As the title suggests I am getting lean AFR's under throttle that suggest somehow there is a large amount of air that is getting in after the MAF, or the MAF is not working correctly. I did some logs and the MAF is only reading in the 150 range max. IIRC it should be a lot higher even for NA. the car is not registering any codes.

I have had my whole UIM off a few times over the last few months, first to diagnose and then swap the SSV solenoid and then to replace clutch master and slave cycinders. I am going to remove and reinstall the UIM this afternoon to make sure everything there is connected correctly and check the gaskets. Honestly the with the MAF reading being off by this much (40-50% if I remember correctly). I checked the Jet Air Bleed last night and it looks good in place. I will remove it and have a look if the UIM does not reveal a problem.

I have a few questions:

What should my MAF be reading (max range) under WOT?
Is there any other area to look for a leak (other than UIM and JAB)?
Would a failing MAF fit the bill for this and whouldn't that throw a code?
Same question for the primary O2 sensor?

Mods are listed in my sig. Anyone have an idea? Any help or suggestions would be great. Thanks for reading.

 

What load are you seeing when you see max g/s? What tune are you running? When you say lean what are your AFR's? Does the car feel okay when you make a WOT run? Typically a stock tune Rx-8 will see about 200g/s at redline.

 

It is very unlikely that you have a leak anywhere near large enough to cause issues at WOT.

Look at the WBO2 or the MAF or the tune if . It isn't stock

 

Check injectors

 

First of all, thanks for the help guys.

I was seeing very lean AFRs like high 14s low 15s at WOT above 6K. Scary stuff. At the same time the MAF was reading 140g/s +/-. The car felt okay below 5.5k and by the time it got over 6 it was falling on its face.
Tune was near stock.


Today I took the entire UIM off to see if something was just loose. I also verified that the Jet Air Bleed was not the source to the air leak. JAB hose held vacuum when I removed the end that attaches to the LIM, so I eliminated that as a cause. I carefully re-installed the UIM and made sure all the bolts were torqued down. I also ceaned the MAF sensor. Reconnected all the vacuum hoses and re-installed the AEM CAI carefully. Reloaded the tune and took the car out. Problem solved. Mid 12 down to mid 11's as I approach redline WOT. MAF is reading 215 g/s and all is good with the world. The only annoying part is I don't know specifically what the cause was. It seemed like on or two of the UIM bolts was not completely tight, but that was the only thing I noticed when I removed everything. Maybe that was it, or maybe one of the last two couplers on the AEM was not seated quite right.

 

Glad you got it fixed, you may never know what it was. Likely an intake screen or something on the intake though. Those AFR's are not scary though, you are NA..........

 

Not critical, but not good either. The car was running like **** at the top end and I suspect the car was pulling timing to avoid det. I have felt that on my MS6 and the feeling was similar.