Fuel trim issues

98 tacoma 2.7 4wd 240k miles with EGR delete

I have done my research and I cannot for the life of me figure this out. My LTFT is +15.0, my understanding is that this means I have "lean condition" and its adding 15% more fuel. Lets just say I have eliminated the possibilities of a vacuum leak, injectors are clean, MAFS is clean and o2 sensors are replaced. Nothing has solved this problem. When I give it gas LTFT goes up to +18.0 and when i floor it it drops to +4.69. could this be a fuel pump problem? This is driving me crazy and help would be appreciated. Also I have no error codes

 

check the brake booster... this is an often over looked vacuum leak.

Given that, what you are describing could be true. Poor fuel delivery due to a filter or pump could be the cause, so could a bad fuel pressure regulator but your WOT fuel trim makes me think that isnt the problem. One test for an intake vacuum leak is just what you did, watch the fuel trims as you raise the engine rpms. With the throttle closed you have a vacuum of -18 ish inches on one side of the throttle blade. On the other you have atmosperic pressure, +14.5 ish positive. That is a 28 inch pressure difference trying to find a way into your motor. As you open the throttle, the vacuum side of the throttle starts to approach atmospheric pressure and there is less of a pressure differential to pull or push in false air. Thats why the fuel trims improve.

 

I have the same problem just installed new injectors today. Still +12-14% ltft. New pump, filter etc. no vac leaks, two known good 02 sensors and mafs; rung out all sensors and everything else to check grounds ... I give up. Tomorrow morning I’m gonna try to reset the ecm after its warmed pulling the ecm fuse for 5 minutes, start it and run for 5 minutes and shut down. I read somewhere that this is gives an absolute clear and if done while warm it has a decent baseline. Who knows but it’s free.. the author said to time the intervals.

 

I plugged the line that runs from the brake booster to the intake and it saw no improvement in fuel trim. I forgot to mention I have a new fuel filter and pressure regulator, so it cant be that. Is it possible my Mass air flow sensor is bad? I'm going to keep searching for a vac leak but i wish there was a way to test my MAFS

 

If the fpr was faulty, what would we expect to see? I have thought about changing it but they are kinda pricey and there really ain’t much that can go wrong with it. Has anyone ever had to change one? Im gonna throw that out there...

 

You answered my question. Thanks

 

how do you know your mafs is working? did you test it or get a new one?

 

It’s pretty important you get an OEM MAF.

To many fake or copies out here and aftermarket ones are a gamble.
I went through 3 of them before getting an OEM from the dealership

 

I would try cleaning the MAF sensor first and see if that changes anything (use MAF specific cleaner...not just a generic electronics cleaner).

I'm not sure how to test the MAF sensor...I think you do it by checking the voltage but you'll have to read up on that or someone else will have to tell you. But if you do replace it, or any sensor for that matter, stick with OEM Denso sensors. Anything else is a big gamble

 

Yeah i have cleaned it multiple times with mass air flow sensor cleaner and it hasn't changed anything. Thats why im thinking it might be bad? but oem is like 700 dollars and i'm not throwing that into it unless i know for sure its not working.

 

Brake booster could be the issue, bad MAF, bad fuel injectors, bad fuel pump, vacuum leak, oxygen sensors, or even PCV could be the issue.

You have to systematically rule out things one at a time. Starting in the easiest order of inspection.

I check for vacuum leaks first, then I check electronic data as in MAF and oxygen sensors data, then brake boost/ PCV valve issues, followed by fuel pressure, and if all that checks out well, THEN I start highly suspecting fuel injectors and gotta take the steps to inspect those, and those are never easy to check for proper mechanical fuel delivery since the injector nozzles are hidden inside of the intake manifold.

A bad MAF would indicate poor absolute load readings under WOT (readings of under 85% indicate poor calculation readings of the MAF which would indicate it is bad) if that registers okay, you need to make sure that the grams per second readings at idle without any loads on especially AC indicate roughly the same grams per second the engine is. If you have a 3.4L the grams per second would indicate 3.4 grams per second, a 3.0/ 3.0 grams per second so on so forth.

Voltage is typically not a good way of diagnosing a bad MAF as I have found in the past.. it's data, yes, but not super useful data as the above stated items.

 

Yeah I would figure out how to test it first. Should be able to find an OEM one for a lot less than $700

Just a quick search showed me this one for my truck for $150

https://parts.olathetoyota.com/oem-parts/toyota-mass-air-flow-sensor-2220421010

 

https://parts.camelbacktoyota.com/o...0YWNvbWEmeT0xOTk4JnQ9YmFzZSZlPTItN2wtbDQtZ2Fz

here's one for mine

 

jesus h christ...that's insane. Had no idea the older 4cyl models had such an expensive MAF. That's nuts

 

I did this mod and works perfectly with an OEM 2004 sensor.
You might be able to do the same thing for the 4 banger, it’s looks like the same design that Imhad originally

https://www.tacomaworld.com/threads...1997-to-1998-3-4-supercharger-upgrade.542496/

 

not to bump a old thread but I have solved the issue. It ended up being my Mass air flow sensor. I was lucky enough to find one at a pick n pull (paid 10 bucks), threw it on my truck and my LTFT dropped below +5.