I recently went through something more extreme. As it turned out my Intake Manifold was not torqued on to specification. I fixed it easily once I figured that out. I'm definitely not saying that is what you are experiencing, but it may be worth a look.

Do you get puff of white smoke from your exhaust pipe? If so, that is an internal leak that is getting into the combustion chamber and ultimately makes its way out the exhaust. You may be able to smell it too.

Oh CRAP!!!! 1989 3.0L Overhaul Fail

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89 Raider - V6, Automatic, rear LSD, A/C Retrofit, Cruise Control Retrofit.