GMC Suburban w/ 5.7L & stuck valve?

[trbankii]

Just a half ton Suburban, but I know that folks here know their stuff.

My neighbor has a 199x Suburban with the 5.7L/350 engine. Taking his son to college the other week, towing a trailer and loaded to the gills with everything, he started losing power. Got there and back, but ran somewhat rough and didn't have the normal power.

Took it to the dealer and they determined that the #6 cylinder didn't have any compression. Their diagnosis is possibly that carbon buildup flaked off and is keeping a valve open. They poured some "snake oil" of some sort into the tank and said to drive around to see if it would work its way loose again. It seems to have improved somewhat, but still isn't normal.

The dealer wants $2K just to open things up to take a further look. Any repairs are on top of that.

He really doesn't want to sell the Suburban - it is in great shape otherwise. But he is also unsure about going ahead with the repairs only to be told that he needs a new engine.

Any advice or diagnosis anyone would suggest? He wasn't sure what was poured into the tank. I've heard people recommend using Seafoam. Any advice on that? That there has been some improvement with the current "snake oil" could suggest that a better solvent would possibly do the trick.

Many thanks for any suggestions.

[a5150nut]

:rolleyes:How about doing his own compression check? :confused:Not that hard to do and a gage is not that expensive. And the Sea Foam is worth a shot too.:D

[trbankii]

Definitely doesn't have compression, checking that isn't the issue.

The question is whether there is any experience or tips to try before having someone tear into it. My neighbor isn't up for doing it himself and I really don't want to get into it - too many of my own projects. But he is going to check with a couple other mechanics rather than going to the dealer if it comes to that.

[DmaxMaverick]

There isn't much you'll be able to "see" without getting the valve cover off.

If a pushrod isn't bent or a valve spring isn't broken, measure the rocker arm throws (compare to known good cylinders). If one is short, could indicate the cam or a lifter. Could also be a stuck valve. With the cover off, you can rotate the engine to the compression/power stroke on that cylinder and add shop air through the plug hole (keep engine from rotating, remove the coolant cap, and use 10 PSI or less). If it won't hold compression, the air will go somewhere. If it's a valve, the air will escape through the intake or exhaust (depending on the valve). If it's a broken ring or piston, it will escape through the crankcase. A blown head gasket will let the air into the coolant (watch for bubbles at the coolant tank, or radiator), or an adjacent cylinder (although this would be indicated by 2 cylinders down on compression).

There are many things you can do/see before removing the head, but you'll need to at least get a look under the valve cover. You could do the air pressure test before removing the cover, but it's less revealing in most cases.

[trbankii]

DMax, Thanks for the suggestions.

They did pull a valve cover and determined that the rod and spring were ok. It doesn't sound like they did any checking beyond that.

Your suggestions were just the sort of thing that I was looking for - tests to do before tearing the whole thing down to give some idea of what is going on. I'll pass them along to my neighbor.

Many thanks! :cool:

[trbankii]

Ok, they tore into it enough to find out what the problem was. Bad #6 cylinder... Said it was a known problem with these engines?

Anyway, looking at new engine and new computer. Guess was that the computer went bad and that killed the cylinder. I think my neighbor was saying about $4200 for the engine, $700 for the computer, and $800 for the labor (he was headed out, so sort of rushed when we talked last night).

It sounds like my neighbor doesn't want to put money into it. Shame is that the rest of the vehicle is in excellent condition for its age. Could be a good target for a diesel swap if someone was so inclined. Or any motor swap if you have a truck/'burb with a good engine and bad body/interior.

If anyone is interested, I can connect you up with my neighbor to talk about it.