low compression! help!

T

ThunderSC1994

Registered User
Hi i own a 1994 thunderbird SC. It ran like crap when i bought a month ago and now it wont start. It has spark and fuel but i checked the compression and all cylinders read 75 psi. I dont know what to do! Can anybody tell me if they have had the same situation or can tell me what the deal is I'd appreciate it!
 
Very odd that all cylinders are reading that low. By any chance does it have aftermarket rockers or a cam ?

Sounds like your rockers are adjusted too tight and the valves aren't closing all the way or they are closing much later than they should.

David
 
valves aren't closing all the way or they are closing much later than they should
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To add to this (and I don't know if this ever happens) could your timing chain have slipped? Maybe it had already slipped a tooth when you bought it, and it recently slipped even more so it won't even start, and is giving low compression readings?
 
i have no idea if it has aftermarket cams but somehow i doubt it

it could be the timing chain but have u heard of that happening before on these cars? my high school auto shop teacher(very experienced) said the motor might just be "worn out". do you know if those would be the symptoms if it was simply worn out?
 
If it was just worn out, I don't think it would suddenly die like that :confused:

Wonder if there's any easy way to test if the chain has slipped, or at least if the chain has a lot of slack? Maybe the other folks here might know better? I'm just a noob.

I wonder if you could check the chain slack by pulling the cover off of the camshaft position sensor? With the key OFF, rotate the crank using a large socket and driver one way about 1/4 turn, then the other way about 1/4 turn. The cam sensor should start moving within a few degrees of the crank when you do this. If you have to turn the crank, say more than 10 degrees, maybe the chain or chain tensioner is the problem?
 
thanks

thank you very much for replying so quickly and i will most definitely check the timing chain tomorrow. i hope all it is a timing chain. im 17 and i only have about a grand left in the bank so i cant afford to be replacing or rebuilding any engines! lol but again thank you for the quick replies and good advice. I will post something after i check the chain tomorrow
 
Just a thought...

Could you possibly be getting a bad reading on the compression test? You might want to get "confirmation" prior to tearing into the engine...
 
I was thinking the same thing.....:rolleyes:

You could have a bad comp. gauge......

How many miles are on the car?
 
ThunderSC1994 said:
Hi i own a 1994 thunderbird SC. It ran like crap when i bought a month ago and now it wont start. It has spark and fuel but i checked the compression and all cylinders read 75 psi. I dont know what to do! Can anybody tell me if they have had the same situation or can tell me what the deal is I'd appreciate it!
Click to expand...
disconnect an o2 sensor from exhaust before cats. if it fires up then your cats are severely clogged.
 
o2 sensor

I will try that. The cats are real real old and one actually has a hole in it i think. But would clogged cats affect the dry compression?
 
compression tester

I am using a standard compression tester. I was going to do a wet compression test (spray oil in cylinders to check the rings) today but i did not have time.
 
ThunderSC1994 said:
I am using a standard compression tester. I was going to do a wet compression test (spray oil in cylinders to check the rings) today but i did not have time.
Click to expand...

Is it the type with a hose and fitting that threads into the spark plug hole, or one of those things with a gauge and a rubber tip you press against the plug hole ??

If the latter, please toss it in the trash and get a good tester.

David
 
That was what I was trying to find out, as well.......

My first compression tester was the rubber tipped one and I couldn't hold it tight enough to the spark plug hole to get consistent readings.....

It shortly ended up in the lake next to our house......:D
 
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