2003 2500hd 6.0 not so random misfire

[Will03]

I agree with the "gamble", but with a 90 day 100% gaurantee on the motor and included components, and at half the cost of a new longblock it's hard for me to justify the difference in cost. I still may just pull these heads and have them reworked. The main thing keeping me from doing that is the "what if the shop misdiagnosed" factor and I'm still in the same boat I'm in now, just with a fresh set of heads.

 

But yes. I'll probably die with this truck, as I will with both of my tacomas and my samurai. I bought the truck to pull a trailer, and that's all it does. For my needs it's perfect.

[Jsdirt]

I hear you there. Gotta do what you gotta do.

 

Since you had a little leakage past the rings and intake valves during the leak down test, that's probably the best thing to do.

[Swimmer8366]

Pull the valve covers yourself I'm gonna pull mine in a few days due to my misfire at idle could be a broken valve spring which is what I'm hoping mine is.

 

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[Swimmer8366]

Pulled my driver side cover today to find the springs are fine not broke or anything but I did find this

 

 

So yay me time to pull heads and get them redone and do gaskets timing chain oil pump would really just like to do a build than drop but money is not there for that can do all the gaskets timing chain and oil pump and water pump for 200-250$ and clearly a couple days of work. I have never seen a head gasket cause a misfire just at idle though??

 

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[Will03]

I've been under the valve covers already checking springs. I was actually surprised how clean it was for the mileage.

 

 

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[Jsdirt]

Pulled my driver side cover today to find the springs are fine not broke or anything but I did find this

 

...

 

So yay me time to pull heads and get them redone and do gaskets timing chain oil pump would really just like to do a build than drop but money is not there for that can do all the gaskets timing chain and oil pump and water pump for 200-250$ and clearly a couple days of work. I have never seen a head gasket cause a misfire just at idle though??

 

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Idle is high vacuum, since the throttle plate is shut. Cruise and idle will pull the highest vacuum - those 2 instances will be when coolant or oil is drawn into the combustion chamber. The leak is probably small enough to only create an issue at idle - anything above that and it just burns the coolant. If it's a compression-related misfire, higher RPM will overcome that too. More speed = less time for leakage.

[Will03]

I got the motor pulled this morning and the motor mount on the passenger side is wore out. Think it's possible that was causing the "misfire"? I've pulled the head and removed heads and springs and the valve guides are tight and the seats are in good shape kind of disproving the valve movement and not sealing so I'm kind of back to square one, but with the engine removed.

[Jsdirt]

That could explain why you didn't feel the misfire. This also highlights the importance of THOROUGH testing.

 

It's possible, but not 100% convinced that could cause that problem, since the cam/crank sensors have to detect a slowing of the crankshaft when there should be a speeding up, due to a particular cylinder's firing event. Timing chain slop could certainly trick the computer into thinking the engine slowed. I would think that would throw a correlation code, but you never know with these vehicles today. What happens 20x in a row could be totally different on the next one that comes in the shop. Nothing is set in stone anymore.

 

Since you already have it apart, I'd send the heads out to be magnafluxed and rebuilt - that will eliminate any possibility of leaks of any kind. The machine shop can measure the guides and either confirm or disprove the worn guide theory. Timing chain and oil pump would be next, along with new head gaskets of course, knock sensors, intake gaskets (upper and lower), and I'd want to inspect the cam and lifters as well. If it were me I'd just do it all. Don't forget a new oil pan gasket and rear main seal. Might as well.

 

If the engine was quiet, you probably have several years left on the lower end. Since it's apart, you could throw a set of rings in there easily, and LIGHTLY hone the cylinders, and then check the lower end bearings while you're there. Kind of a tough call to say when enough is enough, but since you have it apart, I'd do ALL the work NOW while it's out.

 

It sucks removing an engine the second time - been there, done that! Any time I have tried to save a buck on a job like this, it ALWAYS bites me in the ass later. Do it all, do it right, and do it ONCE. But at the end of the day, you can only do what you have a budget for. Your call there.

[Will03]

That could explain why you didn't feel the misfire. This also highlights the importance of THOROUGH testing.

 

It's possible, but not 100% convinced that could cause that problem, since the cam/crank sensors have to detect a slowing of the crankshaft when there should be a speeding up, due to a particular cylinder's firing event. Timing chain slop could certainly trick the computer into thinking the engine slowed. I would think that would throw a correlation code, but you never know with these vehicles today. What happens 20x in a row could be totally different on the next one that comes in the shop. Nothing is set in stone anymore.

 

Since you already have it apart, I'd send the heads out to be magnafluxed and rebuilt - that will eliminate any possibility of leaks of any kind. The machine shop can measure the guides and either confirm or disprove the worn guide theory. Timing chain and oil pump would be next, along with new head gaskets of course, knock sensors, intake gaskets (upper and lower), and I'd want to inspect the cam and lifters as well. If it were me I'd just do it all. Don't forget a new oil pan gasket and rear main seal. Might as well.

 

If the engine was quiet, you probably have several years left on the lower end. Since it's apart, you could throw a set of rings in there easily, and LIGHTLY hone the cylinders, and then check the lower end bearings while you're there. Kind of a tough call to say when enough is enough, but since you have it apart, I'd do ALL the work NOW while it's out.

 

It sucks removing an engine the second time - been there, done that! Any time I have tried to save a buck on a job like this, it ALWAYS bites me in the ass later. Do it all, do it right, and do it ONCE. But at the end of the day, you can only do what you have a budget for. Your call there.

I already have a replacement engine with 105k sitting in the shop ready to drop in. for the money and time involved a replacement is a better solution for me right now. I am keeping my core and I'll be going through it as I have the time.

 

What made me think the motor mount could cause the misfire, I have read several cases (more on the 5.3, but still the same thing pretty much) of people getting a p0300 from a slightly stretched belt, or slightly worn tensioner causing vibrations through the engine.

[Jsdirt]

Yeah definitely quicker, easier job to throw that replacement engine in - didn't know you had it already.

 

 

 

I've heard that too - now that you say that, I can see how that's possible.

 

I had a '04 Oldsmobile Alero here that ripped the rocker bolt right out of the head, and was knocking LOUDLY as the rocker got slammed into the head and valve cover. That car had a P0300. Good example of that.

 

http://vid297.photobucket.com/albums/mm215/jjs05polaris/Forum%20pics/0114171130a_zpsgj3lqoyi.mp4

[Will03]

Yeah definitely quicker, easier job to throw that replacement engine in - didn't know you had it already.

 

 

 

I've heard that too - now that you say that, I can see how that's possible.

 

I had a '04 Oldsmobile Alero here that ripped the rocker bolt right out of the head, and was knocking LOUDLY as the rocker got slammed into the head and valve cover. That car had a P0300. Good example of that.

 

http://vid297.photobucket.com/albums/mm215/jjs05polaris/Forum%20pics/0114171130a_zpsgj3lqoyi.mp4

Yeah I picked up an engine Friday. 2004 lq9 with 140k for $850. Couldn't pass that deal up. Should know by this weekend if the problem is solved or not.

[Jsdirt]

Nice - good deal. Keep us posted.

[Will03]

New motor is in and the truck runs great. I haven't had a crank relearn done yet but there is no more CEL flashing. Very happy I decided to take the motor swap route. I didn't realize how tired the old engine was until now.

 

 

Just a side note for anyone swapping an LQ4 to an LQ9, a computer from an LQ4 vehicle will work fine on an LQ9 (assuming you're using the trans the computer is for). 90% of everything I read said I would need a tune or to reflash it.

[XSKIER]

Have you done a Crank Variation Relearn?

[Jsdirt]

Good deal William - glad you've got it fixed!

 

Always a huge change comparing worn to good engines back to back. I'll never forget the seat-of-the-pants increase in power I got in my '89 S10 Blazer - I yanked the original engine (odometer said 77k, but I think they rewound it from 277k, as I had odometer issues later on) that burned a quart of 20w-50 every 50 miles in the dead of winter. Had a spark plug defouler installed on #2 it was so bad - would foul that plug every 3 days (about 170 miles). I grabbed an engine out of my '00 Jimmy that was having non-stop failures. Ripped all the EFI crap off and installed an Edelbrock 1404 & a HEI ignition system, & dropped it in the Blazer. Felt like a 200HP gain compared back to back - night and day difference!

 

When I tore the old 4.3 down, I found each cylinder had at least a 1/8" ridge at the top of the cylinders - that's some serious wear! It's a wonder the engine ever ran!

 

Here's a pic I love showing of just how bad that engine was - this was from the exhaust after warming the engine up after a blizzard hit: