My manual calls for .042"-.046" gap on the plugs.
I always set them to the narrow side of spec, as they will always be opening up with wear.

Narrower gap will make for a hotter spark & maybe better cold weather starts.

 

I went through every page in the manual and had a co-worker (working the fire station today) do the same. The only reference to spark plugs is how often to change them. Don't know if that's a Mazda thing or what. Any way, Cowboy's instruction on .052 must have been right. That was the gap out of the box. Road test tomorrow morning when we get off work. Thanks all.

 

In my gallery (misc), last photo. Note desc.

On edit: never assume that a plug out of the box has the correct gap, always check.

 

Must be a Mazda thing. Oh well, it came in my Ranger manual from '94.

 

Well, I had to bring this thread back up 'cause things still ain't quite right. Here's what all I've done:
A: EGR valve replaced
B: 3 cans of PM-3 used to decarbon engine
C: throttle body intake cleaned
D: MAF sensor cleaned
E: Platinum Motorcraft plugs installed with new wires
F: Oil changed after all said and done

Truck runs about 50% better. It stills spark knocks quite a bit under load. When the engine is cold, a squeaking noise (like a squeaking fan belt) starts out slow and gets faster until it finally stops (about 5-10 minutes). It's not the belt. I pull a 14' single axle trailer with one Hustler mower and light equipment. About 2500 lbs or less. The truck when pulling this feels like a parachute is back there. Back in '99 I had a 2.9L with a 12' trailer and it pulled way better than this 4.0L does. I just can't imagine this is too much for this truck.
Since I cleaned the MAF, the check engine light has never come on again. I had the battery unhooked for about 30 minutes; is the code gone? Will hooking it up to a diagnostic show anything?
I've done so much to this truck (hitch, 3 truck boxes,etc.) I really don't want to start over but I'm just about ready to sell it and try another truck.
Any suggestions? Thanks

 

On the ping problem, some additional thoughts for consideration.

I don't see on the "DONE" list, some items that could affect the air/fuel mixture, like fuel filter, air filter & O2 sensor switching test.

The fuel filter, if clogged can affect fuel pressure & flow & delivery, causing a lean mixture.

The air filter, if a low quality paper brand, can shed fibers that'll mess with the MAF, even if you've cleaned it. If you have a foam or oiled gauze type, they can pass more particles & dirty up the MAF, plus if you over oil them, It can contaminate the MAF.

If the MAF was dirty, you need to find out why, sounds like you have a air leak in the air inlet system somewhere between it & the filter.

Also the 4.0L is known to be prone to lower intake manafold leaks. as this is well past the MAF, so it doesn't know about & can't detect & adjust for those kinds of leaks, so the mixture will go lean.

Lazy O2 sensors can mess with the fuel mixture too & with the mileage on this ride, they are at least suspect in my mind, so check them out.

The rapid coming & going of the spark knock, sorta makes me lean toward a fuel delivery problem of some sort, so a fuel pressure test, O2 sensor switching test & maybe another MAF cleaning, then a new MotorCraft air filter might be good things to consider.

Keep us posted on your findings, hang in there, when you get her right, she'll lug & tug with the best of them!!!!

 

Did you ever get your codes pulled?

 

Hello gentlemen, thanks for the responses. Sorry pawpaw, I did change the fuel filter right after the MAF cleaning. Done so much stuff, starting to forget. The air filter looks good but I do have a new Purolator I will stick in there. I'm going to look in here on how to check O2 sensors.

RangerPilot, I have not pulled codes. Will having the battery unplugged for the 30 minutes erase all that? I'm not sure if the "check engine" light has to come on to create any codes or not.

I've had several people ask if I've had the cat checked to see if it's clogging up. Any credibility to that idea?

Thanks to you both.

 

OK, good feedback on the fuel filter, so we can probably set that one aside.

Somewhere along the line, you'll probably want to check the fuel rail pressure too, just in case the fuel pressure regulator or fuel pump are acting out.

Yup, if you've pulled the battery cable for that long, all previous codes will likely be erased.

However any new pending codes will be in there & they may not have occured enough times to turn on the CEL yet, so I like Ranger Pilot's scan the computer again idea!!!!
It could yield some helpful clues on where to focus your attention.

With the mileage you have on this engine, be sure to have the before cat O2 sensor's switching rate checked.

A lazy O2 sensor, even though it's working, if lazy, it's switching rate can be be too slow to adjust fuel mixture quickly enough & can adversley mess with the air fuel ratio too!!!!

As you don't seem to be sure of this rides past maintenance history & thus aren't sure of the Cat Converters condition, you could probably get a fair idea if it's blocked badly enough to increase back pressure & cause the engine to run hot enough to cause ping, by using a vacuum gauge to monitor the intake manafold vacuum pattern & by going through the test sequnce listed in it's instructions for a clogged exhaust, kinda get an idea if exhaust back pressure is gross.

On the Purolater air filter, I've read of reports of these having air box rubber seal fit problems in Rangers, so make sure it's seating & sealing properly, so dirty air won't be bypassed & dirty up the MAF again.

While Im on the MAF thing, FWIW, I've read of folks having to have the danged thing cleaned as many as three times, to get it right!!!! So don't be surprised if you have to do it again!!!

You might check those lower intake manafold bolts to see if any seem to be particulary loose.
Sometimes just re~torquing them will work, IF the intake gasket hasn't been sucked in, in which case it'll have to be replaced.

You can check for vacuum leaks, with a propane bottle, surgical rubber hose & I like to use one of those needles for blowing up basket ***** & such, with it's end cut off to make one hole, in the rubber hose end, to more precisely apply the propane, when checking for under hood vacuum leaks.
If you get a sudden rise in idle speed, you've found the leak area & thus should be able to pinpoint it with the needle!!!!

So if you feel the need, check the intake manafold & for that mater, any vacuum hose or fitting for leaks, thusly.

Just some additional thoughts for consideration.

 

Pawpaw, what would be the best suggestion you have for where to hook up a manifold vacuum gauge? Very good post you gave there though.

 

A rather easy intake side vacuum access, would be the brake booster vacuum hose.

You could "T" into it, if you need to drive the vehicle while monitoring intake vacuum & you'd still have brake boost while driving, or if you just want to monitor vacuum without driving, pull the hose loose & connect the vacuum gauge directly to it.

 

Hmm...thinking a vacuum gauge may be a permenant addition to my truck soon. Seems like something to keep an eye on.

 

Well I don't know if I'd make a permanent connection, at the brake booster vacuum hose, maybe "T" off a metal screw in fitting on the engine intake side somewhere, if you can find metal now days!!!! lol

 

I was having spark knock problems for a while, new plugs and wires fixed it. (one of the plug wires was broke)

 

Thanks pawpaw. Coil maybe anyone?