Dropping Cylinder/No check engine light

[ramoulton]

Hello- I'm new to this forum and I made a similar post to the Newbie forum. Got 41 reviews but no answers to my problem.

Here is what is frustrating me and my mechanic. When my 1994 Explorer 4wd XLT 4.0 6cyl stock Explorer, meticulously maintained, and just turned 175,000 miles is doing. When it reaches normal temperature it does a quick skip, like it is dropping a cylinder. Sometimes 4 or 5 times at a red light. Then it will run sweet as usual and then it may skip once in awhile when driving. Done the plugs, plug wires, coil, and fuel injectors. also added Lucus fuel treatment and Lucus oil additive thinking I may have a valve sticking. No help. Seems to be a problem when the engine is hot and outside temperature is warm.

Any help will be super appreciated. Been doing this for 5 months now. I'm baffled but I have no mechanical skills. Thanks in advance. Enjoying this forum.
Dick

 

[Anime]

What sort of 'skip' is it you're referring to? You mean a 'miss' like one of the cylinders isn't firing every so often?

Have you not done the Mass Air Flow sensor cleaning? That seems to fix a lot of basic problems. You may have a cylinder with low compression, either from a failing gasket, cracked head, or other such issues.

Generally it'd be easiest to take it apart to discover any issue that might be from something that isn't just easily diagnosed. If it's not throwing a check engine light, you are left to discover possible mechanical causes, or try a lot of other things in hopes you'll stumble upon it.

I had a knock/miss that was like someone hitting the side of the engine block with a sledge hammer when I would hit the gas. The issue turned out to be low quality gas that had gummed up the fuel system. The fix was as easy as using higher quality gas, and after a few weeks/months it never happened again.

You might also check for even simpler things, could even be a wire rubbing on something and occasionally shorting out and causing an issue that just last a second or two each time it happens.

 

[arco777]

Sounds to me like an intermittent electrical issue with a sensor or other part of the EEC system.

When checking for codes you already ran a KOEO test, but you may want to try a KOER test instead. This will test the engine as it is actually running, and if you run the test when the engine is warm, you may be more likely to have a useful code pop up. Once you run the KOER test you can also run a cylinder balance test. This will tell you if one of your cylinders is weaker than another and may help you track down the issue if it is confined to one or two problem cylinders.