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Discussion Starter #1
My 2006 with 128,000 miles on it has developed a bad misfire while the engine is cold. The Check Engine light alternates between solid and flashing and the truck really runs crappy until it gets up to normal operating temperature at which point is runs much better. On the OBD2 scanner I get P0304 code (misfire cylinder 4), but when I run the diagnostics for a 15 minute drive or so, I get a few misfires (2 - 25 or so) in several of the cylinders with cylinder #4 having like 2,000+ misfires.

Steps taken so far:

Replaced #4 MDS solenoid (I was getting a P1414 (bad MDS) code as well.)

Switched coil pack (misfire stays on cylinder 4).

Switched fuel injectors (misfire stays on cylinder 4).

Replaced spark plugs on cylinder 4.

(By the way, I did replace all the lifters a year ago (about 8,000 miles ago) because one of the lifters collapsed. The cam looked fine and none of the lifters had a seized roller. I also replaced all spark plugs at that time too.)

Tomorrow, I plan on taking the valve cover off to see if the valve springs look ok. Anyone else got any idea what else might be causing this issue?

Also, anyone know how to shut fuel off on this thing so I can crank the engine without it starting? I can't find the relay.
 

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Red Trucker
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Run a compression test, se ehow that cylinder compares to the others. Also check your pushrods carefully, sometimes if they aren't exactly seated (both ends) right it'll cause issues. I got a Magnum R/T cheap because dude couldn't figure out what was wrong with it, one cylinder read high and tuned out to be an intake pushrod out of place on the rocker arm.
 

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Discussion Starter #3
I checked the pushrods and looked at the valve springs as I've seen lots of posts where a cracked spring could cause this issue. I was also getting an EGR valve test failure in my ODB 2 scanner so I replaced that.

Everything looks good visually.

I took it out for a drive and it seems that as soon as I start the truck it runs fine for about 3 seconds and then it starts misfiring really badly in cylinder 4. Then I get it out on the road and for the first 5 minutes or so the truck just runs horribly. Shaking the vehicle really badly when the MDS is kicked in (I think).

After it get up to operating temperature, it runs great. I take a look at the test results that I had running for the 10 - 15 minute drive and I've got several hundred misfires on cylinder 4 and between 0 and 100 misfires on all other cylinders.

Moving fuel injectors and coils between cylinders still keeps the misfire problem on cylinder 4. It really does seem like an engine management bugaboo and not something mechanical to me.
 

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I admire your persistence. Three things come to mind. #1 This engine needs a "smoke check".That is were you pressurize the engine up to approx. "1 psi" with smoke. Look up online (google-it) and you will understand the principles and tools required. .Theoretically if the intake manifold is sucking "un-metered" air through a bad sealing gasket,the air fuel mixture will run LEAN. When the engine warms-up the sealing surfaces close together and the leak is temporarilydiminished....ALSO...This can be checked with a small spray of aerosol brake cleaner, a little spray at a time ,when the engine is COLD. When you find the unmetered air leak,the RPM of the engine will come up/increase momentarily. Propane in a very small metered amounts works great/fine-also . DO NOT use carb cleaner ,it's too FLAMMABLE !!!. #2 If your problem is mechanical ,do a compression check-cranking, COLD,then HOT. A "running"-compression test will uncover dynamic-deficiency. ( Same/same, google it ) run the engine at idle and witness the needle movement of the gage on a GOOD cylinder,then do the same test on #4 cylinder. #3 deactivating the ignition or power to the fuel injector is a poor -man's cylinder drop test.if the cylinder is fire and making power,then when you do the cylinder drop test ,on one cylinder at a time then the engine RPM should drop enough to indicate /or-not if its contributing to the overall power/rpm. AutoZone may have the tools on a borrow/buy program. I hope these ideas help in your troubleshooting. Youtube has many very good videos on proper- technique in performing these test . Mongoman in Albuquerque
 
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