Lean condition at part throttle

[Noyz5o]

Having an odd issue right now. LTFT both banks are going to +20 when cruising down the road at part throttle. I also get sporadic spark knock when im crusing at 2k rpm and lean into the trottle. They normalize when I go 50% or more throttle.
I currently run E85 and have verified 85%.
I have replaced the O2 sensors, checked fuel pressure (60psi), smoke tested the intake manifold(no leaks), checked the vacuum booster, verified purge valve is not leaking and reflashed the tune. I'm out of ideas right now. What are the odds it's a MAF sensor. The car was tuned by Lund years ago with no issue so the tune i doubt is no good. Please help

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[sk47]

Hello; Let me tell a story. First let me say the story may not apply to your problem. A little over a year ago I looked at a 2023 Dodge Challenger with a six speed manual & the 5.7 v8. I had been assured the car would run on 87 octane gas. When i read the owners manual it stated 91 or greater octane was required. Showed this to the salesman & service manager. They had to look it up on their computers and were surprised such was true.
Seems the same car with an automatic can run on 87 octane. However the manual could have a situation which caused pre-ignition (knock) at low RPM's in sixth gear. I call it lugging an engine.

A simple solution for an informed driver would be to never run the engine in 5th or 6th gear under 4000 RPM's. But a corporate fix was to require 91 octane. So, my short-term suggestion is to be rev happy and keep the RPM's up some more. I am making a risky assumption that you have a manual trans.

Long term I suspect you need a tweaked tune. Likely on the engine but possibly on the transmission if it is an automatic. I gather you are looking for performance because you run E85. The ENGINE MASTERS and other such programs I have watched which used E85 do raise the question of fuel supply quality. That you have verified the source narrows down a possible cause.

I am not knowledgeable of alcohol blended fuels. I think the alcohol gets a higher octane rating than gasoline which is good for preventing spark knock. However, the energy density is less than gasoline so my take is more volume of alcohol fuels needs to flow. In the dyno runs I have watched they have to use modified carburetors to run E85. Those that flow more fuel.
Pretty sure the same is true for fuel injected engines.

Wish i knew more and could make better suggestions. I will follow the thread and hope to learn.

Good luck.

 

[Noyz5o]

Hello; Let me tell a story. First let me say the story may not apply to your problem. A little over a year ago I looked at a 2023 Dodge Challenger with a six speed manual & the 5.7 v8. I had been assured the car would run on 87 octane gas. When i read the owners manual it stated 91 or greater octane was required. Showed this to the salesman & service manager. They had to look it up on their computers and were surprised such was true.
Seems the same car with an automatic can run on 87 octane. However the manual could have a situation which caused pre-ignition (knock) at low RPM's in sixth gear. I call it lugging an engine.

A simple solution for an informed driver would be to never run the engine in 5th or 6th gear under 4000 RPM's. But a corporate fix was to require 91 octane. So, my short-term suggestion is to be rev happy and keep the RPM's up some more. I am making a risky assumption that you have a manual trans.

Long term I suspect you need a tweaked tune. Likely on the engine but possibly on the transmission if it is an automatic. I gather you are looking for performance because you run E85. The ENGINE MASTERS and other such programs I have watched which used E85 do raise the question of fuel supply quality. That you have verified the source narrows down a possible cause.

I am not knowledgeable of alcohol blended fuels. I think the alcohol gets a higher octane rating than gasoline which is good for preventing spark knock. However, the energy density is less than gasoline so my take is more volume of alcohol fuels needs to flow. In the dyno runs I have watched they have to use modified carburetors to run E85. Those that flow more fuel.
Pretty sure the same is true for fuel injected engines.

Wish i knew more and could make better suggestions. I will follow the thread and hope to learn.

Good luck.

Thank you for taking the time to provide your insight. My car is a manual. This issue just started a couple weeks ago. It has also been very cool and dry here lately. Not sure if that is a factor.

 

[deanm11]

Having an odd issue right now. LTFT both banks are going to +20 when cruising down the road at part throttle. I also get sporadic spark knock when im crusing at 2k rpm and lean into the trottle. They normalize when I go 50% or more throttle.
I currently run E85 and have verified 85%.
I have replaced the O2 sensors, checked fuel pressure (60psi), smoke tested the intake manifold(no leaks), checked the vacuum booster, verified purge valve is not leaking and reflashed the tune. I'm out of ideas right now. What are the odds it's a MAF sensor. The car was tuned by Lund years ago with no issue so the tune i doubt is no good. Please help

Happy to help, can you provide a log? I'd like to see LTFT, STFT, MAF lb/min, MAF period and ideally a part-throttle pull up into mid RPMS and one wide open throttle to near redline.

 

[sk47]

A simple solution for an informed driver would be to never run the engine in 5th or 6th gear under 4000 RPM's.

My car is a manual.

It has also been very cool and dry here lately. Not sure if that is a factor.

Hello; After some thought I see my 4000 RPMs suggestion for running in 5th or 6th is not practical. That would mean running very fast. The point is to not lug the engine in a tall gear. Say do not cruise at 40 mph in 6th and then try to accelerate in that gear. Downshift to a lower gear. I do not actually know the speeds and gears needed to use. In my manual cars i get a feedback of different sorts from the car when i am in too tall of gear.

Hello; I do not know if fuel separation might be a factor. E85 is a blend of gasoline and alcohol. I have seen dissimilar fluids separate into layers relative to density. Raw milk will do such a thing. That is why being homogenized is used to keep it mixed. Just a wild thought as i do not know if alcohol and gas do separate nor how long such a thing might take.
Another wild thought ( WAG = wild a-- guess) has to do with weather and evaporation. This idea would depend on how long the fuel has been in the tank. Also which fuel (the alcohol or gas) tends to evaporate quicker.
I seem to recall having read about these two things when storing fuel for lawnmowers. E10 to E15 fuels. many authorities suggest using pure gas for lawnmowers because the fuel sits a long time often. I add marine formula Stabil gas treatments to my mower fuels the last decades and no longer have to rebuild carbs so often.

Good luck.

 

[Pistol_91]

Long terms are learned.
How recently have you switched from say 93 to e85? If recently how many miles do you have on that tank?
Is it pegging the knock sensor to 10 degrees or are you seeing 1 or 2 degrees?

Try reflashing your tune, drive a little, see what long terms look like after that.

 

[Noyz5o]

Thank you everyone for your responses. I have been running e85 all year since spring. I always switch back before storage for the winter. I drive this car often so the fuel is not old. I also checked the alcohol % recently and it read 85%. I did notice another issue of a slight hesitation when accelerating from a stop and between gears. Looking back, I believe the filter has gotten wet from car washes. Maybe it's possible water has gotten into the MAF and ruining the heater element? What's a normal reading I should see from the MAF?

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