2.5L ('98-'01) 1998 2.5l fuel issues

[Tenper616]

I've posted on here a few times about this truck, and I've not figured it out yet, I've been doing research for a long while, and I can't seem to figure it out, but basically my long term fuel trim likes to stay at around -25% and my short term fuel trim seems to like to be anywhere from 1 to -15 but has gone to -25 as well, at this point I just need to know where to start with this information

 

[sgtsandman]

Do you have any check engine light codes?

 

[Tenper616]

No, there are no codes, someone before me cut the cat off and just ran the poor truck into the ground, so far I've put a new motor in it, most sensors have been replaced and a new ECM, I've also put new injectors in it, and a new fuel sending unit, just trying to get it back to how it's supposed to run

 

[sgtsandman]

Does it have a cat now? With or without, if ECM isn't getting a signal from the O2 sensor(s), that may be the issue. It depends on signals from the sensors to adjust fuel trim.

 

[Tenper616]

Still does not have a cat, however the downstream O2 just verify that the cat is doing job, nothing to do with fuel trim correct,

 

[scotts90ranger]

That's correct.

I'd question the MAF, some people like to "port" the area where the sensor is to trick the sensor so I would be suspicious of that...

 

[Tenper616]

I did replace the MAF and I always inspect new parts before they go on, also my scanner said that it was reading fine, I'll get screenshots later to show what everything is reading at, I know down stream O2 was maxed, upstream O2 seemed fine MAF looked good, the only thing that is not was the stft and the ltft, which is reading that it's pulling fuel like crazy and it even smells rich from the exhaust, I ran it with out the evap purge valve connected and that vacuum blocked off and that did not do anything to help,

 

[Tenper616]

Here's a screenshot

 

[scotts90ranger]

Have you checked the fuel pressure? I think that should be a returnless system which means the regulator is in or near the tank (don't remember) and if it isn't working right and the pressure is high it'd be all wacky...

 

[Tenper616]

I'm going to be getting a fuel pressure gauge very soon to check it, however the regulator is on the sending unit which I have replaced,

 

[scotts90ranger]

dumb thought since things seem to be worse at lower speeds but if the evap solenoid wasn't closing it could be letting fumes into the intake... I think usually they don't start in that situation but hey...

 

[Tenper616]

That's what I was thinking too, it clears up a little bit between 2000 and 2500 rpm, then again over 3500, but I pulled off the house from the other valve and blocking it off, which would mean it's not the eval system right

 

[Tenper616]

I grew up working on old carbureted stuff, I know some fuel injected things but dish is easy more complicated,

 

[Tenper616]

After some reading and math I'm sitting at around 4.3 grams/second as far as the MAF reading, which is almost twice what it should be reading correct? I'll redo the readings tonight and redo the math, but I should be reading around 2.5 right

 

[scotts90ranger]

That's my understanding and would definitely explain things, I unfortunately don't know how the MAF reads if it's resistance or frequency or whatnot... if it's resistance it could be a dirty contact somewhere.