[iviaillet]

I bought a manual transmission V which already had a tune, cold air intake, and 2.5 inch exhaust and it also came with a light throttle(24%) jerking/bucking, more noticeable going downhill. I swapped in ID1050X, 1 7/8 long tube headers with no cats, a 2.55 pulley, and a AEM wideband. Its temporarily running on a MAF only tune and runs pretty good besides the jerking at light throttle roughly around 24% throttle, doesn't matter what RPM. At first I thought it might have been one of my spark tables, then I noticed its leaning out to 18:1 while this is happening, also noticed the MAF reading is bouncing around a lot while holding steady throttle. I had an issue with the car dying after driving off and going above 2000rpm and realized it was the MAF so I already replaced it with a new OEM, also replaced the o2's when I replaced the exhaust manifolds. I was wondering if anyone has any suggestions, should I try to run both SD tune with MAF? Should I try to replace the cheaper cold air intake? Honey comb before the MAF? Is this abnormal for a MAF only tune? I'm going to attach a HP tuners screen shot while the issue is happening...

Let me know if there's anything else I can contribute to help diagnosis my issue

 

[specialp]

Light fuel demand will always not be as good as stock due to the very short pulses needed with the bigger injectors. But you can get it working quite well by tuning proportional fueling in HP tuners. You want to get it where the 02 sensors are oscillating and STFT is going around +/- 3%. The long tube headers will require an increase in the proportional fuel delay so you aren't having your fueling correct again before the new reading comes in. Then with the injectors you want to lower the amount of fueling change adjustment

Otherwise your fueling overcorrects and occasionally reduces fuel so much that the injector doesn't fire or is really close to the short pulse limit and misfires. Then fueling corrects too much for this false lean reading and goes too rich and this compounds. I am not sure if there is a way to upload the logs and tune but I can share what I did later. Every car will be different but it will be some combination of lowering the fuel corrections and increased delay

Why aren't you in closed loop there? your fuel trims are all zero and this will definitely cause you issues as well because the car is not altering fueling.

 

[iviaillet]

Light fuel demand will always not be as good as stock due to the very short pulses needed with the bigger injectors. But you can get it working quite well by tuning proportional fueling in HP tuners. You want to get it where the 02 sensors are oscillating and STFT is going around +/- 3%. The long tube headers will require an increase in the proportional fuel delay so you aren't having your fueling correct again before the new reading comes in. Then with the injectors you want to lower the amount of fueling change adjustment

Otherwise your fueling overcorrects and occasionally reduces fuel so much that the injector doesn't fire or is really close to the short pulse limit and misfires. Then fueling corrects too much for this false lean reading and goes too rich and this compounds. I am not sure if there is a way to upload the logs and tune but I can share what I did later. Every car will be different but it will be some combination of lowering the fuel corrections and increased delay

Why aren't you in closed loop there? your fuel trims are all zero and this will definitely cause you issues as well because the car is not altering fueling.

I have closed loop disabled in order to adjust the MAF sensor with my wideband. The issue was still present with the stock injectors and exhaust manifolds. I entered the injector data supplied by Injector Dynamics, but you're saying that I still need to adjust the injector delay and fuel corrections? The car idles fine, and will accelerate normally, the problem occurs when I am coasting between accel and deaccel even when my rpms are up around 3000.

 

[specialp]

If you were having this issue stock as well you might want to look for a vacuum leak. When your car is coasting downhill it is going to be pulling a lot of vacuum and also fueling is going to be especially sensitive because it is so low. So if a bit of unmetered air is coming in this would cause erratic fueling and lean conditions in open loop.

Also do you have DFCO off? you probably do for tuning but one reason it exists other than saving a bit of fuel is to avoid this situation. I keep it on and filter it out. If it is off, try turning it on and see if that covers your problematic areas

 

[07GTS]

any swap in injectors will need fueling to be corrected as all injectors are different, the good data get them close and will be good for consistency, add the wideband into the chart v time overlapped with eqratio commanded with the same scale and u should be able to see what fueling is like much better the wideband should follow the eqratio line as close as it can good visual to watch, then u will have to correct fueling for maf and SD

 

[iviaillet]

If you were having this issue stock as well you might want to look for a vacuum leak. When your car is coasting downhill it is going to be pulling a lot of vacuum and also fueling is going to be especially sensitive because it is so low. So if a bit of unmetered air is coming in this would cause erratic fueling and lean conditions in open loop.

Also do you have DFCO off? you probably do for tuning but one reason it exists other than saving a bit of fuel is to avoid this situation. I keep it on and filter it out. If it is off, try turning it on and see if that covers your problematic areas

There are no vacuum leaks, it still was jerking with the DFCO but I'm going to turn it back on and check if it helps. I'm also going to try to switch to a blended tune and see if it helps the issue.

 

[07GTS]

u are always blended u cant turn off the VVE if ur lean in that point then add fuel also if 43 is your spark take 10 deg out of that area see if that helps

 

[specialp]

Is that screenshot going down a hill? You can see the very low airmass and small injector pulsewidth with high vacuum along with lean WB. The ID1050 is non linear at .7ms pulsewidth and it could vary the amount of fuel that is sent in to the point it can become a lean misfire.

The advice to retard your timing at low airmass some will help too. Think about it as if the error range on your fuel injected is increased at very short pulsewidths. So if you get slightly less fuel some pulses and the timing is quite advanced it might not have enough fuel density to ignite. Also at those low airmasses the margin for fueling error to result in a misfire is much smaller. So having closed loop corrections might help as well.

But this is something we have to deal with with larger injectors, and my car misfires occasionally on low load. That is why when a car comes stock it is sized with an injector that covers the max fuel it needs and not much larger. The larger the injector is, the lower the pulse width will be for small fuel volumes. Injectors are sized to stay out of the short pulse region as much as possible while being able to supply enough fuel for max demand.

 

[iviaillet]

Replaced the intake with an AFE and the issue is gone.

 

[MrSurly]

No other changes?

 

[PGA2B]

What brand did you originally have?

 

[iviaillet]

No other changes?

No, that’s the only thing I replaced. After reading a couple threads describing a similar issue I wanted to make sure that was the issue, especially since my engine was having trouble at a little bit different MAF frequency. If that wasn’t the issue I was going to assume it was either a vacuum leak or a bad TPS.

What brand did you originally have?

4.5 New Era Performance