spark knocking


New Member
Hello ,
I have a 99 Chevy 1500 4x4 350 ext cab. Anyway I have been hearing a knock coming from the engine under load ,going up hills ect. I didn't think this was spark knock, although that's what it was sounding like, because I have always used the same gas 90 octane with 10% ethanol blend. I was worried the noise I was hearing was maybe a piston or wrist pin. My truck is still under warranty so I took it to the dealer for inspection. The tech told me it was spark knocking because I was running the ethanol blended gas. He said he checked the fuel in the tank and it tested out to 8% ethanol. He said if the vehicle does not state it can run on blended fuel you should not use it! I am going to run what gas I have in the tank out then try some ethanol free fuel and see if I see a difference.
I would appreciate any comments on this because this is a new one on me .
my v6 dakota(99) would get spark knock if I didn't run mid-grade gas in it all the time. my v8 dakota does not have that problem.
my buddy that worked at the chrysler dealership said it is very common & they get alot of vehicles in with this problem.
That's baaaaloneeey. All vehicles should run at the octane listed in the owners manual, no matter what the "blend" In many areas of the country you cannot even get gas that isn't enthanol blended anymore. Anything up to 10% is fine, and 8% is below that limit.

Try going to 93 for a few tanks. If the knock goes away, feel good, its a spark knock and you can deal with it. Do or have an upper engine cleaning done to remove the deposits in the cylinders and check the other items below.

If its still there, head back to dealer because something esle is wrong. If you are technical enough, you may wish to check EGR operation, it might be hanging up and not working right, causing the knock. Also change the fuel filter, and check fuel pump pressure -might be running lean. Change the O2 sensor as well. Did the 99s still have a mechanical distributor? My 97 Tahoe did. Check base timing, maybe a bit high....

If this STILL doesn't fix it - there is something mechanical thrust bearing worn, rod knocking, wrist pins worn, etc. - check it out...

The downside to ethanol blend (of any amount) - it alchohol eats the rubber parts in the fuel system, one of the big culprits is the fuel pressure regulator, as well as various seals and gaskets. If its designed to run on 87 and you are running 90 - ethanol or not, it should not be pinging. Get it checked out and fixed!
tjthorson ,
thanks for the info. I agree with you . I think there is something else going on. I have ran the same gas in my trucks for the last ten years . 92,96 and my 99 Chevy all 350's and I have never heard the noise I am hearing.
I am under 1/4 of a tank and I am going to fill up with some good gas from Shell or amaco when I am empty . I will post the results.