Famous miss/ studder/ cut out at wot

[RS12Turbo]

well...it's back. Last time it happened it was a vac hose was leaking. This time, vac hoses are good. Unplugged each coil pack one at a time, and the engine ran rough when i unplugged each one......so I assume they are good. Where should i check next...plugs? They've been in there for a good year+. One degree colder ngk iridiums.....wonder if they're fouling out? What else should I check...thanks

[Ca_Silvia]

MAF-try the swap testorYour hitting boost cut, did you up the boost recently?

[RS12Turbo]

Nope...same boost, about 12-13psi. Been at the same boost for a couple of years.I'll try cleaning the maf.......as I don't have another one except my ca18et maf, which looks identical, but not sure if they are the same

[Ca_Silvia]

definatly not the same maf, Strange that at 12-13 this happen all-of-a-sudden. When i was rocking my CA MAF i was hitting fuel/boost cut around 12psi.

Good luck man

[KEMP]

i have had the same problem plenty. i finally fixed it.

i cleaned the MAF with maf cleaner, i mounted the power transistor to the shock tower, and ran a seperate ground wire from it to another body part, then i also cleaned out all the idle control and that whole block of BS, with carb cleaner, and it runs fine.

[RS12Turbo]

Good to know.....I'll try all of that and see if it cures it. Thanks a bunch

[MeanGreenS13]

try changing plugs. i had a cracked plug and i didnt even know it causing breakup at WOT on my Green S13 with SR20

[RS12Turbo]

Think I got it taken care of.......Replaced the ngk iridiums with an old set of ngk coppers (with low miles), cleaned coil pack connectors/ plugs with maf cleaner, cleaned maf and maf plug/ connector with crc maf cleaner, sucked down some throttle cleaner through intake mani vac line, and added a ground strap from the ignitor to the head.Not sure which of these cured it but no more studder all the way to redline @ 15-16 psi.Thanks for all of the help everyone

[Nali]

Think I got it taken care of.......Replaced the ngk iridiums with an old set of ngk coppers (with low miles), cleaned coil pack connectors/ plugs with maf cleaner, cleaned maf and maf plug/ connector with crc maf cleaner, sucked down some throttle cleaner through intake mani vac line, and added a ground strap from the ignitor to the head.Not sure which of these cured it but no more studder all the way to redline @ 15-16 psi.Thanks for all of the help everyone

We really do need to get a sticky version of the dreaded CA studder fix.

I personally have had this problem like 3 times. And new threads start every few months.If anyone has the time to get all the solutions together, please do.If i have time the weekend and no one has on done, ill do my best by going through all the old threads and getting everyones solutions in listing them.

SO far it seems these are always listed.MAFSSparkplugsCoilpacks.Bad groundinga general clean of the intake stuffs.etc......

[RS12Turbo]

Well......looks like I spoke too soon. Symptoms returned

One of my buddies told me maybe it's leaning out or running rich and I should try adjusting the s-afc at the rpms it starts cutting out. It starts around 3200 rpms at wot. My afc settings from there to 4200 rpms was -9 which all of my settings were set a couple of years ago when dyno tuned. Anywho, I tried to richen it up from -9 to -1......that seemed to make it a whole lot worse. Next I leaned it out some more from -9 to -15....and now once again the studder has vanished . I'll check it out again tomorrow and see if it comes back...hopefully this was the problem....but if it is.....what would make the settings I have been using not be any good anymore Stock fpr crapping out? bad O2 sensor? I really need to hook up my wide band

[Anu]

I dont think the stock o2 sensor causes the problem, afaik the o2 sensor signal has no influence when on WOT .

I also had some problemen with studdering, for me it starten on WOT around 4k rpm, causes by a slightly loose CAS sensor cable, the vibration of the engine caused the cable to loose connection at times, causing the studdering, perhaps you have a loose wire somewhere as well?

[RS12Turbo]

Leaning the safc settings out seemed to take care of it. I'm going to blame the stock fpr dumping too much fuel from the walbro 255. I'll report back if the studder returns

[progman]

Check your fuel pressure. It probably change a lot. An engine will run a quite a large range of A/F ratios. at WOT it is more sensitive but if your feeling something wrong then it is probably below 10:1 or higher than 14:1, any black smoke at WOT? 10:1 will make black smoke.

Anu is right, the o2 sensor does not come into play when at WOT. The computer is reading directly from your MAF and other sensors.

[RS12Turbo]

No visible black smoke........so if there was, it was very light. I know when I got it dyno tuned a couple years back the base line afr's were off the chart....lower than 10:1, thats why they leaned out the afc settings. How about the coolant temp sensor....doesn't that play a role in the afr's?I'll check out the fuel pressure.....what should it be again at idle? Like I said though......no more studdering at wot

[Ca_Silvia]

No visible black smoke........so if there was, it was very light. I know when I got it dyno tuned a couple years back the base line afr's were off the chart....lower than 10:1, thats why they leaned out the afc settings. How about the coolant temp sensor....doesn't that play a role in the afr's?I'll check out the fuel pressure.....what should it be again at idle? Like I said though......no more studdering at wot

Yes, your coolent temp sensor plays a big role and its cheap and easy to do. But if its running better now then i wouldn't worry about it.

[RS12Turbo]

Yeah..thats what I thought. I'm getting ready to pull the head off to put on a Cometic HG, and my custom top mounty....so i'll go ahead and throw a new water temp sensor on, especially since i'll finally be installing my wide band...that way I can just start fresh with the afc settings

[RS12Turbo]

Arg....it's back!

I'm starting to think it's my walbro 255 or stock fpr. Today I noticed my fuel pressure gauge under the hood was 22-24 psi @ idle. Not sure off hand what the pressure is suppose to be at idle...but i'm thinking it should be closer to 30psi

[r34 gtr]

Well, I know its 36psi static, but I don't know, 22psi at idle doesn't sound so bad. Haha I was just about to offer to go measure mine real quick but I just remembered my engine block is in a Rubbermaid container under my parent's house. Sorry!!

[RS12Turbo]

Just remembered....lol. Thanks anyways

[r34 gtr]

Hey sometimes it slips my mind. I'm so used to it just being there, parked outside, that I just sort of take it for granted.

[RS12Turbo]

So I am in the process of unplugging all of the harness connectors on top of the motor, so I can pull the head and noticed the knock sensor harness plug was just laying there unplugged. Could this cause the miss/ studder issue?

[ser20det]

Well, I know its 36psi static, but I don't know, 22psi at idle doesn't sound so bad. Haha I was just about to offer to go measure mine real quick but I just remembered my engine block is in a Rubbermaid container under my parent's house. Sorry!!

suppose to be 28psi at idle.