Really strange Fuel trim problem

[linksys42]

I have been having this problem for like a month and a half now. And I am getting ready to put my 650's in and I really need to figure this out. At Idle my LTFT is at like -7 but if I am putting any load on the car it jumps too +1 to +4? Also if I free rev sitting in neutral up to the rpm I typically cruise at with load on the engine (2500rpms) the LTFT it will sit at -7?What would make it do that if I had a boost leak it would read lean all the time correct? Why is it only going lean with a load on the car? O2 has just been replaced and its still doing it. Thanks

 

[linksys42]

Does anyone have any info why the trims would be in the negatives (rich) when at idle or free revving to my safc ne points? But if I go to the same rpm points when driving at a steady speed/load/throttle they go to a +trim (lean). What could cause that? Thanks

 

[blcknspo0ln]

You're just describing a "normal" operation of fuel trims. If you are trying to tune your LTFT's then you need to do this.

Get in the car and go on the highway for 10 minutes. Cruise at 70 mph and look where your fuel trim are. DO NOT MAKE AN ADJUSTMENT, just write down the number it's at (ex. -5).

Then, get home and let the car idle for 5 minutes. Then record the LTFT idle trim.

If the two numbers are within 1 or 2 % of each other, then your settings are OK. If they are not, then adjust your LO settings accordingly. When tuning an SAFC with bigger injectors, you are not tuning LTFT idle and cruise to 0, you are tuning to the DIFFERENCE of idle and cruise to 0.

example,
idle = +4 and cruise = +5 - your settings are OK because the difference is only 1
or
idle = -4 and cruise = +1 - your settings are BAD because the difference is 5

oh, and don't bump your own thread.

 

[linksys42]

Ok, well then I have a problem. This is with the stock 450's still installed with a 190L walbro and aeromotive AFPR set at 44 PSI at idle, I would like to get this ironed out before I put the 650's in. First off my LTFT at 70mph are at +8 and at idle after the drive they come down to –4 so they are off 12. Another problem I noticed was that after I drive for a good distance/time my fuel pressure starts to drop off? An example is that I set the pressure at 44psi before the trip and pull over after a while and the pressure falls down to 41psi I bump it back up and drive for a while, stop again and it has dropped again?????? I have been going thru my fuel system to try and figure out what is causing it, pulled the pump and reinstalled it, when I took it out the spacer, o-ring was cocked to one side and when I took the assembly out the cap that was supplied with the install kit just fell off and will not stay on??? So I put the old stock pumps cap on the 190L and it clipped on with no problem, I also put a couple o-rings behind the spacer so that it would give the sealing o-ring and spacer behind the cap more support and installed it. Also redid the crush washers on the fuel filter. I don't get it I do not have any leaks in the lines or fittings anywhere? Anyone have any ideas? Thanks again

 

[linksys42]

Hey guys, I am still having the problem and im afraid to drive the car like this. I was wondering if anyone has an idea on how I can make sure the pump is sealing in the flared fitting on the fuel pump housing or is there any what I could set it up to eliminate the o-ring all together? Because, the only thing I can think of is the warmer the engine gets the and the longer the pump is running the o-ring that is sealing allows pressure to leak? Unless anyone else has any other ideas on what to check or look at to figure this out? I could really use the help. Thanks