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Can a worn timing belt cause lower compression ? All 4 cylinders are at 130 lbs compression. The engine runs fine except in 5th on the highway. MPG is 26 to 29. I was going to pull the trans to replace the rear seal but ran a comression test first. Then I was going to put on a used Calmini 2" header and eliminate the catylitic converter and add new exhaust. The engine has 102000 miles on it. Any ideas? Thanks Ken:p
 

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I don't think a worn timing belt would change any compression readings unless it's so worn that the camshaft is out of time with the pistons. If the valves aren't closing when they are supposed to, the compression would be off.

Since you only have engine problems in 5th gear, could it be related to the "5th gear switch" on the transmission? I'm not clear exactly WHAT that switch tells the ECM to do, but since it's the only gear position with a switch, it may be worth learning more about what it's supposed to do.

As a quick test, I would disconnect it and then see if the problem remains.

Phil
 

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I don't think a worn timing belt would change any compression readings unless it's so worn that the camshaft is out of time with the pistons. If the valves aren't closing when they are supposed to, the compression would be off.

Since you only have engine problems in 5th gear, could it be related to the "5th gear switch" on the transmission? I'm not clear exactly WHAT that switch tells the ECM to do, but since it's the only gear position with a switch, it may be worth learning more about what it's supposed to do.

As a quick test, I would disconnect it and then see if the problem remains.

Phil
Thanks, I knew that switch was there but I never looked into what it did. Ken
 
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