mx5med

Well, I'm really hoping I found what is causing the fuel trim issue...

I started up the car tonight and it hasn't been started since yesterday, so it was a cold start. I checked the fuel trim once it went to closed loop and STFT was at 14% roughly.

I pulled and plugged my vacuum line from the fuel pressure regulator and instantly the STFT dropped to 4-5%, and once the car was fully warm, the STFT was at 0-2%, right where I believe they should be.

So, would everyone agree that my pressure regulator is bad? (I'm hoping it is so that this issue is finally solved).

Side note: I did do a pressure test a while back, and had 37 psi with the vacuum line hooked up, and 43 psi with it disconnected, but I neglected to rev the engine at all with the gauge hooked up and I didn't let it sit long after I shut the car down before disconnecting. The pressure held for the 5 or so minutes after the car was off. Looking back, I know I should have left it on longer to see if I had a pressure drop.

mx5med

Well, my issue is solved. It turned out to be my fuel pressure regulator even though I was within spec with the car running at idle. I neglected to check how long I held pressure after shutting the car down though.

I pulled my vac line off the regulator while watching my stft, and it went perfect. So yesterday I was able to get a junkyard regulator off a 98 accord and my stft was at 5-6% on an ice cold start, and once the car was fully warm stft was at 1.9-3%.

Only question I now have is are the regulators different between the accord and civic? I know the accord was a 2.3l. While my stft was perfect at idle, while running highway speeds (70mph) my stft was running -7% roughly the whole time. Is that because made to give enough pressure to a 2.3l engine so my ecu was cutting back? I'll try to get my hands on a regulator from a y7 and see what happens.

mac25

Good to here, hopefully the oil consumption stops as well.

ezone

Is fuel pressure any different now that you replaced the regulator?

mx5med

I still need to rent the pressure tester check again. Do you know the differences in regulators between civic and accord? I could just be seeing an improvement in my fuel trims due to the injectors recieving more psi.

At idle my stft is perfect, but cruising I'm running between -5 to -3%

ezone

The fuel pressure specs are very different, by 8 or 9 psi......


So it seems you just installed a new problem that kinda masks the original problem

mx5med

Ok, that makes sense.

Today I was able to swap on a fuel rail with injectors and pressure regulator and I noticed something odd. The car I swapped them from had fuel in the return line and mine did not. It was from a '97 Y7 in great mechanical condition. Is that normal or is it possible I have a fault somewhere along my return line? Aside from that, I saw fairly improved STFT at 7-8%. Those components had 150k on them. I also tried just the pressure regulator on my rail with my injectors and that didn't change anything from what I've been seeing.

ezone

So, ummm.....it would seem your injectors were the culprit?


hard to speculate about a return line, Was there still vacuum in the fuel tank?

mx5med

what exactly do you mean by vacuum in the tank? I noticed it when I had both rails pulled off the cars. My brothers car held fuel in the return line the whole time I was swapping his in to test it and mine didn't have any as soon as I disconnect it from the pressure regulator.

Not sure if it's related, but I very rarely hear a vacuum "hiss" when I open my gas cap. I do only if the car has run for a minute or two and I open right after I shut it down, otherwise nothing when I stop to fuel up.

ezone

Nothing really, was kinda wondering out loud

I doubt this is significant