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1998 3.0 L misfire


New Member
Mar 24, 2014
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I have a 1998 Ranger with a 3.0V6. It has 187,000 miles and has always run well. Last week I noticed a weird vibration and noise while driving home. When I got home the truck would barely run and had a very bad misfire.

I took it to Advance Auto and ran their computer on it. It showed Cylinders 5 and 6 misfiring. I put in new plugs and wires (found #6 wire had a split and was probably arcing to the block.

With the new plugs and wires there was a slight improvement. Next I cleaned the Mass Airflow Sensor and the Throttle Body (with the right solvents for each job). Again there was a slight improvement. Now computer was showing no misfire but that the left bank was running lean.

I did a spark test with an HEI plug tester and had spark on all cylinders. Number 6 looks a bit weak though.

Today I pulled the plugs I installed last week. 1,2,3, and 4 still look brand new. 5 is black and fouled. 6 is somewhat black but not as bad.

Did a compression test today. On my gauge most cylinders were between 149-150psi. Number 5 shows zero compression. So we are down to either a broken valve spring or missing rings. Going to try the oil test tomorrow to see if I can narrow it down that way. Doesn't really matter at this point, either way the valve over comes off. Just hoping I don't have to replace a piston too and the cylinder itself is still relatively intact.

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