Need Help-Compression Issue has my mechanic stumped
 

I have a 90 chevy 1/2 ton with a 3 yr old 5.7 in it with TBI. drove it sunday ran fine but had a slight miss. Was planning on new plugs tue. Monday would not start, backfired through tbi to include flames a couple times but not start. Heard a clicking when running starter and sounded like one click per revolution of engine. Towed truck to buddies house-he is a mechanic. He figured timing chain, we checked compression on #1 and nothing so we pulled timing chain cover and it is fine. timing marks are close to being aligned so it appears to still be in time. so we pulled valve cover to check and see if cam was broke and all valves are moving properly. So we ran a compression test and we have 150 on 5 and 7 and 120 on 6 and nothing on the rest. (0). When we put air pressure to #1 I could feel it through the tbi so we ran a comp test on it again and it had 100, a while later we tested #1 again and 0.
Now I had two mechanics there and both are stumped. Also when we pulled the plugs about half were wet and half were dry. And #7 and #8 had so much fuel in them that it ran out on the floor into a puddle.

Help please.
Thank you
Steve

Hmmmmmm what about the valve springs? any broken or collapsed? how about lifters? I would pull the heads and check the valves and the lifters while you are there look at your piston tops

Broken crank?

crank is not broken if it was it would not be driving the timing chain and it is.

no broken valve springs and all lifters are working.

has everyone stumped.

Has it been ran low/out of oil, was it broken in right? Put a little oil in each cyl and recheck compression, if it goes up your rings are shot. Also check the distributer, cap, and rotor, make sure everything is tight and that they look good (not worn or broken), then check timing. Pretty sure the timing has to be checked with a scan tool.

Good luck!

nah you can check timing the old fashion wayturn the motor over by hand....bring # 1 to TDC AFTER the exhaust stroke and check your timing gears they should be lined up if not you jumped time and a timing light works great too..........valves are as follows IE EI IE EI I= Intake valve E= Exhaust valve......or maybe on an outside chance your fuel preassue regulator went bad causing the fuel build up in the cylinders

"timing marks are close to being aligned so it appears to still be in time."

What does "close to being aligned" mean. They either are or they aren't.

Since they are just "close" the evidence would suggest it jumped time and should be properly re-aligned or worst case you could've bent a few valves. I hope it's not the latter.

Try to loosen all of the springs and apply air pressure to each cylinder. If they all hold air, then install steel gears, a new chain, align the timing marks, adjust the valve springs, put all the stuff back on and drive the beast home.

I fired the mechanic. He was a idiot, even I could see that a couple valves were not moving. So The new mechanic (and yes he was worth the tow bill) pointed out that at least one valve was stuck so he pulled the heads and guess what? 4 valves are stuck open= no compression. Can't figure out why because I use vavoline at oil changes. It was a factory crate motor and it has been using oil since I put it in. Now we see it was leaking oil through two valve guides. Well I used cheap oil when it was low and the mechanic thinks I got some junk oil that really screwed things up. So we are going to fix it and then I am treating it with prolong to help prevent problems in the future.

VALVES stuck open= bend valves= jump in time as said by Drifter59 retime it with a new chain and gear set also not having the motor timed right will bend valves and tear up valve guides..................glad you got it figured out..........and by the way cheap oil is NO different than expensive oil....dont get me wrong Im a Valvoline guy too..and honestly any mechanic that tells you he thinks the brand of oil you put in causes problems has problems.......(penzoil excluded we ALL know what penzoil does(sludge))