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Discussion Starter #1 (Edited by Moderator)
Hey guys,

Here's something I discovered today using my scan tool software that I have. I only get misfires on cylinder #4 between 2k-3k RPMs. Any lower, and they are negligible They completely disappear above 3k RPMs. Anyone seen this before? I have replaced just about everything on this **** truck trying to fix this issue.
 

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Discussion Starter #3
2 to 3 k while parked, or with a load on the motor?

Flashing CEL?
While parked today, but this has been going on for a while. The code was set while at 2300 RPMs yesterday, as the freeze frame data showed.
 

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Discussion Starter #4
I had the flashing CEL a couple weeks ago, but I replaced the cap, rotor and wires last week. It didn't help. The code came right back. I also have a new distributor, and my cam retard is -2 degrees.
 

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I chased the same problem on mine for a long time, and replaced all of the usual suspects to no avail. It ended up being a lazy valve spring.

If you do a search you’ll find a TSB regarding the flashing CEL
 

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Discussion Starter #6
Yeh, I kinda figured it would probably be a mechanical issue. Replacing all the usual suspects - new MPFI a couple years ago, fuel pump, and all the electrical stuff would probably mean it would turn out to be mechanical. Thx for the help.
 

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Discussion Starter #7
I did a compression test back in the early summer, and all cylinders were between 180-182 lbs, even between them when I did the test. Would this mean the valve(s) are floating to some degree?
 

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Hopefully not at 2300 rpms. And it'd get worse at higher rpms.
It's not terribly hard to replace the springs on one cylinder with the right tool.
Just be sure that piston is all the way up in case something slips.
Might be worth a try.
Most 4.3's spend a lot of time in that 2-2300 range. Unless you only drive in town,
 

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Discussion Starter #9
Hopefully not at 2300 rpms. And it'd get worse at higher rpms.
It's not terribly hard to replace the springs on one cylinder with the right tool.
Just be sure that piston is all the way up in case something slips.
Might be worth a try.
Most 4.3's spend a lot of time in that 2-2300 range. Unless you only drive in town,
Here's something weird though. Back in the mid summer, I replaced the crankshaft sensor. I did a relearn with my scan tool at the time, obviously. However, before I replaced it I was getting a P0300/P0306!!!! So, after the relearn, it moved from #6 cylinder to #4 cylinder. I don't understand that at all, if it indeed is a mechanical problem with #4, when it originated on #6. P0304 never occurred until I replaced the crankshaft sensor, and then did the relearn. Weird.........:unsure::unsure:
 

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Discussion Starter #10
Guys,

This link of a video I made yesterday with my scan tool may shed some light for you all to tell me what you think. Thanks.

 
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