TPS voltage
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,753
Likes: 1,661
From: Summerville SC
TPS voltage
1986 L98 engine. Just breaking it in and I have the at idle reading set at .540 volts. At WOT I can only get it to 3.8 volts but I am under the impression it should be at least 4.0. The issue I am trying to resolve is a miss at WOT. I am also going to check my plug wire routing. It’s a new tps switch, but that doesn’t mean anything these days. Looking at simple things first. Thx.
Oil Producer
Joined: Apr 2014
Posts: 9,349
Likes: 2,726
if the throttle blades are not opening all the way.....
check the pedal actuator bar for being bent.
major cable slack should be easy to see
or some weird buildup of carpet/underlay below the pedal.
check the pedal actuator bar for being bent.
major cable slack should be easy to see
or some weird buildup of carpet/underlay below the pedal.
Last edited by VikingTrad3r; Apr 15, 2021 at 10:31 AM.
Racer
Joined: Mar 2020
Posts: 384
Likes: 144
From: Langton, Ontario, Canada
2025 C4 of the Year Finalist - Unmodified
So, the question is this:
Is the throttle body opening all the way as much as it can?
If no, then cable adjustment or replacement is necessary. If yes, then try removing the TPS and measuring it OFF the throttle body.and see if it actually is capable of going to 4.0.
If no, then you need to replace it.
If yes, then possibly remounting it may change things, but at that point, I'd be looking again at the throttle body.
Is the throttle body opening all the way as much as it can?
If no, then cable adjustment or replacement is necessary. If yes, then try removing the TPS and measuring it OFF the throttle body.and see if it actually is capable of going to 4.0.
If no, then you need to replace it.
If yes, then possibly remounting it may change things, but at that point, I'd be looking again at the throttle body.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,753
Likes: 1,661
From: Summerville SC
LiveWire I think it is opening. I will pull the pieces off the front of the TB to verify. Then I will pull the TPS off the TB and just move it by hand. I just wanted to confirm that my 3.8 or.9 was too low a reading, then figure out why. This engine is in a C3, so nothing is stock but the pedal is pulling the TB open as far as it will go with the stop at the top of the linkage making contact with the houseing. I Will follow up later when I get it apart. Thx.
Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,753
Likes: 1,661
From: Summerville SC
Disconnected all linkage and cannot get it over 3.9. Throttle wide open. Took the switch off and by hand I can get it to go up to almost 5.0, but I can't get that number with it installed without the .540 at idle being off. So it is the switch. As for it not affecting the misfire, seems to me in previous vehicles that the TPS was one of the most critical components telling the computer where the throttle was positioned, and that voltage to the ecu translated to a signal going to the injectors regulating fuel somehow. Not an expert by any means but it must have something to do with throttle/fuel/air or why would it be attached to the throttle blades.
Drifting
Joined: Aug 2019
Posts: 1,334
Likes: 225
It does seem to be off. But the MAF sensor is the load sensor that the ecm uses for fuel calculation. What part number TPS did you buy? You need to isolate the misfire as to whether it's one cylinder or more.
Last edited by Mrvettenick; Apr 15, 2021 at 06:52 PM.
Oil Producer
Joined: Apr 2014
Posts: 9,349
Likes: 2,726
Disconnected all linkage and cannot get it over 3.9. Throttle wide open. Took the switch off and by hand I can get it to go up to almost 5.0, but I can't get that number with it installed without the .540 at idle being off. So it is the switch. As for it not affecting the misfire, seems to me in previous vehicles that the TPS was one of the most critical components telling the computer where the throttle was positioned, and that voltage to the ecu translated to a signal going to the injectors regulating fuel somehow. Not an expert by any means but it must have something to do with throttle/fuel/air or why would it be attached to the throttle blades.
you are saying that even rotating the tb by hand you canny get the tps to read over 3.9?
but if you rotate the tps lever by hand it will go full range?
how open are your throttle blades in the resting position? can u upload a bunch of pics
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Thread Starter
Safety Car
Joined: Dec 2012
Posts: 3,753
Likes: 1,661
From: Summerville SC
Correct. If I take off the throttle cable and the trans kickdown cable, take off the hose connecting throttle body to air filter I can move the blades so they are wide open, I can only get it up to 3.8 or maybe 3.9. If I take the sensor off the throttle body and move it with my hands I can get it over 4.0. I definitely seems like the switch is bad. Like there isn't enough available travel when hooked to throttle body. I will try and get some pics tomorrow. When the blades are resting, my idle is perfect at about 650rpm. And the voltge is .540, which is in spec. I even tried backing off the idle adjustment screw completely and it did not make any difference in reaching the over 4.0 number. Then I had trouble getting it back to the .540. Thanks for all the feedback.
Melting Slicks
Joined: Aug 2003
Posts: 3,378
Likes: 388
From: Lakeville MI
3.8-3.9 volts at WOT should be fine. You only need enough tps voltage for the ecm to enter power enrichment mode which normally occurs at 70% throttle. This can occur below 3 volts.
Pwr Enrichment TPS Treshold vs RPM
RPM % TPS
4800 70.31
3200 70.31
2000 70.31
1200 70.31
400 70.31
Here's a recent log from another tps-challenged member in order to illustrate: https://datazap.me/u/elijah/fixed-ti...3900-3936-3954
Observe the throttle position and target afr signals. Due to the rapid rate of throttle opening and slow sample rate, you can't see the exact voltage the instant that power enrichment mode is entered, but you get the idea. Power enrichment mode entry can be seen when the target afr drops below 14.73. In this case, 14.73:1 -> 12:1. Power enrichment exit can also be seen later on as the throttle is closed.
Another example from the same log with PE entry at or below 2.52 volts: https://datazap.me/u/elijah/fixed-ti...5265-5269-5276
Pwr Enrichment TPS Treshold vs RPM
RPM % TPS
4800 70.31
3200 70.31
2000 70.31
1200 70.31
400 70.31
Here's a recent log from another tps-challenged member in order to illustrate: https://datazap.me/u/elijah/fixed-ti...3900-3936-3954
Observe the throttle position and target afr signals. Due to the rapid rate of throttle opening and slow sample rate, you can't see the exact voltage the instant that power enrichment mode is entered, but you get the idea. Power enrichment mode entry can be seen when the target afr drops below 14.73. In this case, 14.73:1 -> 12:1. Power enrichment exit can also be seen later on as the throttle is closed.
Another example from the same log with PE entry at or below 2.52 volts: https://datazap.me/u/elijah/fixed-ti...5265-5269-5276
Last edited by tequilaboy; Apr 16, 2021 at 02:47 PM.