alright ive been having this annoying problem with my lnf lately where the engine studders. if i start driving the car without it warming up it studders violently and i know thats how these di engines are but recently it has been alot worse since i had the head rebuilt. i will usually let it warm up to about 140F in the driveway and when i start driving through 1st it accelerates very very rough almost like in stages with constant pedal pressure. once its warmed up to 190F and im cruising at say 45 mph at about 1600 rpm it has a constant light studder (i think only because its in 5th gear). if i stick around 1500-2000 in 1st 2nd or 3rd its alot more noticeable. my afrs also bounce around a bit while its studdering from 13.5 to 15.5ish

when the engine is in higher rpms it runs great, no studder that i can feel and the afrs seem to stick around 14.5-14.9. cruising at 75 it runs great no problems there. the problem is between 1500-2000 rpm with light acceleration or cruising.

now possible causes that i have found:

spark plugs? i bought the cars with ngk bkr6es-11 which is a wide gap non-iridium plug and seems like totally not the right one for a turbo swap lnf. but no misfire codes ever so idk...

fuel pump? it feels like the fuel pump maybe going out but then why does it run great at higher rpm

and... to make it easier here are cliff notes

-studders violently when coolant temp is below 160F
-once warmed up still studders under light load/cruising between 1.5k to 2k rpm
-runs great over 2.5k rpm or under heavy load
-afrs bounce around 13.5-15.5 during studdering, at higher rpm they are stable around 14.7

any help would be apprecitated, maybe other lnf owners have the same problem?

 

Start with your basics.

Change your plugs back to stock ASAP.
Clean your MAF. A lot of driveablility issues can be cause by a dirty MAF in these cars.
Check and clean your MAP. Although that's more precautionary right now as I don't think it's part of your problem.
How many miles are on the car and why did you have your head rebuilt?

 

i dont have the stock plugs lol i bought the car with these. car has 31k on it and the head was rebuilt because redline was at 7k and i dropped a valve and chipped the piston. all replaced tho by a shop that specializes in cylinder heads.

i will try cleaning both sensors and see what that does. how bad does ur car studder if you dont let it warm up before driving?

 

Mine doesn't stutter at all unless I try and redline it and nls when under opperating temp (which is NEVER done and should never be done).

For now, until you can get new stock AC Delco plugs, re-gap the ones you have to .030.

Once you've done that and clean the sensors (mostly the MAF), check and see if it helps. We'll go from there if it doesn't.

 

stock gap on the plugs is .042 and i read it wasnt good to go under .035 with a wide gap plug so i regapped them to .035 and it is the same issue... im going to get new plugs and clean the sensors and i will post back here. i appreciate the help gremlin! if anyone else has ideas please post

 

Those plugs have got to be contributing. I gapped my stock AC Delco's to .030 and the car runs mint. 0 Misfires, ever.

 

hey bro just seen this. change your plugs!!! get the stockers and gap accordingly. id say start with .035 gappage and go down.. Has your car been retuned (Cuz if there is a issue it will more then likly be seen in the datalogging) hope that helps!

 

Start with plugs... but what about the head being rebuilt?

What was done to it? Were new seals installed for the fuel injectors if they were removed?

 

My first thought was plugs...but if you've done work to the engine then there are a host of other things that it could be related to. Do you have an aftermarket clutch? If so there might be an issue there

 

yeah im going to change the plugs this week and get that bung welded in for the boost reference then i will head over for a tune. we shall see

fuel injectors were never pulled because the head i bought already had injectors thanks to chevycobaltss3!

clutch has to be aftermarket to hold the power. it scares me to think its the clutch and it does kinda feel like a clutch issue but the afrs get kinda wacky when it studders and makes me think its engine related

 

Yeah it actually sounds plug related lol....... Have u changed the plugs yet bro...

And did they leave the injectors in the head when they acid tanked it and did the milling?

 

If they did that, I would never go back to them ever again lol. Shame on them! haha

Plugs, dude. Do the plugs!

 

you're scaring me mark haha they might have milled the head but they definitely did not acid tank it... im 99% sure they kept the injectors in but if they didnt and the seals were leaking, wouldnt it be a completely different issue? i want to rule out the busted seal idea to make me feel better...

ok spark plugs are ready to be picked up, im going with the stock ac delcos and gapping them down to .030, got them for 5.24 a piece booyah anyway stay tuned for update with that

 

yeah i was thinking plugs or sensors too stay with stock plugs

 

changed the plugs about 30 min ago and... poof... every issue is completely gone! im so happy now and im back to lovin my ss/tc. afrs are smack dab at 14.7 all the time, the car idles so smooth now i cant even tell the engine is running, and no studders even when the engine is still cold. thanks for all the help guys! car has never ran this good since i got it!

 

Told yuh so lol... Btw my name is james

 

I'd like to turn your attention to post #2

 

^^^ ahh hahaha got u beat he called and asked me and i.said it before u so i win damnit.... Ah hahaahahah

 

:lol" lame.

At least it's fixed and it wasn't anything serious.

 

Yeah thats a good thing. Lol

 

Most LNF's run a gap of .032-.035. Id either pick up a set of stock plugs(41-108) or NGK 3787. Check the maf and map sensors for residue. Any codes? Like maybe a Evap purge code? Ive heard of many LNF's (mine included) with that studder cruising around 2k rpm. Mine did it stock and once Trifecta tuned. It went away when I switched to my E60 BYT tune. I also has BYT turn off cat warm up which completely took away the bucking your getting if you dont let the car warm up.

FML!!!

 

nailed it.. thanks for the help

ding ding ding. thanks for all the help mark i mean james haha sry i think i got you confused with exsoccer1921

haha thanks anyway man, im glad its running great again