Low compression in engine

Tiny
GAILKNUCKLES22
  • MEMBER
  • 2004 CADILLAC CTS
  • 6 CYL
  • 11,600 MILES
I had a used engine installed and the car is experiencing a misfire in the fifth injector. Does that mean engine is no good? Car drives good but when you stop it is shaking a little or if engine is running you can see a little shaking in the engine. I replaced the fuel injector and put in new spark plugs. Mechanic seems to think engine is bad.
Saturday, June 2nd, 2018 AT 7:29 AM

5 Replies

Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
Engine is bad is a term that mechanics should not use.
It is better to just say what they believe to be bad, whether it be a leaking cylinder head gasket, a worn down camshaft lobe, a valve not seating, a broken piston ring, etc, because these things can all be fixed.
A bad engine would basically have to have a cracked engine block for it to be so called "bad".
You mentioned "low compression", did you or someone actually do a compression test and if so what were the readings?
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Saturday, June 2nd, 2018 AT 7:35 AM
Tiny
GAILKNUCKLES22
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  • 3 POSTS
The mechanic did the test stated that it was low. I do not know the reading. He stated that the engine should be replaced.
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Saturday, June 2nd, 2018 AT 7:44 AM
Tiny
PATENTED_REPAIR_PRO
  • MECHANIC
  • 1,853 POSTS
I think you should ask him again, if it would be less expensive to either replace the engine either with a new engine, rebuilt engine, salvage engine or repair what is there.
Then also ask him what the compression readings were and if he did a compression test on all cylinders or just on number five cylinder. What the readings were and if just low on number five, if he repeated the compression test with a little motor oil in the cylinder, called a wet test to see if maybe it is a piston ring worn down and/or completed a leak-down test to find out exactly where the compression is being lost, from a blown head gasket, a intake or exhaust valve not seating, a broken piston ring/hole in a piston or what?
Have him tell you specifically why the engine is bad and then tell me what he says, because simply replacing the entire engine for something that can be repaired makes no sense to me.
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Saturday, June 2nd, 2018 AT 7:55 AM
Tiny
GAILKNUCKLES22
  • MEMBER
  • 3 POSTS
Thanks for your time, it was very helpful.
Will contact you with an update.
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Saturday, June 2nd, 2018 AT 7:58 AM
Tiny
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  • MECHANIC
  • 1,853 POSTS
Okay, I will be here.
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Saturday, June 2nd, 2018 AT 8:08 AM

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