Throttle Position Sensor
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Joined: Aug 2012
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Throttle Position Sensor
Hello,
I have a '84 corvette (since new, 37K miles) – Last Sat, when starting the car, and turning on the AC, I felt the RPM’s fall off, and then the check engine displayed on the dash.
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed.
I disconnected the neg battery, and reconnected the battery 40 min later. Drove the car 10 miles without the AC, and check engine did NOT come on.
A week later I drove the car to a local car show, 5 miles, and no problem. Then when I started the car to go home, at start-up, without the AC running, the engine lost some RPM’s and the check engine light displayed on the dash.
I replaced the Throttle Position Sensor (TPS) 5 years ago (about 1k miles).
From what I read, if there is a voltage cutoff the TPS will trigger a error (21) code.
I’m wondering if there is problem with my fuel filter (replaced 5k miles ago) or my fuel pump (original)?
All comments are welcomed. . .
I have a '84 corvette (since new, 37K miles) – Last Sat, when starting the car, and turning on the AC, I felt the RPM’s fall off, and then the check engine displayed on the dash.
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed.
I disconnected the neg battery, and reconnected the battery 40 min later. Drove the car 10 miles without the AC, and check engine did NOT come on.
A week later I drove the car to a local car show, 5 miles, and no problem. Then when I started the car to go home, at start-up, without the AC running, the engine lost some RPM’s and the check engine light displayed on the dash.
I replaced the Throttle Position Sensor (TPS) 5 years ago (about 1k miles).
From what I read, if there is a voltage cutoff the TPS will trigger a error (21) code.
I’m wondering if there is problem with my fuel filter (replaced 5k miles ago) or my fuel pump (original)?
All comments are welcomed. . .
Safety Car
Joined: Nov 2005
Posts: 3,532
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
Well, first of all there isn't a fuel rail and there isn't a shrader valve to check fuel pressure...this is crossfire injection with two throttle bodies. You must check the fuel pressure in-between the throttle bodies if you are going to check it correctly. The FP should be set to 13psi if stock and adjusted in the rear TB.
You replaced the TPS sensor, did you set the voltage on the new one correctly? Key ON, engine OFF and set it to .525vdc? If you did anything to the TBs in the way of balancing them, YOU MUST reset the TPS to .525vdc or it will not know where idle is.
Also, do you have a 84 GM service manual? If not, buy one. It has all the info you need to properly maintain your 84 CFI.
SPLIT29... If you don't know anything about a CFI motor, please refrain from repling to those threads. All it does is confuse the OP and help to spread more misinformation about crossfire injection. There IS already much too much of that out there already. Thanks.
You replaced the TPS sensor, did you set the voltage on the new one correctly? Key ON, engine OFF and set it to .525vdc? If you did anything to the TBs in the way of balancing them, YOU MUST reset the TPS to .525vdc or it will not know where idle is.
Also, do you have a 84 GM service manual? If not, buy one. It has all the info you need to properly maintain your 84 CFI.
SPLIT29... If you don't know anything about a CFI motor, please refrain from repling to those threads. All it does is confuse the OP and help to spread more misinformation about crossfire injection. There IS already much too much of that out there already. Thanks.
Last edited by Buccaneer; Jul 15, 2019 at 10:35 PM.
Cruising
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Well, first of all there isn't a fuel rail and there isn't a shrader valve to check fuel pressure...this is crossfire injection with two throttle bodies. You must check the fuel pressure in-between the throttle bodies if you are going to check it correctly. The FP should be set to 13psi if stock and adjusted in the rear TB.
You replaced the TPS sensor, did you set the voltage on the new one correctly? Key ON, engine OFF and set it to .525vdc? If you did anything to the TBs in the way of balancing them, YOU MUST reset the TPS to .525vdc or it will not know where idle is.
Also, do you have a 84 GM service manual? If not, buy one. It has all the info you need to properly maintain your 84 CFI.
SPLIT29... If you don't know anything about a CFI motor, please refrain from repling to those threads. All it does is confuse the OP and help to spread more misinformation about crossfire injection. There IS already much too much of that out there already. Thanks.
You replaced the TPS sensor, did you set the voltage on the new one correctly? Key ON, engine OFF and set it to .525vdc? If you did anything to the TBs in the way of balancing them, YOU MUST reset the TPS to .525vdc or it will not know where idle is.
Also, do you have a 84 GM service manual? If not, buy one. It has all the info you need to properly maintain your 84 CFI.
SPLIT29... If you don't know anything about a CFI motor, please refrain from repling to those threads. All it does is confuse the OP and help to spread more misinformation about crossfire injection. There IS already much too much of that out there already. Thanks.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Hello,
I have a '84 corvette (since new, 37K miles) – Last Sat, when starting the car, and turning on the AC, I felt the RPM’s fall off, and then the check engine displayed on the dash.
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed.
I disconnected the neg battery, and reconnected the battery 40 min later. Drove the car 10 miles without the AC, and check engine did NOT come on.
A week later I drove the car to a local car show, 5 miles, and no problem. Then when I started the car to go home, at start-up, without the AC running, the engine lost some RPM’s and the check engine light displayed on the dash.
I replaced the Throttle Position Sensor (TPS) 5 years ago (about 1k miles).
From what I read, if there is a voltage cutoff the TPS will trigger a error (21) code.
I’m wondering if there is problem with my fuel filter (replaced 5k miles ago) or my fuel pump (original)?
All comments are welcomed. . .
I have a '84 corvette (since new, 37K miles) – Last Sat, when starting the car, and turning on the AC, I felt the RPM’s fall off, and then the check engine displayed on the dash.
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed.
I disconnected the neg battery, and reconnected the battery 40 min later. Drove the car 10 miles without the AC, and check engine did NOT come on.
A week later I drove the car to a local car show, 5 miles, and no problem. Then when I started the car to go home, at start-up, without the AC running, the engine lost some RPM’s and the check engine light displayed on the dash.
I replaced the Throttle Position Sensor (TPS) 5 years ago (about 1k miles).
From what I read, if there is a voltage cutoff the TPS will trigger a error (21) code.
I’m wondering if there is problem with my fuel filter (replaced 5k miles ago) or my fuel pump (original)?
All comments are welcomed. . .
With the TPS you can back probe the connector with a voltmeter and measure volts. At closed throttle 0.54v plus or minus 0.02 (from memory). At WOT anything over 4v is ok (again from memory). These measurements should be done with key on but engine not running. If you have a scanner or WinALDL you can monitor the TPS voltage that way. WinALDL will also report throttle percentage open so you can confirm that the ECM is interpreting the information correctly.
Thread Starter
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Joined: Aug 2012
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Buccaneer,
Many thx for your comments:
When I replaced the TPS (with ACDELCO) sensor, the voltage was set to .525vdc.
GregMartin,
Many thx for your comments:
You asked: Why do you think it might be fuel related?
I felt it MIGHT be fuel related, as I had replaced the TPS 2K miles ago, and when I turned on the AC the rpms dropped, and I thought with a drop in RPMS, there may have been drop in voltage at the TPS, which trigged the 21 code = TPS.
Moments ago, I just had the fuel filter replaced, so I'll do more driving to see if the check engine code goes away.
Again, all your comments are greatly appreciated . . .
Many thx for your comments:
When I replaced the TPS (with ACDELCO) sensor, the voltage was set to .525vdc.
GregMartin,
Many thx for your comments:
You asked: Why do you think it might be fuel related?
I felt it MIGHT be fuel related, as I had replaced the TPS 2K miles ago, and when I turned on the AC the rpms dropped, and I thought with a drop in RPMS, there may have been drop in voltage at the TPS, which trigged the 21 code = TPS.
Moments ago, I just had the fuel filter replaced, so I'll do more driving to see if the check engine code goes away.
Again, all your comments are greatly appreciated . . .
Safety Car
Joined: Nov 2005
Posts: 3,532
Likes: 1,185
From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
OK, no problem. I'm a little confused on your thinking though, since code 21 is TPS high, which is not fuel related. The CFI motor is fuel pressure sensitive, but the issue seems to lye with your TPS sensor or TPS circuit. I would use the 84 service manual to troubleshoot that end first, but it doesn't hurt to replace the filter, just more than likely not the issue.
I think if you take a logical approach to the problem along with the service manual, you will track down the issue in short order. Good luck and post up progress.
I think if you take a logical approach to the problem along with the service manual, you will track down the issue in short order. Good luck and post up progress.
Last edited by Buccaneer; Jul 16, 2019 at 02:05 PM.
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OK, no problem. I'm a little confused on your thinking though, since code 21 is TPS high, which is not fuel related. The CFI motor is fuel pressure sensitive, but the issue seems to lye with your TPS sensor or TPS circuit. I would use the 84 service manual to troubleshoot that end first, but it doesn't hurt to replace the filter, just more than likely not the issue.
I think if you take a logical approach to the problem along with the service manual, you will track down the issue in short order. Good luck and post up progress.
I think if you take a logical approach to the problem along with the service manual, you will track down the issue in short order. Good luck and post up progress.
https://www.corvetteforum.com/forums...solutions.html
Last edited by FASTAZU; Jul 16, 2019 at 02:25 PM.
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Thread Starter
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Joined: Aug 2012
Posts: 54
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Gents, Many thanks for taking time to provide your comments & attachments for the FSM for the TPS. . .
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this error code .. .
All the best,
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this error code .. .
All the best,
Thread Starter
Advanced
Joined: Aug 2012
Posts: 54
Likes: 1
Once again, Gents, Many thanks for taking time to provide your comments & attachments for the FSM for the TPS. . .
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this check engine code .. .
I replaced the fuel filter thinking it MIGHT be part of the problem - but as one or more above suggested that did not fix the problem.
With the check engine light on, I had a working OBD1 reader test the car for codes, ran the test (3) times and no codes were found.
Some are suggesting to replace the coolant temperature sensor on the front of the engine, as this communicates with the ECM.
Your thoughts?
All the best,
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this check engine code .. .
I replaced the fuel filter thinking it MIGHT be part of the problem - but as one or more above suggested that did not fix the problem.
With the check engine light on, I had a working OBD1 reader test the car for codes, ran the test (3) times and no codes were found.
Some are suggesting to replace the coolant temperature sensor on the front of the engine, as this communicates with the ECM.
Your thoughts?
All the best,
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
Once again, Gents, Many thanks for taking time to provide your comments & attachments for the FSM for the TPS. . .
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this check engine code .. .
I replaced the fuel filter thinking it MIGHT be part of the problem - but as one or more above suggested that did not fix the problem.
With the check engine light on, I had a working OBD1 reader test the car for codes, ran the test (3) times and no codes were found.
Some are suggesting to replace the coolant temperature sensor on the front of the engine, as this communicates with the ECM.
Your thoughts?
All the best,
This is all "very" helpful, as I'm not a mechanic, just trying to resolve this check engine code .. .
I replaced the fuel filter thinking it MIGHT be part of the problem - but as one or more above suggested that did not fix the problem.
With the check engine light on, I had a working OBD1 reader test the car for codes, ran the test (3) times and no codes were found.
Some are suggesting to replace the coolant temperature sensor on the front of the engine, as this communicates with the ECM.
Your thoughts?
All the best,
Did you measure or scan the TPS and if so what were the results.
These cars are actually very simple, the sensors input readings to the ECM and the ECM acts accordingly.
Validate the sensor inputs with a scanner, WinALDL or a volt meter and go from there.
Last edited by GregMartin; Jul 17, 2019 at 05:54 PM.
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GregMartin & all,
Many thanks.
Since O'Reilly auto were UNABLE to find any error codes using their OBD1 reader (tested 3 times) , I did some reading on the WINALDL GregMartin noted above.
Now that WINALDL program looks amazing.
Have you tried it on an Android smartphone, here's the URL: https://play.google.com/store/apps/d...ales.aldl.scan
All comments welcome . . .
Many thanks.
Since O'Reilly auto were UNABLE to find any error codes using their OBD1 reader (tested 3 times) , I did some reading on the WINALDL GregMartin noted above.
Now that WINALDL program looks amazing.
Have you tried it on an Android smartphone, here's the URL: https://play.google.com/store/apps/d...ales.aldl.scan
All comments welcome . . .
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
GregMartin & all,
Many thanks.
Since O'Reilly auto were UNABLE to find any error codes using their OBD1 reader (tested 3 times) , I did some reading on the WINALDL GregMartin noted above.
Now that WINALDL program looks amazing.
Have you tried it on an Android smartphone, here's the URL: https://play.google.com/store/apps/d...ales.aldl.scan
All comments welcome . . .
Many thanks.
Since O'Reilly auto were UNABLE to find any error codes using their OBD1 reader (tested 3 times) , I did some reading on the WINALDL GregMartin noted above.
Now that WINALDL program looks amazing.
Have you tried it on an Android smartphone, here's the URL: https://play.google.com/store/apps/d...ales.aldl.scan
All comments welcome . . .
Thread Starter
Advanced
Joined: Aug 2012
Posts: 54
Likes: 1
GregMartin,
Agreed need to have the error codes pulled from the ECM. As noted above, the Check Engine light stays on, went to O'Reilly Auto where they were UNABLE to find any error codes using their working OBD1 reader (tested 3 times) tested two times with the ignition on (but motor not running) and one time with the motor running, again no error codes were found.
I then removed the neg battery cable, and let it sit for 20 min, then reconnect the neg battery and drive / test, check engine light comes back on.
It's getting harder to find auto part stores that test OBD1 today, I'm trying to find someone local who has the WIN ALDL working . . .
Again, Many thanks, I'm learning a great deal from our interaction . . .
Agreed need to have the error codes pulled from the ECM. As noted above, the Check Engine light stays on, went to O'Reilly Auto where they were UNABLE to find any error codes using their working OBD1 reader (tested 3 times) tested two times with the ignition on (but motor not running) and one time with the motor running, again no error codes were found.
I then removed the neg battery cable, and let it sit for 20 min, then reconnect the neg battery and drive / test, check engine light comes back on.
It's getting harder to find auto part stores that test OBD1 today, I'm trying to find someone local who has the WIN ALDL working . . .
Again, Many thanks, I'm learning a great deal from our interaction . . .
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
GregMartin,
Agreed need to have the error codes pulled from the ECM. As noted above, the Check Engine light stays on, went to O'Reilly Auto where they were UNABLE to find any error codes using their working OBD1 reader (tested 3 times) tested two times with the ignition on (but motor not running) and one time with the motor running, again no error codes were found.
I then removed the neg battery cable, and let it sit for 20 min, then reconnect the neg battery and drive / test, check engine light comes back on.
It's getting harder to find auto part stores that test OBD1 today, I'm trying to find someone local who has the WIN ALDL working . . .
Again, Many thanks, I'm learning a great deal from our interaction . . .
Agreed need to have the error codes pulled from the ECM. As noted above, the Check Engine light stays on, went to O'Reilly Auto where they were UNABLE to find any error codes using their working OBD1 reader (tested 3 times) tested two times with the ignition on (but motor not running) and one time with the motor running, again no error codes were found.
I then removed the neg battery cable, and let it sit for 20 min, then reconnect the neg battery and drive / test, check engine light comes back on.
It's getting harder to find auto part stores that test OBD1 today, I'm trying to find someone local who has the WIN ALDL working . . .
Again, Many thanks, I'm learning a great deal from our interaction . . .
so if the CEL came back on there is a hard fault. You can short between pins A and B and count the flashes to determine the code ie one flash followed by two flashes equals 12 which just means it ready to display the codes. It will do it three times then it will display the codes the same way.
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Joined: Aug 2012
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GregMartin,
Yes I did short between pins A and B and count the flashes to determine the code ie one flash followed by two flashes equals 12 which just means it ready to display the codes. It will do it three times then it will display the codes the same way. I thought I had counted an error code 21, two flashes, then 1 pause and then one flash - but I may have not counted the flashes correctly, that's why I took it to O'Reilly Auto - to get a correct read on the errors.
Yes O'Reilly Auto were able to communicate their OBD1 scanner, the OBD1 scanner they used was in great shape, and they used a power cord to my cig lighter to get power to the OBD1 scanner, but no codes were present.
Yes I did short between pins A and B and count the flashes to determine the code ie one flash followed by two flashes equals 12 which just means it ready to display the codes. It will do it three times then it will display the codes the same way. I thought I had counted an error code 21, two flashes, then 1 pause and then one flash - but I may have not counted the flashes correctly, that's why I took it to O'Reilly Auto - to get a correct read on the errors.
Yes O'Reilly Auto were able to communicate their OBD1 scanner, the OBD1 scanner they used was in great shape, and they used a power cord to my cig lighter to get power to the OBD1 scanner, but no codes were present.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
GregMartin,
Yes I did short between pins A and B and count the flashes to determine the code ie one flash followed by two flashes equals 12 which just means it ready to display the codes. It will do it three times then it will display the codes the same way. I thought I had counted an error code 21, two flashes, then 1 pause and then one flash - but I may have not counted the flashes correctly, that's why I took it to O'Reilly Auto - to get a correct read on the errors.
Yes O'Reilly Auto were able to communicate their OBD1 scanner, the OBD1 scanner they used was in great shape, and they used a power cord to my cig lighter to get power to the OBD1 scanner, but no codes were present.
Yes I did short between pins A and B and count the flashes to determine the code ie one flash followed by two flashes equals 12 which just means it ready to display the codes. It will do it three times then it will display the codes the same way. I thought I had counted an error code 21, two flashes, then 1 pause and then one flash - but I may have not counted the flashes correctly, that's why I took it to O'Reilly Auto - to get a correct read on the errors.
Yes O'Reilly Auto were able to communicate their OBD1 scanner, the OBD1 scanner they used was in great shape, and they used a power cord to my cig lighter to get power to the OBD1 scanner, but no codes were present.
Back when that car was new GM used the Tech 1 scanner, I wonder what happened to them all?
Anyway WinALDL is a good option.
Last edited by GregMartin; Jul 20, 2019 at 08:38 AM.
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"Many Thanks" to all . . .
Here's an update:
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed. I was not sure I read the flash, flash, pause, flash = error code 21
Then went O'Reilly Auto, they tested 4 times and no codes were found.
Then went to PEP boys where they had an expensive Snapon testing machine, they confirmed error code 21, TPS high volt error.
Since I replaced the ACDELCO 213-902, 6 years ago (2K miles) I thought this one should not fail in that timeframe. So I cleaned the ground, and still have the error code 21.
I do not have the proper thin multimeter back probes (ordered them as well) , to properly back probe and test for the 5 volt and other tests.
So I ordered another new ACDELCO 213-902 TPS - should have it next week.
Here's an update:
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed. I was not sure I read the flash, flash, pause, flash = error code 21
Then went O'Reilly Auto, they tested 4 times and no codes were found.
Then went to PEP boys where they had an expensive Snapon testing machine, they confirmed error code 21, TPS high volt error.
Since I replaced the ACDELCO 213-902, 6 years ago (2K miles) I thought this one should not fail in that timeframe. So I cleaned the ground, and still have the error code 21.
I do not have the proper thin multimeter back probes (ordered them as well) , to properly back probe and test for the 5 volt and other tests.
So I ordered another new ACDELCO 213-902 TPS - should have it next week.
Drifting
Joined: Jun 2018
Posts: 1,402
Likes: 287
From: Brisbane Australia
C4 of Year Finalist (performance mods) 2019
"Many Thanks" to all . . .
Here's an update:
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed. I was not sure I read the flash, flash, pause, flash = error code 21
Then went O'Reilly Auto, they tested 4 times and no codes were found.
Then went to PEP boys where they had an expensive Snapon testing machine, they confirmed error code 21, TPS high volt error.
Since I replaced the ACDELCO 213-902, 6 years ago (2K miles) I thought this one should not fail in that timeframe. So I cleaned the ground, and still have the error code 21.
I do not have the proper thin multimeter back probes (ordered them as well) , to properly back probe and test for the 5 volt and other tests.
So I ordered another new ACDELCO 213-902 TPS - should have it next week.
Here's an update:
Using a two pin connector, with the ignition on but the motor not running, I plugged the 2 pin connector into the OBD port.
A Throttle Position Sensor (check engine code) = 21 displayed. I was not sure I read the flash, flash, pause, flash = error code 21
Then went O'Reilly Auto, they tested 4 times and no codes were found.
Then went to PEP boys where they had an expensive Snapon testing machine, they confirmed error code 21, TPS high volt error.
Since I replaced the ACDELCO 213-902, 6 years ago (2K miles) I thought this one should not fail in that timeframe. So I cleaned the ground, and still have the error code 21.
I do not have the proper thin multimeter back probes (ordered them as well) , to properly back probe and test for the 5 volt and other tests.
So I ordered another new ACDELCO 213-902 TPS - should have it next week.