Engine Pinging - I've tried everything

Engine Pinging - I've tried everything

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I live at 4000ft elevation. My 1979 Chev Caprice (350 V8 engine) runs like a million bucks at just under 200,000 miles.

When I take road trips, once my car gets down to 2000 ft I start getting intermittant engine ping. I can usually feather the throttle to find a throttle position the car is happy with.

At sea level, no such luck. I absolutely cannot get the relentleess engine pinging to go away. The fact this engine has torn itself apart just shows what a fantastic engine the 350 is. Nevertheless, it has mechanical vacuum advance. I have tried every conceivable timing position at sea level, nothing helps the pinging problem.

Higher octane gas if of little use. No noticeable improvement.

Engine is in tip-top shape, no vacuum leaks, EGR works, EGR passageways squeaky clean, EFE works, thermac works, etc. No knock sensor or computer controls in this car. Just vacuum driven advance.

It can't be the timing chain or anything mechanical, cause once I climb a long grade and get above 3000ft, it purrs like a kitten.

Its only a 3spd (no overdrive), so downshifting isn't an option at freeway speeds.

I've read that GM sold "high altitude carbs" for cars delivered to certain markets... is that true? I also read that some 70s carbs had "aneroid altitude compensators" that were supposed to raise and lower metering rods to adjust fuel mixture? ... I've got not clue whatever that is or looks like???

Would appreciate any thoughts or experience on that.

It's gotta be either fuel mixture (more oxygen so leaner at sea level), or maybe at sea level the ported vacuum is different and timing doesn't advance properly?

Hope someone can help me with this, riddle I haven't been able to solve.

Thanks

I've hears the same thing about "high altitude" cars. Perhaps you have one. Have you tried running a can of GM Top Engine Cleaner through it? Get the aerosol version and give it try. Maybe there are some carbon deposits that need knocked loose.....

Engine Pinging - I've tried everything

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I live at 4000ft elevation. My 1979 Chev Caprice (350 V8 engine) runs like a million bucks at just under 200,000 miles.

When I take road trips, once my car gets down to 2000 ft I start getting intermittant engine ping. I can usually feather the throttle to find a throttle position the car is happy with.

At sea level, no such luck. I absolutely cannot get the relentleess engine pinging to go away. The fact this engine has torn itself apart just shows what a fantastic engine the 350 is. Nevertheless, it has mechanical vacuum advance. I have tried every conceivable timing position at sea level, nothing helps the pinging problem.

Higher octane gas if of little use. No noticeable improvement.

Engine is in tip-top shape, no vacuum leaks, EGR works, EGR passageways squeaky clean, EFE works, thermac works, etc. No knock sensor or computer controls in this car. Just vacuum driven advance.

It can't be the timing chain or anything mechanical, cause once I climb a long grade and get above 3000ft, it purrs like a kitten.

Its only a 3spd (no overdrive), so downshifting isn't an option at freeway speeds.

I've read that GM sold "high altitude carbs" for cars delivered to certain markets... is that true? I also read that some 70s carbs had "aneroid altitude compensators" that were supposed to raise and lower metering rods to adjust fuel mixture? ... I've got not clue whatever that is or looks like???

Would appreciate any thoughts or experience on that.

It's gotta be either fuel mixture (more oxygen so leaner at sea level), or maybe at sea level the ported vacuum is different and timing doesn't advance properly?

Hope someone can help me with this, riddle I haven't been able to solve.

Thanks

What type of fuel does the car's book say to use? Try e-10 or some other octane-enhanced fuel. Obviously you're not having any mechanical problems.

Engine Pinging - I've tried everything

--------------------------------------------------------------------------------

I live at 4000ft elevation. My 1979 Chev Caprice (350 V8 engine) runs like a million bucks at just under 200,000 miles.

When I take road trips, once my car gets down to 2000 ft I start getting intermittant engine ping. I can usually feather the throttle to find a throttle position the car is happy with.

At sea level, no such luck. I absolutely cannot get the relentleess engine pinging to go away. The fact this engine has torn itself apart just shows what a fantastic engine the 350 is. Nevertheless, it has mechanical vacuum advance. I have tried every conceivable timing position at sea level, nothing helps the pinging problem.

Higher octane gas if of little use. No noticeable improvement.

Engine is in tip-top shape, no vacuum leaks, EGR works, EGR passageways squeaky clean, EFE works, thermac works, etc. No knock sensor or computer controls in this car. Just vacuum driven advance.

It can't be the timing chain or anything mechanical, cause once I climb a long grade and get above 3000ft, it purrs like a kitten.

Its only a 3spd (no overdrive), so downshifting isn't an option at freeway speeds.

I've read that GM sold "high altitude carbs" for cars delivered to certain markets... is that true? I also read that some 70s carbs had "aneroid altitude compensators" that were supposed to raise and lower metering rods to adjust fuel mixture? ... I've got not clue whatever that is or looks like???

Would appreciate any thoughts or experience on that.

It's gotta be either fuel mixture (more oxygen so leaner at sea level), or maybe at sea level the ported vacuum is different and timing doesn't advance properly?

Hope someone can help me with this, riddle I haven't been able to solve.

Thanks

There could be some other issue causing the problem, but high-altitude carbs are jetted at a slightly leaner A/F ratio to maintain the 14:1 balance. Running it in the lower altitudes can cause it to lean out too far. Your car has the M4MC carb, made in the mid 70s - 1980. The aneroid is a bellows-like device that mounts inside the bowl area of the carb, and it is adjustable (if I remember right, you have to take the top off to get to it. It's been 13 years since I had one). The aneroid is located in the lower left of the carb, if you look directly down at it with the bowl facing you. It is in the place where the later E4ME carb has its M/C solenoid connector.

Yeah my '84 is having similar pinging problems. The problem sure isnt mechanical in your case. I use premium fuel and it helps a lot. other than that, there is this product called Seafoam. it is great. buy 3 bottles. with the engine running at idle, pour one into the carb throat until the car stalls. let it sit for around 30 minutes (i know it says five but trust me). for this to work best you will have to warm up the engine first. after 30 minutes start the engine and take off. there will be a lot of smoke so it is best to do it in a place where you can go full out and not have to stop. do some hard accels to work the carbon deposits out of your engine. at your next fill up, add the remaining seafoam to your tank. this will continue to help clean things out.
this helped a LOT for me.

Bought my car in South Dakota (about 3300ft ASL). As we moved east, it developed the same kinda problem (and we have C3).

Premium fuel helps, but Seafoam blasted enough carbon loose to allow me to run regular.

The carb was rebuilt at 80k, and replaced at 350k.

I'd have a look at the vacuum advance can to ensure it's functioning, and the distributor advance springs may be a little tred after 200k miles.

Thanks for the feedback. It sounds like it is fuel mixture related. Now that I know where the "aneroid altitude compensator" is, I might try lubricating or adjusting that. Might be seized up.

I've run GM Top Engine Cleaner through it. Lots of smoke, but no noticeable improvement. So don't think carbon is an issue.

Car runs great at 4000 ft on 85/87, but at sea level, even 91 won't keep it quiet. I"ve tried lots of octane boosters and they didn't work either, at least not noticeably.

Just so you all know: I've been told that apparently those octane boosters you buy from the store, that are called (+5), (+8) etc... its actually 0.5 or 0.8 extra octane you're getting...they conveniently omit the decimal when they market the product!

So to go from 87 to 89 octane, you'd have to buy 3 bottles to treat a given volume of gas. So you're usually better off opting for the extra 10-20cents/gallon than the cost of the treatments in a bottle. FYI

Thanks for the info.

There used to be a carbon buster, probably comparable to Seafoam, that was largely an ammonia and water mixture. We would pour it down the carb with the engine running and it would blast the deposits off the pistons, valves, etc. It usually worked well.

I've also seen real old timers do the same thing with just plain water down the carb. They would pour about a quart in with the engine running, holding the throttle open so it wouldn't stall.

Bob

I heard if you use just water though, and the engine does stall, then you can get something called hydolock?? Supposedly it destroys the engine if it happens.

That's hydro-static lock. It usually involves a lot of water, either by vandalism or a serious water jacket leak.

I've never had a problem with it, the trick is to pour very slowly and keep the revs up. You would have to dump the whole quart into the motor with it being off, then try to start it to do some damage. Water will compress to a point, but not very much.

If the car is hot and running and you did happen to stall it out accidentally, most of it would evaporate due to the heat within seconds. Again, this is an old time mechanic trick and if you are not comfortable doing it, don't do it.

That's hydro-static lock. It usually involves a lot of water, either by vandalism or a serious water jacket leak.

I've never had a problem with it, the trick is to pour very slowly and keep the revs up. You would have to dump the whole quart into the motor with it being off, then try to start it to do some damage. Water will compress to a point, but not very much.

If the car is hot and running and you did happen to stall it out accidentally, most of it would evaporate due to the heat within seconds. Again, this is an old time mechanic trick and if you are not comfortable doing it, don't do it.

Water does NOT compress, not even one cubic centimeter in a 150-ton reservoir. Hydrolock, or hydrostatic lock, is definitely possible with this procedure. As you have said, the trick is to keep the RPMs up and slowly pour in the water. Though, I would use a cup and not a quart. At the least, a hydrolock will blow your head gaskets and can cause bent rods, spun bearings, bent valves and broken pistons. Proceed carefully! RPM = 2000 and no less during the procedure.

FWIW, I've done this procedure numerous times over the years with great success, but know the pitfalls of a potential failure so you can keep your senses during the procedure.

If you do this, immediately afterward, take the car out to a long stretch of empty road and WOT to 60MPH or so, coast down to 30, WOT to 60 etc. Do this 5 times as if you're breaking in a brand new engine. This will clear any remaining combustion chamber carbon and run it out the tailpipe.

Well guys, I tried the wwater trick.... I kept the engine at 3000 RPM and while pouring the water down its kinda stumbled down to the 1800-2200 rpm range, but I kept very steady and used all senses to make sure the engine didn't die. I used about one quart of water total Afterwards I took the car out and kept it at WOT letting it get to about 4500 - 5000 RPM before letting the tranny shift gears, and bringing the car up to about 70 MPH and then back down and then repeated a few times. After that I took the car home at a normal pace, and it really did help. There wasn't anything wrong with my engine to begin with (I did it out of curiosity) but it made the car run much better. Its idles smoother, accelerates stonger, and is more responsive. It wasn't any drastic improvement, but it was definately noticable. Tomorrow, I'm gonna try it on my '89 GMC Sierra (4 Bolt Main 350, TBI)

I'm just wondering one thing... how could something like just water do so mcuh to remove carbon?

I'm just wondering one thing... how could something like just water do so mcuh to remove carbon?

Same way steam can clean an engine. The water soaks into the carbon and the expanding steam breaks it up.

Wow... Thats pretty "cool". It did wonders on my truck today too.

That's one of he main reasons that SeaFoam helps clean engines. It is 40% water. Instead of a $6 can of oily water with some rubbing alcohol in it, I use regular water, a vacuum hose, and a small valve to meter/administer the water. The small amount of water administered by engine vacuum nearly eliminates the possibility of hydrolock, and provides enough water vapor to effectively loosen carbon and fuel additive deposits.

If you're feeling really loose with your cash, you can use windshield washer solvent (water with methanol mixed in) to help clean the chambers. At 99¢ a gallon, it's still more cost effective than SeaFoam, and works better.

If you want a real anaylsis of SeaFoam, check the threads at www.thirdgen.org, and you'll see why you'll NEVER want to use this as a fuel additive in an injected engine. Then again, it's your warranty.