Subaru target AFR?

BJ_buggyfab

BJ_buggyfab

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Had new engine tuned in September with 80s ambient temps. Ran good over thanksgiving in 65-75 * temps. Just took out the car in 55* and it misfires some under load. Feels like it’s flat when on boost but not consistent. 
When it was tuned the guy targeted 10:1 afr. 
Im running a intercooler at 8psi. 
The question is … Is that too rich? Would that cause the issues am having? 
 

Ecu is old green/white Link. Map sensor ,cam,crank only. 

previous engine never did this. 
Any ideas? 
John@outfront

 
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Holy smokes 10 to 1?  That might be ok at 50 psi of boost but is stupid rich!!!  8 psi should be more like 12 to 12.5 to 1. Have it retuned

 
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Fuel is leftover from Thanksgiving. 
I had a similar issue when I first got it back from the dyno and found plug gap was to big. Reset the gap to.025 and ran much better. Had no issues at the dunes. Now it seems to be back?? 

 
John@Outfront said:
Holy smokes 10 to 1?  That might be ok at 50 psi of boost but is stupid rich!!!  8 psi should be more like 12 to 12.5 to 1. Have it retuned
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Would that cause misfires under load or getting into boost? 

 
Likely unrelated but I once had an engine misfire under load due to insufficient grounding. In the dark you could actually see the spark jumping from plug wire to plug wire or plug wire to anything metal. Got new plug wires and regrounded everything, good to go. 

 
Dylanshaffer said:
Likely unrelated but I once had an engine misfire under load due to insufficient grounding. In the dark you could actually see the spark jumping from plug wire to plug wire or plug wire to anything metal. Got new plug wires and regrounded everything, good to go. 
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This is coil on plug set up so I don’t think I could see anything in the plug channel arc out. Could check the boots on the coils tho 👍🏻

 
You need to see 12+ regardless of temp. Save a motor bro.

 
John@Outfront said:
Yes sir. That is puke rich. And lots of power loss. You have heard “ lean is mean” well rich is lazy too. 
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So can I increase boost a few psi some and see if it helps? For test purposes before retune. 

 
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Not for boosted engines. I’ve often heard 12-13:1 but this guy wanted to use fuel to cool cylinder temperature to curb detonation 

 
BJ_buggyfab said:
So can I increase boost a few psi some and see if it helps? For test purposes before retune. 
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Won’t help. Air/fuel ratio is not even remotely close. Trying to suppress detonation by adding that much fuel is not smart nor promotes power. It’s actually harmful to the engine

 
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There are many factors to have detonation. And it’s always a balancing act between many factors. Air temp, fuel octane, static compression, boost, throttle position, ignition map,  cam profile, coolant temp and the list goes on, you can change any one or combination of them above to help.

increase octane, lower boost, lower static compression, pull timing, take your foot off the gas. etc. but one thing you don’t see that I listed is air’fuel ratio. There are ranges for optimum hp air/fuel rations and regardless of the other items mentioned above it should stay in those ranges. Using that as detonation suppression is the wrong method. On any engine!

 
It is possible to have a combination that just can’t work. I have customers all the time that come to me and simply say I have a 400 hp motor at 15psi on race gas and the motor has 10-1 compression ratio. and say I won’t to tune it for pump gas. That can’t work. I tell them you need to have someone else tune it so when you melt a piston you can cry elsewhere

 
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John@Outfront said:
There are many factors to have detonation. And it’s always a balancing act between many factors. Air temp, fuel octane, static compression, boost, throttle position, ignition map,  cam profile, coolant temp and the list goes on, you can change any one or combination of them above to help.

increase octane, lower boost, lower static compression, pull timing, take your foot off the gas. etc. but one thing you don’t see that I listed is air’fuel ratio. There are ranges for optimum hp air/fuel rations and regardless of the other items mentioned above it should stay in those ranges. Using that as detonation suppression is the wrong method. On any engine!
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This is the plug. I’ve noticed some guys in street Subaru set ups are saying 10 to 11.5 is ok. Possibly why my tuner aimed that way?

any case do I take it back to him and try again or lose the money and start over with another tuner. 🤔🤔

D0C1583F-BC57-4DA9-8558-AFE57B259F32.jpeg

 
onanysunday said:
You have an expert that has come into this thread telling you what to do.  :bangin:
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Sure but having John retune is not a great option at the moment. If it was i would have had him do it originally. I live out of state. 

 
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