ls1 backfire help

[madsav]

hi guys over time ive noticed that this problem seems to be getting worse .
its in my vt sedan 5.7 ,6speed manual
doing 60km/h in 4th gear if i hit the accelerator it will backfire and shutter then pick up the pace and go ,
same thing if im doing 60km/h in 3rd it has aslight shutter then goes .
Any ideas?
Replaced spark plugs with new set from holden
Replaced Spark plug leads with Top gun 10mm .
Was thinking of changing injectors and coils next

[oscar03]

could be a detonation issue how many ks has it done? also is it on gas? i'v seen this happen alot on gas fed cars.

[1SIKR8]

Also try change the fuel filter mate, might not be getting enough fuel

[madsav]

Running 95 unleaded no gas on the car, changed the fuel filter about amonth ago , and it's done 230,000k

[1SIKR8]

Try 98 and see if there is a change, could well be the coil packs

[oska]

a backfire on a EFI engine is impossible

sounds like you might have a transmission problem

[Sabby]

i had the same problem, and it was none of the above
it was the exhaust cable had melted away onto the extractors, have a look at that maybe

[matqld]

wHat are you doin 60kpm in 4th for bro LOL hehe, or evin in 3rd, LOL try second at 60 n floor'a :P much better approach..

[rb26dett]

Check your o2 sensors.

[madsav]

lol , i slap it back to 2nd t 60km/h and there is no backfire or shutter pure power, but when i have the clutch in and rev it same thing smooth rev no backfire.
seems to be only underload . its only started doing it worse since i put the pacemaker`s and cats in. i checked the o2 secsor seems to be fine .
only things i touched was spark plugs, leads and coils when putting the pacemakers in. so im guessing is 1 of the above.
set of coils from commwreck was $150

[itsagixa]

def sounds like a fueling issue, possibly a vacuum line aswell?

[stuntmanmike]

Could it be an exhaust leak somewhere between the headers and mufflers if not the coil packs/ignition leads?

[Not_An_Abba_Fan]

Check the plugs, it is very common to crack one when pulling them out and putting them back.

[madsav]

Hi again guys, just got back inside after playing wit hthe car again, mates got a vx 5.7, so i tryed his coils and leads on mine and the backfire is still there, 2morrow at work i will check the plugs like Not_An_Abba_Fan said.
Also there is no engine like or errors poping up. is it possable it might be 1 of the oxygen sensors? just checking over the things i touched just to be safe lol

[Big P]

I have a similar problem with my vt ss 5.0 auto its not on gas, only had a major service done on it including plugs, fuel filter and it had a new distributor and leads put on it roughly a year ago, the car has 275000 kms an runs great starts everytime, the problem is a misfire between 3500 and 4200 rpm after dat it pulls smooth and fast i have tried 91,95,98,v-power and e-10 fuel and its all de same no difference which 1 you have it on but here is de weird part its random, it could misfire everytime you put the foot down on a drive and on the way back it might not do it or maybe just the once the missfire its self is quiet harsh and could last 2 or 3 seconds i need help brain storming?

[rb26dett]

Sometimes the O2 sensors wont throw up a code.

[DLFHUB666]

I would say after installing new headers an cats, the o2 sensors will be farrked.

[machone]

when you change your headers and cats your tune is out i would say your car is running rich due to the performance modifications you have been doing which are messing with the A/F ratio...have it tuned the change in back pressure with your new system is likely causing issues

[madsav]

Hey guys, i checked the oxygen sensors today, they were full of soot so abit of WD40 and slap them back in problem still remained.
So i thought id do the easy thing and check the spark plugs and guess what?????
3rd spark plug on the drivers side was cracked in 2 lol so the car is running fine now cheers guys for the help
Also got a mailorder mafless tune and the oxygen sensors dont show up now very happy man

[phaedo]

Rather than start a new topic, I thought I would ask a similar question here. Bought a VU 18 months ago (LS1) from the Holden dealer, 100,000km. had it 300kms and a backfire started to occur. Turns out the issue was the same as what the OP has described - cracked plug. Fixed under warranty etc. However, didn't fix the issue. Has been to the Holden dealer 3 times to fix by which time I had lost 3 full days of work (use the ute for my business) and gave up with their incompetence. 25,000km later it still backfires. They apparently replaced 'some' of the 02 sensors, which they reckoned there were 2 per cylinder, yet another mechanic reckons there are only 2 (I think) in total, that didn't fix the problem, spark plugs were changed, a faulty HT lead was replaced, basically they decided it was 'electronic' and would need to look at it again, and maybe again, and again until they found the cause. As I said, I gave up on them.
Anyway, I am sick of the issue, it is happening when sitting at low revs - 1500rpm just cruising around 80kph, under load (when towing) under acceleration, when taking off from lights, the list goes on. But it seems to be a lot better when cold, and if at high revs it seems fine - if I get it to kick down a gear to bring the revs up, it will be fine at the higher revs. Thoughts? Maybe Holden didn't really change all the plugs perhaps, or broke one of the other ignition leads?

[DLFHUB666]

Hey phaedo
I would start by changing all the plugs an leads yourself, it could also be a coil pack. An there are only 2 o2 sensors on the vu ls1's.

[phaedo]

Ok, will do. Thanks for confirmation of there only being 2 oxygen sensors, I am wondering if the holden service dept. actually did anything in the first place...