6.5 TD Compression Test Results

[BobFunGhoul]

I have acquired a 1997 Suburban 2500 TD that has a rough idle and is smoking tremendously (blue smoke, 197,000mi). When I did a compression test, 7 of the cylinders would come up to 200psi on the first compression stroke and then another 50 psi with each subsequent compression stroke until they peaked out at about 415 + or - 10 psi. The #7 cylinder came up to 200psi on the first stroke and stopped there. When I bled the gauge and attempted the test again, #7 refused to give me any compression at all. I understand that there is something afoul with lucky 7, but I can not comprehend why it would have given me any compression at all with it's first stroke. Before I open it up, is there anyone that may have had a similar experience who could give me an idea of what I might find when I pull the head? Thank you.

[More Power]

Pull the valve cover first, then look for the proper operation of the intake/exhaust valves. If you're lucky you may see that a rocker or pushrod has a problem, which could be a fairly easy fix.

Jim

[Robyn]

I agree with Jim on this.

The rockers are aligned on the shaft with little plastic buttons that have a barbed stem that presses into the shaft.

These buttons can and do break and allow the rockers to fall off the valve.

This is an easy and cheap fix.

You could also have a broken spring that has turned inside itself and is not holding the valve closed properly.

When the engine is running doe it POP out the intake??
This can indicate issues with the intake valve.

There is also a possibility that you have a lifter issue.

Keep us posted

Robyn

[BobFunGhoul]

Thanks for the info. I will be pulling the valve cover this Thursday, and I will keep you posted. I am not getting any popping out of the intake, nor do I have any blowby. I was thinking (and hoping) that maybe it's just a hung up exhaust valve. I will know more this Thurs. Thanks again.

[Robyn]

A broken spring on the exhaust valve could allow a nasty leak.
Also an intake rocker thats off the valve due to a guide button failure will casue the intake NOT to function. This would explain the one (1) PUFF and then no more.

Good luck and keep us posted

Robyn

[BobFunGhoul]

We pulled the rocker cover today and found that the pushrod for the intake valve on #7 slipped out of the rocker arm and became wedged between the rocker arm and the head. When we removed the assembly and inspected further we found that the tappet was collapsed and the roller on the bottom was flattened. It doesn't appear that the cam has sustained any damage. We were able to remove the tappet and it's retainers without removing the cylinder head. My new parts should be in tomorrow and hopefully we can button it up this weekend. I cannot imagine why the lifter had failed or why it jammed the pushrod in the position it was in. Thank you Jim and thank you Robyn for the information. Your consideration is greatly appreciated.

[More Power]

Dirty oil is the usual cause for lifter collapse. The 6.5 needs to have its oil changed every 3000 miles or so due mostly to soot accumulation. If the oil looks more like black paint, I'd change it now, then again in a couple hundred miles.

Glad the fix wasn't too bad...

Jim

[Robyn]

I hate to paint a nasty picture, but I would be very suspect of the cam if the roller on the lifter was flat.

The rollers are very hard and to have worn it that badly could have done serious damage to the cam lobe.

Inspecting a cam on the engine is almost impossible on one of these engines due to the location.

I would be thinking about removing the cam and looking it over well.
The other method would be to use a small scope that will allow very close inspection of the cam lobe while looking from a distance.

Hope all comes out well.

Robyn

[BobFunGhoul]

I'm brand new here so I don't know if I am allowed to endorse any commercial establishments in this forum, but Rockauto.com rocks. I ordered the parts yesterday at 2:00 P.M. standard shipping and FedEx was ringing my doorbell this morning at 10:00.

From what we could see of the camshaft, it seemed undamaged. We put the new parts in and bumped the starter a few times to make sure the engine turned freely. It appeared that the lift on that specific cam lobe was equal to all of the others. So we buttoned her up and cranked her over. She fired up as if never apart. Smoke billowed out of the tail pipe initially, but it started to diminish shortly thereafter. The engine was as smooth as anyone could hope and the smoke was completely dissipated after about 1/2 hour of idling. I guess the exhaust system had been loaded up with raw fuel, and I don't know how long it had been run with the bad cylinder. We took her out for a test drive(about 30 miles) and she ran beautifully with power to spare.

Jim, you are correct. The oil was the dirtiest oil that I have ever seen. When my buddy and I were done, we looked like we belonged in a minstrel show. The stuff not only looks like paint, but it coats like paint too. We changed the oil even before doing the job, and I expect to perform a number of oil changes every 200 - 300 miles until it cleans up.

Once again, Jim and Robyn, thank you very much. Your assistance is immensely appreciated.

[ToddMeister]

Bob,

Does this vehicle have a cat converter? It could be getting plugged, which will create a ton of back pressure, makes it rough on the valvetrain.

[BobFunGhoul]

That's a good question. There are 2 exhaust components under there. I didn't know that diesels had cats. I was told that one is a muffler and the other is either a resonator or a soot collector. Are there any identifying characteristics that I can look for? It appears that the exhaust is free flowing. She has plenty of power and cruises smoothly. Thanks.

[trbankii]

From other discussions that I've seen, the "soot trap" is the cat converter. My '93 only has the muffler - nothing else from the downpipe to the end of the tailpipe.

I had been looking at online parts catalogs to see if it should have a cat as I'm pretty sure the exhaust on mine has been replaced at some point. But using things like RockAuto, I haven't seen a cat, soot trap, or anything else listed for any of the years under either exhaust or emissions components.

I'm not sure what year they started putting the cat in there.

[Robyn]

94 and later will have a CAT unless it got LOST somewhere.

These do plug over time and will really cause a serious power loss as well as keep a lot of heat bottled up in the engine.

If the rig has over 100K on the clock its a good bet the Cat is pretty well stoked full of crud