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Old 06-02-2009, 09:01 AM   #5
Rippin-J
OurLadyofBlessedAccelerat ion
 
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Join Date: Aug 2007
Location: Denver, CO
Posts: 148
Re: 87 454 tbi black smoke

randomly happened onto your thread ...I am no expert, but your point about the motor running rough for a bit when you applied throttle sounded familiar.

my motor has been doing the same thing and the net result was a valve issue in the heads. why it sputtered (and blew smoke) so badly when I applied throttle was that there was at least one cylinder that wasn't combusting correctly. BUT, if I increased the rpms is 'appeared' to smooth itself out. my theory there is that the motor is firing fast enough that that one (or more) bad cylinders became less noticeable.

my other new theory is that I also heard a 'knocking' sound, but perhaps my untrained ears mistook an actual knocking sound for 150psi of pressure escaping through the tiny leaks in my valves (which if muffled by things like an intake manifold or exhaust headers) may sound deceivingly like a 'knock.'

I don't mean to underestimate your ability to sonically diagnose anything, but this is all stuff I have recently discovered and figured I would share considering our symptoms seemed to be somewhat related. honestly you're probably better off if the computer will fix it for you vs having to tear apart the motor!
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1968 Chevy C-20 w/ 396
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