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Old 06-04-2012, 01:11 PM   #1
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Unhappy engine ping with accelleration backfire

Hello again!

I posted a few months ago about my engine pinging (knock?) and an intermittent mis. Well the mis is taken care of but I still have the following problem:

When I am accelerating, moderate and up, I hear what sounds like a pinging noise in the engine. If I don't let up on the accelerator the engine will start backfiring, acting like it wants to die out. I have to ease off and accelerate much slower which is a real problem, especially entering a freeway. I might go almost a mile just to get up to 45mph. Seems like more than just a backfire; the engine seems to momentarily want to shut down. I would like to hook it up to a diagnostic machine but I live in Santa Barbara, Ca which is no-man's-land for RV or truck repair facilitates. I have replaced the plugs (wires were good), distributor cap, and rotor. Helped a little but not much.

This is a 1984 Holiday Rambler Imperial, 34', p30 (32?), 454 engine with carburator, and 91,000 well maintained miles. Owned it for almost 20 years. I'm also afraid of this causing more severe engine damage.

So there's my problem. Sure would appreciate any help you folks might have. Also if anyone lives in this area a recommendation for a good mechanic.

Thanks for any and all help.

nakoni
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Old 06-04-2012, 01:33 PM   #2
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Have you checked the fuel filters? Do not forget the one in the carburator.
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Old 06-04-2012, 01:48 PM   #3
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I would replace points, plugs, rotor, cap and set the timing to the factory specs. Pinging is caused by 2 things, low octane fuel and timing too far advanced. A small track inside the distributor cap is hard to find and will cause misfiring and it is much easier to just replace it.
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Old 06-04-2012, 01:50 PM   #4
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I'm thinking vacuum leak. The gasket underneath that 4 barrel carb in notorious for cracking. Vacuum hoses crack and leak as well. Fought this with our '89 454.

Here's one way to test: pull off the dog house and remove the air filter. Run the engine at idle. Use a can of WD40 with the red tube and spray lightly & briefly under the carb and and in spots around the various vacuum hoses, vacuum advance on the distributor, etc. If you have a vacuum leak, it will suck in the WD40 at that point and the idle will change briefly. Be careful since the WD40 is a petroleum product- don't do this while the engine is hot.

Both the pinging and the backfiring can indicate timing issues- did you adjust the distributor at all while you were working on the ping?
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Old 06-04-2012, 01:51 PM   #5
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Sounds like the distributor is too far advanced, firing the spark plugs before the pistons get all the way to the top of their travel. Could be the vacuum advance unit on the dist is stuck or a problem with the vacuum line going to it. You don't want to run it too long with pinging since it could do some internal damage to the engine.
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Old 06-04-2012, 01:55 PM   #6
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And pinging can be caused by a to lean condition like a vacuum leak or a full fuel filter(restricts fuel flow). And the filter in the carb is often forgotten because no one sees it.
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Old 06-04-2012, 01:55 PM   #7
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I'm thinking timing..

have your timing checked,

check your vacuum advance canister and vac line to it and that its on the correct vac port,

check your distributors weights and springs...
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Old 06-04-2012, 01:55 PM   #8
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I agree check the timing from under side of Motor you will use #5 be sort to disconnect the vacuum hose also make sure the weights in the distributor are not stuck
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Old 06-04-2012, 02:03 PM   #9
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The pinging certainly sounds like too-advanced timing, but I believe the heavy backfiring under acceleration sounds like a vacuum leak.

He said he'd already replaced plugs, rotor and distributor.

OP, do you have a vacuum gauge installed?
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Old 06-04-2012, 04:05 PM   #10
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Those 454's have a very small fuel filter and it does not take much to reduce its flow. Having to back off the accelerator is a classic sign of fuel starvation. Which also cause the engine to go lean and ping. I used to carry to spare fuel filters with my 454 and changed them every oil change.

It is in the frame passinger side about 5 feet behind the front wheel.

The other classic problem with 454's is bad ignition wires. If they are more than 3 or 4 years old I would change them out.
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Old 06-04-2012, 06:40 PM   #11
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This is a common problem with older engines that are not daily drivers.

Review this post.
backfire/vaccum problem 454 chevy

They had a similar engine with same problem, there is a great amount of basic troubleshooting tips, review them and take small steps to avoid wasting money.

You have an older gas carburated engine, these required what we called in the old days a "Major tune up"

Plugs, points (if used) rotor, cap, wires, clean or rebuild carb. inspect replace hoses etc.

It is a lost art as now the computers indicate what to change, the things you need to know today are a lot more advanced, but the deep skills are much different.

Good luck!
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Old 06-04-2012, 10:15 PM   #12
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Does yours have the dual fuel option (propane-gasoline) that was very common on that era HR Imperials. I have the same MH as yours. On mine the wire to the gasoline cutoff valve that is next to the carb had fatigued to the point it was just barely touching the contact on the valve. When I would accelerate the engine would shift just enough for the wire to lose connection but when I let off the throttle it would touch again. The cutoff valve MUST have power to it or it will close. This was only on the dual fuel motors but would account for what you are experiencing. Mine was doing exactly the same thing. After rebuilding the carb, I removed the entire propane system to the engine. There is a lot more to it than just a hose from the propane tank.
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Old 06-04-2012, 10:42 PM   #13
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If you have a Thermostatic Air Cleaner that blends hot air with the cold air coming into the air cleaner housing and it sticks in the hot position it will create pinging. It is part of the emission control system and can fail with age. Not very hard to check/test it. I'm sure that Google will lead you to all the info that you need.
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Old 06-05-2012, 12:13 AM   #14
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Quote:
Originally Posted by bluepill View Post
If you have a Thermostatic Air Cleaner that blends hot air with the cold air coming into the air cleaner housing and it sticks in the hot position it will create pinging. It is part of the emission control system and can fail with age. Not very hard to check/test it. I'm sure that Google will lead you to all the info that you need.
OP has a 1984 - likely there is no emissions stuff on it
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