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gdog

Check your TPS if performance is sluggish

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FYI: if your car's throttle response is off, might want to check your throttle position sensor (TPS).  Been noticing of late my car has been sluggish.  Will go into more details in another post, but the more I thought about it, the engine was acting like it was not getting full throttle. 

So I took a log w/several WFO runs, and sure enough, it was maxing out at 60% throttle!  Note with tunerPro logs, >75% is considered WFO.  I.e. the ecu was never getting a full throttle signal.

Pulled the intake boot off of the throttle body and mechanically it was all adjusted properly, as the throttle plate was going horizontal with the foot down.  So had to be the TPS I figured.  Found this guy's youtube here: https://www.youtube.com/watch?v=m_6dhZzWM54

which eventually tells you to expect about 0.5 volts at closed and 4.5 volts at WFO on the TPS signal wire/pin.  I was getting slightly over 3 volt at WFO!  With new TPS, it's amazing the difference it's made.

Will add more details later..  Hopefully this helps someone.

 

Edited by gdog
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I had a broken wire on the harness to the TPS.  It would mostly hold together, but would randomly have idle issues among other problems.  It took me 6 months to track it down.  The break was right at the plug, so I bought a new plug and spliced it into the harness.  No codes on it either.

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On 12/5/2019 at 9:00 AM, Zappo said:

I had a broken wire on the harness to the TPS.  It would mostly hold together, but would randomly have idle issues among other problems.  It took me 6 months to track it down.  The break was right at the plug, so I bought a new plug and spliced it into the harness.  No codes on it either.

That's funny, I had a similar issue in my old '98 V70 GLT. I'd be sitting at a light and it would surge down a little bit, then idle normally again. The TPS was the one thing I never checked/replaced.

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More details..

Yeah the guy in the utube is back probing the TPS connector and measuring voltage on the signal pin with key in RUN.  Should see about 0.5v at idle/closed and roughly 4.5v at WFO.  Give or take a few tenths of a volt.

You can do that, but IMO it's easier to pop out the ECU and then probe the TPS pins at the ECU connector (key in OFF position).  Here are the TPS pins at the ECU:

  • A15: TPS 5v supply from ECU
  • A16: TPS signal pin
  • A18: signal reference (ground)

Get an ohmmeter, two small paper clips and two alligator clip leads.  Using the paper clips, carefully insert one end on the side of the ECU connector; do not damage or bend the ECU connectors.

Measure between A16 and A18:  should see about 1300 ohms at idle and about 3300 ohms at WFO.  I'd say +/- about 100 ohms or so.  Off by much more than that, and I'd suggest a new one.

Can get one at pic-n-pull but bring an ohmmeter so you can check it there.

If you go with new one, do NOT spend a hundred dollars on the blue box one; get that exact same part in Bosch OE.

BTW: the other advantage of measuring the resistance from the ECU pins is that you're ohming out the wiring in the harness too.  If you suspect bad wiring, hook up your ohmmeter at the ECU connector as described above and then wiggle the harness, especially near the TPS connector.  If the readings change while moving the harness, you just found some bad wiring.

Edited by gdog
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i would recommend AGAINST probing directly into any connector. when the connections bend you only created more problems. 

 

the best way is to use a backprobe as per video. very little chance to damage the connector and you can measure voltage while the system is active. which is WAYYYY more accurate than measuring resistance.

(If the wire is hanging by just one string, resistance will be fine, however when current is running,(when sensor active) you will see a voltage drop. )

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Hmm, maybe this is my problem too.

I'm getting the same idle drop that bmdubya noted. Would this potentially result in irregular voltage readings in logs (random spiking) whenever on throttle?

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8 hours ago, quiksilver said:

Hmm, maybe this is my problem too.

I'm getting the same idle drop that bmdubya noted. Would this potentially result in irregular voltage readings in logs (random spiking) whenever on throttle?

Yes.  That is how I found mine as well, the log graph looked jagged. 

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I have a lot of experience breaking shit on my car.  :)

 

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On 12/17/2019 at 10:14 AM, ChristiaanW200 said:

i would recommend AGAINST probing directly into any connector. when the connections bend you only created more problems. 

 

the best way is to use a backprobe as per video. very little chance to damage the connector and you can measure voltage while the system is active. which is WAYYYY more accurate than measuring resistance.

(If the wire is hanging by just one string, resistance will be fine, however when current is running,(when sensor active) you will see a voltage drop. )

 

Well, like I said, be careful when probing the ecu connectors.  It can easily be done w/o damaging them.  I found there was enough room to probe on the sides of the connector fingers w/o bending or damaging anything.

Yes, back-probing the TPS connector (as in the utube) is fine, but keep in mind the TPS connector is not too easily accessible, and doing this will definitely disturb/move the TPS wire harness.  I.e. the pressure of back-probing may make a bad connection good (temporarily).  One can back-probe from the ecu side w/o touching the TPS or harness at all.

And as far as measuring a circuit when there's current flowing in it, if this was a load circuit (low impedance), then I'd agree with you.  But this is a high impedance sensor circuit; the current flowing through this circuit is on the order of 1 to 4 mA.  I.e. measuring via a decent ohmmeter is just fine here.  You certainly don't want to measure some kind dynamic load (like a motor e.g.) with an ohmmeter, but that's not the case here.

And as I mentioned, probing from the ecu gives the added diagnostic of vetting the harness.  What if you saw a good voltage reading at the TPS signal pin on the TPS connector, but that wire had a intermittent break in it between there and the ecu?  Then that good reading at the TPS pin is not doing anybody any good, since the ecu is not seeing it.

As @Zappo  mentioned, the least intrusive way to diagnose this is to look at your logs of the TPS sensor!  :laugh:

Edited by gdog

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