EFIDynoTuning Forum

I've been trying to dial in fuel trims for 3 years and every single time they are different. Saturday night, I spent an hour dialing in fuel, making sure it was 1.0 from 160 to 400 ad counts in open loop (kams clear on key off). Drive the car around for a while in closed loop, Ltft stays right about 1.0 in all the cells including idle. Last night, i drive it. It gets up to temperature, now the exact same fuel settings are extremely rich with the wide band showing .85 lambda, after 10 minutes of idling in the drive thru it's still at .88 so i load an old tune from the day before, now it's at 1.0 lambda. Since the drive thru was slow i idle another 25 minutes, now my car is idling at 1.17 lambda. Ltft is still 1.0 because i have the car set to go into open loop while idling. This is my experience every time i try to dial in fuel. I can't turn on o2 feedback because idling it sits there and keeps pulling and more fuel until it starts misfiring at idle, i lock it in open loop, it gets leaner and leaner until it's misfiring at idle. If i richen it up today, the next time i drive it, it's super rich at idle, it's a constant battle at changing fuel by 10-15% back and forth. What is stoich today is not stoich tomorrow... This shit is getting old and i really want to find a solution. If this because my fuel pump is a 340?

sounds like your injectors are junk

what injectors do you have and whered you get them?

Siemens 80s from PAS.

then gotta be fuel temp or you got some other issues

Ok, that pretty much confirms it then. Im gonna switch out the main fuel pump for a 155lph hoping that will help eliminate the extra heat. Is it still a no-no to use the wideband analog output in place of a hego? At least the wideband can report accurate AFR at long idle periods.

yeah thats never a good idea

I'm starting to think it's heat soaked fuel rails. Car had been sitting for hours, started it up, it's super lean again, earlier when i drove it my fuel trim is 99.6 at idle after a 30 minute drive. I think the returnless system makes it worse since fuel is trapped in the rails until used.

all you gotta do is raise the fuel pressure

Im having a hard time understanding how changing fuel pressure will resolve the issue? Correct me if I am wrong but I thought fuel consumption is the same regardless of pressure.. As an example, if I have perfectly dialed in fuel and double the fuel pressure, wouldnt pulse width just be divided in half? I fail to see how the extra pressure will help. I must be missing something.

I've never had a hot fuel issue but I believe higher pressure helps from boiling bc it raises the boiling pt