VicViper

Hi everyone,i have a 2001 gmc denali with a lq4,had a bad lifter and damaged the lobe of the cam,so i replaced it with a summit racing pro ls truck cam sum-8718,cam specs 205/217 112+2 .500/.500 lift,truck runs great but has misfire at idle,no misfires during wot or cruising,performed cam crank relearn with scan tool,so im getting p0300 and can see the misfires with my scan tool,i've read that aftermarket cams will cause this but from what summit said this cam shouldn't cause this

I have replaced the spark plugs,swapped coils,i performed a compression test before i started dissembling the motor to replace the cam and lifters and all was good,kind of in a bind right now and cant figure it out,i know the next step might be tuning so im thinking of getting hp tuner so i can fix the idle,i live in California and have read about tuning software and how it affects the cvn #,any help will be great,thanks.

G Atsma

Sounds like it might be in the tune. New cam threw the calibration off just enough to possibly lean it out at idle just enough to not fire occasionally.
Where in our fine valley are you? I live in Hanford, and have a 2004 Tahoe

SoCalDave

Did you keep the stock coils? Maybe try the original coils on your Denali before you do anything major. Sometimes new/different parts are not as good as the original part it replaced.

VicViper

I live in manteca,i think 1 coil has been replaced by previous owner,the top is black and the others are not,i might be able to swap the coils with another vehicle,i will try that

LilJayV10

iTrader: (39)

Is it actually misfiring or does the PCM just think it is?

Most of the time, you have to raise the misfire threshold at idle and lower speeds. The PCM will say it's misfiring when it's really not.

stockA4

hopefully it just needs this fixed, was it doing it before the cam swap?

Even the smallest cam will throw that 300 code in my experience though. I had a 212/218 115lsa in a stock 4.8 with a stock converter and it drove perfect with very little tuning but it threw that code right away even though it drove fine(stock 5.7 tune). I put that Same camshaft in a 6.2L that I just built and it "swallowed" the cam so to speak. Its very interesting to me really, it has very similar sound but louder, but all of the little rough stuff that you would hear at lower rpms with the smaller engine is completely missing now lol

00pooterSS

iTrader: (40)

I would absolutely start with a tune if it isn't tuned.

And can you actually feel it misfire? If so chase that down. If not, tune it. If you don't know for sure find a experienced mechanic or drive it by a performance shop and ask someone to sit in it and tell you what they think.

VicViper

thanks for the input,summit says it shouldn't cause a misfire,so yeah tune is going to be the next thing

andy burdess

I’ve used this cam and while they say not needed a tune really is. You need to optimize airflow and timing tables and lower the misfire sensitivity through out the idle portions of the tables and some light load off throttle portions as well. If you can get a read off of the computer with hp tuners or efi live id be willing to help you out with some of the data/tables that I’ve massaged for my set up.