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Bad Erratic Misfire/Not Spark Plugs

phil.o

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My 1998 Ford Explorer 4.0L OHV recently started misfiring erratically. I took it to the shop and had them take a look but since I'm rather low on funds I had them do my brakes and I decided to do the plugs, wires, and ignition coil myself. This is the first car I've ever worked on. I replaced the alternator last summer and now am trying to remedy this problem, so I'm a relative novice.

After getting those three things done-there was one bad spark plug that I could tell just from the difference in color-I started the engine and nothing significantly different. It maybe ran a bit smoother than it had before but has quickly deteriorated to the point where I'm hesitant to drive it any distance.

Now, I don't know if this matters but when it's sitting in park it runs rather smooth even if I rev the engine up to 4kRPM. It will smoothly accelerate and decelerate in neutral. As soon as I put it into gear I get an erratic knock and at high speeds while accelerating the occasional ping(sounds like its hitting the hood). But the acceleration in gear is awful and makes the car run worse; I can definitely feel a lack of power.

I took it up and had them run the computer on it. The computer read out cylinders 5 and 6 misfiring with the list of causes: intake manifold gasket, mass air flow sensor, plugs, wires, coil. After that I cleaned the mass air flow sensor and throttle control sensor but that didn't work either.

This brought me to the point of thinking maybe it was the manifold intake gaskets but people around me who know some things about engines don't understand how that would cause my car to run that bad. And also there is no liquid of any type on the pavement under my car ever.

So, the only two other things I can think to try before I have to take it to a shop are replacing the EGR valve and the fuel filter. The car was sitting undriven for three years before I bought it(very cheaply) and I know that neither of these things have been replaced.

Any thoughts or help would be great, it's killing me trying to figure this out.



Other things I've noticed since I've started working on it:

The fuel economy is atrocious, I would say that my fuel economy has been cut by at least 1/3.

There was a slight coolant smell every now and again after the car ran for awhile.

The transmission sticks.

There is some fluid that comes out of the tailpipe, though not much.

Is there any chance that this is a symptom of somebody putting something in my gas tank?
 



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Engine misfire procedure

Engine misfire procedure

With the exception of the crankshaft position sensor you've eliminated ignition as the misfire cause.

If I purchased a vehicle that had set for more than a year I would empty the fuel tank, replace the fuel filter, then add five gallons of fuel and a bottle of Techron fuel injector cleaner.

If cylinders #5 and #6 are the only ones that misfire then you could have clogged injectors, or low compression due to blown head gasket, cracked head, or burned valves.

I suggest that you perform a compression test. If that checks good then replace the fuel filter and add fuel injector cleaner. Also, clear the codes, drive the vehicle, and then read the codes again to make sure the misfire is limited to #5 and #6.
 






Is it possible that I replaced cylinders 5 and 6 spark plugs but cross threaded them so now they're misfiring? I thought I was careful but I could go back and try them again. Cylinder 6 is such a pain to get to the spark plugs.
 






Is it possible that I replaced cylinders 5 and 6 spark plugs but cross threaded them so now they're misfiring? I thought I was careful but I could go back and try them again. Cylinder 6 is such a pain to get to the spark plugs.

You said one plug was "different" when you changed them - what cylinder was it?
Cross-threading rarely causes misfires, probably not your issue, especialy since you had misfire issue before changing plugs.
Did you use dielectric grease on both ends of plug wires when you replaced them?
+1 to StreetRods suggestions.
 






The cross threading thing was definitely not it. I just pulled the plugs from cylinder 5 and 6 and they were fine. I did not however use dielectric grease on any of the wires. But the other 4 cylinders are running fine without it.

The picture below(if I attached it right) shows three spark plugs. The cleanest one is from one of the good cylinders. The one in the middle is from cylinder 5 and has only been in there for a few days and certainly less than 100 miles of drive time. The other dirty one is the old one I pulled out of cylinder 5 when I did the spark plugs this weekend. I know this must tell me something but I'm not sure what.


mail


I also did find a small coolant leak today while underneath my car. It's slight but I can definitely tell that it's coolant, possibly with a little water mixed in.

Anymore help would be greatly appreciated. Thanks guys.
 






The picture below(if I attached it right) shows three spark plugs. The cleanest one is from one of the good cylinders. The one in the middle is from cylinder 5 and has only been in there for a few days and certainly less than 100 miles of drive time. The other dirty one is the old one I pulled out of cylinder 5 when I did the spark plugs this weekend. I know this must tell me something but I'm not sure what.


mail

Could not see picture.
 






I'm not sure why I can't post pictures but none of the FAQ answers helped.

What you would see if you could view the picture is two spark plugs that came out of cylinder 5 that from the bottom of the threads all the way to the gap and ground electrode are completely black. Nothing is caked on but they are completely black. One I took out after having it in there for only a few days.

Any ideas?
 






I'm not sure why I can't post pictures but none of the FAQ answers helped.

What you would see if you could view the picture is two spark plugs that came out of cylinder 5 that from the bottom of the threads all the way to the gap and ground electrode are completely black. Nothing is caked on but they are completely black. One I took out after having it in there for only a few days.

Any ideas?

Check out this link - good pics and causes.
http://www.flickr.com/photos/westytech/1826285762/
Black usually means oil in cylinder - either up thru rings or down thru valve stems. Neither is good. Really need to do a compression check.
 






I took it up and had them run the computer on it. The computer read out cylinders 5 and 6 misfiring with the list of causes: intake manifold gasket, mass air flow sensor, plugs, wires, coil. After that I cleaned the mass air flow sensor and throttle control sensor but that didn't work either.

Since the computer spit out intake manifold gasket codes should I just listen do the uppers this weekend? The computer has given the same codes twice now. Is the computer generally correct in its diagnosis?
 






I'm not sure if it's the head gasket or manifold intake gasket. There is a coolant leak but my oil is not milky and it only puts out white smoke a very little bit(even in the cold) when it starts. Can anyone help?
 






Subscribing. Mine (96, 4.0L OHV) has started the same thing, and the OBD said same thing - misfire in 5 and 6. The light came on, and I hadn't felt any problems. It was running fine. The light then went off, but came on a day or three later. The problem got worse and now it's running terribly. No funds, so have to make it work a little longer. Hoping to fix it this weekend. I'll start with plugs, then wires, and then hit up a shop. Hoping it won't be too expensive.

Any update from the OP? It's been 5+ months since, so wondering what you found/did/corrected, etc.
 






Brand new spark plugs and intake manifold gaskets just changed, but apparently one of the wires got damaged pushing it on at the plug! I have found that getting to the spark plug 2nd from the back, (Cylinder 5), on the driver's side is a real problem! The oil stick assembly is directly in the way! When it started raining, this cylinder started missing bad! The new wire's boot is damaged at the plug! I tried getting to it from the top of the engine compartment but it's almost impossible! Does anyone know how to successfully get to that plug so I can shove the replacement wire firmly on it? Hopefully I do not have to remove the dipstick assembly to do this! Engine is the 4.0 liter OHV.
 






I'm not sure if it's the head gasket or manifold intake gasket. There is a coolant leak but my oil is not milky and it only puts out white smoke a very little bit(even in the cold) when it starts. Can anyone help?

Phil: I suspect your problem is the intake manifold gaskets. If you're losing coolant and it's not easily traced where it is coming out of, this might be the problem! The cylinder head gaskets are pretty robust in my 4.0 OHV and someone else I knew got over 500-thousand miles on the first set! My 4.0 OHV engine finally started showing coolant coming out at where the upper intake manifold meets the lower manifold. When I got this fixed, there was almost nothing left of the upper intake manifold gaskets. There is no coolant circulating in the upper intake manifold and this water was coming from a leak in the lower manifold gaskets, so you'll have to pull and replace BOTH gaskets! Get a complete set of gaskets. Make sure to tighten down the lower intake manifold like you would a head gasket, (diagonal tightening), and tighten to 72 in-lbs, then to 144 in-lbs, and a final tightness of 192 in-lbs. I decided to take mine in and have someone do this and found the Felpro gasket kit works great! Hope this helps!
 






Brand new spark plugs and intake manifold gaskets just changed, but apparently one of the wires got damaged pushing it on at the plug! I have found that getting to the spark plug 2nd from the back, (Cylinder 5), on the driver's side is a real problem! The oil stick assembly is directly in the way! When it started raining, this cylinder started missing bad! The new wire's boot is damaged at the plug! I tried getting to it from the top of the engine compartment but it's almost impossible! Does anyone know how to successfully get to that plug so I can shove the replacement wire firmly on it? Hopefully I do not have to remove the dipstick assembly to do this! Engine is the 4.0 liter OHV.

That spark plug is very easy to reach from the wheel well. Pull the splash guard and its right in front of you with plenty of room.
 






The most common cause of this is improper firing order. All of us have done it. Triple check that the driver side plug wires are going to the correct plugs. It is a very common mistake.

Next step I would perform is a compression check before tearing into anything.
 






Update?

I have the exact same problem (well, close anyway) wherein without any load the engine runs smooth. I can rev it to 4-5k and it runs strong, but when driving I get pinging and misfires (coughing?). This started happening after changing the cylinder head gaskets, manifold gaskets, one injector, all 6 spark plugs and wires. I verified the firing order is good. I'm dubious about the injector: the new one came without the seal (not the o-rings but the cushion) and I stupidly threw away the older one. I'm also doubting the gas since the car was sitting there for 4-5 months.
Did any of you guys solve your problem?
 






Hey guys, My 2000 4.0 sohc has the same issues. Well, I should say symptoms, I don't know the issues
It started with a slight hesitation, but only at speed, going up or down hill. Yes, I immediately blamed the EGR valve, then tested the EGR valve, EGR vac solenoid and DPFE sensor. Sadly, these were fine. The hesitations got bad enough that I parked it until it's fixed. It sat for a year before I got it. Before I parked it, I took it to O'reillys had them scan for codes. It said a misfire on the number three cylinder and the evaporative canister system needed to checked. Any advice
on busting over torqued rusted plugs? Without busting them? In what order does the swivel, socket and extension need to remove the #3 spark plug?!! I cant get any leverage.
 






UPDATE: I finally got the number 1 plug out. The crimped wire connector stayed with the plug when I removed the boot. Except for a little corrosion from a yrs worth of non use, the plug looks good.
still trying to loosen the #3, which is the suspect of the misfire. As for the absorption canister problem, there is no absorption canister. There are two aluminum tubes, coming from the front along the frame, I assume are inflow/outflow, and two wire plug in connector, red/blue and purple/white wires.( for the solenoid?) Coming from above the tank is a short hose plugged with a bolt. A vent tube to the canister. It would all make sense. I'll be back.
 






Anyone here familiar with the 5.0 v8. Mine is missing bad replaced plugs wires coil packs iac valve maf sensor. And injectors. What else could it be??
 



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I have a 6 cylinder SOHC Sport Trac 4x4 pickup, motor has 90,000 miles on it. It has a misfire in the #5 cyl. I have replaced the coil pack, spark plug wires and plugs. Please help with this problem. Problem is most severe when warning light is flashing.
 






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