C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette
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Help, engine sick, not sure what the problem is!

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Old Dec 21, 2013 | 03:55 PM
  #21  
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Originally Posted by Haggisbash
Checking the valve lash with the engine running, I backed off the adjuster until the valve started to clatter and then started to tighten ( I was advised to tighten 3/4 of a turn) but when I did this the engine revs started to drop a lot so I quickly backed the adjustment off again and settled for a little under 1/2 a turn, is this normal??
normal.. 1/2 turn is fine, you did both? if vacuum gauge is steady, and around 17-18 in hg on stock motor, your valve train is probably not responsible. try this with gauge connected... •on a Normal Engine when Throttle is quickly Snapped Open and Closed..

Vacuum should drop to 3 or 4 and then momentarily climb to 25 – 28 before settling back at the previous value. This indicates that the valves and rings are OK......
Do you have headers? could the plug wire boot be melted slightly and spark jumping to header? You replaced Dist cap? no evidence of carbon tracking in the old one?

Last edited by fishslayer143; Dec 21, 2013 at 04:02 PM.
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Old Dec 23, 2013 | 09:08 PM
  #22  
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Guru had a look at my engine, he thought that it was mechanically sound and produced 150psi on his comp tester, but found replacement dist cap is faulty. Effected a temp repair with some glue and have ordered another. But driving the car home there was still a miss, it started to rain, turned on the wipers and they didn't work wtf? Were okay when I checked for vac leaks at the start of this saga, anyway I blocked off the vac hoses except to the dist and the miss fire has disappeared so it seems I'm the victim of two faults almost simultaneously. Will now suck my way round the hoses to find that fault!
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Old Dec 23, 2013 | 10:16 PM
  #23  
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backfiring and misfiring to me indicates a timing issue. Check your timing if it is off check your distributor and timing chain.
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Old Dec 24, 2013 | 04:47 PM
  #24  
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Default A little discouraging to hear

1st a Distributor cap and then a vacuum leak.

Moral, guys that say they have checked everything usually haven't or not sufficiently and that comes with experience. Thus get the cap changed, and make sure a vacuum leak that would most definitely cause a misfire (too much air sucked in, leaning out fuel mixture) is fixed first. Thus glad you found someone to look over what you were doing and looking at. Good Luck!
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