Dead cylinder, everything tests good

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Feb 22, 2023 | 06:31 AM

JayP63

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Dead cylinder, everything tests good

#8 cylinder in my 1990 5.0 is completely dead. but everything looks good

Compression checks good.
Rockers move fine.
Plug smells like gas.
Spark at distributor and timing light flashes.

Confirming its #8 by pulling the plug wire off the distributor while running. No drop in vaccum or rpm. Whereas any other cylinder both drop when unplugged.

At first thought it was oil fouling but even running a brand new plug and checking after a few seconds of running it’s still not firing.

after running a while the plug looks like it hasn’t fired at all and is just dirty

ideas?

Feb 22, 2023 | 07:00 AM

tjc transport

i ain't rite

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From: Marlboro Mental Hospital.

either a bad plug, bad wire, or bad cap.

Feb 22, 2023 | 07:41 AM

JayP63

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I wish. Already put a new cap, rotor, wires, and several new plugs on. Same cylinder not firing.

Feb 22, 2023 | 07:46 AM

tjc transport

i ain't rite

Joined: Mar 2005

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From: Marlboro Mental Hospital.

alrite, next step is move injector to different hole and see if problem follows injector.

Feb 22, 2023 | 09:15 AM

GoinBoarding

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From: Laramie, WY

What was the compression?

Feb 22, 2023 | 09:33 AM

JayP63

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Cold was around 120 psi and hot around 150.

Feb 22, 2023 | 04:59 PM

hobohilton

Fleet Mechanic

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From: Northwest

Swap the # 6 plug wire with the # 8 plug wire.
Does # 8 still miss ?
If it still misses you have a fuel issue and not an ignition issue.

As Tom pointed out (above) may be a dirty injector.