My 95 GMC c1500 has a 305 tbi in it and a 4l60e trans. when i'm driving down the road and my rpms are at about 1300, when i speed up without it downshifting there is a pinging sound (like metal on metal contact) and it gets harder and faster when i push the pedal more until it downshifts to pick up rpms then it goes away. what would be the cause of this? i run 89 octane fuel in it and it has newer injectors. could it be a timing issue causing detonation? at first i thought it was piston slap but then i heard it more clearly and that's not it. it also has a longer crank to start it after sitting overnight, about 5 seconds to start and after that it'll start the first 2 seconds all day long.

 

Pinging can be corrected by using a higher octane gas or retarding the timing, which will decrease performance. I have heard that if there is a lot of carbon build up at the top of the cylinder, it will get real hot and cause pre ignition.

 

It sounds like timing as you are already using 89 octane. I would check your timing, pull your plugs and check them for gap, oil, carbon buildup and replace if needed.

 

the plugs and wires are brand new on it, the old ones were factory plugs and wires. i have access to a timing light but i am always busy. would the timing also cause kind of a stumble at idle? every now and then it'll sound like a miss and drops the rpms down a little and it goes back to normal right away. but it almost died doing that today in park, it would stumble and rpms dropped to 400. i think i may need a timing chain if the timing is changing like that

 

The timing chains will stretch over the years. it still sounds like your timing just needs a little massage. My family have three an 89, 91, and 95. If you are time strapped just loosen the distributor hold down strap start the engine and turn the distributor just a little until the engine picks up a little rpm and tighten it down. Give it a quick run around the block. If you get the time, use the timing light but you may find it runs better with a little more advance. Good luck and let us know.

 

Stumble at idle could also be a dirty Idle Air Control valve, carbon build up at the throttle plate or even a really worn throttle bore...

 

i found out what the stumble at idle is now. driving to bowling league tonight and my check engine light comes on and starts idling like sh** so i pull over and pop the air cleaner lid off and my passenger side injector isn't spraying and the gasket for the pod broke and is spraying fuel directly into the throttle body. going to buy the entire tbi rebuild kit tomorrow morning and put new injectors in it, hopefully fixing the idle and i'll try doing the timing tomorrow after i get that done

 

use a higher octane like 91 or purchase an octane booster

 

new injectors in and runs great now with barely any stumble at idle, just need to adjust timing. thanks guys