low rpm intermittent miss

[randyfristoe]

91 explorer, manual, 200,000 miles

So, I have had an odd intermittent miss during normal driving acceleration.
It idles fine but acts like it has a bad plug wire once I start to accelerate, but then as I get close to the 3000rpm range it cleans up and acts like I hit a power band.

The computer does not throw any codes and so on my own I have changed plugs, wires, fuel filter, but nothing has had any effect.

I've dumped a bunch of injector cleaner in the tank over the past few months, but that hasn't been the miracle cure either.

There are days that it runs smooth as a whistle and other days that it will barely hold a cruising speed. This morning it drove just fine, but this afternoon it acted like it was just straight up missing a cylinder.

I'm at a loss as to whether this is fuel or electrical.


any thoughts?

 

[Daniel77]

Check your EGR valve . Get a vacuum hand pump . Pull hose off egr valve.
attach vacuum pump listen to valve as you pump it up . You should hear it pop at 5 pounds. My 94 ex 4.0 was doing this same thing . changed EGR valve .
Solved my problem . Its $45. at auto zone .

 

[randyfristoe]

91 and 92 models don't have an egr valve. 93 on up do.

 

[huntman58]

91 and 92 if first sold in Calif. did have an EGR system on them as it was a CARB mandate. (Check Rock Auto they even sale the EGR sensor for them)
If this is your case check the vacuum at the sensor for the EGR system and the sensor it’s self.

Also what Plugs and wires did you use?
I know I have had trouble as many have here with any thing but Autolights or Motorcraft.
Even new plugs and wires can give problems and many here have had that experience as I have.

 

[randyfristoe]

I do not know for sure if it is plugs or wires, but I will find out tomorrow.

I've kinda thought that it was a bad injector/signal problem due to the hit or miss nature of the problem. I have been kinda leaning towards the cam sensor or even a coil, but I do not have the equipment or knowledge to test these parts.

 

[huntman58]

To test the coil use a DMM. (Digital multi meter) to read the OHMS.
Primary resistance
Use an ohmmeter and measure the resistance between the fallowing terminals (were the coil power plug, plugs in to the coil not the spark plug wires)

B+ to coil 1
B+ to coil 2
B+ to coil 3
Should be 0.3 - 1.0 if lower or higher replace coil.

Secondary resistance (spark plug towers)
Again using the Ohmmeter
term.3 (coil 1) - spark plugs 1 and 5
term.2 (coil 3) - spark plugs 2 and 6
term.1 (coil 2) - spark plugs 3 and 4

Reading should be between 6,500 - 11,500 OHMS. If less then or more 6,500 or more then 11,500 replace the coil pack.

As for checking the rest sorry can not help out there.
Hope this helps ya out some.

 

[randyfristoe]

Plugs, plugs, plugs. Screw the Bosch platinum. After only about 5000 miles two of the 6 had broken porcelain at the electrode. Back to Autolite where I shoulda gone in the first place.

 

[huntman58]

Plugs, plugs, plugs. Screw the Bosch platinum. After only about 5000 miles two of the 6 had broken porcelain at the electrode. Back to Autolite where I shoulda gone in the first place.

Had the same problem with some of there 4+4 plugs.

I also had a set of Accel 8.8 wires but after that mess my years of trusting Accel any thing has changed to not on my motor! Not only did the wires give me nothing but problems running every time I had to pull on the dang things came apart. Second time I had some thing from Accel that turned out to be Junk there not the company they were back in the 70's and 80"s any more!

Now I use nothing but Autolight or Motorcraft and from doing that I have not once had a plug or wire problem since.

 

[randyfristoe]

oh the things we learn...or rather relearn.

 

[92exp4x4]

91 and 92 if first sold in Calif. did have an EGR system on them as it was a CARB mandate. (Check Rock Auto they even sale the EGR sensor for them)QUOTE]

Are you sure? I'm not saying you are wrong, but there is nothing in my Ford service manuals for this system in 91-92. I have the 91,92,93, and 94 EVTMs. There is only a differentiation with the 93 and up vehicles and nothing at all for the previous years. I know all 94s had the system and some 93s.

P.S. Only Motorcraft parts used in my garage - when available.

 

[randyfristoe]

all I know is that my 91 xlt (early january code) does not have an egr. It is a manual, not sure if that matters.