'99 4.0 sporadic missing and lopes at 35mph

[skfullen]

I have an '00 Explorer that had this same problem, and a few tankfuls of concentrated fuel-injector cleaner seemed to do the trick.

I have a 99 XLS with the same 4.0 (OHV) exactly like my 2000 except for the color and trim. About 2 months ago it started to miss while sitting at a red-light for an extended period of time. Not really a miss, more like a jolt. At first I thought someone had kicked the bumper on my car and I looked around to see what had happened. Then it did it again. After the jolt, it runs fine for. It could do it again within seconds, or it may not do it again for days.

It runs great while accelerating and at all constant speeds except between 30mph and 40 mph. At this speed, it misses intermittently. Step on the gas and it smooths out and runs like a spotted ape!

It has 85,000 on it and was I just replaced plugs, wires, fuel-filter, as general maintenance. A couple hundred miles later these present symptons developed. I replaced the IAC valve thinking it was the culprit. It did not help. I took the IAC and MAF off the 2000 Explorer and put them on the '99. It made zero difference and the symptons continue. I've done the Sea-foam treatment twice and Deep Creeped the throttle body. It seems to help some, but within days the symptoms have returned. I've also ran two cans of Seafoam through the tank with 20 gallons of gas.

Does this sound like a coil-pack or perhaps an injector? The same symptons plagued my 2000 for about a month, but a few tanks of injector cleaner fixed it, and that has been 10,000 miles ago and it hasn't returned.

I'm open to suggestions and advice.

Thanks for your answers...this is an awesome sight.

 

[skfullen]

Any help, advice, or comments would be appreciated.

 

[heatxcape]

engine misfire

I too, had a similiar problem wiht my 99. It ran fine under acceleration, but often misfired or stuttered....today I changed the plug wires and so far so good. Even though i changed plugs and wires 6 months ago, it ran fine for 4 months then developed the problem. new wires, keep your fingers crossed, seemed to do the trick.

 

[skfullen]

Just replaced the wires. No difference. I would still appreciate help/advice.

 

[dreamr]

Check all your plugs and wires just to make sure they are on tight, and there are no cracks.

I just recently went through all of this and did a lot of testing only to have the power in the garage go out. In the dark I could see my problem quite well.

If that does not work we can move up to testing the coil pack. If you have a Haynes or Chilton's manual the process is described quite clearly. Test both Primary and the three secondaries........

Still having an issue? Well let's move to fuel.

- how old is that fuel filter? (sorry if answered in your first post)
- Any noises from the fuel pump?
- Lastly pick up a fuel pressure gauge and check the pressure on the fuel rail (schrader valve) Once again the haynes or chiltons can guide you.
- Ford injectors are not a likely culprit


Still huh?

Could be a vacuum leak.....

-check all those vacuum lines. Ford likes this crappy plastic that breaks down ubnder heat
- Intake leaks? Some soapy water will help here to find 'em.

by the way did you change your PCV in your recent tune-up



Still....
There be more to look at.......come back for advice
My next is a compression test though.......


Before you actually do any of this though, you did check for any trouble codes right?

 

[skfullen]

I did not change the PCV. I'll try that. I've done all the rest.

 

[dreamr]

I did not change the PCV. I'll try that. I've done all the rest.

As in all the rest of the parts? or Tests?

If you are sure all the parts are in good order including vacuum lines. Ya really need to move on to Fuel pressure and compression.........

(You can thank 410 Fortune for making me do all this a couple days ago )
Don't get me wrong, he is right, I was just well stupid and missed the fact that 2 wires were arcing