'98 4.0 intermittent miss under load

[bmerr98]

Noticed an occasional miss under acceleration in the 1500-2000 rpm range a while back. Changed plugs (Autolite) and wires (store brand). Got radio interference. Put the old (original) wires back on and the radio noise went away, but I still have the miss and it's getting worse. 229K on my Ranger.

Guess I should break down and get a new set of Motorcraft wires as a logical starting point...

Any other suggestions?

 

[Lil-Pony]

Was the miss present with the wires that gave radio interference?

 

[AgPete139]

Could this also be a fuel issue?

 

[RonD]

I would also clean the MAF, it is a common source of missing.

http://www.therangerstation.com/tech_library/CleanMAF.html

It is important to disconnect the neg. battery terminal when doing sensor work, yes for safety.....but also because this resets the PCM(computer) so it will relearn the sensors new parameters, if it was cleaned or replaced.


Radio interference is usually caused by arcing on the high voltage side of the ignition system, so spark plugs wires are a common source of that interference.
New wires might not have seated on all the plugs all the way, one bad connection and you will get a "tick, tick, tick" on the radio.

If you pop the hood at night, no light, and start the engine you can often see the arcing causing the problem.

 

[JimRummy]

Yeah, definitely stick with motorcraft wires, and especially the plugs. From what I hear these engines eat any plugs except motorcraft (although I hear autolites are manufactured by motorcraft). Clean the MAF like mentioned, and also maybe give it a seafoam. It could be your coil pack as well, so get out your multimeter and check it out.

 

[AgPete139]

No Bosche. I've tried them and failed when I first got my truck.

Only get Motorcraft or Autolite plugs. Both are inexpensive.

 

[AgPete139]

Oh, but I wants to ask how the spark plugs looked? You HAVE pulled them, right? How's the gap?

 

[bmerr98]

Since last posting I cleaned the MAF sensor and put a shiny new set of Motorcraft plug wires on. I also rolled over 230,000 miles, just saying. I cleaned the MAF sensor first and noticed my idle speed dropped 200-300 rpms which makes sense. Fuel mileage improved a bit too. Definitely recommend regular (every air filter change) cleaning of this often forgotten sensor. Later I replaced the plug wires. I will never use anything less than Motorcraft wires again on a Ford. The miss subsided at first but has returned, although the engine runs smoother between misses. Forgot to mention that I checked resistance on the coil and it matched a new one out of the box. Of course, new just means new, not necessarily good. Going to take a closer look at the plugs and change the fuel filter. I'll keep you posted...

 

[bmerr98]

Oh, but I wants to ask how the spark plugs looked? You HAVE pulled them, right? How's the gap?

I actually had not pulled the plugs, but once again, it's usually the basics. Per your suggestion I pulled mine today. I was a bit surprised to see that I had put Denso plugs in last time. I must have been Low Budget Louie that day. Anyway, they all had a grayish brown residue which seems normal, but the gaps were all over the place. I'm usually pretty good about checking them before installation, but I must have been slacking. Anyway, set all the gaps to .050 and reinstalled...so far, problem solved. I put a few miles on it trying to get it to miss and it just won't. Can't believe I went that long without doing the most obvious thing. Live and learn I suppose.

 

[macd7919]

Take a look at my thread, very similar issue. I had a correctly gapped Autolite plug fail with 4k miles (probably less) on it which caused me all sorts of issues. There's a list of all the things I replaced in my thread, here's a link if it will help:

http://www.therangerstation.com/forums/showthread.php?t=143138