my car all of a sudden seems to misfire in 5th gear when there is a high load...i changed the spark plugs and coil pack and it still doing it...im going to pick up plug wires later to see if thats the problem...anyone know what it could be ? thanks

 

Did you fix this issue? I'm getting the same problem but in 4th gear.

 

what kind of fuel are you running? Are you running meth?

 

this is crazy. my car jus started doing a misfire in 4th gear only. i only use shell 93 only n im runnin meth. only does it wen boostin like at 5700 rpm with the hta86. but regular driving its perfect. gotta setup n appointment with ivey ill post back wen i find out anything.

 

sounds like an overboost issue

 

i had the same problem once and it was the plugs. then it started up again and turned out I had to get a retune since the temperature started to get warmer.

 

I'm running Q16 with AFRs around 11.8-12.0 at 2.3Bar of boost on a GT4094R in AZ heat. Injector duty cycle is around 85 at the top of third gear.

I've replaced the plugs - No fix
Replaced the plug boots for the coils - No fix
Coils are less than 6 months old so don't want to replace until eliminated other possible causes

When I removed the plugs yesterday the plug for cylinder 1 looks different to the others. It looks like it is running leaner than the others.

Planning to pull injectors out and have them flow checked tomorrow. Other potential causes that I will be checking are.

- Injector seals. Seem to smell some fuel in the engine bay. This is the root cause I'm interested in looking into.
- Boost leak.
- Bad fuel. Had the fuel in a drum since Feb could have gone bad.
- Clogged fuel filter. Not likely since I would have noticed the car leaning out but worth a check if everything else doesn't identify the issue.
- Faulty fuel pumps. Not likely again since I would have noticed the car leaning out but worth a check too.

If all doesn't work I could just replace the whole ingition with a SparkTech coil on plug, and replace all of my injectors. But I'll do that when I start getting desperate for answers.

 

Sounds like we have similar issues. Does your car boost ok in 1st, 2nd and 3rd? I have no problems revving out those gears at WOT, but as soon as I get into 4th. Pop pop pop spat spat spat.

I was at Speedworld yesterday doing a run, everything was going well until 4th, so I let out at the 1/8 mile and ended up running a 12.5 at 90MPH lol.

 

I just had my injectors checked and cleaned. It turns out that one of my injectors is a little dirtier than the others. I'm hoping this is the cause of my problem. I plan to put the injectors back in later tonight. Will be running some tests on the car. Hopefully I can be back up for the track tomorrow night.

 

i had the problem i tried everything to fix it.. i just went tothe delaership and got a ecu flash 88$

 

I'm running the motec and constantly adjust my tune.

 

My issue is fixed. The problem was injector related.

- Had them flow checked where issues were found. Flowing 100%, 95%, 95%, 98%
- Had them cleaned. Now flowing 100%, 100%, 98%, 98%
- New seals

Put them on lastnight and the car is running good. Infact I'm breaking lose in 2nd now which hasn't happened before.

 

i found my problem also. it was my spark plugs. they were gapped too far apart. gapped them down to i think it was .20 really close n that has cured my spat. where do u go to get your injectors flow tested at.