Trying to learn about fuel trim. Comments on these graphs. On fuel trim, no number is idle and number is RPM.

 

Last spring I replaced my xjr maff. Imeasured downstream o2 voltages and looked for the maf g/s value and voltage. Everywhere else than WOT egr is always ajar more or less. So it pulls maf readings very low. With old and new maff I had under 10 g/s airflow to the engine at idle. What is very low. Only thing what can bee seen from the maf voltage is how it behaves at wot. It should reach over 4V somewhere over 4k rpm. My old maff did not at all. It stayded barely over 3 volts. This causes multiple different driveabilty issues and those +25% shorts and longterm trims. Engine may still run smooth as a silk.
So if downstream O2 volts drops down 0V instantly when you step on it and stays there all the way to the rpm limiter and same time maff voltage does not rise over 4V anywhere. I'd say you have bad or just dirty maff.
I tried to clean mine. I sprayed maff cleaner spray to it, wiggled it and nothing changed. After putting new one in I took the old one apart. Measure heads in the air channels were still heavily coated with very fine drit. I could clean them manually now when they wrere exposed via hacksaw.. So the cleaning doesn't always do the trick. It did do the trick to my daily driver Volvo though.
I recommend to do ecm learning reset right after replacing maff. I used IDS to it and engine ran very very poorly untill ecm got to the closed loop. After couple of days and multiple driving cycles long term trims stays way under +-6% all the way.

I have same foxwell reader and I can not connect to my car with it easily as it should. It does not list x308 correctly. I can not trust it. It has latest frimware and updates.

 

I've been trying to figure out what's amiss with my fuel trims as suspect the MAF is either whacked or not programmed to read the higher flow with my CAI.
My trims are like 112% LTFT and 129% STFT even after a hard reset. But my O2 Relativity(I think upstream) is like 1%.
I don't recall voltages but airflow is like 5gs at idle but quickly jumps over 40 accelerating.
Never throw a code and runs great. Leads me to believe the MAF is whacked or just can't handle the change.
Cleaned the MAF and no change either.

 

Drive to work this morning. Crusing at 65 mph on flat ground. Short term on both banks hovers between -0.8 and +1.6. Long term stays at 19.5 on both.

 

Long is way off. Assuming there is no vacuum leaks and fuel pressure is ok. Measure maff voltages durin wot.

 

Long never goes below 19.5. Is 19.5 the maximum that can be read and actually possibly higher.

 

yes

 

There are many, many Youtubes and tutorials on the Web explaining fuel trims. You are too lean (the ECU is enriichening to compensate). I think you still have an air leak (leaks) affecting both banks. Possibly the O-rings, still; likely along the air tube from the air filter to throttle; maybe the O-ring on the dip-stick. There are ways to check (unlit propane along gasket edges, for instance).

If this just started with cold weather maybe a stuck temperature sensor. Lots of threads on this issue.

 

You mean the coolant temp sensor and not the one in the MAF? New coolant temp sensor when I replaced the crossover tube a few months ago and scanner tool shows proper temp.

 

One in MAF is a wire from the sensor in the crossover pipe: unless it is stuck (smack it), probably not the issue. Might check the prong on the MAF and connector . . .

Hunt for leaks. Maybe a can of a good fuel system cleaner. Any codes?

 

So what exactly is my scanner reading when it's giving me over 100% on my fuel trims? Also, what's the stock MAF max out at? WOT I get 4 volts and 160g/s. It seemed that 160g/s was pegged is why I ask.
The scanner, a CRP 123 Professional is new to me so I'm not real sure what it means when it says my LTFT is 119% on both banks and my STFT like 127%.

 

Nevermind. The attached pdf explains it I think. It's giving me a numeric on a scale of 0-255 with 128 being 0 in percentage format.
02 equivalency is 1 where ya want to be or greater than 1 is rich, less than 1 is lean. I've varied from .95 to 1.06.
Given what is called good, 14.7:1, I'd want to be on the rich side anyway. 14.7:1 is too lean even for A cruise AFR. Y'all DO get that, right? Max power is made from 12.8:1 to 13.2:1
13.5:1 to 13.8:1 is lean enough for a cruise AFR as far as I'm concerned.

 

Remember that these cars have cat's on them. So anything than 14.7 is off anywhere than wot. Ajv8 and many many other engines designed with cat in mind does work well with stoich mixture. Some same age or slightly newer doesn't even go much richer during low boost. 4V or over is ok. That 4V being right or close enough can be seen from downstream O2 sensor voltage.

 

But the '00-03 AJ27 uses wideband sensors. Which should show accurate AFR at all times. Not just at 14.7:1

 

Well my cats are going bye bye anyway. Last of my performance upgrades.
None of it is good for an engine. There are simulators I linked to awhile back that allow for AFR adjustment and not throw a code. I want nothing leaner than 13.8 at cruise, 13.2 at part throttle, 12.8 @ WOT.
14.7 is just ridicilous.

 

I have scanned three(3) 2002 xjr's with no drive ability issues, codes or fuel pressure issues. They all read 16.x at WOT. All cars also stock. I find that weird. Wish more '00-'03 owners would report their wot afr's.

Would you just hollow the stock pipe, or buy the supersprint downpipes?

 

16.x AFR @ WOT?
I'll probably just gut them unless there's a reason to replace them I'm not aware of yet.
Maybe someone can answer this...what's changed so much in the design of the ICE that optimal idle AFR can go from 12.8 to 14.7.

I wonder how much timing had to be pulled to run WOT @ 16.x AFR without detonation.

 

if you know somebody that will pay for your originals buy the ebay cats and gut those

 

ignore the number

the 4.2 32 bit defaults to 14.69

 

I bet every aj27 xjr will read lean at wot. Is the reading inaccurate? Who knows. But everything else the scanner tells me is spot on.