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Cylinder #6 not firing

3137 Views 12 Replies 4 Participants Last post by  Bill1013
My PSD has a miss. Took the valve covers off to determine which cylinder wasn't firing. #6 cylinder no change in the sound of the engine when I pull the injector wire off. The rest of them caused the engine to stumble even more when I pulled the injector wire off. I replaced the under valve cover harness on both sides with the newer style with integrated harness. Then ohmed the injector and that was good. Checked resistance from #6 all the way to the ECM with no breaks in the wire. Now I'm stumped. The rig only has 102K miles on it (motorhome) so I'm leaning away from a bad injector. Any thoughts?
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It means it's either not getting a signal to fire or not acting on it.

What did you get for solenoid resistance? Should be between 2 and 5 ohms IIRC. Did you check it against any other injector solenoids? They should all be in the same range.

To check the armature gap, you need to remove the solenoid and slip a feeler gauge between the plate and injector body. If it's closer than about 0.0015", then it's probably worn. But the fact that it's spitting oil means that the solenoid is activating the pilot valve (armature) in the injector.

You might have a low compression issue that's causing the fuel being injected not to combust. Could be valves or a cracked piston or ring.

A PSD capable scan tool would allow you to do a buzz test to check the electrical side of the injectors. The buzz test buzzes all the injectors and then in sequence, 1-8. Listening for differences in the sound during the sequence, will sometimes identify a bad injector.

The scan tool will also do a Cylinder Contribution Test, but that will only tell you which cylinder isn't contributing to engine power at idle. It won't differentiate between an injector problem and base engine problem (such as low compression) though.

You could follow up with a compression test, using a gauge that attaches thru the glow plug holes. If you have good compression on all cylinders (lowest within 25% of the highest meets service spec), that would pin it down to the injector itself.
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You should never splice the UVCH, just replace it.
If you meant the outside harness connector, it's done all the time. No problem unless you can't make a good splice (solder recommended.) Stagger the splices within the harness so they still fit inside the loom.
One issue might be corroded pins on the valve cover gasket itself. You might eyeball them closely. If they're corroded it will increase the resistance and decrease the voltage delivered to the injector. In a worst case situation you might need to replace the valve cover gasket. To check the circuits, you just need a multimeter. On a good circuit, you should see less than 2 ohms end to end.
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