Hello, I have a 99 Ranger 4X4 with the 4.0L OHV. I replaced my original spark plugs at 110,000. Well, that lasted 30,000 before one or two of the spark plugs went bad. So, I replaced all of the plugs again at 140,000. Now I'm sitting at 152,000 and I have a serious misfire again (serious bucking when accelerating or under a load and a rough idle). I don't have a check engine light yet, so I'm not sure which plug has gone bad this time, but it definitely seems like I have more serious problem than just plugs and wires. Does anyone have a suggestion on what could be causing my frequent spark plug burn out? It first started in OD, so I thought it was the tranny slipping, but now it does it through out the range and makes for a very rough ride when on the accelerator. Any suggestions would be greatly appreciated. Thanks!

 

Go back to your trans idea... How do you know it isn't the trans? does it idle ok (in neutral) can you rev the motor. From what your saying it doesn't seem like you have ruled out the trans... If it isn't the trans, you might have a bad wire, or a bad coil pack...

 

I took it to a transmission shop this morning and everything checked out (sorry, I left that part out). After I drove it this morning it felt just like the last time my plugs went bad, so I knew it was them but I had the tranny checked to rule it out.

 

+1 on the wires or coild pack, maybe check them or call and ask a local mechanic, they may answer the question without looking-well maybe anyways

 

I think I'm going to try the Screamin' Demon coil pack, can bad fuel injectors cause the spark plugs to have a short life? I'm a little worried that they may be worn out or clogged and was wondering if they could have an adverse effect on the plugs.

 

If you haven't changed your ignition coil when you first changed your plugs, I would start there. A bad ignition coil can make spark plugs go bad. You may want to run a can of sea foam through the gas tank to clean up the injectors too.

 

what brand of plugs are you using? if you ARE NOT using Motorcraft plugs, that is your problem.........DO A SEARCH! this has come up many of times and has been tried/tested/decided that Motorcraft perform the best in a 4.0 Ranger.....

 

Coil pack.

 

I'm using motorcraft plugs on my ranger (went with Bosch on the Explorer with SOHC). I drove the truck home tonight and the bucking calmed down once the motor was at normal operating tempature. It still seemed rough when running in 4th or 5th and under a load. So, based on what I'm hearing on here I should go with motorcraft plugs and the screamin' demon coil. Is there are reason why the motorcraft plugs work better with the OHV? Should I be concerned with using Bosch platinum on the explorer?

 

No one around here sells the motorcraft double platinum. Where do you guys buy them on-line? Rockauto doesn't appear to have the double platinum.

 

Ford dealer....

From what I understand motorcraft plugs are best for both 4.0 motors. I always use NGK in everything but I guess motorcraft is the way to go in a Ranger (explorer).

 

If plugs keeps fouling in the same cylinder, then I'd suspect either a bad fuel injector or some sort of base engine concern (leaky intake or head gasket, for example).

How's your coolant level been lately?

 

I had a coolant leak at one time (I think it was near the water pump), but since a ran a coolant stop leak product through there, I've had no problem with losing coolant. My exhaust has had a funny smell for sometime now, but I think that is just the cats going bad and not coolant in the motor or anything.

 

Update: Since the check engine code was for cylinder 4, we pulled the plug and found the plug to look rusty. The insulator around the electrode was rust colored instead of white. The threads on the plug were even rusty looking. We pulled #5 right next to it, but it looked fine. So, we replaced the plug in #4, started her up and #5 was arcing like crazy. So, put a new plug in #5 and it's back to normal. So, it looks like it might be a fuel injector problem on #4. I'm going to wait until the new coil and plug wires get here to replace all the plugs and the injector for #4. Is it better to replace all injectors or just the trouble child?

 

Injectors are not usually cheap. So that's up to you andhow much longer you plan on keeping the truck.

Rich

 

I'll have it for a couple more years. It seems like they range in the 40 - 50 dollar range.

 

You can send your injectors off to be professionally cleaned and tested. The testing will prove for sure whether the injector is bad. Not only that, the cleaning will bring the injectors up to 100% and you get new screens and seals in the deal. IMO it's a much better option than just going off and buying new injectors.

I had the injectors on my '98 done a few years ago, found one to be bad, so I replaced it. Notice how much of an improvement the cleaning made:

'98 4.0L Fuel Injector Cleaning & Testing Report

 

fastball25: Any update on this? Did you ever determine what it was with certainty. I'm having the same issue with my truck (2000 4.0L 4x4) & I'm really tired of replacing the #4 spark plug once a year. I'm really hoping it's not something expensive (gaskets, etc). If all I need is the Screamin' Demon Coil Pack, I'm game for it, but don't want to spend the money on that if it's just a clogged injector.

 

sounds like a fuel injector sticking closed causing lean condition. Prob not sticking open or the plug would have been black and would have a strong fuel smell odor.

 

PM me for injectors

 

I dunno, I'm leaning towards coil pack now. I've done an ohm test on it & the primary resistance on all three negative terminals checks out at 1.0 (0.3 - 1.0 being acceptable) & the secondary resistance check goes as follows for each pair (6.5 - 11.5K acceptable):

1 & 5 = 15.01
2 & 6 = 14.37
3 & 4 = 14.40

I've tested multiple times & get REAL close to the same readings, so I'm pretty confident I'm getting a good reading. However, my acceptable ranges come from the Haynes manual for my wife's 2000 Explorer (which lists a 4.0L OHV). I'm thinking same year, same size & type of motor & only one set of accpetable ranges. So with that I'm assuming they all used the same coil pack. I don't know that for sure...and it's too late to go pick up a Haynes manual for the truck. If ANYONE has a Haynes Manual for a 2000 Ranger & can confirm these specs for the 4.0L OHV, I'd be greatly appreciative. Somebody on these boards must have one.

Also, my only other concern is that all 3 pairs are way out of range, I was under the impression that most of the time, you'd have only one pair go bad. But then again, I've got one pair that's pretty far from the other two. I HAVE been fighting this problem for the better part of two years, so it may be possible that all three are on their way out after so long. Who knows? Maybe they are? Maybe I've got the wrong specs? Maybe I could quit being so cheap & just buy a Haynes manual tomorrow. I was just hoping maybe someone could help me out before I get off work tomorrow.

 

I couldn't find any specs on the coilpack resistance in the shop manual. However, I really doubt that your problem is a coilpack. If it were, you should see symptoms on spark plugs #3 & #4, not just on #4. It might be worthwhile to check the PCM for trouble codes to see if the Misfire Monitor is picking up any misfire on cylinders other than #4.

Assuming that the misfire is only on #4, the most logical approach is to look for problems that can only affect that cylinder: plug wire, injector issue, vacuum leak only/primarily at the #4 runner, etc.

 

Alright, so...the comment about it always being #4 was exaggerated & said out of frustration that the problem had visited me for the 3rd time. A little back history:

I bought the pickup in February of 2006. The first code it threw was the ECT sensor never reaching temperature to run in closed loop. So I replaced the sensor (yeah, I know, replace what might throw that sensor off first...I know that now). The next time I had problems was around October of 2006 & it was running really rough & was definitely misfiring. It never threw any codes & the problem went away after replacing all 6 plugs (damned expensive from the stealership btw). Around February of 2007 it came back again. This time the weather was cold enough to bring back the ECT code (weirdly enough at the same time my wife's 2000 Explorer threw the same code). So I replaced the thermostat in both vehicles (a biotch to do in the Explorer). My issue didn't go away & finally got bad enough that the misfire cause the PCM to throw a code (PO304). I replaced that plug & the problem went away (as did the cold weather...which is when it always runs poorly). I attributed the issue to a long term bad thermostat. Then about 4 days ago, my old friend misfire returned for a visit. That's when I spent about 6 hours combing these forums looking for an answer (y'all have helped me with quite a few issues with my vehicles over the past few years). Decided to start testing the crap I could test & try to eliminate that first. Sprayed everything that looked like a hose that might require vacuum with starter fluid, nothing. Ran the truck home today with the MAF sensor unplugged, nothing (except for finding out that, for whatever reason, that caused a really hard shift between 1st & 2nd). Decided to ohm test the coil pack & that's where I am now. So as for it definitely being #4 everytime, I really don't have any real proof of that. Shortly after I posted last, on a hunch I checked out the Chilton for my old '92 Ranger (91 - 99 Ranger/Explorer/Mountaineer) & it shows the same exact tolerances for the coil pack as what the Haynes manual did for my wife's Explorer. And there weren't different tolerances listed for each engine, it only showed the one set of ranges. Maybe I'm an ID10T for thinking this, but it would seem to me that I could just about bet everything on it being the same for this pickup. Maybe I just need to quit whining & pony up the $137 for the screamin' demon & some 8mm wires (oh and another $25 or so for some more plugs, only not from the stealership this time).

I dunno, does any of the extra history tell a different story? I mean, I may as well put new wires in it regardless of whether or not the coil pack is bad. Which is why I'm thinking I should just quit whining & pony up. I'm just so frustrated with this problem & if I could fix the root cause, this would be an awesome pickup (my 3rd Ranger & I know I don't keep buying them just 'cause).

 

What does the bad plug look like? Can you post a pic of it?

btw, I know it's not the proper way to problem solve. But the coil and the wires are at the end of thier intended life anyway. Might as well R&R them.

Rich

 

When the misfire occurs, is it more noticeable under load or at idle? A miss at idle or light throttle might point more toward a vac leak; misfire under heavier load could mean an ignition or fuel delivery problem. BTW, 4.0L OHV engines are notorious for intake manifold gasket leaks and PCV system leaks.

If you have replaced the plugs but not the ignition wires, then the wires are highly suspect. Pop the hood at night in a dark area and watch with the engine idling. If your wires are old, you'll probably see a considerable amount of glowing and arcing, especially near the plug boots and coil pack.