6.0 Backfire?

[6.5 Detroit Diesel]

Running my Dad's 2000 2500 w/6.0 liter back from up north with about 4,000 lbs on. Lots of hills and corners. In cruise we would start up a hill and it would occasionally drop two gear and kick the revs up to between 4-4,500 rpm's. When this happened it would start to backfire very quickly until I kicked it out of gear and slowed the truck down. Any ideas as to what could be causing this?

[Mark Rinker]

My 2003 K3500 6.0L gasser (long since traded off) had a tendancy to downshift at inopportune times, and overrev like you describe. It was the worst written factory set of shift points I have ever seen coming from GM in a work truck. Basically all wrong for the powerplant / transmission combo.

Never had the backfiring - but that would most likely be from 'floating' an intake valve at too high RPMs...sounds like it would be best to keep out of cruise control when towing in the hills with that one. Broken or very tired valve springs could be next.

However, 4-4500 rpms like you stated isn't that high. Maybe a new air filter, set of fresh plugs, injector cleaner and some higher octance gas could straighten things up...

[6.5 Detroit Diesel]

Ya, I will get him to try those things. Like you said, I am worried about floating a lifter off, having already done that with a truck before.
The truck has 200,000 kms, (125,000 miles) on it, the springs shouldn't be getting weak already should they?

[Mark Rinker]

I bailed out of my '03 6.0L at about 90K miles because we had experienced miserable fuel economy, poor towing characteristics, a known 'average' transmission in the 4L80E, and so many downshifts with over-revving that it was apparent that something was gonna give in a major way if left in constant tow-duty.

It needed an easier role in life, like carrying hay bales out to the cows.

[6.5 Detroit Diesel]

Unfortunatlely, Dad went with this truck for all around use. He dumped his 95' 6.5TD after putting over $4,000 into the engine and then having the TC go.

[Mark Rinker]

Can you blame him? Good news is the DMax'es are getting cheaper and cheaper...

[6.5 Detroit Diesel]

No, the only problem is that now he has all but sworn to never buy another diesel. And believe me, I have tried to explain that the 6.6 and the 6.5 are two different stable mates.

[DieselMonk]

I bailed out of my '03 6.0L at about 90K miles because we had experienced miserable fuel economy, poor towing characteristics, a known 'average' transmission in the 4L80E, and so many downshifts with over-revving that it was apparent that something was gonna give in a major way if left in constant tow-duty.

It needed an easier role in life, like carrying hay bales out to the cows.

That was the reason i dumped my 00 YukonXL 2500 with a 6.0L at 90k km. I needed a new tranny at 60k km. Gas milage was unreal and towing was a joke compared to my 07 DMax.

[6.5 Detroit Diesel]

Truck is fixed, though it wasn't what we thought it would be. The truck died and wouldn't start. Turns out the in-tank fuel pump was shot. $1000 later with an updated pump in, the truck runs fine, can hit high RPM's without making noise, and a slight miss that was noticeable at idle is gone. :)

[Mark Rinker]

Glad to hear its solved, and nothing internal engine related. Most of the time its something simple - but not always that simple to find.