LT1 back fire

[paul67]

When cold no problem but when it gets warm about 10mins on tick over starts backfiring in the exhaust ,could this be an exhaust leak, due for ministry test thrusday.

[68TTT]

a friend of mine had a similar problem on his tahoe with a 5.3L. turned out to be a bad knock sensor. the computer was messing with the timing so bad it was causing bad backfires thru the exhaust. if you can get a scan tool on it you might be able to find out if any of the sensors have gone bad.

[Mark Smith]

did you recently wash the engine or get into some high standing water?could be the opti spark has moisture in it.

[TA219]

a friend of mine had a similar problem on his tahoe with a 5.3L. turned out to be a bad knock sensor. the computer was messing with the timing so bad it was causing bad backfires thru the exhaust. if you can get a scan tool on it you might be able to find out if any of the sensors have gone bad.

As soon as i read that this was happening after the engine is warm i thought about the knock sensor also. The LT1's were notorious for pulling timing, the LT4 knock modual may help your problem. This is a good part to have even if your LT1 KM isnt bad. and it is a easy / cheap thing to do.

[paul67]

Ok took it for test today, just about got there 5mls , if its under load ie going up hill it stumbles realy bad, but if i went manual in 1st about 4k revs it would go sort of ok till went back into drive at about 1500 then start to bog down , any way after getting to the test station and giving it a good revving ,black smoke comes out of drivers side, took 1 plug out realy sooty , rh side sort of ok, I'm sure it a faulty o2 ,managing to borrow an auto x ray scanner tomorrow friday so hopefully should know more.

[curly]

Your problem sounds just like my T/A. I have been told to check the O2s but I've ben too lazy to jack the car up to get to them . It feels like it has bad cam surge in the ~1600rpm range, almost like a torque convertor locking/unlocking. The guy that tuned the car told me that he would bet it was an O2 going bad (said I would not get a SES light until it actually failed).

I have got to get off my rear and get mine fixed so I will see what my heads / cam setup will really do! Good luck!

[TA219]

does your car still have the emissions equipment? specifically, the EGR valve? I dont think that would be it b/c the problem would probably happen all of the time if that were the case... but i thought i would throw it out there

Hurry and get that scan tool!!

[paul67]

No emissions,theres a small exhaust leak just in front of the O2 sensor going to fix that first monday and give another go.

[curly]

Who wouldn't have all of their emissions in place ? Let's just say that all of the stuff that's missing on my car has been 'tuned out'. I've wondered if there was a small leak (even after the O2s) on my car if that could cause false readings? I have read that running open headers can actually 'pull' air in after the 02s and cause problems? I have to take my car to an exhaust shop and have the over-the-axle pipe adjusted so it won't hit the axle on bumps so I might get them to run through the entire exhaust to see if I have any issues.

[paul67]

Ok been grovling about under car,removed O2 's , I had to splice the wire on 1 side as the O2 I had, had a differant plug,that is 1 that was playing up.
Lesson 1 been told you cannot splice sensors as they have a special cable.
Leason 2 If you are running O2 with a RED wire it has titainium,if it does not then it has a zercoinum , some cars you cannot mix which is what I have found with mine ,
Now trying to hunt down said O2.
Will keep you posted.

[paul67]

Well after hunting and found an O2 sensor I then found that the comp wires to the sensors were the wrong way round ,after market loom which did not matter till 1 side played up, looks like i have a duff injector on number 2 plug clean looks like when its put in, and not firing on number 1 cyl which is the cyl backfiring . Plug gap recomendations as to me 50"thou looks masive,bosch v groove plugs.

[paul67]

Well finally fitted a new opti spark ,fired it and it now running on 8 and i now have 2 black tyre marks on the drive, been like this for about 3 yrs running what i though was 7 cyl ,over time must have messed the o2 and thats what realy started messing the engine about and makng it back fire.

[curly]

Congrats! I know yuo are happy to have it running right again. I really need to get my 'gremlin' figured out and find out what the heads / cam will do .

[Lawrence]

Just in time for the weather to go crap again eh mate? Good news on the opti tho!