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The dark shall be with us
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Discussion Starter #1 (Edited)
I'm having problem recently with my car that just started having lean stutter at full throttle and high boost. I have replied fuel filter and fuel pump socks so far and nothing changed. Even replaced the maf sensor with a new one. No idea what to look for since everything is new pretty much besides my afr. The injections, fuel pump, maft all are new. Spark plugs are only a couple thousands miles old. I did a Dyno run at a Dyno day and the first pull was totally fine and even ran rich. On the 2nd pull the car started running lean and stutter so he let off. What could cause this? I'm going to change the spark plugs again and see how it'll do. If not the. I'll rebuild the afr because it's pretty old but not sure how it'll cause it only under full throttle. Partial throttle under boost the car runs smooth. Could it be the fuel injection are clogged or maybe the fuel pump is bad? Can a bad e85 do that? Fuel is not that old and it didn't do it until recently with this fuel in the tank.

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Is the problem repeatable at WOT? Or intermittent?

Is the fuel pump hotwired?

A misfire (like spark blowout or other) can cause the wideband to read lean because of the unburnt O2 in the exhaust.

When you say "afr" what do you mean? AFR = air/fuel ratio to me... do you mean your fuel pressure regulator?
 

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The dark shall be with us
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7,344 Posts
Discussion Starter #3
Yeah fpr I meant. It's only under wot so I guess it could be spark blowout. I'm surprised the plugged didn't last that long though. Most miles on the car are racing miles but I was hoping to see them last more than 2-3k miles. I'll change plugs and report back.
Fuel pump had boost a pump on it and the guy did the Dyno said it's running a bit rich for e85. I have removed the boost a pump since I was thinking maybe something's wrong with it and I hot wired the pump instead. Even with hot wire pump I can make it run rich so I have plenty of fuel.
 

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The dark shall be with us
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7,344 Posts
Discussion Starter #5 (Edited)
I do but It's a gauge on the fpr itself so the only way to look at it is to put it on the Dyno. I'm thinking of removing my oil pressure gauge sensor and use the sensor for the fpr if changing plugs didn't solve the issue.

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The dark shall be with us
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7,344 Posts
Discussion Starter #6
I think I figured out the problem. My thermostat temperature is too low for e85 so sometimes I get incomplete burn. Today it was in the 70s outside and the car pulled all the way through no problem multiple times.

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1G Foglights b!tches
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misfire showing lean on gauge as others have said. new plugs, gap them down if you are that close to the limit.

I run 25psi+ no problem on e85 at 165-170* coolant temps. I would say that's basically irrelevant. (And that’s a lot of fuel volume with 11:1 on ethanol with a lot of methanol/water)
 
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