Hey guys,

Thanks for taking the time to read this and any help is much appreciated. >>Here is a thread with a similar problem <<but the idle on this truck is not really rough at all, for the most part it seems to run fine.

I have a friend who has a 2001 Mazda B3000 (3.0L v6, RWD, 5 speed manual) and it has recently started to misfire on cylinders 2 and 6 and we are scratching our heads.The only codes are p0302 and p0306. We've reset them a couple times to try and figure out when it happens. Seems that freeze frame data always shows it happening around 25mph, most recently he noted he was in 2nd gear. After a code reset it takes about 20-30 min of driving to hit again.

Here is a quick history with links to some data/invoices:

Invoices of work done <<

Some Data while we were driving <<

Truck was working fine other than it maybe sounded loud, no codes and brought in for a checkup in Dec. Oil change in this truck was likely over due also. You can see everything they did on the Dec invoice/s. After getting the car back while driving it home the check engine light turned on. Unfortunately we aren't sure what the codes were after this first visit. A few days later he brought it back to Big O (yeah, we know) and showed them the check engine and they did everything you see in the Jan invoice. He got the car back with the check engine light still on and we've been trying to figure it out ever since.

Here is relevant info I can think of in bullet point format

• Sometimes the CEL flashes when it trips (indicating a misfire that's bad for the cat I believe)
• On second visit we got all new spark plugs, wires, and coilpack (installed by BigO, I did notice that the terminal boot on cyl 2 is different color than the reset)
• The engine doesn't really shake that much at all, and for the most part seems to run fine.
• On first visit they changed the water pump and serpentine belt
• according to some forums cylinder 6 and 2 on the coilpack fire from the same coil, which could point to the coilpack, but that was replaced and we got the misfires before it was replaced. Unfortunately we aren't sure if it was still 302 and 306 in between the visits.
• we did give her some seafoam , both regular and top engine clean with no change to codes. It did run smoother though (much less loud which was part of the reason for first visit anyway, he asked for a 'checkup')
• I have put a rod to the injectors on 1, 2, 3 (they are easier to get to) and they all have the same sound as far as I can tell but I don't have a lot to compare it to
• We are going to try and give her an 'injector clean' dose of seafoam as previously it was pretty dilute due to it being on a full tank
• We have spark on the spark plug wire for cyl 2 (have to remove intake manifold to check 6 which we haven't done yet)
• Pulling wire for cyl 2 while running did make the engine run a lot worse and idle rough, so cyl 2 is contributing, and with low/no shake I would assume contributing most of the time?
• Engine has 115k on it

That's all I can think of for now. I have been doing tons of research on car repair for the last 6 months but haven't gotten my hands as dirty as I'd like so just looking for some direction. Should we go straight to compression from here? I assume I am going to have to buy a new intake manifold gasket if I want to get to plug 6, which also makes it hard to 'power balance' test plug 6 like I did with 2.

Thank you for taking the time to read this, I appreciate any help. Thanks!

 

Welcome to the forum

The 1995-2008 Ranger 3.0l uses a Waste Spark system
There are only 3 coils inside the coil pack
The coil pack wiring will look like this
3 4
2 6
1 5
front

3/4 share one coil, both spark at the same time, one is on power stroke the other on exhaust stroke(wasted spark) hence the name Waste Spark System

So 2 and 6 also share the same coil in the pack.......................................

P0302 and P0306 at the same time would set off red flags that there is an issue with coil pack either not getting the spark signal for that coil, or coil itself is bad, new or not

On the invoice I am curious as to what "pigtail to coil" means??????

Coil pack has 4 wires
12volt wire, key on 12volts
Coil 1 ground
Coil 2 ground
Coil 3 ground
The computer pulses the ground wire to spark/fire each coil

So best guess is that the coil 2 ground wire is not working now and then if misfires come and go, or #2 coil in the pack is intermitant

There were a couple of different coil packs used, and they had different wiring connectors, I am wondering if shop used different coil pack that needed "the pigtail"?

 

Hi RonD,

Thanks for your insight on this! I have been scouring these forums and others for information and have seen many of your greatly helpful posts, I appreciate it. I am going to inspect the 'pigtail to coil' more closely and see about trying another coil pack (unfortunately we no longer have the old one). Maybe there is intermittent electrical connection on one of the 4 wires you mentioned (sounds like specifically coil 2 ground wire). I actually repair electronics for a living so I like it when it's electrical haha.

hat is the best method for testing those ground wires? pull the wires and run coil 2 ground to ground through a test light? I assume a multimeter wouldn't respond quick enough. With it being intermittent I may need to get a scope and record any missed ground from the computer. (If I'm understanding all of this correctly.

Anyway, I'll see what I can find and report back.

 

With coil pack wire disconnected you can test internal coil pack wiring with an OHM meter

Watch this video:


Problem with ignition coils is the low OHMs used means after the coil gets HOT, which it does, the OHMs can change causing the misfires, so while a coil CAN test BAD, it can NOT test GOOD, so not a definitive test, there really isn't one
The coil tower OHMS do offer a better test to see if coil is "good'

Then we have the computer side wires, yes when cranking with coil pack connector off, you could test #2 coil wire with meter set to DC volts and hooked to 12volt
Voltage should pulse but at 200rpm cranking speed it is pretty fast pulsing

If you can get your hands on a old timing light you can test 2 or 6 spark plug wire for steady timing flash, raising RPMs and maybe testing after engine is fully warmed up, coil is HOT
See if its dropping pulses, it is pretty easy to see that with timing light strobe effect

 

Hi guys,

It's been a good while but I wanted to update for anyone doing some googling. Thanks RonD for you awesome knowledge also!

Anyway, the issue still exists. We still get P302 and P306, the coil pack tested fine and we even took it to 2 shops to have them diagnose it and they could not figure out the cause either. As stated the 'misfires' are very mild and the engine sounds like it's running find and doesn't vibrate more than normal. At this point we are just running it as is for now and it has been running just fine. It will probably have further issues later (just a guess) and at that point the owner (who isn't me) wants to just sell it and move on. Not a 'happy ending' but it has been running fine but still throwing those codes. Thanks for all the help everyone!

 

Thanks for the update

 

The 4 wire molded (factory sealed/glued) pigtail (from wiring harness)that plugs into coil, go bad. When it's running rough, wiggle the 4 wires on coil plug-in pigtail on top of the coil & see if it smooths out. I just replaced one pigtail, and now 6 months later, I need to do it again.
I replaced EVERYTHING trying to fix this intermittent misfire throwing the same fault codes=Bad "molded" pigtail. I cant find the part #. Spotty internet...