Hi all,

The problem with my car is, the car cuts and has extreme misfires at high rpms (after 5500 rpm). I found out that the misfire is gone if i tune it leaner (like AFR>12.0) but the misfire continues increasingly as i enrichen the AF mix. I tend to use low 11.0s as I'm boosting around 14 psi. Also another thing I've found out is that, the misfire is more severe with the increasing boost pressure. It looks like the ignition is not working correctly, and it is not enough for the power produced. I've installed new plugs (gapped for FI), coils, HKS DLI II, grounding kit etc to solve it but they helped only a little bit.
I'm getting multiple misfire codes all the time and nothing else. I've read somewhere in iATN network some guy mentioning a problem like this and he says he changed the variable timing oil control valves to solve the issue, do you think this can also solve my issue ?

The changes I've made to the car before the problem started were:

Cosworth cylinder heads,
Scott's Stage2 Cams,
New valve buckets to maintain the valve lash with in specs.

The car is in the shop for 1.5 months now and I'd greatly appriciate if anyone has any kind of information or idea to solve the issue.

 

BTW I'm using 3 different AFR gauges on the car to ensure that i'm not getting false readings about AFR ( TXS Tuner, AEM and Motec gauges).

 

it sounds odd, but have you tried putting a stock plug gap back on the plugs? a few people have reported more misfires with tighter plug gaps.

I am having a misfire problem at high rpm too. (flashing CEL) only at the top of 4th and 5th gears. I am going to try copper NGKs at stock gap. I have them here; I just haven't gotten around to installing them yet.

 

closing the gap does not cause misfire. Keeping the gap open leaves the spark a chance to be blown out (which is likely what is happening to him)

 

yeah tried plugs with larger gaps too but didnt help.

 

Did u ever fix this Problem

 

If you look at mistaboosta's posts he hasn't been on since 2007. I doubt he will reply. However, he did solve his ignition problem:

https://my350z.com/forum/3792672-post51.html

 

Ha I was thinking 'I wonder if he has a UTEC'.

 

I'm having a similar prob. How he fix it?