zero compression on cylinder # 2

[monsoon]

I just drove my 92 navajo 400 miles and it starting idling rough towards the end of the trip.

Got the plugs changed ( some were completely shot ) and did a compression test

problem

cylinder 2 is at ZERO!
cylinder 5 is at 70%

do I need to do an expensive valve job here? Could anything else be dropping the compression to cylinder 2?

dead injector? stuck valve?

Hoping i do not have to rebulid although she has 130K miles on her and I love the truck too much to scrapp it

anyone has any ideas it would sure help!

 

[aldive]

Was it using oil?

 

[monsoon]

yep looks like she was drinking about 1 quart every 400miles---thought it was a little crank drip and oilpan---had that done about 6 months ago but job wasn't great. So I thought that the oil use was still from that issue---

 

[monsoon]

expensive?

 

[scholzee]

Make sure the compression gauge is sealing good at the spark threads, it is hard to get 0 psi even if a valve is hung open usually the gauge will at least flutter. If you pull the valve cover you can crank it and see if the valves are moving. If a intake valve is hung open you may hear air rushing in the intake. If you get that cylinder to top dead center, both valves closed hold the crank from rotating you can pressurize the cylinder with air and listen for a leak out the dipstick tube(worn rings), intake manifold (burnt or open valve) or exhaust system ( burnt or open exhaust valve)

 

[MrShorty]

Another test to perform on a cylinder with low pressure is to squirt a little oil into the cylinder(s) with low pressure and retest the compression. If the compression pressure doesn't change, then it's probably a valve or cylinder head issue. If the pressure is higher, then it's probably a bad piston ring.

 

[Glacier991]

I too am curious about the "zero" reading. That's a GROSS leak. Rings seem unlikely, even a broken ring will generate SOME pressure. If it's truly zero my money is on a hung valve.

Happy Exploring

Chris

 

[monsoon]

Chris,
Thanks for the reply---Man i love this board!
If ist is a hung valve what does it cost to fix it---do i need a full valve job? complete rebuild?

any clue on the costs?

 

[Glacier991]

Well, if you can find someone with a leakdown tester (it is a fitting that hooks to air and introduces air into the cylinder through the spark plug hole, you can tell pretty quickly if THAT is what you have, you will hear it in the intake or exhaust. I have not dealt with this exact problem (a hung valve) other than theoretically, so someone who has might offer better advice, but for what it is worth, I am going to suspect that head will need to come off, and the offending valve and it's guide need work. (That part I have done more times than I can count) But as long as you have the head off, depending on miles I'd grind the valves in that head and check the valve seals and springs, and clean up the head - in other words a half valve job. As in every one of these cases it's easy to incrementally jump into something far larger (E.g. gee if I am going to do one head, I might as well do both!)

HTH...

Happy Exploring

Chris

ps. If you are serious about auto mechanics, a leak down tester can be had for about $75 and beats a compression tester hands down. In aviation it's ALL they use.

 

[monsoon]

I'm wondering if it will become worth it to replace the engine with one with less mile? My friend has a spotless 94 engine with 77K when he parted out.

Do you think it makes sense to just swap it out--the $ on the work may be the same as doing the heads?

your thoughts

 

[aldive]

If you are going to the trouble of jerking the motor to replace, get a new rebuild not an old motor.

Good luck.....

 

[monsoon]

makes sense---my friend will give me the old motor for $300 and rebuilds cost about $1000 more---that's my dilemma-

 

[aldive]

That used motor is 9 years old abd gas 72k miles.... find a way to make up the difference in dollars.... you won't regret it.

Good luck.