i've got a weird problem.... my car runs weird.... 88 firebird w/ 91 3.1 long block--all the rest is 2.8 except the injectors... car bogs badly off idle when ambient temp is above about 55 degrees and the engine is "cold"--like a carbed car w/ no choke. clears up within a block or 10. it's had 3 different cts's in it and 2 mat's. between buying it and swapping the engine, i think every sensor was either checked or replaced "while i was in there" also, it seems a little peaky. it pulls ok, but there is a marked difference between just a hair short of wot and actual wot. actual wot, it takes off like a rocket (relatively) it's not throwing any codes, and it was this way w/ the 2.8, even. fuel pressure is ok, everything else seems ok. i'm wondering if the "peakiness" might indicate an irregularity in the tps? anyone come across anything similar or have any ideas? once it's warm it runs fine outside of the peaky thing.

 

How's the timing?

TPS spec for the v6 is 0.055 +/- 0.05 volts at idle (butterfly closed)... to check it, go to thirdgen.org's main page (not these forums) and go in the tech articles section, and look for the TPS tech article. But don't adjust idle and don't follow the V8 spec given, use 0.055 +/- 0.05 volts as the spec.

 

timing is at 10btdc, IIRC (whatever the sticker says--same timing on both motors) tps is set at .056v, both motors.

 

A dead spot will give you problems, but most of the time the dead spot appears in the first 1/4 of the sensor's travel. Hook up the meter and open/close the throttle slowly(Key On, Engine Off) and see if you have anywhere that the voltage just kind of drops out.

 

Yeah, good point! An analog meter's best for that- but don't hook it in-line with the computer. Hook it right to the TPS sensor- one probe to the middle pin, one probe to an end pin (bottom or top doesn't matter). Put the meter on the ohms scale and move the TB butterfly...then, just watch the needle.

(Same could be done with digital meters, but the sampling rate interferes with getting a smooth reading. You'd still see a "dead spot" though.)

 

Don't use an analog meter!!! When you hook up an analog meter in parallel with a circuit, the internal resistance of the meter is usually lower than the resistance of the sensor and can pull too much current through the ECM, killing it. I've seen it done more than once. GMs are better about it because they have current limiting circuitry, but would you want to risk it?

Unless a test specifies the use of an analog meter, use a digital one, just to be on the safe side, I know it's easier to use the analog, but I don't think the risk is worth it.

 

i think that was what he was saying.... i'll have to give it a shot. i tested it for a dead spot w/ a digital, but didn't see anything. an older mechanic i used to know said he used to cycle it slowly w/ an analog meter (checking for resistance) and videotaped the meter while he did it and played it back at slow speed---seems kinda extreme, but he swore by it...

 

You can test teh TPS by itself, with an analog meter, but DISCONNET THE SENSOR FROM THE HARNESS FIRST.

 

right, i think that's what we meant.... that's what i was assuming, anyway...