04 LB7 bent exhaust pushrods

[SiFlyBy]

Well, I gues this is my introduction post. My name is Chris and I am diesel and automotive technician. Most of my experience and training is from Ford but I recently started working for an independent shop which is becoming an exciting and, as you read on, a challenging experience. I have a problem with a Duramax that, so far, no one I have talked to( and alot of GM experienced fellows in there) has ever come across. So here it is:

I have a 04 LB7 that would not run, I checked everything I could think of and came to the conclusion that it was a problem of bad fuel. I disconnected the suction line to the pump and fed it clean fuel from a funnel. After a minute or so of cranking it started, but was running very poorly and backfiring through the intake. I decided to take a closer look, removed the fuel injector lines and found rusty deposits in them and the fuel injectors. After seeing this I decided it was time for 8 new injectors and a new injection pump. While I was replacing the injectors I also noticed that ALL 8 exhaust pushrods are bent...So my boss and I tossed some theories around and didnt' worry about it much. I installed the injectors, pump and pushrods. Reassembled the engine and got it started after bleeding the air from the fuel system. It ran good for a short while, shut it down and started back up and it was missing and rattling and running generally crappy backfiring out the intake again. I removed the RH valvecover today and what do I find? Bent exhaust pushrods.

I talked with a former co-worker who is also a Ford Senior Master Tech and I think he had the most reasonable thoughts on the matter: That somehow the injection timing is off...thinking about it know it may make sense that it is about 180 degrees off(by crankshaft revolutions) to cause all and only the exhaust pushrods to bend.

If anyone has any thoughts I would much appreciate it.

Thanks in advance,
Chris

 

[DPC]

Did you happen to scan it to see what kind of codes it is throwing? The timing is all controlled by the ECM electronically. Is the truck stock? How many miles are on the truck? What was the owner doing with the vehicle when stopped?

 

[SiFlyBy]

I will double check on the codes, but Im sure there were not any. The CEL was not on. About 92,000 on truck. Bone stock. Auto trans(no mechanical overrev). The owner(who I take to be a no B.S. kind of guy) was towing a small trailer with 6 hogs in it, nothing major.

I know its all electronically controlled. It just seems that either the PCM is getting an incorrect engine position reading, or there is an internal fault that has caused it to open injectors at the wrong time.

My biggest problem here is: why all 8 exhaust pushrods? twice?

 

[DPC]

Some codes will not set the CEL. Not sure why only the exhaust push rods were bent even if by some chance the timing was 180 off. Did you check all the push rods?
If it were my truck I would pull the valve covers and have someone turn the engine over by hand while watching the valve train. Check to make sure all the valves and components are working like they are suppost to, exhaust valves open on exhaust stroke etc.

 

[Diesel Tech]

My guess is what you will find is the camshaft has had the pin that locates the timing gear broken off. The pin breaks and it allows the gear to rotate on the camshaft and the exhaust valves are now out of time. When the pistons and the valves meet the pushrods bend.

 

[JD4440]

My guess is what you will find is the camshaft has had the pin that locates the timing gear broken off. The pin breaks and it allows the gear to rotate on the camshaft and the exhaust valves are now out of time. When the pistons and the valves meet the pushrods bend.

I didn't know but I was wondering if that was a result of a sheared cam pin. Thanks Steve.

 

[DPC]

I didn't know but I was wondering if that was a result of a sheared cam pin. Thanks Steve.

I was thinking about that but wasn't sure if that would only bend the exhaust pushrods. I figured it would damage both.

 

[SiFlyBy]

My guess is what you will find is the camshaft has had the pin that locates the timing gear broken off. The pin breaks and it allows the gear to rotate on the camshaft and the exhaust valves are now out of time. When the pistons and the valves meet the pushrods bend.

You are the man. I didn't get a chance to update yesterday but I came to the same conclusion, pulled the front cover, removed the cam pulley and that damn pin sheared off.

Thanks for the help, Gentlemen!!

Chris

 

[White Knight]

I was thinking about that but wasn't sure if that would only bend the exhaust pushrods. I figured it would damage both.

The piston chases the exhaust valves. The intake valves don't open until the piston is on the way down.

 

[Warpig]

You are the man. I didn't get a chance to update yesterday but I came to the same conclusion, pulled the front cover, removed the cam pulley and that damn pin sheared off.

Thanks for the help, Gentlemen!!

Chris

See, ya got your money back from the CompD subscription fee already!!!!!! That's why CompD is the best forum on the interwebby!!

 

[DPC]

The piston chases the exhaust valves. The intake valves don't open until the piston is on the way down.

:doh: exhaust valve has to be open for the piston to push the exhaust out and closes just before the piston reaches the top of the stroke, thanks.

 

[wideopen]

Good Info!

 

[BradJ]

Good Info!

Yes, you are correct. Found this thread a little to late. Helped awhile back with the same problem. Ended up being a sheared cam pin. Not very common in stock trucks but does happen and as power goes up, so does the chance of it happening.

 

[5150ram]

When the pin shears off does it ruin the cam. Whats the best fix for a stock truck. Thanks Chris

 

[GRotman]

Best fix is to cut a key way where the pin is, before the pin breaks preferably.

 

[5150ram]

May be too late for this one its popping exhaust out the intake. Chris

 

[GRotman]

They also shear the crank pins. If your in that far, you might as well key both and be done wit it.

 

[SiFlyBy]

May be too late for this one its popping exhaust out the intake. Chris

This one was doing the same. If you need a cam pin, the dealer could only get me a pack of 10. I have 8 left(lost one). If you need one LMK. I will send it to you for the price of a stamp.

 

[BradJ]

This one was doing the same. If you need a cam pin, the dealer could only get me a pack of 10. I have 8 left(lost one). If you need one LMK. I will send it to you for the price of a stamp.

Wow, you need to fire your dealership and find another one that will actually sell you one pin instead of making you buy the entire package.

 

[SiFlyBy]

Wow, you need to fire your dealership and find another one that will actually sell you one pin instead of making you buy the entire package.

yeah, I thought that was pretty crappy of them. they had never sold a pushrod or one of these pins before so I guess they didnt want to have them sitting on the shelf...whatever, the truck is fixed, runs good and I learned a ton about Dmax's. All is well