miles last night with no issues but want to clear up the small things so wife is secure.
Thanks again for all your help, This is for a 1988 c-4 coupe
Last edited by tonyb123; Aug 20, 2017 at 09:37 AM. Reason: added year of car
Race Director
Joined: Aug 2000
Posts: 11,470
Likes: 763
Hello again, thanks for the help on my first post, but here we go again, first let me say that the car does run ok, but some minor issues we are tracing. Here goes it may be long but I will try and be correct as possible as my son is doing the checking.
ECM: Sees .5v at idle for TPS but only sees 1.3v at WOT
At sensor .5v at idle for TPS but goes to 3.7v at WOT with volt meter. we are changing TPS
All wiring from 3 sensors to ECM are at .6 to .9 ohms
ECM ground pins D1,D3,D10, were at 11 ohms to ground after cleaning all now at .6-.9 ohms
ECM reads ECT coolant temp, 104 degrees cold and MAT temp corresponds have already changed coolant sensor
but after about 2 minutes of run time, ECT spikes to approx. 230degrees and actual temp is still low 140ish.
Ref voltage @ECT is approx. 3.8v should be 5v, checked ref volts @ ECT to ground at frame and TPS ground is 3.8v.
TPS ref voltage is 5v
mat ref voltage is 5v
Now here is the screwy part,
MAT: wiring, tan wire at Mat has continuity to ECM ground @ D2, but no continuity @ C12 signal wire at pin
But when checking tan and black wires, they show reversed. black(ground) is showing at D2,should be tan wire
Tan (signal) showing at C12 at ECM and black at sensor.
So to get meter to read you put one end at sensor on black,but you have to probe tan wire for response. and visa-versa, there is no connection between the two when disconnected from ECM.
I hope I explained everything correct.
We have cleaned all known grounds, maybe the computer is causing all of this, just don't know, you would think car won't move but it runs fine except for a code now and then, took it about 100 miles last night with no issues but want to clear up the small things so wife is secure.
Thanks again for all your help,
ECM: Sees .5v at idle for TPS but only sees 1.3v at WOT
At sensor .5v at idle for TPS but goes to 3.7v at WOT with volt meter. we are changing TPS
All wiring from 3 sensors to ECM are at .6 to .9 ohms
ECM ground pins D1,D3,D10, were at 11 ohms to ground after cleaning all now at .6-.9 ohms
ECM reads ECT coolant temp, 104 degrees cold and MAT temp corresponds have already changed coolant sensor
but after about 2 minutes of run time, ECT spikes to approx. 230degrees and actual temp is still low 140ish.
Ref voltage @ECT is approx. 3.8v should be 5v, checked ref volts @ ECT to ground at frame and TPS ground is 3.8v.
TPS ref voltage is 5v
mat ref voltage is 5v
Now here is the screwy part,
MAT: wiring, tan wire at Mat has continuity to ECM ground @ D2, but no continuity @ C12 signal wire at pin
But when checking tan and black wires, they show reversed. black(ground) is showing at D2,should be tan wire
Tan (signal) showing at C12 at ECM and black at sensor.
So to get meter to read you put one end at sensor on black,but you have to probe tan wire for response. and visa-versa, there is no connection between the two when disconnected from ECM.
I hope I explained everything correct.
We have cleaned all known grounds, maybe the computer is causing all of this, just don't know, you would think car won't move but it runs fine except for a code now and then, took it about 100 miles last night with no issues but want to clear up the small things so wife is secure.
Thanks again for all your help,
second, DO YOU HAVE A FSM? in particular, volume 2, electrical supplement. it sounds like you do, since you're referencing detailed pinout information of components. if you don't have a FSM, GET ONE!
I have one basic question - are you running any kind of (ground) resistance or continuity checks through your ECM? just asking....
Thread Starter
Heel & Toe
Joined: Jul 2017
Posts: 22
Likes: 0
From: silver creek,ny
Sorry about the year and model info. We were not running checks through the ecm. we had unplugged connectors from it and ran all wiring checks direct. My son has a printout of electrical functions from (all data) he gets through his dealership.
Again, thanks for the help.
Again, thanks for the help.
Thread Starter
Heel & Toe
Joined: Jul 2017
Posts: 22
Likes: 0
From: silver creek,ny
Update on code issues. we were lucky enough to borrow a ecm from an 87 vette with no codes, runs well, and scan tool showed all sensors were correct. Installed in ours with our prom and all issues went away. So after good results, ordered ecm, installed and all sensors are correct. thanks for the help
