How Can You Tell If a TPS is Worn Out?

[85 Cutlass Brougham]

Well, I am curious as to what the symptoms are for a worn out TPS sensor. My 98 Nissan Frontier ( 2.4 Liter SEFI L4) has it's original sensor at 280,000 miles. The thing is, the truck now idles great after fixing a problem with a bad injector and plugged EGR passages. It throws no codes and seems to have a pretty linear acceleration curve. However, it does feel like it is surging a little under acceleration and it can buck a bit under low speed driving (5-10mph, like in a parking lot). It just feels like it is being held back, kinda like a carb with too small jetting. Fuel pressure is good with 36-45 PSI, varying within spec according to the FSM. I have also seen my city fuel economy drop from 23-24 mpg to 20-21 mpg. The tire pressure is 45 psi all around and checked weekly, so I know that's not it. I am replacing the fuel filter tomorrow since it is about 30k miles old. This is a VERY anal-retentively maintained truck, so I doubt it is a normal tune up item that is bad (It gets looked over every week and anything it needs gets done almost immediately). Heck, the engine is so clean inside that you can't easily read the dipstick after an oil change, or for 500 miles after that! ( I flush it with cheap oil every 2 changes and do a double change)

 

[pontiacgp]

I have no idea but here's what I found ...

"Old or worn out TPS sensors cause poor gas mileage, hesitation, stumbling, poor emissions and other performance related problems. TPS sensors have a limited life span and over time build up resistance which in turn give intermittent false signals to the ECU. If you have over 100k miles and your engine is experiencing the above symptoms your TPS sensor could be the culprit. "

according to that it sounds like the sensor could be your problem except that yours isn't giving any codes......

 

[85 Cutlass Brougham]

I am thinking it may be on the way out, but not bad enough to set a code. I just scanned it again, and got an all clear on all systems. According to the scanner, it would even pass a smog test! In my experience, even the really picky OBD II systems like this truck has do not always set a code when there is a minor fault. I may just spend the $56 for the part and see if it helps it any. I just hate parting with the money without feeling that it will really make a difference.

 

[pontiacgp]

in that blurb that I posted they didn't say if the intermittent problem it would trigger a code or not...it does sound that your on the right path tho...and like yourself I hate guessing when it comes to buying parts...

 

[megaladon6]

it's probably the TPS. they can develop a very small bad spot that will cause exactly your symptoms. the way to catch it is to have the TPS PID displayed on a factory level scanner and slowly move the throttle and monitor the position data on the scanner and the voltage with a seperate DVOM. you can also (with a factory level scanner) drive the car at ascending throttle positions and look for the specific spot where it has problems, hit the same problem at the same % throttle and thats it. in other words it's a pain in the *ss.

you can try backprobing the connector and monitor the voltage with a DVOM also. look for the voltage to drop out.

unfortunately the OBDII system only triggers the CEL when a problem is bad enough to cause excessive emissions. ford are notorious for having a major spark misfire and not setting the light because the ECM shuts off the injector at that cylinder--no fuel, no emissions.

 

[87MonteSS]

You can also measure the resistance of it while it's disconnected. You have to be pretty smooth and steady, but watch the resistance as you rotate it through from idle to WOT. You're looking for a sudden drop or increase in resistance in one spot.

I had the same problem with my Monte SS and found it that way, but it took a few tries at it to get the feel for smooth and slow movement.

 

[79LT1Monte]

If you have access to a scope you can sweep the throttle and graph the tps voltage and if you have a bad spot you will have no problem finding it. If all you have is a voltmeter you can watch the voltage while you sweep it slowly and look for a bad spot, but it will be harder to see.

 

[85 Cutlass Brougham]

Unfortunately, I only have a fairly basic OBDII scanner that checks for codes and if the computer has reset something to do with emissions tests. I can't actually read the inputs to the ECU, and having Nissan check it is $100-150!!! I may just go out and buy it as it is cheaper than the price of the Nissan "Consult II" factory scanner check. I have tried reading it with my DVOM before, but the resolution is not good enough for real time readings as it takes a second or two to get a reading. (That's what you get for $1.99 at Harbor Freight! LOL) It is at it's worst when trying to go 5mph or so and creep along, probably because it has spent so much time at that position over the years as it has delivered pizza since it was 2 days old. At worst, I will have a spare TPS in stock in case it ever goes when I do not have the money to replace it.

 

[Uncletruck]

Well, it's about $50 to get a new TPS and try it. But, this symptom still sounds like something related to the EGR valve and passages to me which tend to be the cause the most off-idle problems. Check the throttle body for wear and leaks too, with that kind of mileage anything that moves even slightly will have some wear on it.

-UT-

 

[megaladon6]

just in case clean the MAF