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8~~~> I tried everthing!...help with misfire <~~~8

3K views 42 replies 10 participants last post by  NewfieSRT4 
#1 ·
I am trying to figure out a P0303 misfire. I changed my spark plugs gapped them lower to .32 gap(NGK4306). My coil is a granatelli and wires are magnecor, both only have probably around 5k miles on them. I switched wires from cyl 3 to cyl2 to see if the code followed and it did not. I pulled the wires one by one off the plugs while the car was running to see if they were sparking and they all are sparking. I had all my mopar stage2 injectors professionally tested and cleaned. I even put a brand new mopar stage 2 injector in cyl 3. I replaced my intake manifold gasket and did a boost leak test with careful attention to my intake manifold and injectors. I did a compression test which resulted in 120psi on all four cylinders (yes with the engine warm and WOT).:stab:

I have searched and read a lot of posts about misfires, if not all of them, I would really appreciate some help.


MODS: 3bar MAP and TIP, Stage2 mopar injectors, AGP wastegate, Manual turboXS boost controller, 3" magnaflow exhaust, AEM long ram CAI, MINDMELT tune, PLX gen4 wideband.
side note: AFR idle = 14.3-14.9
 
#2 ·
First off I must say you did well so far in trying to diagnose the misfire. When is the misfire occurring? All the time or under load. You might try with the plug out and grounded watching the spark the coil is producing and compare with another cylinder. I don't trust any aftermarket coil packs. Only oem.
 
#5 · (Edited)
Very thorough Diag. I know it's a new injector but swap injector 3 with injector 1, pay close attention to the injector o-rings also. I do have to agree hiccups are normal but they are infrequent. A misfire at idle is noticeable because you can just about count them.
 
#6 ·
I highly doubt the injector is the source at this point. I still say coil is the probable problem. Many years ago many owners switched to msd coil packs for "more performance" but found them fail at an alarming rate and proceeded to go back to the Oem. If you pull a plug and ground it while cranking the motor over it should be a bright blue color. If it is orange the coil is weak. From there if it checks ok I would do a cylinder leak down test to ensure a proper valve seal on cylinder 3. This checks the seal of the cylinder. Compression tests only check the ability to build pressure. Not exactly a complete and accurate picture of the shape of the engine. If the loss is 30% or more then a valve job is in order.
 
#7 · (Edited)
8~~~&gt; I tried everthing!...help with misfire &lt;~~~8

Have you checked the porcelain on the spark plug for carbon tracking afterwards? A plug wire that has a cracked boot on the inside can easily ruin the plug. It happened to me when I had the mopar performance wires, ruined 2 plugs like that. You might see a white line on the inside of the boot. Gray pencil like marks on the porcelain means the wire is junk and so is that plug.


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#8 ·
I checked the coil by pulling the cyl 3 spark plug out, grounding the spark plug and pulling the fuse relay out. Then had someone crank the engine, with the plug in the wire so I could watch the spark (in the dark). Put it back in and repeated to compare it to cyl 2. Both looked the same. So I then switched injector 3 with inj 4 and reset the codes. The code followed the injector, (now displays P0304). I also noticed when I looked at the injectors that all of the tips looked the same except for cyl 3. Cyl 3 looked almost red, like a maroon color around the injector tip.
 
#11 ·
Weird. Have a look at this site, then look at #3 . By what your saying about the injector being coloured, sounds like injector #3 was subjected to heat soak.





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Hmmmm....considering the color of the injector tip, I would have to agree the idea of heat soak is highly probable.
Here are some pictures of the injector and another for comparison.


"Suspected problem injector"

"Suspected problem injector"


........NORMAL
 
#12 ·
sub'd. Interested to know what the cause is.
 
#13 ·
I checked the coil by pulling the cyl 3 spark plug out, grounding the spark plug and pulling the fuse relay out. Then had someone crank the engine, with the plug in the wire so I could watch the spark (in the dark). Put it back in and repeated to compare it to cyl 2. Both looked the same. So I then switched injector 3 with inj 4 and reset the codes. The code followed the injector, (now displays P0304). I also noticed when I looked at the injectors that all of the tips looked the same except for cyl 3. Cyl 3 looked almost red, like a maroon color around the injector tip.
Maybe didn't see this post?
 
#16 ·
Ok so I had a spare stage 2 injector laying around (yes I had it professionally flow tested and cleaned). So I took the injector out of cyl 4 (which was the brand new injector with the supposed problem) and put the spare injector in. I reset the codes and it took probably 7 or so trips to work and back, driving around a bit for a code to pop up. It just popped up right before I got home tonight, code is P0300 multiple cylinder random misfire. WTF is going on? ugh......Im thinking just drive it around for a while until I find a pond to drive it into?.... lol
 
#17 ·
Just a random thought, maybe bad coil and/or lose ground? Maybe it vibrates lose as you're going? Intermittent problems are so freaking annoying.

Can you do some data logging ?
 
#20 · (Edited)
Yes i do have the ability to data log, but what pid is important to log in this case?

cyl 1-4 act spark? at idle? idk.....

I'll have to get a coil pack from a junk yard or something. It just sucks because I just bought this granatelli coil from modernperformance in January. I found one new at a discount mopar site for $85 though.
 
#19 ·
I have a spare stock coil if you want. I'll send it to you, just cover shipping.
 
#22 ·
So after driving around a bit today, another code popped up. Now I have P0300 but also P0304. Again I had this injector as well as the rest of them currently installed professionally leak tested, flow tested and cleaned. I am going to a junk yard today to get a used coil to give that a try anyway.
 
#25 ·
If the coil doesn't work out, you may need to dive deep using a scope. I know they're pricey, but it's saved me from throwing tons of money in parts at something I wasn't sure about.

The two key things at datalogging a random misfire issue is crank sensor and either a cam sensor, injector, or coil (not the high voltage side) as a trigger. You can then see the deceleration between crank signals. It's tedious, but with enough staring over results you should be able to pinpoint if it's truly random, or it's a couple problematic cylinders. The cool thing about a scope is you can datalog nearly every sensor in the raw form, on any car. Even rail pressures (diagnose sticky injectors), map sensor signals (diagnose valve issues, intake leaks), injector and spark wave forms (which can lead you to a failing injector driver circuit in the PCM). If you see something wonky across all inputs at the same exact time even for a millisecond, that could clue you in on an electrical fault, whether grounding issue or shorting. If you have friends that know the basics, you could rent it out to them an recoup some of the cost.

It's not rocket science to learn, but there is a curve if you don't have a background in electronics, sensors, or PCMs and how they function. Definitely a good skill and tool to have, and all of the information is out there on the web to learn the basics.

I use an older version of Parallax, but you may be able to find a used one off ebay versus buying new. Parallax PropScope USB Oscilloscope - RobotShop


Has anyone else seen random misfires with their compression numbers being in the 120 range? To me that doesn't sound tired enough to be an issue.
 
#27 · (Edited)
+1 on the scope. There are less expensive alternatives especially with the recent explosion of arduino/atmel powered devices. See : [ame]http://www.amazon.com/DSO-Nano-Oscilloscope-v3-Seeedstudio/dp/B015X6LZFO/ref=sr_1_6?ie=UTF8&qid=1445999476&sr=8-6[/ame]

Also 120psi is plenty compression to make a boom. I think the threshold is around 80-90 in the fsm. I had a 1gn that has 80 in one cylinder due to bent valves. At idle it was clearly missing and once revved slightly it fired just fine as the piston was moving fast enough to build higher compression before it leaked by the valve.
 
#28 · (Edited)
Yes I did check the harness where the wires meet the injectors, I'll check again more thoroughly. I haven't made it to the yard yet but that scope sounds pretty cool. I would need a good amount of research to put that to use though, as I have no background in electronics,PCM's and such.
 
#29 · (Edited)
Also, idk if this helps at all towards diagnosing the misfire, but another code came up tonight in the way home from work. P1188-tip sensor performance (yes I have 3bar map/tip sensors) P0452-nvld pressure switch sense circuit low. I also noticed the cell flashing for a couple seconds or less a few different times during the ride to and from work.
 
#30 ·
The blinking cel is a warning of possible cat damage and also typically misfires.

Just to make sure we're clear you were getting p0303, moved the injector came up with p0304, swapped that injector with another and still getting p0304?

It sounds like you have 2 bad injectors. I know it doesn't sound right but an injector can spec out AND not operate properly.

If something was wrong with your wiring you would have had p0303 and 304 to begin with. But you only had p0303. When you moved the the initial injector the code moved also proving that the injector you moved was having an issue.

Swapping 1 or 2 with 4 should give you the answer. And only takes a few minutes to swap.
 
#31 ·
So I bought an OEM coil from the junk yard. I also swapped injector 4 to cyl 1 and visa versa. I drove my car for approx 50 miles before a code popped up. It is displaying code P0300. no other codes as of yet and I have driven now approx 90 miles. Still trying to figure this thing out.....:drinkup:
 
#32 ·
Jesus. So what constitutes as a misfire according to the ECM? How does it know there was a misfire? Maybe something in that process is bad and it's not actually misfiring?
 
#33 ·
So still no other codes besides P0300 so far. Question........ If my car is running rich at times, could this cause the P0300 code?
Idle is at 14.3-14.9, primarily around 14.6 but when I check the highest and lowest recorded afr on my gauge for the trip, it displays as much as 10.1 afr
 
#34 ·
I would think so, but I am not sure how the ECU determines a misfire. When I installed the NGK 2315 the gap was far too wide and I'd get blow-out but the car never complained about it. I imagine that would be the same situation as running too rich?
 
#38 ·
I would just order crank, cam and cam magnet just for the hell of it. I've had terrible luck with crank sensors on this car. They are cheap enough and you'll probably have to do it soon anyway. Hopefully they fix the issue for you.
 
#41 · (Edited)
I am having the same misfire issues as well. have new motor with 120 psi comp. new ngk plugs and wires with new coil pak. still sputters randomly with codes p0300 and sometimes p0304. so I hooked up my data logger and watched the misfire count from the pids and watched number 4 cylinder misfire over 150 times in a couple minutes with a few here and there in all cylinders. under cruising load there were no misfires for a while. so I swapped the 1 and 4 injectors and as I suspected cyl 1 was misfiring. So I am trying sea foam and changing the fuel filter. if it still don't fix the problem will get the injectors cleaned. hope this helps. curious if you guys found the issue on your car?
 
#42 ·
Do not use seafoam. Why is your compression only 120 psi?
 
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