I know there are lots of threads with similar issue but I am having a hard time understanding what I am looking at.


I have a picture of my (LTFT 22%) and STFT (-0.8%)

I didn’t get a picture of the maf reading up it is above 5.0g/s.

from what I am reading on the forum, because my LTFT is high the upstream o2 is reading a lean condition so it is adding 22% more fuel??? Meaning I have a vacuum leak somewhere? This has started happening after I disconnected my battery last week to install my new starter (which would have reset my trims). Should I be checking every vacuum line? Reset my fuel trims again?

I have a new fuel pump ordered already for a spare as my fuel pump is pushing 20 years+ now (looks original) I also am gonna get rivnuts to repair the maf threaded inserts as it feels loose (no rpm increase from break clean spray around maf).

I just don’t really understand the fuel % thing. If someone can explain in simpler terms then the other threads so I can learn for myself for future needs that be awesome. Thanks (This image was taken at “warm” 75° oil and coolant roughly)

 

How long has it run since the battery was reconnected? It takes time for it to learn the trims. You're correct that it's adding 22% more fuel, but if your airflow is on target (5.5-5.6g/sec at 850 rpm idle) then the problem is less likely to be too much air and more likely to be not enough fuel for whatever reason. Poor fuel pressure, clogged injector, etc.
So that airflow number is really important.

 

Hi Loki thanks for the information. I am sitting at 5.2-5.4g/s at 850 rpm… but would that missing half percent actually cause a 22% increase in fuel? I will look at all my vacuum lines around the air box again…maybe I cracked something on the vfad….One second thought I’ll just cap it off reset my trims and look again…because that’s last think I had off.

Regarding fuel pressure…I have ordered a new pump so will throw it in….I really hope it’s not an ejector issue…It’s so tedious to change those

 

You can think of fuel trim % as % of total airflow. So if you see 5.2g/sec, and the ECU is adding 22% of fuel trim to get the correct AFR, it means it's providing fuel equivalent to 5.2+5.2*0.22=6.34g/sec. That's too much air for idle throttle 850rpm, so either..
- the MAF is reading wrong airflow
- for some reason there's an undersupply of fuel so it has to run more injector duty cycle to get the required amount of fuel (low fuel pressure for example)
- there's a small vacuum leak + one of the above
- it learned a weird fuel trim due to a past issue that it will unlearn with more driving. It shouldn't take long.

Simple things first, definitely check for vacuum leaks, check the spark plugs condition. If you have a small vacuum leak, fuel trims in higher regimes (i think the threshold is 2000 and 6000rpm, but could be wrong) at steady throttle cruise should be smaller because the throttle is flowing more air but the leak is only so big, so it's a smaller problem.

One other thing is to check the idle jet air vacuum lines at the bottom of the LIM. They help mix air and fuel at idle speeds and if blocked, kinked or broken could lead to issues. Usually worse issues than what you're seeing.

 

One other thing, your engine load at idle is 39%. That seems high, but my car is put away for winter so I can't check what it should be. Maybe someone else can chime in. It's possible something is dragging the engine, maybe a slightly engaged clutch or an accessory on its way to seizing. This would require the throttle to open more to maintain idle rpm, AND you would have a vacuum leak that causes airflow to read low, leading to the fuel trim. Is this a manual or automatic?
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Thanks again for the insight.

it’s a manual…I replaced my master and slave for clutch not to long ago and my pedal still sticks to the floor sometimes (I believe my pedals bracket could be the issue with that) (I bleed r everything 1000x) But when fully released I see free plat between the rod on pedal and master cylinder plunger.

I also did notice a crack on my vfad nipple…I’m going to cap off that system and report back when I have time to do so.

 

I totally forgot to add that I also changed my belts, idk if that helps with the higher calc load at idle.

I also did some testing during my lunch break. At 1000 rpm (i only went to 1000 to not **** off everyone at my work) the calc load drops to 26% moving or not. Correct me if I am wrong but if a pulley was tight the calc load would not drop correct?
I was messing around more but once my fuel pump arrives I will throw it in and report back.

 

Well I have good news, I spent countless hours here and there trying to solve this stupid system to lean/ rough idle with weird fuel trims.

I did 2 things at same time so I am not 100% sure which one fixed it, but I waited a week for good luck and seems to have worked.

So long story short I was having some slow cranking speeds while starting one day took the batter out to get load tested. It failed so bad under load.

Got home swapped the battery. But before I started the car I went under and cleaned all the grounding points near starter and on engine.

For some reason I had the idea I should just press on all the ignition leads to make sure they where all in.

Started the car (obviously the code disappeared from battery removal)

I have been driving all week fuel trims are pretty much normal as par as I can tell, no CEl for sys to lean, no rough idle, and obviously the crank speed is good from new battery.

Lesson learned for someone in the future tracing this down... Yes you in 2032 reading this. Check your ignition leads are still fully on plug or coil even if you didn't work on them maybe it vibrated loose somehow. also check your battery under load, you will see more then you can with just multimeter. Maybe the battery is cutting amps and volts to pump or even coil. idk all I know is that its been a week and my issues are gone....I hope this post does not mean the return.


Let me know your guys thoughts on this maybe shed some light on how the car picks voltage priority or if I am just an idiot for not looking at leads to make sure they hadn't come loose.