Why are my fuel trims so damn inconsistent?

[dleach1407]

I figured it out. For anyone who reads this, what I didnt understand was I can use the fnpw_*comp to calculate the accurate slope/breakpoint/offset data for 20 to 60 psi. Since I always tune 95 and older, Ive never needed or used those before. this information is found on the ford performance data sheet for Lu80 injectors found here.

[dleach1407]

for me the K-constant stuff just muddies all of this up and I dont know how to correctly make changes to injector data. If i change the high slope, it changes all the other parameters. the parameter notes say to copy all of the information from the existing tune, change high slope to 30 (im assuming save it) then enter the new high slope and save it and then go back and enter all of the old info for low slope, breakpoint, voltage cid and maf transfer? I dont see how any of that will work.

I feel like instead I would do the changes to the high slope first, save it, then go in and change the remaining injector settings to the new settings for 60psi and return the maf and tps failure and cid back to the previous setting.

[PaulC-turbo5.0]

I've been following along on this as I always do and am also curious as to how upping the pressure is going to help the lack of consistency from heat? I dont have an adjustable regulator anymore but if this works I may consider trying to get one back in somewhere, although my car does seem a bit better now that ive heat shielded my lines.

In the OPs case where he is going OL at idle I can understand the need for more consistency but when running CL why is it really that important to be within 3% or less and always adding? If I am not logging you would never know if my trims were at .98 or 1.08, once I go WOT its always right at .75 lambda on the WB which is where its important.

[dleach1407]

Increasing the pressure increases the boiling point of the fuel. This is apparently true with all liquids. Im not versed in fluid mechanics so I had to look it up after it was mentioned. FWIW, most of your dead head cars run up to 70psi especially during hot start when fuel is most likely to boil. I am positive the issues im having are boiling fuel in the rails plus additional heat from the 340. Its the only thing that makes sense. You must be making gobs of power/boost to be commanding .75 lambda.

[decipha]

Raising the boiling point so it cant vapor lock.

positive trims can never cause a lean stumble. Its not critical but why not?

[PaulC-turbo5.0]

So does increasing pressure just help prevent boiling and vapor lock or will it also help the trims be more consistent?

What are you commanding at WOT? I’m running 10 lbs of boost on a stock 302 and from all my reading .76 or 11.2 is where you want to be for safety. Decipha has .76 in the A9L2 table.

The lean stumble thing makes sense but are we driving ourselves nuts for no reason on trying to keep the trims near perfect? Does adding 10-15% at times really matter?

[decipha]

one in the same if its vaporizing its not atomizing properly

im pretty sure its .8

It only takes me 1 drive and im done to getting the fuel right. If its taking you longer your probably over compensating.

No it wont make a difference if its adding that much but thats about the maximum before hinting at having other issues.

[dleach1407]

.785 is what i command only in "high" boost which really is still low boost(10lbs). Street boost which is 6.5 lbs im seeing .82-.80 depending on rpm. I could probably get away with that in "high" boost but i also have aluminum heads. I just saw you have iron heads but i still would think you could lean it out a little. Maybe save you some gas money. I figured you were above 15 lbs with .75 but at least you know you're safe.

[dleach1407]

It only takes me 1 drive and im done to getting the fuel right.

If i do 30 minute drives mine are consistent. When i start adding in long idle periods or extended drives, that's when I start seeing the trims adding more fuel.

[dleach1407]

I feel like instead I would do the changes to the high slope first, save it, then go in and change the remaining injector settings to the new settings for 60psi and return the maf and tps failure and cid back to the previous setting.

Is this accurate?