Engine dies when STFT start
Thread Starter
Teching In
Joined: Jan 2021
Posts: 26
Likes: 1
From: Grew up in Manhattan Kansas, live in Saint Louis
Engine dies when STFT start My engine will start cold and idle (albeit not very smoothly) but as soon as my short term fuel trims kick on, they go up immediately, then the engine will surge and stall within a couple seconds. O2 sensors are new, but I am not convinced there isn't a problem there. Any help would be appreciated. Scan is attached.
Thread Starter
Teching In
Joined: Jan 2021
Posts: 26
Likes: 1
From: Grew up in Manhattan Kansas, live in Saint Louis
Pulled a 6.0 out of a 1999 2500 truck, and the last time it drove it was stock
stroked and bored .005 over for 403ci
new cam - 236/244 112+3
New heads - TFS 225 CNC Cathedral ports
Fast LSXRT intake w/ 102mm throttle body and long tube headers
around 11.4:1 compression
engine is on a test stand not in the vehicle, but accessories are installed.
I noticed the low mV too - but as soon as the STFT start it surges like its overly rich, which made me wonder if I am getting good readings from the O2 sensors. The mV do rise with the fuel trims though, which I think is what I should expect to see
stroked and bored .005 over for 403ci
new cam - 236/244 112+3
New heads - TFS 225 CNC Cathedral ports
Fast LSXRT intake w/ 102mm throttle body and long tube headers
around 11.4:1 compression
engine is on a test stand not in the vehicle, but accessories are installed.
I noticed the low mV too - but as soon as the STFT start it surges like its overly rich, which made me wonder if I am getting good readings from the O2 sensors. The mV do rise with the fuel trims though, which I think is what I should expect to see
Last edited by MHK5; Jun 29, 2021 at 03:35 PM. Reason: clarification
Thread Starter
Teching In
Joined: Jan 2021
Posts: 26
Likes: 1
From: Grew up in Manhattan Kansas, live in Saint Louis
O2 sensors are in the header collector with an 18" extension clamped on after. I thought that would be enough to prevent them from seeing fresh air, but maybe at idle that isn't true?
If my O2 are seeing fresh air, I'm probably as far as I can go on the stand without any engine load. My goal on the stand is/was to make sure the engine started and no major mechanical issues came up, let it go through a heat cycle, and work on the idle.
Haven't changed VE (I thought you needed to read commanded AFR vs actual AFR, and if my O2's aren't reading right OR are being contaminated, that wouldn't work)
MAF is stock, so I didn't change any calibration on that. At idle, I would think it has plenty of range to read correct air flow
Injector data come from deatschwerks website. I did double check that I had the right part number.
If my O2 are seeing fresh air, I'm probably as far as I can go on the stand without any engine load. My goal on the stand is/was to make sure the engine started and no major mechanical issues came up, let it go through a heat cycle, and work on the idle.
Haven't changed VE (I thought you needed to read commanded AFR vs actual AFR, and if my O2's aren't reading right OR are being contaminated, that wouldn't work)
MAF is stock, so I didn't change any calibration on that. At idle, I would think it has plenty of range to read correct air flow
Injector data come from deatschwerks website. I did double check that I had the right part number.
