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valleybusman
Top Member

USA
815 Posts

Posted - 06/05/2023 :  08:12:13 AM  Show Profile  Send valleybusman an AOL message  Reply with Quote
A while back this bus came in to the shop missing and spitting raw gas. The bus has 178000 miles on her with all original equipment like spark plugs. So we figured must be spark plugs and wires since they were original. Changed them out and showed number 8 had a really bad miss. Ran a compression check and it was below 100 psi. Thought was maybe bad injector washing the rings down with gas. Changed injector ran engine again. Still miss in number 8 but compression jumped to 125.Thought maybe bad coil. So we moved all the ignition parts to number 6 ( coil, spark plug and wire) to see if it followed. It did not. Could we have a bad injector again? Number 5 and 6 have a slight miss but aren't dead like number 8. What could I be missing? Thanks

Bluenozer
Top Member

Canada
655 Posts

Posted - 06/05/2023 :  08:40:04 AM  Show Profile  Reply with Quote
swap the injector plug in to another injector and see if it follows, to eliminate injector or harness
do these engines have cam issues , lifter issues
the 4.8 vortex have knock sensor issues cause misfire codes
vortex5300 has issues with cracked heads
does it have the AFN lifter ( does it drop cylinders for fuel eco?)

OEM trained in wiring and all engine platforms for over 20 years

Edited by - Bluenozer on 06/05/2023 08:46:40 AM
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valleybusman
Top Member

USA
815 Posts

Posted - 06/08/2023 :  05:58:13 AM  Show Profile  Send valleybusman an AOL message  Reply with Quote
No it doesn't have afn lifter
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dsalinas1939
Top Member

USA
1328 Posts

Posted - 06/08/2023 :  09:57:13 AM  Show Profile  Reply with Quote
check the valve springs have had to replace a few valve srings on higher mileage buses they usually break u will notice it if u take valve cover off that could be the cause of your compression jumping aroung they are very simple to change in the bus
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valleybusman
Top Member

USA
815 Posts

Posted - 06/09/2023 :  1:27:33 PM  Show Profile  Send valleybusman an AOL message  Reply with Quote
I am wondering about the valve spring. I took another look today. I took the plug wire off number 8 and ran the bus for a little bit. Got a really strong spark from the coil. Then removed the plug to see if the plug was wet with gas. Dry as a bone. So either the new injector is bad or nothing is turning the injector on?
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dsalinas1939
Top Member

USA
1328 Posts

Posted - 06/12/2023 :  03:57:39 AM  Show Profile  Reply with Quote
did u check for signal at imjector those are comin for the injector connecter as well
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valleybusman
Top Member

USA
815 Posts

Posted - 06/12/2023 :  08:11:56 AM  Show Profile  Send valleybusman an AOL message  Reply with Quote
That is the next step
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