Troubleshooting TPSdot and MAPdot fluctuations
 

Hey all. I've been working with 18PSI to get my car remote tuned and he found a strange issue. My MAPdot and TPSdot values are "swinging wildly like a sewing machine needle, or a saw blade. this happens only in boost which is super weird, at idle it's perfectly normal as it should be".

https://cimg5.ibsrv.net/gimg/www.mia...cff9b05e84.png

First though was that it might be a ground issue so I tested with an multimeter set to Ohm ( 200 scale ). Going from the TPS plug ground to battery negative read about 1.1. I removed the ground cable from the harness and ran it straight to the head. It now reads about .9 .. for reference on my multimeter when the two prongs are touching it read about .7 .. so I think this means the ground was good before and is better now .. but it didn't help much.

Also reset the TPS voltage in MS for 0 and full throttle and it was very close to the previous value. I think this is more confirmation that the ground is good ?

Also moved the MAP vacuum line to its own port vs sharing with FPR / boost controller. That didn't help much either.

Also checked the throttle cable and it was moving smoothly with throttle application and nothing is loose.
Also did same check to the butterfly valve inside the throttle body. Everything seems "solid".

Vlad help me numb down the map and the car drives a bit better now though log still show the same fluctuation. Thought MAYBE something is wrong with MS .. I reached out to Reverant a couple days ago and sent maps / logs .. waiting to hear back now.

Just figure while I wait I should pick the collective brain and see if any one has had similar issues before or have a different suggestion as to what is the cause.

Attached is log and map. Thanks all.

First things that are popping into my head (not necessarily

Are you using a boost controller?

Do you have Coil on Plug or using Mounted Coil with wires, if so are any of your sensor wires running near any of the HT leads?
It's possible that under boost your getting higher spark voltages due to the increased air density (it's harder to create a spark across gap, so higher voltage is required), this could be effecting the sensor if grounded to same place as coils, or wires run nearby HT leads.

Also worth checking that your Serial cable isn't getting any interference, since from what I can tell literally all your data looks like a saw-tooth.

Quick update ...
Reverant helped me test the MS by driving with the TPS removed and a static TPS value set and determined it was working within the correct parameters.

I put on my big boy pants and tore the wire harness apart looking for possible cause as venetox suggested ( and to clean things up a bit )

I found the 80 AMP main relay looking like this .. *cringe*. Fuse was intact though.

https://cimg1.ibsrv.net/gimg/www.mia...e5887df268.jpg


Hoping that's the cause of my intermittent signals. Seems to me like this would cause the same symptoms as a bad ground.

My current theory is maybe at higher RPM there is a higher demand for 12v power that the bad connection wasn't able to fully supply ? Or since my car has pretty high NVH, at higher vibration the wire was working itself lose intermittently ?

Upon trying to remove the fuse / wire there, I discovered that the bolt holding the ground wire side in was loose and the terminal could wiggle back / forth. I guess it WAS a bad ground after all. Fingers crossed anyways. :)

:likecat: hopefully that works

Thanks now lets see if I could put all this ish back and not mess up MORE things ...

https://cimg8.ibsrv.net/gimg/www.mia...94d215deae.jpg


Then I'll bug you for that tune date when its starts up again .. :skid: