I need to rescale my maf so I will stop idleing pig rich and getting a nasty 500 rpm stumble and belching out black smoke .. I have my 720's scaled to 636 and my latencies are done too. I was told I need to log the LTFT and see if it was positive or negitive..but how do I do that? I do see in evo scan the fuel trim low, med , high. what else? I really need to get this crap fixed. So please help out if you can.

 

LTFT is Long Term Fuel Trim. These are the ECU stored adjustments for drivability. They are ECU controlled and are based on several engine factors. In short, LTFT is the "fuel trim" low , med and high you see in EvoScan. Your goal is to get the trims to + / - 5%. This value is well in the ball park.

There is the STFT, which is the Short Term Fuel Trim. Think of it as the "now" adjustment. It should jump all around all the time. If your injectors and MAF are scaled correctly, the STFT should hover +/- 5% at idle. Cams and hard pipes make this difficult to accomplish.

The fuel trim low in EvoScan is the one to be concerned with when it comes to idle. Since you have an 03 VIII then you will have to reset your battery each time you make a MAF or injector scaling change. Then you will have to idle and drive quite a bit for the ECU to start to make asjustments.

I hope you read the how to posts on MAF scaling and Injector scaling. All the information you need is there.

If you are running hard pipes and cams....tuning for idle is going to be a PITA.

One final note, you will not get the LTFT Low to adjust if your MAF Hz is not below 40.

 

My mf hz is 44 @ reg. idle and 50.32 when the stumble happens...humm thanks for the reply appricate the input.

 

What intake pipe and filter are you using?

 

Also since you have an EVO 8, you need to reset the ECU everytime you make a change to the latencies or injector scaling. Good luck to you. Also take a look at this thread, as it has a lot of good information in it about scaling injectors:
https://www.evolutionm.net/forums/ec...injectors.html

 

The reset also applies to MAF scaling. What you are doing is resetting the fuel trims to zero. And since you are looking to fix trims with MAF scaling you need to reset for it as well.

 

I have a crappy weapon R hard pipe..(came with car to lazy to change it) and a custom in fender intake 4" off the maf with huge K&N filter. HKS 272's, 9 mr bov, bbk full. Injectors i'm sure they are scaled right..720's to 636 scaling and latencies are from brian @ GST. Again thanks for the info, a lot.
Question..could I cut my head ache by switching up to a maf translator?

 

The MAF T will help you, but your headache will remain because setting it up is often a PITA.

The hard pipe won't allow your MAF to read low enough for the LTFT low to adjust. I found that if you smooth the flow after the MAF you will get the Hz low enough to allow the LTFT low to adjust. Basically the MAF Hz must be below 40Hz before the LTFT low will adjust.

The way I got my HKS pipe to work well with the MAF was to insert a 3in rubber coupler onto the MAF and then slip the MAF back into the hard pipe as I normally would. The coupler inside the hard pipe smooths the MAF hz from the 50+Hz I used to have to about 35Hz. Then my LTFT low adjusted accordingly and voila.....idle has become normal again.....just a lot more lopy because of the cams.

Another method is to play with the MAF scaling until you can get it to read lower in the Hz at idle. The top three blocs on the EcuFlash table are the ones you will need to play with. Keep in mind that you need to keep the MAF scaling curve as smooth as possible to avoid drivability issues. Also, MAF scaling will adjust your LTFTs.

In time you can get the car to purr like a kitten....you just need to be patient and work slowly with the MAF scaling, injector scaling, idle RPM, idle timing, and idle AFR.

 

Thanks man, looks like I have my work cut out for me. lots of logging and battery disconnecting..hahah really do app. you help Appauldd and the others with the added info.

 

Ok logged the HZ again and the STFT The low was @ %100 mid %90 high %50. The HZ was a best of 44 and it would swing between 44-50 hz. I played around with the piping and I now have it idling at 31-37 HZ. the low is %100 Mid %95 high %50. The stumble still happens but does not last near as long, or as violent. Will reseting help bring the high closer?

 

CRAP Getting a PO107 code now..might need a new MAF reading the test now.

 

You will need to reset the ECU by disconnecting the battery. Make sure you didn't damage a wire in the MAF plug. Also put some dielectric grease in the plug to ensure moisture free contact. Also, update to the newer version of EvoScan. Once you do, I will give you the more accurate LTFT values from MRFred.

 

I did reset ecu by disconnecting the battery..Low MID High are spot on now. 100 across still have the PO 107. Idle is much better, smoother. It still stumbles at 500 rpm. AFRs are what they should be now. To lessen the stumble which direction should I take the maf values in the first 3 blocks? decrease or increase? what does doing this do, what is it telling the ecu?

 

I found I had to increase the MAF scalings to get the car to idle well. Just try to increase the MAF scaling keeping the basic curve the same. Deviate the curve too much and you could get drivability issues.

If you have cams you may consider raising the base idle timing a bit and the idle RPM settings as well. I found with my Revolver cams the car likes to idle at about 1023 RPM at about 8* timing at approx 37Hz.

You are doing a great job! Take your time.

As for your P0107, check the MDP sensor on the intake manifold. Make sure the connection is tight and that the metal "C" spring is in place. Also, put some dielectric grease in it to seal out moisture.

 

I was able to research the specific code I'm throwing..manifold absolute pressure/baro low input..I checked it on Aldata so I could test the sensor.( I thought it was the one in the mani too). It has you checking the baro input on the maf itself..I don't have the specific tool that mitsu uses but my buddy at the local mitsu dealer does..hes going to check it after hours monday.
Again thanks for the input, its really helping out..I wish the search function worked so I could look up some of the threads refrenced.