98 4.0L OHV Missing under load

[JetTech1966]

I know this is my first post gents but I've got a problem with my baby that is kicking my butt. It's a 1998 explorer, 4.0L, OHV, 2WD that is giving me fits and the ECU refuses to give me any codes. It will miss and hitch under load and I've replaced or done everything I can think of to do. It starts and idles fine, it will run WOT fine, problem occurs when I'm going up a hill or part throttle, slow or fast. It will miss a little and sometimes just fade in and out like there is something tugging on it. Here's what I've checked and done.

1. Replaced the fuel pump and filter.
2. Replaced plugs and wires.
3. Replaced the coil pack, no help and was lucky that autozone took it back.
4. Replaced MAF and IAT from a donor vehicle.
5. Unhooked the EGR, no help.
6. Replaced the DPFC I think it's called.
7. Had the transmission put on an analyzer, no problem.
8. Checked voltage. Good.
9. Checked voltage on the TPS while opening and closing it slowly, checks good.

As you can see I'm pulling my hair out with this ocassional miss that only occurs under load, hot or cold. I can make it miss by stomping on it in park or neutral so I really don't think it's a tranny problem. It shifts great all of the time. I'm leaning towards a faulty fuel injector but I sure could use some ideas because the darn ECU won't even give me a hint. Everytime I plug my code reader in, PASS- No codes found.... grrrrr

Believe it or not I've been a master tech since 1985 but I don't do it for a living. I work on commercial aircraft for a living so I'm not quite up on the inside knowledge for these vehicles. Does anyone have any ideas? I have a digital VOM meter and know how to use it, just please point me in a direction and I will investigate it to no end.

Thanks all,

Dale

 

[JetTech1966]

Finally FIXED!!!

I hope this information helps to keep someone else from pulling their hair out someday but I finally got it and here's what I found.

Last night I removed the plugs and wires and started checking resistance. The wires were Bosch Premiums and the plugs were Autolite Platinums AP103's.

The longest Bosch wire ohmed out at 1800 ohms while the shortest one was 375 ohms. Spec should be 4K to 8K ohms shortest to longest. So then I checked the resistance of the plugs and they were all right around 5800 ohms. I opened the gap to .052 from the .040 they were at and it made it 10x worse than what it was. That's when I knew my problems were centered around resistance, or lack thereof.

This morning I purchased a new set of Motorcraft wires and plugs. The wires ohmed out at 3800 to 7800 ohms, shortest to longest.

Oddly enough the motorcraft plugs were all over the place, the least being 6700 ohms and the highest one at 9300 ohms. I'm not sure their quality control is all that good after seeing that but I did put them in anyways. I put the least resistant plug with the longest wire and worked my way backwards until I had the highest resistant plug with the shortest wire in hopes of evening the resistance out as much as possible.

Bottom line is that fixed all of my high load missing and she's back to running smooth as butter!! Thank goodness....

I don't have any regrets for changing the fuel pump even though it was kind of a pain, after all my truck has 191K miles on it and it was original, so I look at that of more preventative maintenance than anything.

My only regret is that I didn't use Genuine Motorcraft ignition parts to begin with....That's where I will never go wrong again!!

I hope this information helps someone out there and thanks for having such a great forum...

Dale

 

[RGTFanatic]

New Member intro

Hi All that happen onto this post, I am a long time Ford driver (30 years). I currently own a 2001 Explorer Sport and a 2002 Expedition XLT AWD. It's been interesting to say the least over the last few years with these trucks. It seems that as the years go by the problems I have get harder and harder to diagnose. I happened upon these forums when searching for a solution to a problem I have with the explorer now, what a great site. You all seem so much more civilized and willing to help those with problems than I've found in other forums. I am impressed and will be returning frequently....

 

[RGTFanatic]

OK, I though my previous post was in the "New Member section.....sorry.
[MENTION=105740]jettech[/MENTION]- this was a very good post that may just solve a similar problem with my Explorer. My truck is bogging down at 3k rpm exactly whether it's under a load or not. Of course there is no MIL and no codes are present. I'll be ohming out my wires and plugs today.

Thank you for at least giving me a place to start.