TPS will not read 100%, only reading 60% (3.0V) at WOT
11-24-2013, 04:10 AM
#1
TPS will not read 100%, only reading 60% (3.0V) at WOT I've been fighting this for a couple days now and was hoping I could get some help on here.
I'm helping a friend setup a LQ9/4L80E combo in a 1982 K10 Chevy and we're having problems tuning it because the TPS will only read 60% to 65% at wide open throttle. The throttle body is opening all the way. I also tested a completely different throttle body with different sensors with the same results. I have also tested the second throttle body on a 1999 Firebird and it reads 100% for WOT so I know its not a sensor issue.
On the K10, the TPS reads about .85v idle/closed and only 3.0~3.15v at WOT. This is with the truck key on engine off and also key on engine running. I have verified that grey wire on the TPS sensor is receiving 5.0V and have also tested all the wires for high resistance (all under 0.02ohm) and none of the wires are shorting to ground.
I have also checked the 4 PCM grounds (Pin 1 & Pin 40 on each connector) and they are about 0.5ohm to ground on the body, frame, engine, or battery negative. I have also moved the grounds and made sure everything was nice and shiny were they are connected with no changes at all to the TPS reading. I have also tried reflashing the PCM to a couple different tunes with complete rewrites.
My only other concern when I was checking grounds, Pin 4 from the OBDII connector kept sparking. I have Pin 4 & Pin 5 on the OBDII connector sharing the same ground as the PCM grounds. When I was moving the grounds, Pin 4 on the OBDII kept sparking everytime I moved it. When HPTuners is plugged in, Pin 4 becomes hot. This doesn't seem right to me but if I don't put Pin 4 to ground, HPTuners will not read the PCM. I also moved the OBDII grounds to the other side of the vehicle away from the PCM grounds with no changes to the TPS reading.
This LQ9 swap was in a Crown Victoria right before the K10 using the exact same PCM and wire harness with 0 issues, so I'm at a loss. The only thing that was changed from the Crown Victoria to the K10 was the addition of a 4L80E trans, we were running a TH400 in the Crown Vic.
If anyone has any ideas, I would GREATLY appreciate it as I can't think of anything else to try. I brought the PCM home with me and I'm going to test it in another vehicle tomorrow to make sure there isn't something wrong with the PCM itself.
I'm helping a friend setup a LQ9/4L80E combo in a 1982 K10 Chevy and we're having problems tuning it because the TPS will only read 60% to 65% at wide open throttle. The throttle body is opening all the way. I also tested a completely different throttle body with different sensors with the same results. I have also tested the second throttle body on a 1999 Firebird and it reads 100% for WOT so I know its not a sensor issue.
On the K10, the TPS reads about .85v idle/closed and only 3.0~3.15v at WOT. This is with the truck key on engine off and also key on engine running. I have verified that grey wire on the TPS sensor is receiving 5.0V and have also tested all the wires for high resistance (all under 0.02ohm) and none of the wires are shorting to ground.
I have also checked the 4 PCM grounds (Pin 1 & Pin 40 on each connector) and they are about 0.5ohm to ground on the body, frame, engine, or battery negative. I have also moved the grounds and made sure everything was nice and shiny were they are connected with no changes at all to the TPS reading. I have also tried reflashing the PCM to a couple different tunes with complete rewrites.
My only other concern when I was checking grounds, Pin 4 from the OBDII connector kept sparking. I have Pin 4 & Pin 5 on the OBDII connector sharing the same ground as the PCM grounds. When I was moving the grounds, Pin 4 on the OBDII kept sparking everytime I moved it. When HPTuners is plugged in, Pin 4 becomes hot. This doesn't seem right to me but if I don't put Pin 4 to ground, HPTuners will not read the PCM. I also moved the OBDII grounds to the other side of the vehicle away from the PCM grounds with no changes to the TPS reading.
This LQ9 swap was in a Crown Victoria right before the K10 using the exact same PCM and wire harness with 0 issues, so I'm at a loss. The only thing that was changed from the Crown Victoria to the K10 was the addition of a 4L80E trans, we were running a TH400 in the Crown Vic.
If anyone has any ideas, I would GREATLY appreciate it as I can't think of anything else to try. I brought the PCM home with me and I'm going to test it in another vehicle tomorrow to make sure there isn't something wrong with the PCM itself.
11-25-2013, 09:58 AM
#2
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What does the TPS +5V feed say, at WOT? Measured
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
11-25-2013, 10:06 AM
#3
What does the TPS +5V feed say, at WOT? Measured
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
I had all the grounds connected to the body, all at the same screw. It was when I started separating them that I noticed that the OBDII ground became hot when HPtuners was plugged in. When HPTuners isn't plugged in, its not hot.
I have tried separating the grounds to different points, I have tried connecting them all to the same point and even ran a heavy cable straight from the battery negative to the same common screw with the grounds, and have also added a heavy duty cable from the battery to frame. No matter what I check (body to frame, engine to frame, body to engine, body to battery etc) I get about 0.2ohm of resistance or less.
I have also verified the PCM in another vehicle and it reads the TPS right when installed in different vehicles.
11-25-2013, 10:35 AM
#4
An ohm meter is not a valid test for a ground. Voltage drop when loaded is the only valid test. Something can ohm zero and still not carry enough current. One strand in a wire will ohm fine, but won't carry enough current to be of any use.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
11-25-2013, 11:23 AM
#5
An ohm meter is not a valid test for a ground. Voltage drop when loaded is the only valid test. Something can ohm zero and still not carry enough current. One strand in a wire will ohm fine, but won't carry enough current to be of any use.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
11-27-2013, 12:32 PM
#6
What does the TPS +5V feed say, at WOT? Measured
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
against the return (GND) wire?
All the grounds need to be electrically common and
sounds like there's something there that needs sorting.
Like if the OBDII ground becomes "hot" just by plugging
in a load, that "ground" is probably getting pulled to
potential through some sort of secondhand loop but
is not as stiff as it should be.
11-27-2013, 12:33 PM
#7
An ohm meter is not a valid test for a ground. Voltage drop when loaded is the only valid test. Something can ohm zero and still not carry enough current. One strand in a wire will ohm fine, but won't carry enough current to be of any use.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
Quick and dirty, back probe the ground terminals at the PCM connectors, key on. Volt meter black lead grounded to battery negative. Red lead back probing the ground terminals, should see less than 1/2 volt. Usually .2 to .3 volts. If you see voltage you have a poor ground.
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11-27-2013, 12:37 PM
#8
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At WOT you will have a higher electrical load and
that 250mV might become more significant, all
depending on where it is and what it gets into.
Still the PCM sources its own power and ground
so you'd think that if the +5 stays +5 at WOT, it
should read right.
You might want to put the DMM on the signal, and
then the power feed, and look at whether the DMM
and the scan readings diverge, and under what
conditions.
that 250mV might become more significant, all
depending on where it is and what it gets into.
Still the PCM sources its own power and ground
so you'd think that if the +5 stays +5 at WOT, it
should read right.
You might want to put the DMM on the signal, and
then the power feed, and look at whether the DMM
and the scan readings diverge, and under what
conditions.
11-27-2013, 12:42 PM
#9
At WOT you will have a higher electrical load and
that 250mV might become more significant, all
depending on where it is and what it gets into.
Still the PCM sources its own power and ground
so you'd think that if the +5 stays +5 at WOT, it
should read right.
You might want to put the DMM on the signal, and
then the power feed, and look at whether the DMM
and the scan readings diverge, and under what
conditions.
that 250mV might become more significant, all
depending on where it is and what it gets into.
Still the PCM sources its own power and ground
so you'd think that if the +5 stays +5 at WOT, it
should read right.
You might want to put the DMM on the signal, and
then the power feed, and look at whether the DMM
and the scan readings diverge, and under what
conditions.
I tried putting the DMM on the +5V and the Signal wire but couldnt get a reading.
I only had about 10 minutes of access with the truck last night so I had to check everything quickly. I might not of been getting a good connection on the signal wire but I did try probing it a couple of times. I'll have better access to the truck this weekend.
11-27-2013, 12:45 PM
#10
I do have the owner of the truck pulling the harness off the truck, leaving everything connected to the engine and pulling the battery to engine ground off. I'm going to try and hook the harness up to a separate battery and isolate the engine/harness from the truck to verify that it is a problem with the trucks wiring or the engine wiring.
As I said before, this setup was running a two weeks ago with zero problems in a Crown Vic so I assume there is some sort of issue with the truck wiring at this point.
As I said before, this setup was running a two weeks ago with zero problems in a Crown Vic so I assume there is some sort of issue with the truck wiring at this point.
