so i went out for a drive on a cold night and i did a 3rd gear pull and between 3500-5000 rpm i started to get a sputter and or misfire at wot. i changed plugs the next day and the problem went away. i then began to have the same problem again after about 1k miles. it seems to get increasingly worse the colder it gets outside. i feel a slight hesitation and hear a pop out of the exhaust. any ideas what the problem could be? AFR is usually between 12.5 and 11.3 when it happens. i recently installed PTE 880cc injectors.

im currently using NGK iridium 8 heat range plugs
factory original coils
magnecor wires

 

did u gap the new plugs or just toss them in?

 

they are at .022. the problem started on br7es plugs gapped at .018

 

update....

switched to tephra mod which made a huge difference. however im still getting a misfire the moment i hit 4k rpm at wot. afr goes from mid 11s to 10.0 the moment it misses. if i go part throttle, it wont misfire all the way up to redline, but the moment its wot it misses. im starting to think its ignition related.

anybody?

 

Has your boost increased with the colder weather? I usually have to go down 1 round on my mbc during the winter to compensate for the lower temps. Sounds almost like fuel cut/overboost.

 

i first started having the problem at 24psi. i then turned it down to its current setting at 20-21psi.

 

ill try it down at 18ish psi and see what happens.

 

You have a boost gauge? And you been watching it during WOT runs? Do you know for a fact that the boost had increased since the weather got colder? You have ECU controlled boost? How cold has it been when you do these test runs?

 

Has it been getting down near freezing where you are located? Here in Logan, UT, it started getting real chilly since a couple nights ago. BRRRRR!

 

i have a defi boost gauge. and i have a hallman pro set at 21 psi. boost doesnt spike any higher than 21psi on the gauge. and it is now anywhere between 20 and 50 degrees out. also at 4330ft elevation

 

Rule of thumb: The ratio is about 1:10. That is + or - 1 PSI of boost for every 10*F. of change in the ambient air temp. So, if the air temp drops 30 degrees then your boost boost will rise approximately 3 PSI.

 

Do you know which Forge Racing actuator is on your turbo? Is it the newer piston-style or the older diaphragm type?

 

u guessed it. it was boost spikes. ended up turning the hallman down 4 full turns and now it peaks at 20 psi. i need to update my signature, im no longer using the forge wga. im using the one that came with my 20g. so im guessing its oem spec.

 

When there are drastic swings between minimum and maximum ambient air temps you need to be extra careful with peak boost levels. This is especially the case if you are using a MBC as you are. Also be conscious of the fact that perhaps originally you set your boost level peak during the warmer spring months, so air temps have changed significantly since then.

I find that when using a MBC it is best to set peak boost level, that is, do your test runs during the time of day when ambient air temps are at their coldest at night. This way even though your boost level will peak at about 3 PSI less during the day, but at night you won't be overboosting by 3-4 PSI. Otherwise you'll need to adjust boost twice a day.

Keep in mind that although it may not have manifested itself during the warmer months of the year, your turbo may have been on the verge of boost creep. But, during the summer months it was just not noticeable. Now with the colder weather, it may be looking to creep. So, just be careful.

You can try adjusting your MBC knob all the way out counterclockwise to the lowest possible boost setting. Do a 3rd, or 4th gear WOT run with the MBC set this way. See what your peakboost level is and keep an eye on the gauge to see if it creeps after reaching peak boost.

 

that makes sense. i did 3rd-4th gear pulls and at 3600 rpm im hitting 17psi and it creeps to 20-21 by redline. is boost creep something ill just have to deal with or is there a good solution to this?