Anyone experience misfires?

[jprescot]

Hey guys, I recently have been tuning my car on 93 and every time we try to tune it it keeps misfiring around cylinder five and six. Although I have built my engine and we change the spark plugs and coils and it was still doing it. Do you guys have any idea to why it’s misfiring, have you guys experienced this before?

Sponsored

 

[Thraxbert]

Random and intermittent misfires detectable only on a log?

Enough misfires to trigger the corresponding SAE codes?

Or spark blowout towards WOT without codes?

 

[jprescot]

Random and intermittent misfires detectable only on a log?

Enough misfires to trigger the corresponding SAE codes?

Or spark blowout towards WOT without codes?

We Put the car on the dyno and we noticed that the line dropped on the graph around 5000 RPM and we had to stop tuning. It was making power and then it just all the sudden dropped and misfired. The engine is blowing black smoke which is probably excess fuel.

 

[Thraxbert]

What's your spark gap, what plugs, what's your boost target, and what AFR are you seeing in these moments?

At first blush, this sounds like spark blowout. Gap is wrong, plug wrong heat level, coil boots might benefit from dielectric grease.

 

[zrk]

Although I have built my engine

you have a built engine and are tuned for 93?

It does sound like blowout though.

 

[jprescot]

you have a built engine and are tuned for 93?

It does sound like blowout though.

Yes

 

[jprescot]

What's your spark gap, what plugs, what's your boost target, and what AFR are you seeing in these moments?

At first blush, this sounds like spark blowout. Gap is wrong, plug wrong heat level, coil boots might benefit from dielectric grease.

we replaced the spark plugs with 2 step colder ones. Gapped at 18. Also upgraded the coil packs. Seemed to not be the issue.They are thinking it’s the DI injectors

 

[Thraxbert]

That gap is very small for 93. Try 0.025 to 0.028.

Do you have port injection? How is it implemented? What power level are you targeting?

 

[jprescot]

That gap is very small for 93. Try 0.025 to 0.028.

Do you have port injection? How is it implemented? What power level are you targeting?

Before it was 22 and was still misfiring. And yeah I have port. Power goal is 540 wheel and 620tq

 

[Thraxbert]

You have a built engine and port injection to target 540 wheel horsepower? Is this a troll post.

But reducing spark gap is usually the wrong answer, unless you're running really high boost and alcohol fuels. People make this mistake often, as there's a lot of bro science and bad advice out there about spark gap, but I feel it's a highly "over thought" topic at the power levels most people deal with.

I strongly encourage opening the gap back up toward 0.030. Especially at around 600HP, you could likely run up to 0.035 and still be fine. I also think 2 steps colder is total overkill. One step colder would be fine at this power level.

How is your port injection implemented?

 

[jprescot]

You have a built engine and port injection to target 540 wheel horsepower? Is this a troll post.

But reducing spark gap is usually the wrong answer, unless you're running really high boost and alcohol fuels. People make this mistake often, as there's a lot of bro science and bad advice out there about spark gap, but I feel it's a highly "over thought" topic at the power levels most people deal with.

I strongly encourage opening the gap back up toward 0.030. Especially at around 600HP, you could likely run up to 0.035 and still be fine. I also think 2 steps colder is total overkill. One step colder would be fine at this power level.

How is your port injection implemented?

Yeah I don’t have a massive turbo, I built my engine for sustainability. I have eos 750cc port.

 

[zrk]

This has to be a troll post. No one is going to build an engine for ‘sustainability’ or reliability. Built engines are often less reliable because.. well.. non factory parts.
The point is that they’ll take extreme horsepower at least a few times, so the car will make it down the track.

It doesn’t make them invincible. 540 is baby power on this motor.

OP, who built your motor/what specs/parts did you go with?

 

[jprescot]

This has to be a troll post. No one is going to build an engine for ‘sustainability’ or reliability. Built engines are often less reliable because.. well.. non factory parts.
The point is that they’ll take extreme horsepower at least a few times, so the car will make it down the track.

It doesn’t make them invincible. 540 is baby power on this motor.

OP, who built your motor/what specs/parts did you go with?

Not sure why this would be a troll post lol. There’s alot of other limiting factors when it comes to horsepower not just motor lol. Transmission, fuel pump, turbo. Don’t just expect someone builds a motor and gets 1000hp. That’s not my power goal first of all. And yes, No engine is invincible. Carillo rods, upgraded pistons.

Sponsored