Misfire at high RPMs

[Night479]

Hey guys i have a 91 talon awd and i just put a china bay turbo on (i know but i needed a quick cheap fix for my everyday driver b/c my stock turbo took a poop) and it a misfire at high rpms like 5500 to 6500. i have a 190 fuel pump and regulated it to the 38psi idle. new ngk spark plugs gapped at 32. i just gave it a top engine cleaning through the fuel rail to clean the stock injectors. the turbo runs good but just hicups at that rpm range. any help is welcome and i just have to say that this forum has helped me out a bunch and would like to say thanks to everyone.

 

[brute]

Which NGK plugs did you get? You can try shrinking the gap to 30, see if that helps at all.

You should also inspect your spark plug wires to see if there are any holes or cracks. Especially pay attention to the long piece that goes down into the spark plug wells. And while you're in there, make sure there's no oil down in the wells.

 

[jrohner]

You need to gap them to 28 or 26, 32 is too wide, at least it is after some mods. Make sure you have normal plugs (BPR6/7ES, BR6/7ES), not the spendy crap that doesn't work.

 

[alansupra94]

You need to gap them to 28 or 26, 32 is too wide, at least it is after some mods. Make sure you have normal plugs (BPR6/7ES, BR6/7ES), not the spendy crap that doesn't work.

I find it so funny that the standard copper NGKs always work the best. Everyone in the 2JZ supra field runs copper NGKs.

 

[rstchris]

I had this issue just a couple weeks ago, a quick tune up with lots of dielectric grease and i was golden.

 

[illeffekt vr-4]

Set the plug gap to 28 and lower the fuel pressure to 37psi and make sure the vacuum hose is disconnected from the regulator when you set it.

 

[kenamond]

+1 for NGK BPR6ES plugs gapped to 0.028". Also, what boost are you running? With a different turbo and WGA, it might be boosting higher than stock, and you could be leaning out on the top end.

 

[treckin]

^ Or he means 'fuel cut' rather than 'hiccuping' at WOT on the top-end.

 

[kenamond]

^ Or he means 'fuel cut' rather than 'hiccuping' at WOT on the top-end.

But I doubt he'd call fuel cut a missfire or hiccup.

 

[Night479]

im using the ngk's and ill try lowering the gap but i always thought that if ## not upping the boost you'd be fine it could very well be fuelcut out but i've never felt that before so if it is what do i do. i put injectors in b/c tuning and i dont want to over flow the injector by changing fuel pressure? im kinda s*it out of luck i ges. ill intall my boost contoller and take the boost done for now. thanks guy

 

[Night479]

im using the ngk's and ill try lowering the gap but i always thought that if ## not upping the boost you'd be fine it could very well be fuelcut out but i've never felt that before so if it is what do i do. i put injectors in b/c tuning and i dont want to over flow the injector by changing fuel pressure? im kinda s*it out of luck i ges. ill intall my boost contoller and take the boost done for now. thanks guy

sry that was i cant put injectors in

 

[Night479]

sry that was i cant put injectors in

and that was down sry about that stupid fingers

 

[kenamond]

The air/fuel mix the spark has to jump through is an insulator. If the gap is bigger, the spark has a harder time jumping. At high rpm, you're full boost and there is even more air/fuel crammed in the cylinder, and it's even harder for the spark to jump. 0.028" gap on BPR6ES plugs

Fuel cut feels like the motor blew for a second. The ECU cuts spark and fuel so the engine goes from full boost to nothing in a heartbeat.

 

[Dsmj89]

The air/fuel mix the spark has to jump through is an insulator. If the gap is bigger, the spark has a harder time jumping. At high rpm, you're full boost and there is even more air/fuel crammed in the cylinder, and it's even harder for the spark to jump. 0.028" gap on BPR6ES plugs

Fuel cut feels like the motor blew for a second. The ECU cuts spark and fuel so the engine goes from full boost to nothing in a heartbeat.

+1. 32 seems too big of a gap. What spark plugs do you have ? If you don't already have the bpr6's get them and have them gapped to .028 as mentioned.

 

[nkosi]

+1. 32 seems too big of a gap. What spark plugs do you have ? If you don't already have the bpr6's get them and have them gapped to .028 as mentioned.

I had that problem ...check the wires i had the same miss fire and thats what it was ...also the .032 gap is a little big ...bring it down to .028...

 

[Captain D]

I had a high rpm misfire with a new set of plug wires. The problem was I had one wire too close to the mounting bolt for the timing belt cover and it was shorting out the wire. I couldn't see the arc during daylight so I started the car in my garage in total darkness and the arcing wire was easy to spot.

How you install the plug wires is important. Obviously you want to keep the wires away from any metal that can act as a ground. You also want to keep wires to cylinders 1 and 4 away from wires 2 and 3 because they can induce voltage between them causing a misfire. You also want to avoid having the plug wires too high above the valve cover because they could short out against the hood when you close it.

 

[Night479]

hey thanks guy i found the problem the guy i bought the car from said it had the 190 fuelpump when it doesnt. could hear the pump surging after fuel cut and checked it so ya . easy fix though and thanks for the help ill also try a lower gap on those plugs.

 

[tnl]

Im having the exact same problem gonna try changing the plugs and wires this weeknd and c what happens. how loud is the fuel pump? i don't think id be able to hear no matter how loud it was over my exhaust.
and i think my plugs currently are ngk BP7s and my plug wires are msd 8.5mm