67 rs/ss #8 dryfire - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 8 (permalink) Old Sep 9th, 02, 11:20 PM Thread Starter
 
Join Date: Jul 2002
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Can't figure this one out! #8 is missfiring!
I have checked for good compression, spark and fuel. Have figured out that #8 isn't getting any fuel. It's only on #8. Have also checked for vacum leaks. This engine has about 20 miles on it since rebuild. When I do a false richness check by placing my hand over the carb, it begins to fire. Have already re-sealed intake, checked valves and verified spark and compression. I put it on the scope and #8 misfires. Is this carb to lean? Carter AFB 750
Thanks
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post #2 of 8 (permalink) Old Sep 10th, 02, 07:34 AM
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Mark
 
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Check the #8 valve lash just for grins.

-Mark.
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post #3 of 8 (permalink) Old Sep 10th, 02, 10:33 AM
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As Mark suggested, check valve lash as well as valve lift with another cylinder. Either valve may not be opening enough to charge the cylinder.

I would also suggest putting in a vacuum gauge to see that needle is not fluttering due to valves not opening, should be steady reading.

Could be a lean condition. Isn't this where the vacuum is drawn from for brakes and A/C? Unplug all vacuum hoses and cap off nipples to keep engine by itself. Then go from there, hook one hose at a time until the lean one shows up.

You might even pump alittle shop air into the cylinder @TDC and listen to either the carb, exhaust pipe, or crankcase for leaking air. Compare to a good cylinder. Don't forget the radiator cap to check for leakage there also.

The coil may not be outputting enough to jump the gap for a lean condition. With plug wire min 1/4 inch away from ground, should have a nice blue spark if battery is in good charge.

I'm sure you've swap wires and plugs with a good cylinder to verify their condition.

You mentioned using a scope to look at ignition. Man, I thought nobody knew what these where any more. Hook the scope back up and check the right-hand side of the sweep with all eight cylinders superimposed onto to each other, primary side. At the right side of the sweep is point opening. It should not vary more than 4 degrees, otherwise, the shaft is crooked, or cam is worn. Check to make sure all plug firings on parade postion on the secondary side are of even voltage. This signifies all plugs have the same gap. If one plug is higher than the other, by a large amount, as in off the screen, open secondary side for that cylinder.

All the above assumes you have a point system. I'm sure you've tried another distributor and/or carb.

Let us know what it is........

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Everett 68/350/PG/11.90/115mph
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post #4 of 8 (permalink) Old Sep 10th, 02, 12:17 PM Thread Starter
 
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Well, I tried all that stuff with a scope. I even changed out HEI's. I'm getting plenty of blue spark. You mentioned something about maybe the shaft is not straight. Would this be the distributer shaft? I don't think I have a spark problem.
I checked for compression, it holds at 130, wich included leak down test. When I crank the engine over without spark then pull the plug, the plug is dry. No fuel. The only way I can get number 8 to fire is by doing a false richness test by holding hand over the carb. Thanks for your input.
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post #5 of 8 (permalink) Old Sep 10th, 02, 12:29 PM Thread Starter
 
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Ok, I even checked my scope on my chevelle. I was even starting to doubt that obsolete tool. It checks out. I've always heard of carbs being to fat up here in the mile hi city, but to lean?
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post #6 of 8 (permalink) Old Sep 10th, 02, 04:50 PM
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Are there any vacuum ports in the intake runner to the #8 cyl? perhaps the accessory it is "feeding" is faulty...just a thought without seeing Your setup....
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post #7 of 8 (permalink) Old Sep 10th, 02, 05:51 PM
 
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Is your PCV hooked to the vacunm port on # 8?
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post #8 of 8 (permalink) Old Sep 11th, 02, 04:51 AM
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Vacumm leak sounds like the problem, how about the vacumm hose to the trans modulator, may be off at the tranni,
Far off guess might be you flattend the cam lobe on the #8 intake during break in.
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