RE: IML: Misfiring/backfiring...

[RandalPark@xxxxxxx]

These are very good suggestions. 

I will add that since you are working with a good mechanic, he will have a much better chance of correctly diagnosing your problem than we will. He is there and can check, hear, and see everything. All we can do is guess.

The intake manifold leak could have been the result of some other problem that caused the engine to "start bogging" as you put it, on the way to the mechanic's. This could be a weak fuel pump, failing carb, or ignition problem. Once the engine starts backfiring, it can blow gaskets and split vacuum hoses like crazy.

Hopeing for the best, since it ran fine to begin with, and all of this other work was done since the problem developed, I'd suggest that you may have put something back together incorrectly. If there was another problem, I think that your mechanic would have diagnosed it when he found the intake manifold problem.

Other things that can cause these symptoms might be incorrect timing, a massive vacuum leak, too lean of fuel mixture(carbuerator problem), ignition (recheck the spark plug wires as suggested by Robin). There are various mechanical failures that could also cause this, but since your engine is fresh, and you haven't given us reason to believe any damage occured I'll leave those unsaid.

Paul W.



 In an email dated 8/8/2005 6:21:28 pm GMT Daylight time, "Robin Giesbrecht" <robings@xxxxxxxxxxx> writes:

>How much vacuum are you pulling at idle? Putting a vacuum gauge on it will 
>tell you a few things that you need to know. A good stock big block should 
>pull close to 20" at idle with no fluctuation.You can get the timing pretty 
>close by moving the distributor for maximum vacuum at idle.I am just 
>wondering why you used sealer on the intake gaskets? Were they new gaskets? 
>What kind of sealant? I have been an aircraft mechanic for 20 years and some 
>material the aviation world uses is real good and some is not so good. A lot 
>of it is for very specific purposes. Here is a stupid qhestion. Are you sure 
>that the plug wires are all connected to the right plugs(firing order)? A 
>big V8 will run with a couple of cylinders out of sequence but it won't run 
>real well.
>
>Robin Giesbrecht
>1972 Imperial
>
>>From: commenace@xxxxxxxxxxxx
>>Reply-To: mailing-list@xxxxxxxxxxxxxxxx
>>To: mailing-list@xxxxxxxxxxxxxxxx
>>Subject: IML: Misfiring/backfiring...
>>Date: Mon, 08 Aug 2005 12:33:56 -0400
>>
>>Just put about 500 miles on my new 440. ?So it was time for a major 
>>tune-up. ?On my way to my friend's work (he's a very gifted Mopar mechanic) 
>>the engine starting bogging. ?Misfiring and backfiring out of the tailpipe. 
>>?After the tune-up, new plug wires, plugs, timing set, carb tuning, we 
>>noticed it was "missing" as in running roughly as if a plug was not firing. 
>>?All plugs were firing, but we were still "missing." ?My mechanic theorized 
>>I might have an intake manifold leak. ?I tested it by spraying starting 
>>fluid where the intake manifold meets the heads. ?It seemed I did have a 
>>vacuum leak. ?
>>
>>I replaced the intake manifold gaskets using aviation gasket sealer (good 
>>stuff!). ?Started her up yesterday... ? Guess what? ?Still backfiring! ?I 
>>don't really feel it misfiring. ?It seems that all the plugs are firing, 
>>but it is backfiring. ?It should be noted that on one particular backfire, 
>>my muffler exploded. ?This was completely my fault, I won't get into how, 
>>just trust me, it was my fault. ?As such, without a muffler, the engine, 
>>obviously feels rough. ?Therefore it's hard to judge whether or not it's 
>>running smoothly.
>>
>>My qusetion (at last!) is: what other problems would cause a backfire out 
>>the tailpipe (as opposed to in the carb)? ?Could the timing be too 
>>advanced/retarded? ?Would that cause a backfire?
>>
>>Any suggestions would be greatly appreciated...
>>
>>John.
>>1965 Le Baron.
>>
>>
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