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Discussion Starter · #1 ·
The other day I got P0301, misfire cylinder #1. I thought maybe it was a fluke so I reset the CEL with a scan tool. It came back on my next highway trip.

car is:
2004
3.0 5sp
82k miles

I pulled the intake manifold and replaced all 6 spark plugs with NGK's. I also swapped the #1 coil with the #5, on the assumption that if the coil was bad I would get a misfire code on #5 and hence know it was the coil. Issue is, with a different coil and new spark plugs P0301 came back. Once the CEL comes on it will stay on, but if I clear it with the scan tool the ONLY way to get it to come back on is maintaining a high rate of speed (~80 on the highway). If I exceed 80 the CEL will flash, bring it back under 80 and it goes back to solid.

If its not the plugs and not the coils, what else could cause a misfire on #1?

I'm not sure what the next logical step should be. The only mods are: airbox mod, cpe wishbone, awr trans mount.

can anyone confirm that the cylinder numbering is as follows:

windshield
123
456
front of car
 

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Discussion Starter · #2 ·
no one has had a misfire code that wasn't resolved by new plugs/swapped coils? Open to ideas...
 

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Maybe the ignition is putting enough spark to the coil at such a high rate... or it might have a bad or loose connection to the coil. I would check all the wires to see if maybe something might be cut, burnt or anything out of the normal range.
 

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Discussion Starter · #4 ·
Hey guys,

I'm still struggling with this code. I've checked the wiring and everything looks like new. I swapped coils around and reset and the code still returns for cylinder 1. I'm on a new tank of gas now with fuel injector cleaner - still the problem persists.

I can run the engine at any rpm, maintain 45 mph in 2nd gear for 15 seconds, no problem will not trip the check engine. The check engine light is entirely dependent on road speed. Cross ~80 and the check engine light comes on - misfire #1 P0301. I'm baffled! The speed threshold of 80-85 somehow is causing that light to turn on. What can it possibly be? The engine runs great all the time. The only possible thing I can think of is the AWR tranny mount causing more vibration at those speeds and somehow it interprets that as a misfire on #1... but that's pretty far out there. I may throw the stock mount back in just to see though at this point.
 

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I would check for vacuum leaks. I had leak between my TB and IM when I first put the spacer on, and it would sometimes cause this. Also, try holding the RPM at 3.5k in a lower gear at a lower speed and see if that triggers anything.
 

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general procedure for finding missfire.

1st swap plug to next cyl (i know you put new ones in but do it anyway)

then swap coil to 3rd cyl.

test.

if it doesnt move, then swap injector to another cyl.

test.

still doesnt move, check wiring to coil and injectors.

leak test intake a lean cyl can cause a missfire.

if no leak is found, procede to check cyl integrety compression, and leak down test.

it is possible that you have a defective plug, not sure if you swaped that with another yet.
 

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QUOTE (90turbo1 @ Feb 20 2009, 01:16 AM) index.php?act=findpost&pid=1522420
general procedure for finding missfire.

1st swap plug to next cyl (i know you put new ones in but do it anyway)

then swap coil to 3rd cyl.

test.

if it doesnt move, then swap injector to another cyl.

test.

still doesnt move, check wiring to coil and injectors.

leak test intake a lean cyl can cause a missfire.

if no leak is found, procede to check cyl integrety compression, and leak down test.

it is possible that you have a defective plug, not sure if you swaped that with another yet.[/b]
+1 if the coil itself proves out to be good, I'd suspect a tiny clog in the injector.
 

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I had that problem for a while. I guess it could be because of the NGK's... I had G-power in it and it misses like crazy... I swap coils and it still... I than swicth to NGK IX and gap them to .45 and it went away.
 

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wow thats a toughie! i just reiterate what other people said:

1. vacuum leak (i doubt this because it would cause p0300)
2. spark plug gaps (check em!)
3. there's always the slim chance you put another defective plug in..

id switch the coils again to confirm

but my guess is its electrical, which is hard to find. thats such a strange problem! please keep us updated, this is very strange.
 

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Discussion Starter · #10 ·
I haven't had time to dive back into it. I'm rebuilding an engine - diff car - and that has all my attention right now. I agree that I think it's electrical gremlin. For now I keep it under 85 and have no light. On occassion I sneak over that speed I need the obdii reader handy to clear it. That will have to do for now. I don't anticipate having time for it till next month. I thank all of you for your replies. I'll update when I get to the bottom of it.

QUOTE (hot6onaplatter @ Feb 25 2009, 11:03 PM) index.php?act=findpost&pid=1525287
wow thats a toughie! i just reiterate what other people said:

1. vacuum leak (i doubt this because it would cause p0300)
2. spark plug gaps (check em!)
3. there's always the slim chance you put another defective plug in..

id switch the coils again to confirm

but my guess is its electrical, which is hard to find. thats such a strange problem! please keep us updated, this is very strange.[/b]
I haven't had time to dive back into it. I'm rebuilding an engine - diff car - and that has all my attention right now. I agree that I think it's electrical gremlin. For now I keep it under 85 and have no light. On occassion I sneak over that speed I need the obdii reader handy to clear it. That will have to do for now. I don't anticipate having time for it till next month. I thank all of you for your replies. I'll update when I get to the bottom of it.

QUOTE (hot6onaplatter @ Feb 25 2009, 11:03 PM) index.php?act=findpost&pid=1525287
wow thats a toughie! i just reiterate what other people said:

1. vacuum leak (i doubt this because it would cause p0300)
2. spark plug gaps (check em!)
3. there's always the slim chance you put another defective plug in..

id switch the coils again to confirm

but my guess is its electrical, which is hard to find. thats such a strange problem! please keep us updated, this is very strange.[/b]
 

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sounds good. damn gremlins!
 

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QUOTE (6GT @ Feb 25 2009, 11:33 PM) index.php?act=findpost&pid=1525260
I had that problem for a while. I guess it could be because of the NGK's... I had G-power in it and it misses like crazy... I swap coils and it still... I than swicth to NGK IX and gap them to .45 and it went away.[/b]
You are probably thinking of the gapping for the Pulstars. The gapping should be between .051-.057 for our V6 on a mostly stock setup per the owner's manual. You can probably gap a little more if you are using stronger COPs like Sniper or WeaponX. The NGK IXs typically come pregapped at .052 and recommend that gapping for our car. I'd leave the gapping at that. If you already closed the gap, I would open it back up to the .051-.057 range. But I wouldn't recommend closing the gap below that, you'll only risk losing some power and poorer gas mileage.

Paul
 

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QUOTE (VirtualMirage @ Feb 27 2009, 07:38 AM) index.php?act=findpost&pid=1525985
You are probably thinking of the gapping for the Pulstars. The gapping should be between .051-.057 for our V6 on a mostly stock setup per the owner's manual. You can probably gap a little more if you are using stronger COPs like Sniper or WeaponX. The NGK IXs typically come pregapped at .052 and recommend that gapping for our car. I'd leave the gapping at that. If you already closed the gap, I would open it back up to the .051-.057 range. But I wouldn't recommend closing the gap below that, you'll only risk losing some power and poorer gas mileage.

Paul[/b]

I left them at the regualar gap & my car was idle rough... So I went higher and it seem to mis in the high end.. So I gap lower untill the mis went away. Well after so many sparks plug changes, I can changes them in like 20 mins top now. ahah
 

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QUOTE (6GT @ Feb 27 2009, 10:58 AM) index.php?act=findpost&pid=1526026
I left them at the regualar gap & my car was idle rough... So I went higher and it seem to mis in the high end.. So I gap lower untill the mis went away. Well after so many sparks plug changes, I can changes them in like 20 mins top now. ahah[/b]
If you were having rough idle at stock gap and misfires at higher gap, then I would be concerned about your COPs or somewhere else in your ignition system.

Paul
 

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QUOTE (VirtualMirage @ Feb 27 2009, 12:48 PM) index.php?act=findpost&pid=1526211
If you were having rough idle at stock gap and misfires at higher gap, then I would be concerned about your COPs or somewhere else in your ignition system.

Paul[/b]
It was the spark plugs.... I talk to O 'Reilly about it and they said that the box of NGK was drop while reciving. So that was the problem...
 

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Oh, ok. At least there was a reason behind it. :p
 

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what should the gap be on pulsars? i just checked my misfiring cylinder and the plug was burnt out and at 65 lol
 

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Discussion Starter · #18 ·
Update:

Finally had some time to look back into this. I replaced all 6 coils with BRAND NEW Motorcraft coils. I took a look at the plugs while I had the intake manifold off. They look really good - perfect even.

So 6 new coils, perfect plugs with less than 2k on them and sure enough come 85 mph check engine light comes on, push it past 85 and it'll flash indicating a serious misfire. Still P0301.

I am so frustrated at this seemingly unsolvable problem. I've established that its not the plugs, not the coils and the wiring on the coils looks perfect. Only thing left is a bad injector on #1 or a faulty ecm. What is so strange is that it seems to have nothing to do with engine RPM but rather road speed. Though, if I am accelerating hard though I can whiz right past 85 and no CEL. Ease up or coast and it'll pop right on.

What can this be if not coils/plugs? It runs perfect throughout the whole ordeal - if not for the CEL I would never suspect there to be anything wrong. I'd hate to replace the injector and still have the light come on. I don't want to throw more parts at it in hopes of resolving the issue. Has anyone had this happen??
 

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According to the service manual, it could be a bunch of things. It could be the spark plugs, ignition coils, fuel injector, air leak between plenum and intake manifold or intake and cylinder head, low engine compression, bad electrical connection or PCM. It says you can swap the injector with another one. It also says you need a special tool to remove a plastic fuel hose that the injectors are in line with.
 

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Discussion Starter · #20 ·
QUOTE (chilimax21 @ Mar 31 2009, 07:36 PM) index.php?act=findpost&pid=1541049
According to the service manual, it could be a bunch of things. It could be the spark plugs, ignition coils, fuel injector, air leak between plenum and intake manifold or intake and cylinder head, low engine compression, bad electrical connection or PCM. It says you can swap the injector with another one. It also says you need a special tool to remove a plastic fuel hose that the injectors are in line with.[/b]
Excellent idea on swapping the injectors. I'm going to try that and if the misfire jumps to a different cylinder then I know for sure it is the injector. I'm familiar with GM injectors which are easy to remove from the fuel rail, just a metal clip and an o-ring. I'll have to take a look at the ones on the mazda and see how they are secured.

I have a friend who is going through a very similar situation with an 04 RX8.
 
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