'94 5.7 compression

[Todd Savage]

posted yesterday about valve cover gaskets, but I got bigger issues than that. Started missing yesterday, so today I pulled the plugs and #1 plug was almost completely ashed over but it wasn't white ash it was tan colored ash. went ahead and pulled all 8 and two others were somewhat ashed up, but the other 5 looked ok. ran compression check and here's where the bad news comes in.

1-85 2-150
3-171 4-115
5-180 6-175
7-96 8-168

Double checked #1 just to be sure, read 85 again. squirted a little oil in cylinder, rechecked, came up to 112

Truck has 139k on the odometer. I assume it's right due to running the VIN and the mileage adds up to where it should be. Still doesn't mean it's the original engine I guess, but then it again it could be original. Here's my question. How do I determine if it's rings or a valve issue? It goes up and down the road just fine. I wouldn't have ran compression check if the 3 ashed plugs looked ok like the other 5. That's what made me want to check. Comments appreciated.

 

[magimerlin]

That little bit of oil told you its the rings.... oil will not seal valves enough to really notice...

sent from what use to be a great country...

 

[magimerlin]

Small blocks are relatively cheap... buy and build one as time allows as you run your current one you feel it's dead or the new motor is ready... would only take a lazy weekend with hand tools to remove and replace it..

sent from what use to be a great country...

 

[Todd Savage]

yeah at this point I'll just put 8 plugs in it and drive it. guess that's where my quart of oil every 600 miles is going, but it's odd I'm not seeing any smoke

 

[Ironhead]

With oil, it came up to only 112. Compare to the good cylinders at 150 - 180. I'm thinking the valves are the problem. Could be cam lobe wear, could be burnt valves. do a leak-down test. Tells you a lot, and you can hear if it is leaking at the exhaust, or the intake side.

But, if it's a bad cam/lifter, or rocker, this won't help. You need to remove a rocker cover, and use a dial indicator to measure valve travel while the engine is turned over.

 

[slowburb]

I think there are a few things causing the low readings...I agree with Ironhead (we usually do). You have ring sealing problems, and valve sealing problems, and also possibly cam/lifter/valvetrain problems.