1994 850 Compression loss

94850-99XC70 · Post by **94850-99XC70** » 19 Oct 2006, 08:30

Seems like my 850 has lost a bunch of compression over night.
Friday it ran like a champ, Saturday it cranks but won't fire, the mechanic says it doesn't have enough compresion to fire over. Any one ever run inot anything like this? I would hate to have to part out the car.

bobsnow100 · Post by **bobsnow100** » 19 Oct 2006, 09:51

Was it running fine before that or were there any other symtoms?
You might have carboned valves. If they get carbon built up on them(a lot of city driving can cause that) than they might not be closing all the way.
Were all the cylinders low on compression?

94850-99XC70 · Post by **94850-99XC70** » 19 Oct 2006, 10:11

Hi, yep, it ran like a champ all day Friday. I guess the compression is down to 45-90 on various cylinders. 145psi is optimal?

bobsnow100 · Post by **bobsnow100** » 19 Oct 2006, 10:26

My 1994 850 with 160,000 miles had compression at 172psi Highest cylinder and my lowest reading on a cylinder was 164psi
Try squirting a tablespoon of oil into each cylinder and take a compression reading. If it goes up than you have worn piston rings. I still think you have carboned valves because this happened overnight. I just did the head over on my 850 and the intake valves were all caked up.
How is you oil condition? Maybe you have a few hydrolic lifters that are stuck causing your valves not to close

94850-99XC70 · Post by **94850-99XC70** » 19 Oct 2006, 10:31

I'll try that - thanks for your help

Post by **Ozark Lee** » 19 Oct 2006, 14:16

I'm really not buying the compression loss at all and I'm suspicious of the compression test. The plugs set very deep in the 850 head and it might be that the adapters on the compression gauge are getting hung up on the walls of the spark plug hole making it feel tight when it really isn't. It is also important that the throttle body be open when doing the test. Very little air gets around the butterfly if the throttle isn't open. If the throttle body is dirty it is possible that virtually no air is getting around it in the closed position. With little or no air getting into the motor the compression readings will be low.

Have you pulled the codes?

I really believe your problem lies elsewhere, engines just don't loose compression on multiple cylinders overnight.

...Lee

94850-99XC70 · Post by **94850-99XC70** » 19 Oct 2006, 15:35

Thanks Lee, I agree, it wouldn't loose that much pressure within hours.

thanks,
Bob

Post by **robert213** » 19 Oct 2006, 22:38

bobsnow100 wrote:Try squirting a tablespoon of oil into each cylinder and take a compression reading.

I have heard of this problem before. Engine runs just fine the day before. Park the car overnight. Next morning, engine compression so low that engine won't start.

Cause -- Carbon on Valves, such that they won't close properly.

Quick Solution -- Remove all spark plugs. Squirt several tablespoons of oil into each spark plug hole. Re-install the spark plugs. The oil fills in the gaps in between carbon-ed up valves, raises engine compression, and engine starts. Drive car until the engine fully warms up. Problem magically disappears.

Some folks call it the lawn mower syndrome.

steve · Post by **steve** » 20 Oct 2006, 06:32

What is the remedy for the carboned valves? An Italian tune up or what?

Putting oil in each cylinder seems like a quick initial fix just to get it going but it will return.