Cylinder 8 knocking - not the injector or valvetrain, now what?

[toby]

My 89 E-350 has a knocking sound coming from the engine that I'm about 95% sure goes away when I crack the cylinder 8 injector line. Ive replaced the injector not once, but twice - first time with a new BWD unit from O'reilly that I bought on a roadtrip (and which seemed to temporarily reduce the noise a little, but maybe I was imagining it?) and then again when in installed the set of 8 new Delphi D-code injectors I had at home. Since then I've changed the injectors around and the only thing that seems to help is de-activating the injector for cylinder 8. I also pulled the valve cover and all the rockers are nice and tight with the engine at all positions.

So now I'm fairly sure I have an internal engine issue and I've convinced myself its either a rod knock or a bad wrist pin. Is there anything else I can check? I don't think I can drop the oil pan while the engine is in the van. Engine starts and runs smooth and with good power, but this knock is driving me crazy. Is my only option to wait until something blows?
Thanks in advance for any input!

 

[79jasper]

Probably not your problem, but I saw one with a busted piston skirt do that.
Only way I would know to check is pulling the engine and then pan.
No noise out the exhaust or intake?

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[toby]

No noise out of exhaust, but its really hard to tell if any noise is coming of the intake given how damn loud the engine is. It definitely does sound like its coming from the top side of the motor.

 

[Agnem]

So essentially you only have the noise while you have combustion. Curious if you have tried loosening the 7 other lines and cranking only with the #8 active to see if you can hear the noise any better. Be that as it may, I would suspect your hunch is correct, sad as it may be.

 

[rustygold]

Compression test time

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[79jasper]

Won't hurt, but also won't show a bearing problem.

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[rustygold]

Yeah true.. for bearing problem would have to send the oil off yo get tested with out taking the pan off.

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