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BUICK - TPS? Crazy

 
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Twilightoptics
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Joined: 13 Jan 2004
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Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Mar 02, 2015 7:25 pm    Post subject: BUICK - TPS? Crazy Reply with quote

Friend's got a 1992 Buick Skylark 3.3L.

Had a TPS code 22 and O2 code, runs rough and occasionally wont start. She replaced the TPS. I got there, cleared the stored faults - car ran great until warmed up then got the rotten egg smell. Replaced the O2 sensor. It sat 20min, tried to fire up and the ECM is in diagnostic mode all by itself with code 22 back.

I checked TPS voltage per my noggin and the book which says measure terminal A (5vref/Gray) and terminal B (signal to ecm/Blue) for below 1.25v closed, 5v open.

What I got was 5v closed, and .5v open. Same on the old sensor.

Stays in diagnostic mode intermittently with the TPS unplugged too. Diag mode spits the codes out and runs the cooling fan.




I know BOP does weird stuff, should this be 5v closed? ECM dead? Or is the pin probing wrong and it should be signal wire to ground? That's what makes sense to me....

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chevymad
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1987 Pontiac Formula

PostPosted: Mon Mar 02, 2015 7:35 pm    Post subject: Reply with quote

Code is for tps low voltage. Supposed to set if voltage is lower then .24 volt with throttle closed.

After checking that flow chart has you jumper the 5v to the signal to see if you can set code 21. If it does then wiring/ecm are supposedly ok.

Does sound like your getting backwards readings for some reason.
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Twilightoptics
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Joined: 13 Jan 2004
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Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Mar 02, 2015 7:36 pm    Post subject: Reply with quote

So the tps dvom readings should be from signal wire to ground, right? Not from the 5vref to the signal?



It's still throwing me for a loop this thing puts itself into diagnostic mode as if there was a paperclip on ALDL A/B

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chevymad
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1987 Pontiac Formula

PostPosted: Mon Mar 02, 2015 7:37 pm    Post subject: Reply with quote

Wiring diagram also shows that at WOT the signal wire is shorted to the 5v reference. And at idle signal is almost shorted to sensor ground.
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chevymad
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1987 Pontiac Formula

PostPosted: Mon Mar 02, 2015 7:38 pm    Post subject: Reply with quote

Yes.. you should just be reading the voltage off of the signal wire. Not the delta between it and the reference voltage.
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Twilightoptics
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Joined: 13 Jan 2004
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Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Mon Mar 02, 2015 7:51 pm    Post subject: Reply with quote

K, then the sensors are good then but still throws a code 22 and stalls out going into it's own diagnostic mode. Hooray for free cars. She should just junk it lol.

ECM to me.

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chevymad
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1987 Pontiac Formula

PostPosted: Mon Mar 02, 2015 7:58 pm    Post subject: Reply with quote

Did you try the tap test? lol Ya.. I'm getting to where I think that any average car older then obdII should be junked.
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chevymad
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1987 Pontiac Formula

PostPosted: Mon Mar 02, 2015 7:59 pm    Post subject: Reply with quote

Oh and good luck finding an ecm. I needed one awhile back and had to have it shipped out of cali. Last LG4 ecm available in the napa system at the time.
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Twilightoptics
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Location: Auburn , WA

1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Mar 04, 2015 7:17 am    Post subject: Reply with quote

$104 at Oreilly's in the warehouse.
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chevymad
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1987 Pontiac Formula

PostPosted: Wed Mar 04, 2015 7:25 am    Post subject: Reply with quote

Good! Frankly getting pretty fed up with napa parts. So much so I'm ordering most of my stuff on Amazon now. Paying more for something then replacing it 2 or 3x over the next few months/years is pretty stupid.

Here's hoping the ecm solves the whole issue.
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aaron_sK
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1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Mar 04, 2015 8:16 am    Post subject: Reply with quote

I agree that it is likely the ECM, but I have seen issues on GMs of that era with the TPS wires getting kinked coming out of the weatherpack which then screws up the resistance at the ECM. Might be worth probing the wires at the ECM itself since you're going to have it pulled down anyway.
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