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TPS unusable while engine running

 
Old 05-13-2019, 11:40 AM
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Default TPS unusable while engine running

I've had a DIY megasquirt built following the trubokitty guide for a 90-93 installed and running well or a month or so now, but one thing i haven't been able to figure out is the TPS. I have a throttle body from a NB2 including tps and iacv. While the engine is not running, the TPS works perfect. It goes 0%-100% perfectly. But as soon as the engine is running, it is completely random what values come from the TPS. I get random accel and decel events all the time even when not touching the thing. I've attached my current tune and a log of running it for a few minutes.

I had originally thought i just wired a ground wrong or something. Yesterday i rebuilt my adapter harness with a DIYBOB and took special care to make sure the grounds were correct.
I wired the 5 grounds from the "MS EXTRA" harness to pin 4A and 4B. I believe these are essentially the grounds for the coils plus one extra. I also wired the two "GND" pins from the "MS" (not extra) harness to those same pins, (4A and 4B). I wired all the sensor grounds (i think i remember there being two of them?) to 4C and 4D. I also wired my wideband sensor ground to one of these. (i think 4D).

I've been googling this for a while and i've seen some people build a filter circuit for the TPS? do i need that? it seems like i shoudln't but i'm wiling to try anything at this point. Thanks for the help!

EDIT: I forgot to mention that i'm running a 1.8 swap from a 94-97 car.
Attached Files
File Type: msq
CurrentTune.msq (278.1 KB, 3 views)
File Type: msl
2019-05-13_08.16.19.msl (1.74 MB, 3 views)

Last edited by ConnorRigby; 05-13-2019 at 12:07 PM. Reason: Forgot information
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Old 05-13-2019, 09:54 PM
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I had pretty much the same issue as you describe it. Two big things make sure the ground behind the passenger seat is grounded, mine was loose and hidden behind the trim. Check all your grounds again. The second thing I did was use shielded cable (USB) from the TPS to the ECU bypassing all other wiring. These two things solved my problem I have not had any more issue just perfect TPS.
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Old 05-13-2019, 10:16 PM
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Thanks for the reply. I've been trying to avoid running a new wire, but if i can't figure this out soon i might just go for it. My wiring kit came with a nice long shielded wire i can probably use.
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Old 05-20-2019, 01:16 PM
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Welp i got a bit carried away and found where some of my electrons were escaping. i separated the sensor grounds from the engine grounds and did a bunch or rerouting/repairing.


Pulled the engine harness through the firewall.



tracing a short in the loom..


Found em! this was the loom that corners toward the engine right after the firewall grommet


Rewrapping and repair progress..


test fit



Sorry for the gigantic pictures. Don't know why they are so big. Anyway after fixing those worn through wires and rebuilding my sequential injection harness, my car is running. I haven't tested the TPS much yet, but it might be working better. I only tested revving in neutral after calibration and it seemed to be somewhat more responsive than it used to be. I hvae to fix my tune first as it is running _way_ to rich for some reason. (i think my sequential injection wiring mod was done incorrectly last time and my tune was adding extra fuel to compensate)
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