johnnybravo

Got my ta last fall, so I drove it mostly with windows up in the cool weather til i put it away for the winter.

This spring when I got it out, the weather was fine, so a lot of driving with windows down and t-tops off.

Now I'm noticing what sounds like momentary octane rattle or knock. It happens when I shift into 2nd and 3rd, and get on it a wee bit at medium rpm's, usually when I'm going up a slight incline. I use 93 octane fuel, mostly sunoco, sometimes shell. I changed the fuel filter a few weeks ago, just in case. it was due for it anyway.

No ses lights on the dash or anything like that. I read something earlier about a recall on the cats. Could my cats be clogging up? I'm thinking of taking it to the local GM dealer to have it diagnosed, but I'd like to get a heads up on problems unique to the LS1 from you guys first.

Thanks,
John

*98Formula*

iTrader: (2)

It is possible to be rattle from low quality gas. Best way to make sure is to throw in some octane booster from autozone or something. Pour it in the tank and then take it out for a bit. If you leave the car sit for awhile it can cause this problem. I would put some booster in it then rip it up and down the road WOT a few times. This should clear up any build-up in the injectors. Try this first as it is cheap and then let us know if the problem returns.

johnnybravo

Low quality gas? I've been using sunoco for my regular cars for years. Did sunoco make some changes in their fuel that the LS1 motor is sensitive to?

Any suggestions on gas brands? We have shell, citgo, phillips 66, gas america, wal-mart. There are also several other sunoco locations in the area. Maybe the station I frequent has quality issues. I could try another sunoco station.

In the meantime, i will try some octane boost. I'll get back.
Thanks.

taintedmeat

iTrader: (1)

I get the same thing, and it's done it with any gas I've used. I've never been able to tell for sure if it's rattle coming from the motor, or a heatshield or something under the car. It usually only does it when it's hot out, and only right after it shifts like mentioned above. I don't think it's a huge problem since it's done it for the 2+ years I've owned the car, but not knowing what it is is pretty annoying.

Old Geezer

iTrader: (3)

Most octane boosters are junk, and raise the octane only tenths of a point, not full points as suggested on the bottle.
IE: "raises octane 3 points means as from 91, to 91.3, not 94.
Try adding a couple gallons of zylene to a tank of 93, and see what happens.
The knok could be real, as the engine load increases as you go up thru the gears....
Maybe a set of 1 range colder plugs, a look at the tune, engine op temp, etc, may give more clues.

*98Formula*

iTrader: (2)

All of these are valid points. I was trying to give him some cheap alternatives to try and determine if the problem is bad patch of gas or engine rattle. I have had this problem for about 2 years as well. Whenever I put octance booster or seafoam in the tank the problem goes away until I refill. Going to a colder plug will most likely fix my issues especially at higher RPMS. It only does it when it gets really hot out so my take on it is probably ping from to hot of spark plug. Going to a NGK-TR6 will fix it for the spring and summer but may have to back to NGK-TR55 during the winter.

Sneakyws6

Try resetting the ECM and see if it helps. My Formula did this once a trip for some reason when it had never exhibited it before. Reset the ECM and it went back to normal.

johnnybravo

Ok, I put in a bottle of 104+ brand octane boost. Like Old Geezer, I'm not much for octane boosters. I made sure I found one that cleans the injectors. I topped off the tank with 93 octane gas from another station.

I'll drive it this week down to a quarter tank or so to try and get the full benefit of the injector cleaning.

As far as the plugs, this was a one owner trade in when I bought it. I would assume the original plugs are still in there. If so, why would they be too hot? I could go to a colder plug if needed, but only if necessary. I just don't want to get into changing out parts ***** nilly if I'm not sure which part is the problem.

Thanks for the feedback, guys. if anyone else has any ideas or experience with this, I'm all ears.

Thanks,
John

Desert Rat

iTrader: (1)

There's a few things I've been told will help a ping. I'm going to be doing these, so I can't confirm yet they work.

160 degree thermostat - will help marginally by cooling operating temps
Adding a catch can in the path from the PCV to the intake to keep oil out of the combustion process.
There's a sticky at the top of this forum about Seafoaming your engine to remove carbon deposits.

There's 3 things to help a ping, FWIW.