Timing & Ping problem - HELP
Thread Starter
Pro
Joined: Jul 2004
Posts: 668
Likes: 3
From: Platteville WI
Timing & Ping problem - HELP
My engine was set up by a speed shop for 14 base and 34 total. I use the vac adv. It has a Comp Cam 268/280 duration and 477 lift. When I bought it in June, it was pinging under a load. I use 93 Shell V-power. I set the base timing back to 8. Didn't help much. I took it to the Chevy Dealer, to cure the pinging and rough run, who reset it 3 days ago to 14 and 34. There is more power again and it runs great. Except for the pinging. It runs nice at idle & flat roads & going downhill or basically no-load. It pings under slight acceleration going up hills, then, if I increase throttle, it gets louder until I'm about half down with the pedal, and it suddenly goes away. If I keep it there for a few seconds, it comes back. It also pings under WOT. So, anybody know why it seems ok under part throttle sometimes? The dist. bushings and springs were replaced in 2006 due to pinging problems according to service records. I'm not really enthused about playing with the dist. HELP.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
We need some engine *****. What carburetor? Do you know the compression ratio? Just from what you have here it sounds like a couple problems. First, it sounds like the power system is not comming in soon enough. This could account for the rattling on moderate throttle acceleration. You may be able to solve this with a different power valve setting. Also there is probably a problem with the WOT mixture being lean.
BigBlockk
Later.....
BigBlockk
Later.....
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
It sounds like your vacuum advance canister is adding too much advance. Disconnect the vacuum canister and plug the line and then test drive the car.
If the pinging goes away you should look at getting a vacuum canister that only adds about 10 degrees vacuum. The stock canisters can add 20 degrees which is too much when its coupled to an agressive mechanical advance.
If the problem remains even with the vacuum advance disconnected its possible that the mechanical advance is peaking too soon (at too low an rpm). You will have to open up the distributor and swap to heavier springs. This will not effect your total mechanical advance and you will still have the 14/34 settings. What it will do is slow the advance down and make it peak at a higher rpm.
Good luck.
If the pinging goes away you should look at getting a vacuum canister that only adds about 10 degrees vacuum. The stock canisters can add 20 degrees which is too much when its coupled to an agressive mechanical advance.
If the problem remains even with the vacuum advance disconnected its possible that the mechanical advance is peaking too soon (at too low an rpm). You will have to open up the distributor and swap to heavier springs. This will not effect your total mechanical advance and you will still have the 14/34 settings. What it will do is slow the advance down and make it peak at a higher rpm.
Good luck.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
At LEAST tell us something about the engine besides the cam. Cast iron heads? Compression ratio?
Thread Starter
Pro
Joined: Jul 2004
Posts: 668
Likes: 3
From: Platteville WI
1976 original block, bored 20? over to 355. Stock heads, manifold. Carb is original quad. Hooker headers and side pipes. Compression ratio unkown(original is 8.5:1). EGR disconnected and plugged. Vac adv connected to TPS on manifold and back to carb. Vac. at idle is only 7-8. Valves, lifters, pushrods, rockers all rebuilt OE stuff.
If the problem was noisy lifters, wouldn't I hear that as RPMs increase but regardless of load? I'll try the suggestion of disconnecting the vac. advance and test driving.
Thanks.
If the problem was noisy lifters, wouldn't I hear that as RPMs increase but regardless of load? I'll try the suggestion of disconnecting the vac. advance and test driving.
Thanks.
