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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.
Last edited by ConnorRigby; 05-13-2019 at 12:07 PM.
Reason: Forgot information
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.
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.
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)
Another update to the stupid TPS. I'm really at a loss at this point. After rewiring the entire front half of the car every other sensor is working flawlessly, but the damn TPS still is not working. While rewiring, I ran brand new wires "just in case" the existing wires aren't shielded enough (?). Of course I still had TPS issues so I tried the new wires I ran. Still didn't help. So I ran MORE new wires this time I used high quality shielded USB wire. I grounded the shielding to the chassis and used the black wire as sensor ground and I'm STILL having issues. I don't know what to do at this point. I've replaced the wiring twice and I've used two different sensors.
Nothing else has a noisy signal as far as I know, so I don't really think it's a grounding issue. I've also checked that my MS was built correctly several times and from what I can tell by looking at the diagrams, it's correct. Also I have no problems with any other sensor. Any help would be really appreciated..
I recently switched to an NB tps, although in a 94 miata. I noticed an erratically changing idle and then I swapped the +5 ref pin with the Signal pin and everything seemed normal (there are a couple of threads out there with incorrectly labeled pin diagrams for NB tps, but it's not rocket science. Only 3 pins). HOWEVER I would get random tps settings after the car was warmed up even with the correct wiring. The problem would be especially when I first started the car and the tps would be registering anywhere from 2% to 9% even though I wasn't touching the throttle, and it mimicked a sticking throttle cable. Turns out it was the NB tps that I had purchased and the problem was fixed with a different OEM tps.
so i have a NB2 throttle body + TPS on my 94-97 engine in a 92 car. (lol i know) I've tried a couple different TPSs but i hadn't considered my wiring might be wrong based on incorrect diagrams.. From memory, i think i have mine wired so that if you are looking at the throttle body head on, the top wire is +5, middle is signal and bottom is ground. Is that correct?
Thanks! i went out today and depinned the connector and tried it around various different ways. (from memory) i ended up from top to bottom with ground, signal +5vref. that may not be correct tho. I know it was not how it was originally wired. It seems to work somewhat better, but still not great. i also tried with and without grounding the shielding to chassis ground which seemed to have little to no effect.
Holy hell my friend! this solved the issue!! All of this work and all i needed to do was ensure my TPS was pinned correctly. SMH i feel so dumb. Thanks a bunch!
05-13-2019, 11:40 AM
TPS unusable while engine running
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