1998 SOHC 4.0 hesitates on freeway

[msw]

I'm a new poster but have been reading and learning a lot here in the last few days.

My problem is somewhat hard to describe let alone diagnos. My 1998 SOHC 4.0 Explorer runs great in city and on flat ant level freeway, but when you have a slight incline (not even so much as to cause the tranny to shift) I get a momentary hesitation (almost like a miss fire only the idle seems just fine).

For some reason (a hunch), I think this might be a fuel delivery issue and I replaced the fuel filter (no different). I then thought to replace the PCV valve (boy did it need it). still no luck.

I've checked obvious stuff like tranny fluid, but just don't know what to try next. There is no engine warning light on, she starts and runs fine, but the problem described appeared about two months ago and is consistent.

I've read hear about the TPS, EGR, DPFE and IAC and notice that some descriptions call for resetting the computer by disconnecting the battery. Should I do this?

Any help or suggestions will be greatly appreciated.

 

[BrooklynBay]

Welcome to this forum! Try some Techron injector cleaner, and clean the MAF sensor.

 

[uefear]

Check your plugs and wires. One of the wires may be misfiring under load.

 

[Cobraguy]

You know, a TPS will do that if it gets a bad spot. And a bad spot usually develops where the throttle spends the most time...which seems to fit your explanation here. You can test it with a digital meter by probing the wires...but the best procedure is using a Break Out Box. You simply slowly and carefully sweep the TPS across it's entire range and watch for any break in the voltage increase or decrease. It will change from appx 1V to almost 5V. It should be smooth increases and decreases. If you get a jump, you need a new TPS.

 

[msw]

Thanks to All for the valuable advice.

So far I have cleaned the MAF Sensor and on my initial test drive I notice marked improvement but still felt a few bumps at freeway speed under the conditions described above (notably less than before). I'm cautiously optimistic that this is the right track.

I had the plugs changed a while back (looking for my invoice) Only because that back plug on the Passenger side is so difficult to get at... It did cross my mind that the mechanic may have skipped that one... but that never happens right? Plug wires probably should be replaced so I'll probably do that and see if I can get at that tough plug.

The TPS is definitely on my list. I don't own or even know what a breakout box is, but I'm tempted to replace the TPS because I understand that can improve gas mileage too if it is bad. For now, I'm checking on fuel consumption and will probably give the MAF another shot of the MAF sensor cleaner I used (what the heck the can has enough to last a lifetime). I also want to give this a few more days of test driving just to see if the problem can be isolated to the MAF.

I will keep posting the results I have here for others who are experiencing a similar problem. By the Way, My 98 SOHC 4.0 has 123,000 which I failed to mention before.

Thanks again...

Michael

 

[msw]

Further Update. The problem continued so I replaced the TPS hoping this might improve my gas mileage if nothing else. Still no luck. Last night I replaced the plugs and wires. The plugs were still good but since I wanted to have a look at the tough to reach plugs (#2, 3 are awful on this rig) I decided to replace them anyway. The mechanic who did the job last time, bless his heart, did get the tough ones and must have been a lot quicker at it than me or he wouldn't have profited on the job. I did have to pull the right front tire and the lower portion of the inner fender well to get at #2 and 3 plug ( still had a rough time).

Good News. I did about a 40 mile test drive today at freeway speeds and didn't feel a single bump. It looks like one of the plug wires was the problem so uefear gets credit for that one . I'm knocking on wood until I get some more miles in, but I will be a happy man if I don't have to pull injectors.

One things for certain, I learned a lot here and have taken care of some maintenance issues and will be doing some of the other items in turn. Thanks again to all for the helpful information.

Michael

 

[jsealey]

Sounds like you are having the same problem as me. (see "buck/jerk" post). I too changed the plugs and wires and thought I had it solved only to have the problem come back the next day. Do you live in a cold climate like me? Mine only seems to act up when it is freezing cold and damp usually snowing. Lightly accelerating and then it will miss or give me the buck/jerk feeling. It acts like it is a lean missfire.

 

[msw]

I live in Oregon and it has been a bit cold and wet around here lately. I'm really hoping the plug wire does the trick, but I know I need to put some more miles in to be sure.

I am a bit concerned about my Fuel Injectors with 123,000 miles and have put a good quality injector cleaner through the tank.

I also noticed improved performance after getting then new PCV in there. The last one I put in was at 74,000 and it surely did need to be changed. Heck I guess that is close to 50K. I don't know what the manual recommends but for $4.50 I should be replacing that part more frequently.

I wish I had something concrete to offer. I'll keep adding notes here if there are any new developments.

Good luck!

M

 

[jsealey]

Have you checked your MAF sensor? For details see my other post. Mine had some plant material on it.

 

[uefear]

Hows its running now?

 

[aldive]

Have you checked the fuel pressure?

 

[jsealey]

Uefear So far so good but like I said in my other post it only happens under the right conditions. I will be more confident after a week or so of driving.

 

[msw]

Problem is gone

After giving this fix several days of normal driving I haven't had a single problem with the "bump" sensation on the freeway under load (i.e. when going up a slight incline). It appears that this was indeed caused by a bad plug wire causing a misfire under these conditions.

In retrospect, new plug wires should have been on my list of "do the easy stuff first" from the beginning, but then, that is where the value of this forum came in. I didn't suspect a problem with the spark because I knew the plugs had been changed within the last two years (all were still good when I checked them but were replaced anyway). A real mechanic (I'm far from it) would have known that plug wires can be bad too.

Initially, I suspected a fuel delivery issue like maybe a clogged injector. I ran good injector cleaner and replaced the fuel filter, but the problem persisted. I then replaced the PCV value because it was needed, cheap and easy, cleaned the MAF (mass air flow sensor) and replaced the TPS (throttle position sensor). None of these items affected the problem, but I'll chalk them up to general maintenance.

Now I'm closely watching my fuel consumption and considering other maintenance issue that a 1998 Ford Explorer SOHC 4.0 might need at 123,000 miles.

On a separate note: Three months ago my wife called saying something was wrong with this vehicle. When asked to describe the problem she said, "I heard a bad noise, The battery light came on, it's hard to steer AND SOME PARTS FELL OUT ON THE DRIVEWAY." Cringe! This turned out to be a serpentine belt tensioner pulley that simply wore out and popped apart. It was an easy fix... but after 123K one does have to start looking for things that can go wrong. I'm just glad the pulley went in the driveway.

Thanks to everyone here for the insight.

Michael

 

[99ex22]

Welcome fellow oregonian and glad you got your problem solved!

 

[BrooklynBay]

Thanks for the update!

 

[kenora]

I posted the same "issue" last year concerning my 1999 4.0 SOHC Explorer. Mine was so bad that it broke an engine mount the problem is still not resolved and just like yours occurs most often (but not exclusively) between 0 to -10c and especially when snowing. I drove it all summer without a hiccup but its back with the cold weather (I have noticed a few lumps and bumps at -30c and colder as well).
I have cleaned the MAF, checked the usual suspects and come up with no answers so I'll be following this thread carefully.
Thanks for reaffirming that I'm not the only one!

 

[mikepier]

In retrospect, new plug wires should have been on my list of "do the easy stuff first" from the beginning, but then, that is where the value of this forum came in. I didn't suspect a problem with the spark because I knew the plugs had been changed within the last two years (all were still good when I checked them but were replaced anyway). A real mechanic (I'm far from it) would have known that plug wires can be bad too.
Michael

What kind of plugs and wires did you replace with?

 

[msw]

plug wires are BWD Select and plugs are Autolite Platinum. Purchased at Shucks. I didn't really shop around for these so there may be something better on the market.

Hello Russ! I'm in Tualatin so we are practically neighbors.

 

[ellis11]

I had the same sort of problem on my 97 6 cyl OHV. It would miss when it felt like it at higher speed (driving on the freeway). I replaced the plugs and wires when I first bought it and had this problem for about 2 years and eventually replaced the ign coil to no avail. I finally gave up trying to figure it out and took it to a local shop. They said it was the aftermarket wires. They told me to get the Ford OEM ones because they have seen a lot of problems with aftermarket wires on explorers.

I took their advice and put new Ford OEM wires on and the engine ran like it should for the first time. It's been 1 1/2 years with no issues and I am up to about 157,000 miles on car.

 

[aldive]

What aftermarket wires were you using?