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View Full Version : Low compression on all cylinders, runs poorly.


jimayres
08-17-2005, 11:03 PM
My car has been running great and now all of a sudden it runs poorly and the compression test done today showed 80-90 across the board. Can this be a timing chain problem? The engine only has just over 1000 miles on it.

Keller
08-18-2005, 12:12 AM
What do you define as "poorly"?

Can you redo the compression test after squirting some oil in each plug hole?

jimayres
08-18-2005, 10:29 AM
The car runs and drives but has no power; hard to back out of driveway uphill, can be driven on highway without getting on it. because it won't go if you do. If you floor it. it doesn't do anything, no kick in the pants, nothing, just pokes along. Yes I can redo compression by squirting oil in cylinders but I don't see how this will help diagnose when all cyl. are down about 50%.
Thanks, but I still want to know if this can be a cam timing problem,
JIm

JHensberry
08-18-2005, 08:22 PM
Could be fuel problem. What is the status of your fuel system. Does it hold after it is shut off/or build when you are on it. What about TPS. Anyway, the cam helps with your injector timing so the ECM can see where the #1 piston is. Did the engine just get rebuilt?

jimayres
08-19-2005, 10:25 AM
Engine was purchased w/1000 miles on it from someone building a Stage 2 engine and has run perfectly. It has dynoed at 481 RWHP. Fuel system is fine and has been checked out. Last night I pulled the timing cover and everything looked fine at first look, then I notice the cam bolt with roller is loose, so I unscrew it by hand and remove the gear and the part behind it and find that the woodruf key was sheared at the front of the cam gear.
I hope when I get all this put back together it will run like it originally did.
Thanks,

Jim

kenmosher
08-19-2005, 10:35 AM
Check it for bent valves ... if things got far enough out of synch with the loose cam gear, they could have contacted the pistons and bent a few.

acltpvd
08-20-2005, 02:52 PM
With the broken key found it would not supprise me if there was valve-piston contact. Do a wet compression test first and make sure there is no leakage at the gauge. You MIGHT be able to get something in the plug holes to inspect the piston tops. If not I would bite the bullet and pull the heads. If there was contact it would be best, in my opinion, to replace the pistons as well as the valves and related items. This type of problem is usually a mechanical problem and not an ancillary system problem.

jimayres
08-22-2005, 11:38 PM
One of my son's friends has a scope I can borrow to check out the pistons, etc. and I will definitely be using that to determine if there is any internal damage.

Jim

briandu
08-25-2005, 10:35 AM
what type of compression is normal for a turbo motor is 110 125 acceptable?

kenmosher
08-25-2005, 10:52 AM
See above .. all sorts of factors come into play (altitude and procedure are biggies).

IF it's somewhere close to sealevel and procedure is done on a warm motor with throttle WOT... most gauges will show 120-140 psi.

briandu
08-25-2005, 01:33 PM
i wrote that then i read the info (oops) thanks for the answer anyway