very strange tps problem

95cobraguy · Jan 30, 2006

picked the car up tonight from being tuned and the engine light is on. my tuner scanned it and said something about tps voltage too low or some nonsense, i really didn't think much of it since the tps has always worked fine whenever i have adjusted it, etc. i get home, get my voltmeter out and start testing and i have zeros across the board. with the key on i have 0 where it should be 5v on the 5v reference wire, 0 on the ground, (i checked these 2 wires with the sensor unplugged) and naturally nothing on the signal wire going back to the computer which should have under a volt with key on and close to 5v at wot. all this on a car that just made over 500 hp on the dyno. how could this be? i'm gonna get a diagram of the computer pins tomorrow from a friend so i can see if there is 5v coming out of the computer, hopefully there is. if not, what could be causing this bullsh-t.

HISSIN50 · Jan 30, 2006

How did someone "tune" a car with such a large issue? That doesnt make sense to stupid old me.

95cobraguy · Jan 30, 2006

it beats me, he tuned it with a superchip and it came out great. something doesn't make sense. is it possible u can turn off a tps function in a chip, similar to shutting off egr and other emission functions? maybe he fried my computer when tuning?

HISSIN50 · Jan 31, 2006

It is one thing to turn off an ancillary function like EGR, but the engine management relies heavily upon the TPS for throttle opening info (and perhaps more importantly, to note rate of change in throttle position, since the vac readings and other inputs can lag if on and off the gas a lot, like heel/toeing while Auto X'ing).

I would look for bad wiring. And disco' the TPS connector and turn the key to on (dont start it) and recheck the Vref. See if it is at 5 volts now.

Others will have much better advice. This thread might have done well in the new 'Tuning' child-forum.

Grady, Don, Chris et al will have great ideas for you.

Good luck.

mo_dingo · Jan 31, 2006

95cobraguy said:
picked the car up tonight from being tuned and the engine light is on. my tuner scanned it and said something about tps voltage too low or some nonsense, i really didn't think much of it since the tps has always worked fine whenever i have adjusted it, etc. i get home, get my voltmeter out and start testing and i have zeros across the board. with the key on i have 0 where it should be 5v on the 5v reference wire, 0 on the ground, (i checked these 2 wires with the sensor unplugged) and naturally nothing on the signal wire going back to the computer which should have under a volt with key on and close to 5v at wot. all this on a car that just made over 500 hp on the dyno. how could this be? i'm gonna get a diagram of the computer pins tomorrow from a friend so i can see if there is 5v coming out of the computer, hopefully there is. if not, what could be causing this bullsh-t.

Try this. Remove the plug from the TPS sensor. Take your neg lead on your multimeter, and clamp it to the neg terminal on the battery. Take the pos lead and touch it to each of the 3 tabs on the TPS harness. With the DMM set to continuity, figure out which has continuity to ground. If none, you have an open ground wire.

So assuming your ground wire is ok (label it so you remember which is which), next move the pos test lead to the two other pins with the DMM set to voltage. Keep the neg lead on the battery. With the key on, you should see 5V at one of the other pins. Label that wire as your 5V reference voltage source. If you don't have it, you can do one of 2 things. Trace the wire throughout the car until you go nuts (or get lucky and find the break in the wire). Or, you can steal it from the MAF sensors 5V ref wire. Just run a wire connecting the MAF wire to the TPS wire. Scotch lock or a bell connector will work in this case. That will cure your problem.

Now if you have both ground and the 5V ref voltage, note which wire is the output wire, connect the connector to the TPS and backprobe the output wire (i.e. backprobe = cut small portion of the insulation away and . with the key on, you should read somewhere around 1V (.8 - 1.2 likely). With the throttle all the way open, you should read 4.5-4.8V. If you dont, the potentiometer inside the TPS is bad, or the connector isn't making a good connection (i.e. check tabs).

Post back what you find.
Scott

95cobraguy · Feb 1, 2006

mo_dingo said:
Try this. Remove the plug from the TPS sensor. Take your neg lead on your multimeter, and clamp it to the neg terminal on the battery. Take the pos lead and touch it to each of the 3 tabs on the TPS harness. With the DMM set to continuity, figure out which has continuity to ground. If none, you have an open ground wire.

So assuming your ground wire is ok (label it so you remember which is which), next move the pos test lead to the two other pins with the DMM set to voltage. Keep the neg lead on the battery. With the key on, you should see 5V at one of the other pins. Label that wire as your 5V reference voltage source. If you don't have it, you can do one of 2 things. Trace the wire throughout the car until you go nuts (or get lucky and find the break in the wire). Or, you can steal it from the MAF sensors 5V ref wire. Just run a wire connecting the MAF wire to the TPS wire. Scotch lock or a bell connector will work in this case. That will cure your problem.

Now if you have both ground and the 5V ref voltage, note which wire is the output wire, connect the connector to the TPS and backprobe the output wire (i.e. backprobe = cut small portion of the insulation away and . with the key on, you should read somewhere around 1V (.8 - 1.2 likely). With the throttle all the way open, you should read 4.5-4.8V. If you dont, the potentiometer inside the TPS is bad, or the connector isn't making a good connection (i.e. check tabs).

Post back what you find.
Scott

thanks alot scott, will do. now that u mentioned that there has to be 5 volts coming out of the computer because the maf gets a 5v reference as well and my tuner didn't say anything about a problem with maf voltage, unless the tps and maf sensor have separate 5v references coming out of the comuter. i'm heading to a friends shop now to use his alldata to get some wiring diagrams so i can see exactly which pin out of the computer is the 5v source, i did the few tests u described and have nothing so that is why i'm going right to the computer to see whats going on there first. but taking the maf 5v reference is a great idea if i cant find an open in the wire. scott, your the man.

95cobraguy · Feb 1, 2006

found the problem, broken 5v reference wire going to tps. how it broke is strange and how my tuner dyno'd it with that sh-t goin on is even more strange.

mo_dingo · Feb 1, 2006

95cobraguy said:
found the problem, broken 5v reference wire going to tps. how it broke is strange and how my tuner dyno'd it with that sh-t goin on is even more strange.

Thanks for posting back. Glad you found it. Just for anyones info, you could have just stole power from the 5V ref wire at the maf or any other 5V reference source to fix an open at your TPS. It's a lot faster to do it that way, but since you apparently had the time and patience (and luck that it was that easy to find), your way worked as well.
Scott

BlackVert · Feb 1, 2006

95cobraguy said:
found the problem, broken 5v reference wire going to tps. how it broke is strange and how my tuner dyno'd it with that sh-t goin on is even more strange.

maybe it broke after he finished tuning it and was putting the pcm back into the kick panel (after putting the chip on)?

do you know where the wire went open?

94gts · Feb 1, 2006

95cobraguy said:
found the problem, broken 5v reference wire going to tps. how it broke is strange and how my tuner dyno'd it with that sh-t goin on is even more strange.

who did your dyno tune down there? mustang magic?

95cobraguy · Feb 2, 2006

BlackVert said:
maybe it broke after he finished tuning it and was putting the pcm back into the kick panel (after putting the chip on)?

do you know where the wire went open?

the wire was broken in the harness along the firewall, pretty much right behind the intake. i had to open the harness up to find it.

95cobraguy · Feb 2, 2006

94gts said:
who did your dyno tune down there? mustang magic?

i had mustang magic do a few tunes but wasn't really satisfied with the results so i ended up going to real speed automotive (www.realspeedautomotive.com. i had to get a completely different chip because mustang magic uses autologic chips and dan at real speed uses superchips software. but the tune came out a lot better and dan at realspeed has a mustang dyno and mustang magic uses dynojet and i've heard that tuning on a mustang dyno results in a better tune.

very strange tps problem

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