Mis on cyl 3&8 - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 7 (permalink) Old Jun 10th, 01, 07:07 AM Thread Starter
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Cylinders 3 and 8 are not firing and I need help in finding why. The plugs look new on these cylinders. Grounding the wires at the cap causes no change in RPM. Switching cyl 1 and 3 plugs and wires does not change the problem. All cylinders have good spark when checked with a loose plug. Valve lift is good. Compression is @ 150-160 psi.

I have the following combination of parts. 377 C.I with Vortec heads, R45TS plugs, Q-jet with 72 jets, 50 primary rods, HEI with 10 Ga. wire from firewall connector to distributor.
O2 sensor in the right side exhaust is a constant 860 milivolts. and hydrocarbon exhaust is way high.

Do Vortec heads use a longer reach plug? should I start chasing a carb problem?
Any other Ideas.

Thanks
TTFN
Mat
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post #2 of 7 (permalink) Old Jun 10th, 01, 01:05 PM
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Matt,
You say that 3 and 8 are not firing, and yet you say that all the cylinders have good spark when checked with a loose plug ??? Sounds to me like it might not be an ignition problem. How about a vacuum leak, or could be a carb problem like you said.

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post #3 of 7 (permalink) Old Jun 10th, 01, 01:43 PM
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Matt,

What about the vac port on the #8 runner behind the carb? Don't the #3 and #8 runner connect under the carb in the intake, so if you have a vac leak it will kill both cylinders. Also check for broken valve spring on those cyl's, the valve can close enough to make a good compression check, but not close fast enough to fire when running, and can blow back up the intake, and kill 2 or more cyl's.

Larry
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post #4 of 7 (permalink) Old Jun 10th, 01, 04:07 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Mat Klemp:
Cylinders 3 and 8 are not firing and I need help in finding why. The plugs look new on these cylinders. Grounding the wires at the cap causes no change in RPM. Switching cyl 1 and 3 plugs and wires does not change the problem. All cylinders have good spark when checked with a loose plug. Valve lift is good. Compression is @ 150-160 psi.

I have the following combination of parts. 377 C.I with Vortec heads, R45TS plugs, Q-jet with 72 jets, 50 primary rods, HEI with 10 Ga. wire from firewall connector to distributor.
O2 sensor in the right side exhaust is a constant 860 milivolts. and hydrocarbon exhaust is way high.

Do Vortec heads use a longer reach plug? should I start chasing a carb problem?
Any other Ideas.

Thanks
TTFN
Mat
<HR></BLOCKQUOTE>

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post #5 of 7 (permalink) Old Jun 10th, 01, 04:11 PM
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<BLOCKQUOTE>quote:</font><HR>Originally posted by Mat Klemp:
Cylinders 3 and 8 are not firing and I need help in finding why. The plugs look new on these cylinders. Grounding the wires at the cap causes no change in RPM. Switching cyl 1 and 3 plugs and wires does not change the problem. All cylinders have good spark when checked with a loose plug. Valve lift is good. Compression is @ 150-160 psi.

I have the following combination of parts. 377 C.I with Vortec heads, R45TS plugs, Q-jet with 72 jets, 50 primary rods, HEI with 10 Ga. wire from firewall connector to distributor.
O2 sensor in the right side exhaust is a constant 860 milivolts. and hydrocarbon exhaust is way high.

Do Vortec heads use a longer reach plug? should I start chasing a carb problem?
Any other Ideas.

Thanks
TTFN
Mat
<HR></BLOCKQUOTE>

Hi Mat... just went thru this with plugs. vortech heads use a R43LTS longer or a rapid fire #3, I went to rapid fire
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post #6 of 7 (permalink) Old Jun 11th, 01, 07:03 AM Thread Starter
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Thanks, Bill,Larry and Jim.

I replaced the distributor with no improvement. I knew that ...
I'll try the plugs tonight, Then check valve springs and for a vacuum leak. Maybe try a carb swap.


TTFN
Mat
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post #7 of 7 (permalink) Old Jul 3rd, 01, 07:01 AM Thread Starter
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I put in the long plugs, swapped carbs and retarded the timing. This seems to have done the trick. I passed Emissions! My guess is that the plugs were 90% of the problem.

Thanks & TTFN
Mat
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