bigboarderbuzz

i know i've read it somewhere on here before but ive searched again and can't find it. if i unplug my TPS and it doesn't trip the engine light, does that mean my TPS is bad? thanks in advance for your help

abecedarian

TPS check / adjustment procedures:
http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

bigboarderbuzz

thanks for the link, i have read many threads that hit on the TPS and everyone says that if it is unplugged there will be a trouble code. mine does not. so i was wondering if unplugging the TPS, and it does not throw a code, means that the TPS is bad. i dont have an Ohm meter and would rather not go buy one if i can tell by the symptoms i have that it is bad.

abecedarian

All I can say is that I've provided you a link to a guide to check the TPS.
I'm fairly certain that if you could use the ECU and trouble codes and the like to test the TPS, those procedures would have been mentioned in the guide to testing the TPS.

My only experience regarding unplugging the TPS and getting a trouble code is that my TPS was not adjusted properly and I unplugged it and DID NOT get a trouble code. I'm still chasing down that problem, but suffice it to say that this morning while trying to t-shoot a misfire I disconnected it, got no code and it is brand new and tests the same as the old one...
... and your question was?

bigboarderbuzz

hey thanks for the info abe "... and your question was?" like i said, from what i read unplugging should throw a code. my question was asking if there is no code, is there a problem. i read the link you supplied which is great info it just didn't answer my question. your last post did answer it so thanks.

abecedarian

Wish I could be a better help and say that the ECU would tell you that the TPS was bad, but all the ECU gets is a signal from the TPS that the throttle is closed (@Idle) and a signal that says how far open the throttle is if it's not closed. Unfortunately, the latter signal is a 'range' represented by varying resistance. The only thing the ECU can tell you about the throttle is whether it ever sees 'IDL' or if the TPS sends a value to the ECU that does not correspond to any value it should expect.

thook

The ECU does require a signal from the TPS. It is an entire circuit that includes not only the IDL setting, but also VTA (throttle angle) and Vcc (?). It should throw a code for a short or open signal in the circuit if/when uplugged. And a bad TPS could be the source of the short/open.....but, then it would/should throw a code.

You need to check the ECU. Look in the FSM for ECU testing procedure under the MFI section.

http://personal.utulsa.edu/~nathan-b...ne/44engin.pdf

Edit: I should clarify that the what I mean by a bad TPS is that there would be broken or shorted circuit in the TPS or at the terminals. E2 is the ground, (I believe) Vcc is the voltage supply, VTA is throttle angle, and IDL is idle detect. A worn track in IDL or VTA wouldn't throw a TPS code....they would just be out of range and create poor operating conditions. But, if somehow there was break in those tracks so there was an incomplete circuit, then a code. Likewise for E2 and Vcc.

OH!!!! Right....this just occurred to me and I think this may explain something....which might make checking the ECU moot.

If you have the engine off and the key off and uplug the TPS, at that point power to the diagnostic system (ECU) is off. A code will not be thrown UNLESS you turn the key back on and the ECU registers the circuit input is not there and broken. Likewise, if you unplug the TPS while the key is on, the ECU registers.....or should, anyway...and the throws the code.

I realize this is more or less than what abecedarian said, but I was hoping to add or clarify the situation and help, as well.

bigboarderbuzz

thanks this info helps out guys, it seems i could possibly have more of a problem then i thought. i know when i unplugged the TPS i had the truck off. the reason i unplugged was like abe trying to figure out a miss. the truck seems to run better without the tps plugged in but only at a higher idle. to make matters worse i checked my fuses and i had a blown ECU fuse. i have now clue for how long. i searched for that and didn't come up with much. my next test is to find out if the new fuse made the truck run better or if it was unplugging the TPS. thanks again guys

thook

I don't know how your truck even started with a bad ECU fuse. (You do mean "EFI" fuse, right?). The main relay, ignition circuit, and power to the ECU is rather dependant on it. 12v's have to get through somehow.

Now, some people have found their vehicle ran better initially with the TPS uplugged BECAUSE the TPS was bad. So, you may have a bad one. Just need to test it. You don't have a meter, but it's a good thing to have if you plan on fixing your own vehicle. However, try this.....plug the TPS back and rotate it clockwise and counter clockwise with the screws loose. The rpm should alternate between low and high if the ECU is able to detect the idle position. If it doesn't change in that way, it's bad. But, even IF it does change, you may still have a problem on the throttle angle circuit....like I said.

bigboarderbuzz

okay thanks for the help. i'll have to go get the meter i guess. im sure i'll use it other times as well. but the fuse that was blown is the ECU/ignition fuse in the drivers footwell. i dont know how long it has been blown. i'll try to mess around with the tps and figure it out. thanks again.

john_powderguide

what where the problems that lead you to the tps? i am having some problems with my 90 v6 when it gets hot or running temp I loose rpm, it stumbles and will not rev above 3000 rpm, also when idling its either high or jumping around or searching.. could this be the tps or is there something else going on, I have taken out the cat and added a new O2 sensor