Bad Miss and CEL at Idle

[wvamatt]

Swapped injectors, and the problem did not follow. Still multiple misfires at idle, with #4 being the main culprit. Pretty much a total miss at idle. The problem seems to be getting worse, with noticeable hesitation when pressing the gas off idle to accelerate. I’m at a loss. I still have the SnapOn scanner, and was going to run new scans tomorrow. Is there anything I should pay special attention to or and tests I should run?


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[wvamatt]

Have not done compression test yet.


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[Raptordude]

I would do a compression test next, hopefully there isn't an issue there.

 

 

A leaking intake manifold gasket around cylinder #4 could cause this, and also be the reason your o2 sensor was reading funny. Take a propane torch and blow the propane around the intake manifold around #4. If it revs the motor up or changes the way it runs, you have a leak

 

 

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[wvamatt]

I just replaced intake manifold gasket during the troubleshooting process, so should be able to eliminate that. I have a compression test set ordered and on the way in the mail. Ran some more tests with the scanner in the meantime. Nothing really jumped out at me yet, but maybe it does to someone else. Here are screenshots...

 

https://postimg.org/gallery/2zse1miha/

 

 

[wvamatt]

For anyone else experiencing similar issues, I finally fixed my P0300! Compression checked out OK, so I ran a fuel pressure test - should have done that earlier. The test revealed pressure of 47 PSI, which leaked off after the fuel pump stopped running. I check the vacuum tube connected to the fuel pressure regulator, and it was full of gas. I put on a new FPR, and problem solved! No more hard starting, no misfires!

 

Moral of the story: Check your fuel pressure.