Detonation ping

[Rednek13x]

Ever since Iv owned my truck it would always just randomly should to make this rattling noise while driving down the road. Always thought it was a power steering pulley or something. And then this sprig it started to do it all the time so I started to look further into it. It really did it under load, i run pump 87. My truck is a 1983 c10 305 3 speed colum. All stock. Has 136,000 miles and I daily drive it 100 miles a day.

What I ended up doing was hooking up my vintage 10foot camper to it and pulled it down the road. Once warmed up sure enough it started making this god aweful rattle. So I unhooked and drive the truck a few days until the tank was empty. Then filled with premium 91 and dumped in some octane boost. Hooked up the camper and pulled it down the road and it never made a rattle. So I believe that's what's going on.

Iv tried adjusting the timing all over the place. The best seems to be 4deg at idle with the vac plugged off. That's where it's at now.

All summer Iv just been burning the 91 and havnt really had an issue. Just expensive.

Iv noticed it happens more when it's cooler out, it's getting into the 50s in the mornings and it's actually starting to what I think is ping even with the 91 octane in there.

Does this sound like an detonation issue, why in my soggy 305 does it seem like like a higher octane, even with a lousy timing. Why does colder weather effect this.

Winters coming and I'm driving the truck till the snow falls. Help me get this figured out before I loose a piston.

[MikeB]

Could be that 91 octane is the only cure. However, it certainly won't hurt to check all your vacuum lines for cracks or loose fitting ends, as well as any vacuum-driven devices such as brake booster and EGR valve. And there are other emissions control devices to which vacuum lines connect, such as as TVS, EFE, TVS and more. Even a small vacuum leak can cause detonation and run-on after the engine is shut off. There's a good section on the operation of the emissions devices in my 82 factory service manual. Bottom line: Also, make sure your heat riser valve is opening when the engine warms up.

Hey, a good start might be checking manifold vacuum at idle when the engine is cold, and when it's warmed up. I would estimate that on a stock engine you should see around 20". That doesn't mean there's not a leak at highway RPM and high load, but it's a start.

The problem is worse on cold days because cold air is denser, causing a already lean condition to be leaner.

Finally, what do your spark plugs look like? If almost white, that tells you the mixture is too lean. What you're looking for is tan to brown.

[Rednek13x]

Thanks for the reply! That's another thing I forgot to add! When I was running the 87 it would almost always "diesel" when I would turn the ignition off. With the 91 it doesn't do that. I will look over all the vacuum lines and devises that are hooked up. Last I checked the heater valve on the manifold was indeed working as should but I'll check again. I'll check plugs. Thanks again

[LT7A]

You might want to post this in the engine part of the forum too, but folks in this part are more familiar with your specific engine. I was going to recommend a liquid engine treatment to clean carbon out of the combustion chambers like Seafoam or Berryman B-12 Chemtool and I was not really tracking with the idea of the lean condition that MikeB mentioned. I figured carbon buildup was effectively raising your compression ratio by taking up space in the combustion chamber -- not uncommon. But more pinging in cooler temperature seemed opposite of what should happen. So I thought about Mike's assertion that there might be a lean condition. The vaporization of gasoline is part of what cools the mixture as it goes into the combustion chamber and so if there is denser air, i.e. a higher oxygen to fuel ratio, more pinging is conceivable. Another note is that your engine isn't particularly high mileage either. Let us know what your plugs look like, post pictures if you can. I'm thinking that you may need at least a carburetor adjustment or maybe a rebuild. If you can swing it, new plugs, cap and rotor, plug wires if possible, then have the carb rebuilt and get it tuned. You'll get a better tune with the new parts and probably save in the long run with the distance you drive. You should be able to go back to 87 octane and be burning less of it on a good tune. My personal preference would be to run good gas (Chevron where I live, or Shell if no Chevrons close enough) since the Techron in Chevron gas is an effective cleaner, and then run a reputable fuel system cleaner every few tanks. That way you are also chipping away at any potential problems of carbon buildup. My guess is that your carb is the main source of the problem assuming your timing is on, and that carbon may have been a secondary contributor. Let us know how it goes. Thanks

[cadillac_al]

Do you think the torque converter is staying locked up too much? That will make an engine lug and those lock up converters were new tech at the time. We had an 84 and the lock up converter was always confused.

[Dead Parrot]

I had a 79 Camaro with a 305 that had a minor pinging problem. Manual transmission. If I lugged the engine much at all at slow rpm, would get minor pings. Probably one or two slightly lean cylinders.

Check your THERMAC system for proper operation. If it is stuck on heat, your air mix could be too hot.

Does it want to idle too high? If so, supports the vacuum leak idea. Been chasing a leak on mine. Finally found one where the intake gasket between 2 and 4 had a 1/8 split in it. Did a temp patch with RTV and it is better. Still acts like there is a leak so going to pull the intake and install new gaskets at some point.

Check the riser valve on your exhaust system. If it is stuck partially closed, will both overheat the carb and put additional load on the engine with the increased back pressure.

[kwmech]

The intake manifolds in those years had a tendency to crack through the EGR system and create an internal vac leak. A 305 engine should not have a huge pinging problem unless there another problem, even on 87 octane. When it is cooler out, everything is shrunk down. As things heat up they expand creating a larger leak. Diagnose it or have it diagnosed by somebody that can figure it out. Don't just start by throwing parts at it.

[68longhorn]

I bought my 86 with 305/700r4 in 2008 at 105k, it currently has 197k and has always pinged for me. I ran 91 when i lived in MD and that helped but not perfect. Timing is 8degrees because less than that I have no power. Since moving to Florida i started running rec89 which is ethanol free and the pinging has gotten much better.

What is the ethanol content where you are? In MD we had 15 percent. Ethanol is a real problem for older vehicles

[Rednek13x]

it will be a few days before i can dig in and take a look. i am fully caepible with doing the work my self and have a pretty good understanding with how things effect and engine. i will take all things into consideration and give everything a good look.

mine a manual 3 speed. from a slow roll i can put it in 3rd gear and give it some gas, it lugs and pings. our fuel here is 10% ethenal. we do have 91 non oxy at most places. it does make things better but this truck should run no problem on the 10% eth 87.

what the thermac system?

truck idles right at 650. smooth, revs up and comes right back down real nice.