A doozy of an issue. originally wiring was fried but now car has a rough idle

[Chimera]

Hello, this is my first post. I hope I’m placing this in the right area.

Before I describe the issue I’m having, I’ll give you guys some history of the car. Just a heads-up: this is my first sports car, so sorry for being a noob lol.

I’ll detail the mod list after this, but I bought the car around October of last year (2024). It had no issues, and I met the old owner and found out what had been done to it. It was basically a workhorse while I was in Hawaii for the time being, and I loved every second of driving it, even with traffic. Recently moved back to SoCal earlier this year, and got the car retuned with a notable Supra tuner- I had to take the vehicle to get flashed and updated via their recommendation, so that sucked, but got retuned around June of this year with a base map and a hope to start logging and seeing what this car can actually do reliably.

It was around September when the first issue came up, my fuel pumps went bad, mostly do to wiring I believe, had that fixed and sorted, then after a bit of thinking I left my car at my local shop to get a full rewire and test of my electronics/harnesses to make sure everything was good, found out my motiv harness in my foot well as well as my can input sensor and its harness went bad, got those fixed, went from Visconti to TMS harness for the reflex and the car was running pretty well up until I decided to try the most recent tune from my tuner around Thursday or December 18th, after the car seemed basically good.

Around Thursday the 18th, I tried to start the car multiple times, but the engine flooded each time. We got that sorted. Retested the wiring and found no issues. I spent a good day on it with the mechanic on that one, but we couldn't fix the problem. Swapped spark plugs due to mine looking soiled as shit, flashed back down to my base map, and went home for the day. Came back to my shop and had someone check the motiv to see if it was operational, original motiv with the car (can’t remember the VIN, but it was a box before 2021) wasn't connecting so we swapped in a loaner from my mechanic, updated that motiv and had the spare dude let us know if he saw anything strange. The only odd thing we found out was that my battery was going to 9v from 13.2 (it was a new battery from June) whenever I cranked the car, same issues as Thursday, where the engine flooded. Checked the new spark plugs; they seemed fine. My mechanic (who did the rewire and installed the fuel pumps) checked every wire and pin from Both harnesses. Even tested my crank and cam sensors and found no issues.

We left it at that and planned to bring the car back by January 1st, so he could spend the time he needed to thoroughly check it out. before I drove home I flashed back down to the base tune yet again. Noticed a weird Bog then surge issue on my way back home, pulled over into a parking lot to watch the idle and observed the engine basically bogging like it wanted to die (initially thought the issue was the car still needed to burn off some gas), got home, and left it at that for the night. Came back the following morning; the car started fine for like 5 minutes before it began to sound like the car wanted to kill itself again. The rpm’s didn’t fall, but you could hear the car struggle to maintain a consistent idle. (Don’t have a video of it as of right now, only when I drove it home as well as start up at the shop)
Tried some at-home fixes by leaving the battery off overnight to see if it was a DM E issue. Now I’m planning to buy a new OEM battery from Toyota and swap it in to rule out a battery issue entirely.

Mod list as of now
Pure 850
Tms wiring harness and now motiv
Eos port injection
Titan meth kit
Titan downpipe
Visconti flex fuel kit
1050x port injectors
Titan exhaust
Pure stage 2 transmission(got it for a steal)
Csf radiator and side radiators, as well as the trans cooler.
Running ecutek.

Hopefully, these videos are viewable. Any help is greatly appreciated

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[Chimera]

Forgot to mention, my tuner did let me know when the loaner motiv was hooked up he could not see a synced cam and crank sensor signal.

 

[Gabe]

Do you any OBD codes to share with all that?

that’s a long list of mods for someone’s first sports car. Could be a ton of things.

 

[Chimera]

Do you any OBD codes to share with all that?

that’s a long list of mods for someone’s first sports car. Could be a ton of things.

thats the thing actually…

there’s no codes to begin with. I tried ecutek, the other guy who flashed the motiv checked and saw nothing wrong, we scanned the car with the shops scan tool and it didn’t see anything wrong either.

 

[nanaisu]

I reckon it might be time to load up ISTA and see if there's any faults being reported there that aren't being flagged by standard ODB2 codes?

 

[Gabe]

Isn’t a BMW specific OBD reader be much more reliable than add on readers before going to ISTA?

like, plug Bimmercode and check?

 

[Chimera]

Isn’t a BMW specific OBD reader be much more reliable than add on readers before going to ISTA?

like, plug Bimmercode and check?

I thought of that yesterday, tried it out and couldn't find any weird codes, nothing new except a combustion dropout (140110) that appeared when I tried to check with ecutek again.

I do have good news, it's leaving my house today on a flatbed to go get inspected at the shop that did the work.

 

[Thraxbert]

Explain:

"Fuel pump went bad, mostly due to wiring" (unsubstantiated/confusing)
"Full rewire and test" (extremely unlikely without paying a fortune at a very special shop -- no mere "mechanic")

Why:

What's been done thus far is vague and, frankly, very improbable. So we all need more details to start truly diagnosing this.

 

[Chimera]

Hey, sorry for seeming vague, that wasn't my intention. I'm not well-versed in BMW wordin', so forgive me if this seems even more confusing lol. Included some photos from late September that I got from the dude who worked on my car.

I took it to a local shop, where I met the owner/lead mechanic who specializes in BMW repairs and aftermarket parts installation. He works a lot with s58s and g8x's I'm just one of his handful of supra owners who works with.

To explain everything, the reason my original fuel pumps failed was poor wiring by whoever had previously worked on the car. Simply put, whoever wired this car for the previous owner didn't do an excellent job. They wired two relays from the battery to both the fuel pumps and the Motiv Reflex harness. When it melted randomly (unsure what even caused it to melt), it took out my old fuel pump, my motiv Reflex harness, and, surprisingly, my CAN input sensor with its harness as well. I didn't find out about those other harnesses till a week down the line due to my being busy with my job.

The mechanic who worked on my fuel pumps, I personally asked him to do a wiring inspection and rewire anything that needed to fixed, which then later turned into doing a full wiring check (I called this a rewire when I shouldn't have) to make sure everything was operational and to make sure that the previous dude who worked on the car with the old owner in Hawaii didn't fuck up anything else. At the time, I learned that the original harness for the Motiv was dead (a PTCan kit from Visconti found in the passenger footwell), as was the can input sensor. Got the motiv harness replaced with one from TMS, and the other harness was swapped as well. My tuner also confirmed that he has a good signal from the can input sensor, so I have confirmation that it's working as well. Also found out a couple of days later, after I went to pick up the car, that the motiv reflex box might've been fried as well, but I got that taken care of and have a replacement for it now.

Hope that clarified. The guy who works on my car is a saint. who's offered me multiple good deals on the installs and repairs I've needed for the car.

 

[Chimera]

So the main issue was my fuel pressure regulator: the diaphragm went bad, allowing fuel to enter the intake manifold, and it repeatedly flooded the engine. But that's not the only issue. My meth kit was set to a constant on by whoever modded the car with the old owner through the shabby wiring, just removed it entirely, but it is still operational, I think.

 

[lucky phil]

So the main issue was my fuel pressure regulator: the diaphragm went bad, allowing fuel to enter the intake manifold, and it repeatedly flooded the engine. But that's not the only issue. My meth kit was set to a constant on by whoever modded the car with the old owner through the shabby wiring, just removed it entirely, but it is still operational, I think.

Thanks for the update. The biggest issue buying modded cars. The clowns that may have worked on them previously.

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