Silver NB

iTrader: (1)

***EDIT, just realized I typed tube instead of tune into the title.... no way to change it now****

So I've been helping a friend of mine turbo his '93 Miata and we've hit a bit of a stumbling block. The car has a Kraken hot side with a GT2554 turbo and what are most likely counterfeit RX7 injectors. The ECU is a MS3PNP with firmware 1.5.1. He also added a KIA TPS and moved the jumper in the ECU so it knows it has a variable TPS. The TPS has been calibrated and TunerStudio can see and show the input without any issue. The turbo has been on the car for about three weeks, and it did run well for a little while. When we finished the install, I took it out and made sure AFRs looked good and that his injectors weren't doing anything dumb and then returned a car to him that had a decent street tune.

Since then, he fiddled with some stuff (and screwed up the VE table somewhat, which I've sorted out as best I can given it can't really be driven at the moment) and now the car just doesn't want to run at all. It has a severe stumble between 1000 and 2000 RPMs, and it takes some fancy pedal feathering to get through the stumble. Once through it, the car runs, builds boost, and holds AFR without any trouble (if you can get it moving). After installing the vTPS, I found that the TPSdot jumps around quite a bit even when no throttle input is being given. I switched it back to MAP-based AE because of that, but now that's not triggering either. After looking at the logs, it looks like the MAPdot never reaches the threshold for AE to trigger and I'm relatively confident that's what's causing the stumble. What I'm not sure of is whether this is a tune issue, or if there's something mechanically wrong with the car. I compared his tune to my tune (obviously it's an apples to oranges situation since mine is an NB but I wanted to see if there were any major differences), and I don't see anything totally out of the ordinary. His MAPdot threshold is 85kpa, and I think the highest MAPdot I saw in the logs I took was just shy of 50 kpa once I had the car running. It also looks like his car takes several seconds to really settle into idle (both RPM and MAP) as RPMs fall.

I attached the tune along with a log of the car idling. I can't help but think that since it ran fine for a while that this is something other than a tune issue, but I wanted to consult the hive before moving in that direction. Any and all input is appreciated. Be gentle, though, because the tune is rough. I had it in an OK state, but I left town for 2 weeks and when I got back he had changed some stuff and now it's acting weird. If we can get this stumble sorted out, I'm going to trade cars with him for a week and finally fix the rest of the tune issues.

ravinaziankid

I'm not a professional but I just had an issue with my vTPS using the kia TPS as well where if i even tap the throttle slightly, the TPS% goes up to like 40, instead of normally like 1.2 or something low like that. I re-positioned the vtps adapter and tightened it down as much as I can without potentially stripping or cracking the adapter. After that and re-calibrating it, it was very accurate and there was no stumble like it did before. It could be worth a try, before doing this I was trying to get the accel enrich dialed in for hours and days with no luck but this fixed it.

Silver NB

iTrader: (1)

I'll add that to the list of things to check. His TPS signal is really dirty, and the TPSdot jumps around a lot even you don't have your foot on the pedal. That's why I moved back to MAP-based AE only.

ravinaziankid

Yeah, I was having that same issue..i was constantly re-calibrating it and just the other day I was frustrated with it so I re-positioned the vTPS and it's been good so far.

When you went back to MAP, did you remove the jumper in the ECU and put the 1.6 stock TPS, it might still be using the vTPS which could be the problem.

Silver NB

iTrader: (1)

No, we didn't revert the jumper and put the old TPS back in, and I'm not even sure he still has it. I thought that moving the slider all the way back to MAP-based AE would ignore the TPS signal for AE purposes.