The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support RTM Racing
Please Support Fuel Injector Clinic

2G Low compression

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

John Miller

Proven Member
172
67
Jan 27, 2020
Watertown, Wisconsin
Hello fellow DSM addicts!

I recently tried starting my 1997 eclipse GS-T for the first time since swapping in a used motor. The short block has 120k and the cylinder head around the same. I replaced all the gaskets in the engine, but left all the internals untouched. I couldn't get it to start so i went down the list of things to check. When I was checking compression, cylinder #3 was at 50psi whilst cylinders 1, 2, and 4 where at 150psi. I can't afford to rebuild an engine so it will either be sold or I will store it until I can afford to. My question is: Is it odd that only one cylinder is low on compression? Is there anything I can check without pulling the head off? Does this engine ultimately need a rebuild?

Thanks
 
2 questions:

1. Did you use a MLS or composite head gasket?

2. Were either head or block resurfaced?
 
I see several things here.
Used engine....sometimes you get what you pay for.
Surfaces were inspected. Inspected how?
Did you bleed the lifters down and have you done a leakdown? Find out for sure why its low and from where.
 
I see several things here.
Used engine....sometimes you get what you pay for.
Surfaces were inspected. Inspected how?
Did you bleed the lifters down and have you done a leakdown? Find out for sure why its low and from where.

Inspected with that one gauge you use to measure crank play. I did not bleed the lifters and I have not done a leak down test.
 
Inspected with that one gauge you use to measure crank play. I did not bleed the lifters and I have not done a leak down test.
I would recommend a leakdown and a caliper is not going to cut it for inspection. Leak down will show you where the problem is then you can assess why.
 
Okay I don't have a leak down test kit, but maybe I'll buy one soon.
check local auto parts stores for rental. Not sure they have that. Alternately you can build one.

Saw your other post about surface prep. In my opinion you're putting the cart before the horse. Find out why you have a problem. Then find a solution. If you just want to take it apart anyway then by all means go ahead. If you elect to take it apart you need to check all possible sources of low compression. If you have it apart I would suggest a thorough inspection and subsequent repairs by a qualified machine shop. If that also involves new valves. Pistons. Rings etc then that's what you do.

Have you run this motor yet? Doubled check that one cylinder? I've had a comp tester oring roll on me. I'd hate to see you chasing a ghost
 
Last edited by a moderator:
Start with a leak down test and go from there, if you’re lucky you’ll just have a valve that isn’t sealing properly which is a quick fix and then you’ll be good. Also you probably have another issue if it won’t start. I had low fuel pressure plus 2 melted valves on cylinders 1 and 2 and I still managed to get it started. Check for injector pulse and spark too.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top