Re: LFX Engine Swap (GM V6) at GWR
Posted: Thu Dec 19, 2019 11:05 am
Fuel surge/swirl tank report: it works a treat.
Tested on Sunday, ran the car round and round till it read completely empty in the main tank, got another half lap out of it and then it started to sputter and came to a stop a few turns later. Towed back to the pits, pulled the top fitting from the surge tank and ran a dipstick down it to see how low we ran it. There was only about 3/4" of fuel left in the bottom of the surge tank. That's like, 1/20th of a gallon. Yep, it's working.
With the fuel starvation issue out of the way, I'm able to peel back a layer and find the next issue that was buried a bit deeper. It seems I have a communication issue between the ECU and throttle body, which ALSO sends the ECU into limp mode, just like the fuel starvation. This helps everything make a lot more sense because at GTA Finals we were scratching our heads because sometimes it would go into limp mode under one set of circumstances that we were sure was fuel level related, and then other times it would go into limp mode under circumstances that couldn't possibly be fuel level related. With one out of the way, it was a lot easier to find the second. In the morning it would go straight into limp mode upon startup or after a short bit of driving, then after a good ol' code clear and tug on connectors and wires by hand, it started working. Ryan Helmuth, another LFX Miata head, was at the track the same day and when I had the issue narrowed down to ECU, TB, or wiring, he very awesomely offered to loan me his throttle body for a session to see if that made a difference. I ran a session with his TB, then a session with mine, both successfully, so I feel we've crossed that off the list and I think it's down to the wiring and factory connector. I need to try to find that factory connector in fresh form so I can run new wires from the ECU with proper strain relief, heat protection, etc. and pin a fresh connector at the TB, then go test again.
Tested on Sunday, ran the car round and round till it read completely empty in the main tank, got another half lap out of it and then it started to sputter and came to a stop a few turns later. Towed back to the pits, pulled the top fitting from the surge tank and ran a dipstick down it to see how low we ran it. There was only about 3/4" of fuel left in the bottom of the surge tank. That's like, 1/20th of a gallon. Yep, it's working.
With the fuel starvation issue out of the way, I'm able to peel back a layer and find the next issue that was buried a bit deeper. It seems I have a communication issue between the ECU and throttle body, which ALSO sends the ECU into limp mode, just like the fuel starvation. This helps everything make a lot more sense because at GTA Finals we were scratching our heads because sometimes it would go into limp mode under one set of circumstances that we were sure was fuel level related, and then other times it would go into limp mode under circumstances that couldn't possibly be fuel level related. With one out of the way, it was a lot easier to find the second. In the morning it would go straight into limp mode upon startup or after a short bit of driving, then after a good ol' code clear and tug on connectors and wires by hand, it started working. Ryan Helmuth, another LFX Miata head, was at the track the same day and when I had the issue narrowed down to ECU, TB, or wiring, he very awesomely offered to loan me his throttle body for a session to see if that made a difference. I ran a session with his TB, then a session with mine, both successfully, so I feel we've crossed that off the list and I think it's down to the wiring and factory connector. I need to try to find that factory connector in fresh form so I can run new wires from the ECU with proper strain relief, heat protection, etc. and pin a fresh connector at the TB, then go test again.