diagnose this

Vacuum leaks when cold a fairly common with most flavours of the 4.0 Explorer engine that feature the plastic upper manifold... Easiest way to check for the concern is to smoke test the intake after a cold soak... this type of concern generally doesn't have a coolant leak to accompany it.

The upper intake is sealed to the lower intake with six individual "o-rings" ... any or all of these can leak.

Generic answer: 2 and 5 maybe seeing an improper mix, or may be being 'scrubbed' from a coolant leak into the cylinders.

Yes, one possible guess might be a small coolant leak that only leaks when the engine is turned off. That can foul a plug for a little while at start up. But this thread is old enough, by now one would expect the missing coolant would be noticed.

-jim

"Ulysses" wrote

No coolant loss noticed, no white smoke at startup. I'm not defending the diagnosis or what was done, but this last fix seems to be working, with a couple of thousand miles on the car since the repair. Over the previous 2 years and 10s of thousands of miles the problem always resurfaced (after each of the several other attempts to fix it) the first time I started the car with temps below 50.

Previous attempts to fix the problem included replacing plugs, replacing wiring to the plugs, replacing an/the oxygen sensor, replacing the fuel pump relay, and a couple of other things I don't remember.

Best regards to all.

Bad engine temp sensor?

There doesn't seem to be any missing coolant or any smoke out the back.

It's keeping a steady 35 psi.

Thanks. I'll keep this in mind if my '97 starts doing what yours was doing. As for the other fixes most of them sound like things that probably need to be done anyway so it doesn't sound like you wasted much money on them.

Problem solved.

Shop didn't like the Motorcraft double platinum plugs that were in it, said it shouldn't be using platinum plugs. Told them the plugs only had 8K on them. They couldn't find anything specific with their "test equipment" so they recommended an injector cleaning. Told them to go ahead. Very slight improvement but still not running right. Shop said they were 98% sure new non-plat plugs would fix it. Told them to go ahead. It fixed it. Now it runs fine. Very strange. I've used motorcraft plat plugs for 137,000 miles with no problems till now.

Check the underside of the coil pack to see if the potting compound is cracked. It takes less energy to fire standard plugs than plats.

some engines just don't like platinums, especially older engines that may have a little blowby. They tend to foul and never burn clean. I hear of this most often with Bosch FWIW.

nate

I've heard that about the bosch. But I looked at these plugs (Motorcraft) before I took the truck in and they were clean, the "center" plugs were "too clean" you might say, the porcelain on them was as white as a new plug. The only thing I can think is that those cylinders were running a little lean and the plugs were getting a little too hot and the deposits on them turned to a white glaze that was shorting out the spark. Probably new platinum plugs would have fixed it too. However, you'd think that would have shown up on their test equipment and they claim they didn't see anything that looked bad with the plugs or wires.

When I see Motorcraft I think original. Were these the original plugs from the factory? The original plugs should be opposite plats. Two different part numbers.

They are whatever is sold retail, maybe it's Autolite or something, whatever the "ford" brand is. They are double plats, you can't get the original single special side for the left and right that they put in at the factory.

What an odd assumption... the vehicle in question is nearly 20 years old...

As far as misfiring plugs showing up on anyones "test equipment" - nobody uses an ignition analyzer type scope these days... (disclaimer - Ford supplies us ignition test leads with the current VMM testing module - but techs are seldom directed to use the feature when reading the PC/ED). Occasionally we are directed to perform a coil "stress test". Setting up and performing the test costs more than simply replacing the coil as a diagnostic test step...

The new 6.2 gas engine may offer some interesting symptoms with it's dual plug arrangement.

It only has 130k on it. I see factory plugs at that kind of mileage frequently.