Can you adjust the TPS on a GM TBI??? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 04-11-2003, 11:40 PM Thread Starter
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Can you adjust the TPS on a GM TBI???

Well I got the Jeep hooked up to a laptop. Afetr running some diagnostics on WINALDL. I am able to see that the only difference between my great running Howell CJ8 and my not running DIY-TBI CJ7 are the TPS voltages at idle. The Howell TPS reads -.3 volts at idle, or no throttle. The CJ7 TPS reads almost 3 volts. I pulled the TPSs and swapped them, without any luck. I have rotated the TPS in the CJ7 as far as possible, and I can get the reading down to 2.2 volts, but that is far from -.3 volts. Is there any way to adjust or compensate for this? I drilled out the idle screw and adjusted it back, but then the throttle plates started to catch. The TPSs are the same on both TBIs, but obviously the CJ7 TBI has a different reading at idle. I thought about drilling out the TPS so that I could rotate it some more, but I don't think there is enough material. Any suggestions?

Thanks,
Tom
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post #2 of (permalink) Old 04-12-2003, 02:59 AM
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Re: Can you adjust the TPS on a GM TBI???

1. There is little to no adjustment on the TPS assembly,
2. You've adjusted the Throttle Plates using the idle stop...
3. Now, if there's a problem, there's only two possibilities:[*] There are internal differences in the ECM[*] You'll have to install a resistor in line with the TPS to drop voltage.
4. Try the following:[*] Set Ignition to RUN, with the engine off.[*] Measure the TPS voltage.[*] Remove the screws on the TPS.[*] Remove the TPS.[*] What does the TPS measure at FULL REST?
5. If you can't get the TPS to measure 0.40 and 0.46 volts,
6. There's a problem as the ECM won't see the engine's at idle.
7. This would make me think that the ECM's bad,
8. And supplying too much voltage to the TPS,
9. And that can't be adjusted out.
10. If so, why?
11. My vote, is the ECM is questionable, at best.
12. Are all the other sensor readings within spec?
13. What's the TPS voltage at WOT?
14. Is it possible there's a wiring error?
15. On side of the TPS should be supply voltage,[*]What's this voltage?
16. The other side of the TPS should be Ground.[*]Are you sure you've got a good ground between the TBI and ECM?
17. Have you swapped ECM's and checked voltages?
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