I have a 1994 explorer with the 4.0 V6. A while back it was run hot until it quit running. I had to replace the radiator and have the heads reworked since they were slightly warped. The head gaskets had blown and water was in the oil. When I got it all put back together and started it it was skipping on the No. 1 cylinder. I did a compression check and the results are confusing. Most of the time when I turn the engine over the compression gauge will go up to about 30 lbs and hold there. Sometimes it will spike up to 120lbs and drop. I tried the next cylinder over and it holds 120lbs so I know the gauge is okay. After discussing with a friend we've come up with a couple of possibilities. (1) Broken piston ring. But why would it go to 120lbs sometimes? (2) Valve pushrod out of place. I'm wondering if I missed getting the pushrod on top of the lifter on this cylinder. But then again why would it spike to 120lbs sometimes. (3) Sticking fuel injector. Maybe the injector is stuck open from the water in the system and it closes sometimes and that's why there is a spike. The vehicle sat for about a year after it was run hot so water stayed in the wrong places for a while. Also every now in then there will be a little white smoke coming from the tailpipe. But other than that it has plenty of power and runs pretty good. When it goes into overdrive it really skips and shakes the whole vehicle. I'm thinking of buying an injector and trying that but at $61.00 each I hate to buy one just to try. Any suggestions or comments would be greatly appreciated. Thanks.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>

 

Have it leak down tested, get a leak down tester, or build one. You'll need a manual for determined exactly what the test indicates. It will give you a better scope on what the problem may be. Almost seems like the compression gauge may have a leak somewhere, and how some reason it's not in a position to leak when you're testing the #1 cylinder. I am not sure. You may need to check the valve lift with a dial indicator like in a cam degreeing kit to determine if the valve is not opening properly as you've stated. Though, I would doubt that's the issue. What does #1 plug look like? Re-check the oil for more water.

On my 2.9L V6, I had the heads milled .030". It clearly stated in this performance book I have that the lower intake manifold would need to be milled to compensate for the difference. The machine shop manager a Napa told me it would be fine so I put the engine back together. Sure enough, the lower intake manifold gasket was leaking. Fortunately, they gave me a deal on the intake manifold milling. I wasn't a happy customer, and this one of the main reason I refuse to let another person work on anything I own. I am not sure if your heads had to be milled that aggressively. That's just a thought though, the 60 degree design is a pretty aggressive angle.

Also, did you happen to change the oil after the head gasket job to get the excess water out? The water will fry the bearings over time.

How to build a leak down tester:
http://www.xs11.com/tips/misc/misc3.shtml

Pete

 

Thanks Pete,
I changed the oil after I saw the water in it and I've changed it again since. The oil stays clean and the gauge holds pressure. I replaced all the spark plugs and after driving the vehicle some this one looks better than the one next to it. I don't think its firing. I'll ask the machine shop that did my work about the lower intake gasket. Thanks for your comments.