Hi all. I have a lemon-y 1998 Ford Explorer (Exploder) 6 cylinder engine that two, three times a year has the "Check Engine" light come on and it's always the sdame thing: misfiring #4 spark plug cylinder. Problem resolves by replacing the plug (no one "re-gaps" anymore do they?). Question is: which plug is the #4 plug since I'd like to try replacing it myself? If I am standing in front of the open hood, is it on the passenger side of the car or the driver's side? And once the side is determined, is it the plug closest to me (the grill), closest to the firewall (farthest from me), or in the middle? Trying to avoid an $80 charge for what I know is a plug replacement from the dealer. Thank you!

 

# 4 is at the front driver side of engine, close to the left front head light.

 

The problem is that you need to figure out why that plug is fouling. Just a word of wisdom up front, get the genuine Motorcraft double platinum plugs for this job. RockAuto.com always has them and at good prices. You can use the OE spec Autolite double platinum as well, it is the same thing as the Motorcraft.

As for why the plug may be fouling, you could have a intake leak leaning it out, a dirty of plugged injector that is either leaning it out or getting stuck open, fouling it out. You could have a leaky valve stem letting excess oil in. I would rule out rings for now, because leaking rings that are bad enough to foul a plug will almost always trigger a CEL by themselves. Take a look at the plug, and if its not too much trouble, post a picture of it on this forum.

 

Ah ha! You are of course correct in asking WHY this plug fouls frequently when the others do not. We bought the Explorer used (Red Flag #1). When we started having mechanical problems with it, we took it to both Ford and then an independent dealer. Ford replaced a number of things on it ($$$) that had nothing to do with the actual problem itself (they replaced the "shift motor", etc.). The independent garage told us that there is a crack somewhere (I forget where, honestly) that is allowing, over time, coolant to be contaminated with oil and vice versa. (Serious problem, actually, although it happens very slowly). His advice? "I'd be looking to get rid of it." Which is probably true. However, what I elected to do was monitor fluid levels and cleanliness frequently (4 - 6 times a year) and change those when there is a problem; and change the plugs twice a year. All this is being done for me by a mechanic. They generally are telling me things are acceptable, the plugs are ok, but the #4 plug will keep fouling. I am going to drive it into the ground but I treat it as carefully as I know how. Just one of those things...what can you do? I also have a Toyota RAV4 2006. No problems to speak of, yet. Thanks for your help and insight - I do appreciate it!

 

Had a similar problem with #3, misfire every +-3000km, finally re threaded the SP hole, installed a cooler plug, and 40K later have had no further problems.

My guess, either it was running to lean(hot) or not a good conduction to the block (too hot) or poor electrical connection, (weak spark).

Only con, loss of 2MPG in cold weather.
BUT, if it works, don't fix

 

Ah ha! You are of course correct in asking WHY this plug fouls frequently when the others do not. We bought the Explorer used (Red Flag #1). When we started having mechanical problems with it, we took it to both Ford and then an independent dealer. Ford replaced a number of things on it ($$$) that had nothing to do with the actual problem itself (they replaced the "shift motor", etc.). The independent garage told us that there is a crack somewhere (I forget where, honestly) that is allowing, over time, coolant to be contaminated with oil and vice versa. (Serious problem, actually, although it happens very slowly). His advice? "I'd be looking to get rid of it." Which is probably true. However, what I elected to do was monitor fluid levels and cleanliness frequently (4 - 6 times a year) and change those when there is a problem; and change the plugs twice a year. All this is being done for me by a mechanic. They generally are telling me things are acceptable, the plugs are ok, but the #4 plug will keep fouling. I am going to drive it into the ground but I treat it as carefully as I know how. Just one of those things...what can you do? I also have a Toyota RAV4 2006. No problems to speak of, yet. Thanks for your help and insight - I do appreciate it!

 

Ah ha! You are of course correct in asking WHY this plug fouls frequently when the others do not. We bought the Explorer used (Red Flag #1). When we started having mechanical problems with it, we took it to both Ford and then an independent dealer. Ford replaced a number of things on it ($$$) that had nothing to do with the actual problem itself (they replaced the "shift motor", etc.). The independent garage told us that there is a crack somewhere (I forget where, honestly) that is allowing, over time, coolant to be contaminated with oil and vice versa. (Serious problem, actually, although it happens very slowly). His advice? "I'd be looking to get rid of it." Which is probably true. However, what I elected to do was monitor fluid levels and cleanliness frequently (4 - 6 times a year) and change those when there is a problem; and change the plugs twice a year. All this is being done for me by a mechanic. They generally are telling me things are acceptable, the plugs are ok, but the #4 plug will keep fouling. I am going to drive it into the ground but I treat it as carefully as I know how. Just one of those things...what can you do? I also have a Toyota RAV4 2006. No problems to speak of, yet. Thanks for your help and insight - I do appreciate it!