Celica Forums General Discussion Exterior running lean

From reading some of your forums I noticed a lot of people complain about their celica running lean with some sort of intake installed. I have a rod millen intake on my 2000 GTS and an air/fuel ratio gauge and I have noticed that at idle the air/fuel ratio is extremly lean. It also seems to be lean when driving at 2000 to 3500 rpm with trottle position at 4-8%. I have the Greddy E-manage and Profec-E01 so I can change the fuel amount, but the damn ecu will over see may changes within a couple of minutes and trim the fuel delivery back to where it was before I made any changes at all. I can set the air/fuel ratio at idle to be well above 12/1 and the ecu will slowly start trimming fuel away until it is back to about 17/1. No matter how much I attempt to modifiy the maf signial it will always over see my changes. I can even add time to the injector pulse width, but the ecu will then trim time away. Why does this car like to run so lean at idle and light cruise?

It runs lean because the intake is designed wrong. It doesn't have the fins around the MAFS like the stock box. This is the main cause of bogging and CELs on every intake out there except TPR. TPR uses fins like the stock airbox to keep the AF ratios safer, and eliminate the possibility of bogging or CELs. If you want, you can do this mod to simulate the TPR intake:

new[/b]celica[b].org/forums/showthread.php?s=&threadid=127861

It's what the TPR CAI was based off of, and has been successfull in removing bogging and CELs on every car that's used the mod (even on RMM instakes ). Since you're modifying the hardware instead of trying to reprogram the ECU, the ECU can't revert back to its original settings and run lean anymore.

it has to do with the piping diameter and the MAF mount location. Since the volume increased because of the bigger piping, the total velocity went down, so the MAF readings measure less air and compensates with the proper fuel/air ratio. There is only two way to deal with this...blue bombers mod or get a TPR intake. If you need CARB compliant, then AEM 2nd gen will be better, but still bogs sometimes

Nope, not really. I've learned a lot since that thread in the link. The RMM intake (and just about every one out there except the old PHR CAI) is 2.5" already, so it's not the piping. The MAFS location is also pretty much irrelevant. Easy_C tested a TPR CAI without the fins (TPR has the best MAFS placement of any CAI), and it still bogged about as bad as the Injen CAI he borrowed for the dyno. I have the MAFS from my modded CAI right on the end of a bend and it works fine. Even the AEM Gen 2 has been known to bog with its updated MAFS location (only reason it was really made was because Gen 1 had hand-welded MAFS mounts, and they were misaligned), which is much improved over the original.

The fins are key to proper MAFS readings and safe fuel ratios, which leads to no bogging or CELs (and also a lot of power, shown in dyno comparisons). Even the Corolla and Matrix have similar fin or "strainer" setups before the MAFS to help out the airflow through it.

Thanks for the info blue bomber. I have finished installing the stock fins on the intake. Throttle response seems alittle better and I don't notice any backfiring through the intake on warm up like I use to. It stills seems to run between 16.5/1and 16/1 around idle, but if the ecu is programed to see a specific voltage on the o2 sensor at idle, then there is not much anyone can do to change that. At this point that must be the case. No matter what I do it will always run alittle lean at idle. May be the fin mod will help with the misfire engine code that I can't seem to get rid of. Now that throttle response is better. Only time will tell.

Considering some intakes run over 18:1 in low end, 16:1 isn't bad at all. With any improvement in airflow, you're gonna run leaner than stock, but with proper parts to insure correct MAFS tuning, you can keep it under control. Besides, the car is programmed to run lean at idle and low end (especially when the car is cold; lean = hot, so it helps warm the engine), and then it gets much richer in lift.