98 B4000 misfires under load; long story, then a question...
 

Howdy all,

I am new here but hoping you can help me. I have done light wrenching before to keep my 2002 6cyl F150 in top running shape, and earlier vehicles, but have been kinda stumped by this Mazda.

It is a 1998 B4000, 4.0L OHC 12 valve V6 with auto, and 80Kmiles I inherited from my dad a couple months ago when he passed. The CEL was on and main symptom was misfire when accelerating lightly so as to stay in a high gear, usually at about 2000 RPM or so, especially if the engine has warmed to operating temp. Sometimes it would accelerate smoothly but usually not if there was any slight upward incline in the road. It also would not skip if the tranny downshifted and RPM went up much above 2000, like 2500. While still at my dad/mom's home I started with

air filter
spark plugs (autolite platinum)
reset the codes by disconnecting the negative battery terminal.

The spark plug wires were not OEM (they were Bosch) and looked fairly new so I did not suspect them yet. I noticed a VERY dirty #4 plug (oil on the threads and wet gas on the insulator) and all the others marginally ok looking (more on this later). Very soon the CEL was back on and a trip to AutoZone confirmed 5 codes (lean/rich on both banks and another code I don't remember). Gas mileage was only about 16-17mpg at this time. I then replaced

O2S (first one in the exhaust pipe on driver's side between engine and cat converter),
PCV valve,
Cleaned the MAF, which already looked clean as a whistle,
reset the codes by disconnecting the negative battery terminal.
(I also ran a can of STP and a can of Seafoam thru the tank.)

The 5 codes never returned. However the original symptom of the misfiring under load when at operating temp continued. I next suspected the EGR system and in three different trips to AutoZone I replaced

EGR valve
EGR Vacuum Solenoid
DPFE Sensor
Reset the codes after each installation.....

One one of these trips the CEL came back on and the indication was the gas cap not sealing. I replaced the gas cap and reset the codes and drove around....Still no improvement in the original symptom of misfiring under load but the CEL remained off.

I took a 150mile trip in the B4000, thinking the whole way and decided that the coil pack must need replacement (that was the trick to fix my F150 earlier this year!). While at my destination I went to another AutoZone and bought the coil pack, installed it. The misfire under load seemed to have gone away for a while, but returned later.

AFter returning to dad's home from the short trip, the CEL came on and AutoZone told me it was #5 misfiring. I finally replaced the spark plug wires and the symptoms went away (first just the #5 wire and voila!)....for a while. I drove the B4000 all the way from my dad's home to my home in TEXAS (800miles) a month ago and it started out running fine (gas mileage about 20.5mpg with air running all the way at 70mph), but the symptoms began to return slowly and by the time I arrived at my home in TEXAS it was the same as before but I was getting NO CEL.

I had done some easy checking of the vacuum system for leaks but about a week ago I took the entire vaccum piping (from manifold to secondary connections) and plugged it and sucked at open end to find if it held air...no leak. I also sucked on each connection vacuum circuit, could not get any to hold air all that much (except the EGR valve itself, but even the EGR Vaccum Solenoid has an air vent that purposely leaks) and don't know what that means.

I recently found this site and two days ago I replaced the IAC valve (and reset codes with batt disconnect), but no change in fundamental misfire under load symptom....it might have even gotten a little worse.

So I cleaned the MAF again and inspected it for damage, none seen. I checked the resistance of the spark plug wires with a VOM and they range from 8Kohm to 15Kohm or so, well in spec. When I had installed the plugs I did not have a gap gauge so this time I gapped them to .052", they had been at about .045". I disconnected the batt again, No change in the fundamental misfire under load symptom.....but;

All the spark plugs were were clean, insulators white as a sheet except for #4. The #4 spark plug came out tan on the insulator (as I might expect them all to be on a carbureted engine) but otherwise quite clean, except the THREADS were very oily....I mean even some sludge in the threads with obvious engine oil! Except for the fact that the insulator was fairly clean this was the way I had originally found the original plug for #4.

I checked with a flashlight around the #4 spark plug hole....no oil evident; dry as a bone. I checked the oil on the dipstick (as I had done regularly) expecting the same level as before and was not disappointed...no evidence of heavy oil consumption and no CEL lighting up.

So here is my question(s):

1) How does engine oil get to be only on the threads of the spark plug at #4 and not be on the outside (as if dripped from the valve cover gasket) and not be coming from the cylinder (as in worn rings)?

Is there a gasket blown there?

2) Could this be my "misfire under load" problem, even though it is not giving me any CEL and lean code?

Thanks in advance for reading this and any help you might give to me!

YHS,
rogerw

PS - I hope the narrative above is readable....I tried!

PSS - I forgot to include that I had replaced the fuel filter before the 800mile trip to TEXAS.

Welcome to FTE.

My you've been busy on this puppy!!!!

A misfire under load is usually a spark problem & seing as how you've had success fixing it, by replacing various ignition system parts, I'd revisit all the parts replaced & look for attachmet problems, internal/external cracked plug insulators, breakdown under the plug boots & along the wires, spark plug breakdown, or mis routed plug wires, make sure each wire is routed Exactly as the factory had them, using ALL the wire looms.

If that checks out, you might consider trying a "wet down" test, using a spray bottle & water, to wet each individual plug wire down, all the way from the coilpack to the plug, with the engine ideling.
Maybe even do it at night & see if you can spot any arcing & sparking!!!

Not sure about the oil on the plug threads just yet.

Wonder why the OEM plug wires were replaced, with so little mileage on it????? Had the OEM plugs been replaced too???

If so, it sounds like someone else has been chasing this miss under load problem too!!!!

A bunch more thoughts for pondering.

Busier than I want to be!
 

PawPaw,

Thank you for your response.

I am not brilliant by a long shot, but I can usually fix one of these problems in less than half as much time and money as this one (two months and more bucks than I care to mention)....on the positive side I have learned a lot about this engine that I did not know, and I have a baseline for any new problems. I also picked up a Haynes manual last week thinking it might give me some ideas, but I really have gotten much more useful info from searching this site than anything else.

I neglected to say, but I did do some earlier drenching of the high tension electrics from the coil pack to the spark plugs and did not induce a worse misfire while the engine was idling. Usually, if I have such a problem this will aggravate it noticeably, sometimes so that it won't run till it dries off. However I used a water hose and was not selective, as you suggest. I will try your suggestion.

I am not aware of a way for oil to get on the spark plug except from worn or broken piston rings, or such. I just don't know how it would get onto the threads of the spark plug and not totally coat the electrodes and insulator... Unless it dripped from the valve cover on the outside, but that would be evident by visual inspection and that is not happening.

Maybe I need to invest in a compression checker, or have a garage do that.

If oil blowby is preventing ignition sometimes on the #4cylinder, a hotter range spark plug would be a temporary fix wouldn't it? I checked with AutoZone and they do not have a range of plugs for different heat ranges specified....what do you think about that?


YHS,
rogerw

btw, after thinking about it, the "sludge" along with the oil I mentioned on the spark plug is probably just some outside-the-plughole dirt that I dragged the oily threads thru.....that engine is so big inside the well, it is hard to get a straight socket on anything..

Well, maybe I have found the misfire problem.......
 

PawPaw, and others,

When I took the #4 and #5 plugs out today I took a pic to illustrate how #4 looks (on the left) and all of the other plugs look like #5 (right). These plugs have only about 2500 miles on them.

http://i6.photobucket.com/albums/y20...2/CIMG2721.jpg

If anything the tan one looks more normal and the white one looks to be running too lean, but my experience with this is almost all 30yrs old and pre-fuel-injection and electronic ignition. These new engine control and spark systems seem to run the spark plug a lot whiter than tan in my very limited experience.

What you cannot see however, and I did not notice until I started to replace these plugs into the engine was that #5 has a crack in the porcelain insulater that runs from top to bottom on the side that has the plug number AP103. PawPaw, thanks for that tip! Was this what caused the misfire that I "fixed" with the new sparkplug wires? I dunno, but I drove over 800 miles on that fix before the problem became prominent again....

So, I also did some searching online and found at the Autolite.com site it says:

"Autolite® spark plug numbers indicate the heat range with the last number of the part number. Everything previous to that, regardless of the number of digits, can only be used to indicate a similar design (spark plug family). For example, a 23 is one heat range colder than a 24. 3924 is one heat range hotter than the 3923. The 23 and 24 will look exactly alike, but they will not look like the 3923 or 3924."

So, I realiized that I had earlier asked the wrong question of the clerk at AutoZone when I asked "Do you have a hotter heat range plug for a B4000 than the stock one?" Instead I asked, "Do you have an AP104?" And it turns out that they did.....

I purposely gapped the AP104 to a little less than .050" and put it in the oil-offending #4cylinder and I put the fresh AP103 (stock plug) gapped at .052" in the #5cylinder where the cracked one had been.

I did not pull the negative terminal this time to clear the engine controller. i wanted to see if this would clear up the misfiring under the same circumstances as it had previously been running under.

for the first two miles getting out of my neigborhood to the hiway, no problems but that was usually the case until the motor really warms up. Then, pulling a long gentle incline with the tach at 2000RPM and going about 55mph........no misfires! I drove for about 20 miles in various kinds of acceleration and loading and did not detect a misfire....but I will wait and see if this holds true. I have seen improvement several times after a "fix" and I hesitate to call this the last word, but it seems so far to be fixed.

I am still worried about what is going on with the oil on that #4plug, but going to a hotter plug gapped a little tighter may well keep her firing....my fingers are crossed! If the engine continues running well, after another thousand or so miles I will pull the #4plug again to see what is going on with it.

Question: If the engine is using/burning oil will that cause the O2 sensor to die eventually?

Maybe I need to do some compression testing.....

YHS,
rogerw
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>

PawPaw, I think that cracked insulator was the culprit...
 

thanks for the tip!

I have now driven over 50miles under all engine speeds and loading (acceleration and hills) and have not caused the engine to misfire again.

I hope this fix lasts!

Here is what the crack on the plug looked like


http://i6.photobucket.com/albums/y20...2/CIMG2724.jpg

I am thinking that I did not need to replace any of the EGR stuff or the IAC.....oh well, live and learn.

I did learn one other thing that might be of use to others on this forum: just because a PCV valve rattles inside does not mean it is working correctly. If you blow thru it one way it should allow air thru; the other way it should close and not allow air thru (holding the valve vertically as it would sit on the valve cover). Mine was a plastic bodied PCV valve and it had worn internally till it would not seal off.....


YHS,
rogerw

That crack if it had a little oil or grease or dirt in it would definitely let the spark jump right to ground!

Good troubleshooting feedback & to hear you believe that miss under load is fixed.

On my then new 99 Ranger 4.0L, I had a miss under load, that was Really bad when it was ranining out, turned out the Dealer had cracked #6 plugs external insulator on installation while doing some warranty work.

They found it with the "wet down" test, I found it while driving uphill in a frog choaking rain storm!!!! lol

On the plug type, our "waste spark ignition system" needs "double platinum" replacement type plugs, so the gap doesn't erode over time.

If it's cold in winter where you live & you get reformulated oxygenated gasoline, you may want to gap those plugs to the min side of spec, as doing that will make the spark a little hotter, to help with cold starts on more diffcult to ignite, ethanol enriched oxygnated winter fuel.

It'll also have the effect of slightly advancing the timing too & seeing as how a spark gap is always opening up with use, they'll stay within the spark gap spec longer, by setting them to the min spec to begin with.

Make sure your using a good quality cushioned spark plug socket & torque the plugs to spec.

BTW we have a 4.0L OHV engine, the SHOC 4.0L didn't come about in the Ranger, until 01.

Seeing as how you like to turn wrenches on your ride, be sure to check the "Tech Info" thread atop this forums thread listing page. It's chocked full of all kinds of good to know things & has a thread about our waste spark system, that you may find interesting, as it explains why doube platinum replacement plugs are neeed.

I'd maybe rethink the hotter plugs, especially if you begin having spark knock problems.

The brown deposits are likely from fuel additives.

If you think the injectors may be need cleaning, try a 20 oz bottle of Chevrons Techron Concentrate Plus, added at the pump before fill up, in a tank of Chevron, Texaco, or CalTex gas & run most of the treated tank out, with some spirtied accelerations & maybe a short road trip or two during the treated tank.

The Techron at the specified treat rate is 10x stronger than the pump gas treat rate add pack & will likely tidy things up inside in one tank.

Just some more thoughts for pondering.

Thanks!
 

I think I must have broken the #5plug insulator myself during the past two months of troubleshooting but I have no idea when....the fact that early on I got CEL and misfire on #5 suggests that it was early on.....however, I did replace the #5 spark wire and the problem abated for much more than 800miles and never lit the CEL again. It may just be coincidental and merely a result of subsequent and more recent mishandling while I searched for it. I just don't know. I shall ENDEAVOR to be more CAREFUL!

BTW, how does the engine controller sense a misfire? If the coil applies a high voltage but no spark occurs there will be no current pulse as there would be during a spark event.....is the absence of current pulse how a misfire is detected? If so, the controller probably has no idea whether the spark plug fired or a spurious path to ground fired? Just wondering.....

During earlier searches of this forum (I think it was mainly in the tech section) I had noticed in several places the point you make about using double platinum plugs; and how the original OEMS were of two different single platinum types on the two different banks, since erosion is affected by spark polarity. Since the plugs I had already bought were single platinum, I had made a mental note to deal with this later though, after I have cleared up the current problem.

I understand your point about additives causing discoloration of the electrode insulator, but how could it only affect the #4plug and not the others?

I tried the one-step-hotter plug on #4 on the assumption that it was causing the misfire. Now that the cracked #5 is cleared up, I will go back to the cooler (stock) discolored plug with normal gapping on #4cyl and see how that runs.

Thanks again for your help.

YHS,
rogerw

Double platinum are very important, one one cylinder bank, the spark jumps the opposite way of normal, which is why you need double platinums, to protect against erosion on both electrodes.

I think the computer senses a RPM change & thus deduces a misfire.

Are you certain the above plug with the deposits, wasn't the one with the cracked ceramic?????

The 4liter is running great now!
 

If I understand your question correctly; No, the plug with the very tan inside ceramic insulator is NOT the one that that had the cracked external insulator. Here is the clarification:

#4cylinder appears to have a little oil coming in from somewhere, perhaps a leaking valveseal. The burned oil is left the center electrode insulator quite tan colored. It is this cylinder alone in which I put a one-step hotter plug (AP104) in to help burn the oil off better. Fortunately the rate of oil leakage is low and not noticeable at the dipstick.

(a conversation with a mechanic friend of mine this afternoon convinced me that a leaking valve seal is a major possibility on #4cylinder. I need to do a compression check and confirm that, but I balked today at spending more bucks for the compression gauge....)

#5cylinder had the cracked plug pictured twice above but in the first pic the crack is turned where you cannot see it. I did not notice the crack until I started to re-install the plug....After I rubbed it a few times more grease collected in the crack and it became much more visible and that is what you see in the second picture.

BTW, I have put over 100miles on the truck since putting the AP104 in the #4cylinder and the new AP103 in the #5cylinder (which is the same as all other cylinder plugs). The truck is still running just fine with no misfires noticeable. Also, the last tank of gas was mixed between before and after the fix (not to mention mixed between light and heavy pedal acceleration to help diagnose the problem) but when I filled up today I calculated 21.5mpg (even with air on the whole time), best yet in two months. Oh, and btw, that included another pint of SeaFoam in the tank; I have no idea what that does to mileage but I am expecting to exceed that with this new tank of gas, and my light-footing it.....!

:-drink I love it when a fix finally works!

YHS,
rogerw

PS - by the time I put 10K miles on these plugs, I will replace them with double platinums to avoid the nasty polarity-erosion problem ya'll have mentioned. -thanks!

OK, good feedback on the plugs.

There is a method to my madness, so just bear with me in trying to slowly be certain about the plug/s pictured.

Seeing as how the cracked plug was the only one with a crack & the plug with color, was the only one with deposits, it was possible you had inadvertently swtched the two in the picture!!!!

But now that we know for sure that isn't so, we can look for other causes for the deposits, which you've done.

Seeing as how you & your friend feel a small valve stem seal leak is a good possibility on #4 cyl, why not consider a "High Mileage" crankcase lube.

The "High Mileage" oils recipe has seal softners in it, to help soften & slightly swell old seals & fix such problems.

They also contain extra detergents to help clean the rings, valve stems, ect, so over time it could also remove things like valve stem varnish deposits, that can cause seal weep problems & carbon behind the ring pack, that can cause sticking rings..

Might be worth a try cost wise.

Most oil companies now offer a "High Milage formula.

There is also a aftermarket "Ester" based lubricant additive, called "Auto-Rx", thats reported to have good slow, safe, cleaning properties by many folks, but it costs about what two or three oil changes with the High Milege oil would.
Auto-Rx Engine Cleaner

On the compression check, if your friend has a scan tool, or you have one, or can come by one on loan, maybe a "cylinder balance" test would suffice, to give you an idea of each cylinders condition & the engines overall health.

It's pretty sensitive, & a heck of a lot easier & faster to do than a compression check, as it can be done while sitting in the front seat with the scantool in your lap & hooked up to the computers diagnostic port, while IT does all the work !!!! lol

Just a bunch more thoughts for consideration. Let us know how it goes.

good inputs.....I have never used an oil additive and was unaware of the "high mileage" formulated oils. But that prompts a question: I noticed on the can of Seafoam that it recommends itself for both gasoline treatment (as I have done) AND oil treatment.... Is that stuff ok to add to oil? OK for the lubricating qualities? I suppose it would also be good for cleaning varnish and deposits?

Just looking for a lower price answer than the Auto-RX stuff. I went to the website and read about it, but the price is pretty steep.

I will try to find some of the high mileage oil locally.

Thanks again!


YHS,
rogerw

High mileage oil is a bunch of snake oil. Even what they define as high mileage is bogus. At 75,000 miles, the engine is for the most part still practically new, and if it has had a proper break in, that first 20 miles of operation and has had proper oil changes, the engine should last at least 400,000 miles, or 15 years, whichever occurs first.

AutoRX is great stuff for removing any build up.

Good safe idea imo to try a high mileage recipe oil, for it's boosted addpack.

It's your engine, so you can pour anything you want too, into it's crankcase. But how "cheap" do you want to be & how much risk do you want, or are willing to incur for this supposed minor problem?????

Would I use Seafoam in the crank case as a lubricant or solvent, Nope, as imo there are other safer things to use in the crankcase, that'll target the suspected problem/s & at this point, valve seal hardening, or valve stem varnish, or carbon deposits, are just that, "suspected", not proven!!!!

But using Seafoam in the gas as a detergent, should help with any intake valve deposits.

The high mileage oils boosted add pack can safely & slowly get after varnish & carbon deposits, or a hardened seal problem, if any.