WHAT IS THE CORRECT COMPRESSION

  • Tiny
  • mooshie42
  • 1996 Mitsubishi Magna

I took my car to a mechanic yesterday he said my compassion was to high the reading was 160/170. My car is an 1996 2.4 litte. 4 cylinder. I think its a TE model I hav spent the day ringin other mechanics only to be told that that compression readin is ok. Any information is appreciated as I was told that I need a new motor. Thanks heaps jackie

Thursday, June 28th, 2012 AT 6:44 AM

5 Answers

  • Tiny
  • caradiodoc
  • Expert
  • 24,900 posts

You do not need a new engine for compression being too high. Some engines do have high readings. A common value is between 120 and 150 pounds. At less than 100 we would start to suspect some engine wear. Other than the design of the engine, the only thing that will cause compression to be too high is carbon buildup. LOTS of carbon buildup, and that is not real common. What is more important is that all cylinders read about the same so it runs smoothly.

What kind of problem are you having?

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Thursday, June 28th, 2012 AT 6:52 AM
  • Tiny
  • mooshie42
  • Member

The car is misfiring he was supposed to check the fuel injection and do a diagnostics on the car to c why it's missfiring. Instead he charged me a fortune told me my compression was to high and the only way to fix it is to get a new engine. My dad rang him to ask what work he had done on the car and he had the nerve to hang up. My compression is 160-170dad has spoke to two mechanics and they have saids it's fine. It's going to a fuel injection specialist tomorrow. Thanks heaps jackie

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Thursday, June 28th, 2012 AT 8:38 AM
  • Tiny
  • caradiodoc
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  • 24,900 posts

You need three things for each cylinder to produce power, fuel and air, spark, and compression, and they must be equal for all cylinders. If compression is low on one cylinder, that will cause it to develop low power and you could feel that as a misfire, but typically you'll have a fuel or spark problem causing the misfire. The Engine Computer on '96 and newer cars can set fault codes telling which cylinder is misfiring. Once that is known, if simple parts replacement doesn't solve the problem, the mechanic will often switch injectors between two cylinders to see if the misfire goes to a different cylinder. On a lot of newer cars that can be done with individual ignition coils too.

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Thursday, June 28th, 2012 AT 8:45 AM
  • Tiny
  • mooshie42
  • Member

I put new sparks plugs in it. Took it to a fuel injection specialist and everything was fine untill this morning when it started blowing thick white smoke. I am now at the end of my tether and wish I never brought the stupid car. Any information will be grateful thanks jackie

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Sunday, July 1st, 2012 AT 10:17 AM
  • Tiny
  • caradiodoc
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  • 24,900 posts

White smoke from the tail pipe is a sign of burning coolant from a leaking head gasket. That is fairly common in all car brands but it is an expensive repair. In addition, most of the time combustion gases get forced into the cooling system and show up as bubbles in the reservoir that make it look like it's boiling. Most mechanics have a tester to verify that. It involves drawing air from the radiator through a glass cylinder with two chambers partially-filled with a special dark blue liquid. If combustion gases are present, that liquid will turn bright yellow.

Head gasket repairs are relatively inexpensive on four-cylinder engines but it could cost around $500.00 to a few hundred more. Once removed, the mechanic will check for cracks in the cylinder head which will cause exactly the same symptoms. That would require a new head and would be considerably more expensive. Unfortunately there's no way to know if a new head is needed or if just a new head gasket is needed until it is taken apart for inspection.

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Sunday, July 1st, 2012 AT 6:27 PM

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