Twin turbo AFR question. Lean spots.

[Ron]

Hey guys, looking for some advise, here's what happening.

1) At idle when I blip the throttle (up to 2.5k - 3k) AFR goes a little rich as expected and then it leans out to high 15's - 16s as rpms are coming down before stabilizing to 14s.

2) While cruising and BARELY on the gas, AFRs go crazy and change from 13s to high 16s back and forth really fast. Again, gas pedal is BARELY depressed, almost disengaged when this happens. You can feel the engine stutter.

3) While cruising and letting off the gas completely, AFR gauge is supposed to go full lean immediately correct? Before it does that and right after I release the throttle, it hangs at 16s-17s for about 2-3seconds and it then goes full lean as expected... OR... it will go full lean when releasing throttle, jump back to 17s for a second or two and then go full lean again as expected.

I assume these are all being caused by the same thing.. any ideas on what needs to be adjusted on the map or do you guys think something other than the tune could be causing it.

Thanks!

[omm370z]

Try to ask that to Guru Sam

[valpozguy]

sounds like an exhaust leak for a charge pipe leak.

sent from my SAMSUNG- SINGLE TURBO SGH-1717

[BigT]

What size fuel injectors and are your fuel trims in check?

[Nixlimited]

I think it's normal to go full lean on decel (with no pedal input) as well as after a rev when the car is not moving for the same reason: the engine is coming down in speed and there is no load so fueling is minimal while the vacuum is still pulling in more air than necessary. Not sure how long your AFRs are staying lean after a blip, but I wouldn't be too worried. I would only really worry about lean conditions under load.

With regard to your cruising AFRs bouncing all over, the car should be in closed loop fueling so could that indicate some issue with the OEM O2 sensors? Or maybe the larger injectors are not spraying consistently at such a low IDC.

[Ron]

I have Bosch 650cc injectors, not sure on the fuel trims, I have to check but I can't get Rom Editor to start logging for some reason.

I know its normal for it to go full lean under decel, what I am not sure is normal is that it hangs at 17s for 2-3 seconds before going full lean. Or it will go full lean, then return to 17-18 and then read full lean again as expected.

AFRs under load are just fine.

[Ron]

At idle, blipping the throttle, you can hear the engine stutter.

[Ron]

Not sure how accurate these are, but these are fuel trim from OBD2 using dashcommand. Long term up top, short term the bottom.

[Baer383]

Originally Posted by Ron

Hey guys, looking for some advise, here's what happening.

1) At idle when I blip the throttle (up to 2.5k - 3k) AFR goes a little rich as expected and then it leans out to high 15's - 16s as rpms are coming down before stabilizing to 14s.

2) While cruising and BARELY on the gas, AFRs go crazy and change from 13s to high 16s back and forth really fast. Again, gas pedal is BARELY depressed, almost disengaged when this happens. You can feel the engine stutter.

3) While cruising and letting off the gas completely, AFR gauge is supposed to go full lean immediately correct? Before it does that and right after I release the throttle, it hangs at 16s-17s for about 2-3seconds and it then goes full lean as expected... OR... it will go full lean when releasing throttle, jump back to 17s for a second or two and then go full lean again as expected.

I assume these are all being caused by the same thing.. any ideas on what needs to be adjusted on the map or do you guys think something other than the tune could be causing it.

Thanks!

Ron, my car does the same thing I bought a upgrade to a tuner cable and in the process of fixing this stuff I have had some success with the stumble off idle and weird afr's but the other stuff I haven't got to.

Frank

[KaienZ34]

subbed

[elperuano]

On my last set-up upon deceleration my afr would read rich, on tapping the gas pedal while cruising the numbers would jump up as well... Honestly on those things I didn't mind cuz I was either barely touching throttle or not at all.. However at wide open throttle my afr was perfect in the 11s which is all I really cared about. Good luck op!

[BigT]

Sounds like its your blow off valve. Not the actual valve, but the fact that we run MAF sensor and not full speed density. The valves are blowing off metered air and thus confusing the ECU. In the DSM and evo world, some cars would run completely fine with vented valves and some would not. The only cure was to either recirculate them or switch out the MAF for a MAP and another ECU.

Plus your fuel trims are adding a ton of fuel. The global scaling is wrong for the injectors.

[Motion Lab]

Originally Posted by Ron

Hey guys, looking for some advise, here's what happening.

1) At idle when I blip the throttle (up to 2.5k - 3k) AFR goes a little rich as expected and then it leans out to high 15's - 16s as rpms are coming down before stabilizing to 14s.

2) While cruising and BARELY on the gas, AFRs go crazy and change from 13s to high 16s back and forth really fast. Again, gas pedal is BARELY depressed, almost disengaged when this happens. You can feel the engine stutter.

3) While cruising and letting off the gas completely, AFR gauge is supposed to go full lean immediately correct? Before it does that and right after I release the throttle, it hangs at 16s-17s for about 2-3seconds and it then goes full lean as expected... OR... it will go full lean when releasing throttle, jump back to 17s for a second or two and then go full lean again as expected.

I assume these are all being caused by the same thing.. any ideas on what needs to be adjusted on the map or do you guys think something other than the tune could be causing it.

Thanks!

1) This is common. The car adds fuel as necessary for throttle tip-in, but on engine deceleration it turns off the injectors and the car acts as a big air pump.

2)It is common for the AFR to jump around during part throttle driving. This is because a MAF based car is going to constantly be making adjustments to target 14.7AFR which is ideal for pump gas. The choppiness could be a result of a erratic fueling map, but most of the time its from having choppy timing tables.

3)In my opinion this most likely has to do with the way the transmission computer controls the throttle for the synchromesh shifting. I do not tune the cars personally here just trying to jump in with some useful info. Todd our tuner might have a different opinion, he is out tuning currently so I didnt have him around to ask.

Thanks,
Alex Goodwin
AlexG@motionlabtuning.com

[roplusbee]

Sub'd

[shadow85]

interesting thread, no more updates?

Did the OP find a solution or get to the bottom this?