Misfire codes, I give

[ViperGMC]

I give. P0304/P0309 #4/#9 misfire code. Changed the plugs, the wires and injectors but is still persists. Rebuilt engine less than 2K miles. I do not know what else to do at this point. Compression & leak down look fine. #4 & #9 are on different coils so the chance that they both went bad at the same time is slim to none. Any thoughts?

 

[uvbnbit]

Would a bad/faulty sensor (cam/crank) etc, cause a misfire?
BTW, we missed you last weekend.

 

[ViperGMC]

Hmmm . . I would think that that either positioning sensor would through off a multitude of codes, most likely not allow the engine to run at all. I am consistently getting these 2 misfire codes. And I memory serves, when I damaged the crank sensor before (I believe it was whooping you in Kentucky on the drag strip), the car would not start at all.

I tried very hard to make it and I was very disappointed that I did not. From the pics, it looked like a great time.

 

[uvbnbit]

Hmmm . . I would think that that either positioning sensor would through off a multitude of codes, most likely not allow the engine to run at all. I am consistently getting these 2 misfire codes. And I memory serves, when I damaged the crank sensor before (I believe it was whooping you in Kentucky on the drag strip), the car would not start at all.

I tried very hard to make it and I was very disappointed that I did not. From the pics, it looked like a great time.

Your memory does NOT serve! That was Jackson, TN when you damaged the sensor. KY was when you spun all the teeth off your Paxton belt.
Is there a way to check the "firing" consistency while running? Have you changed any of the timing/fuel maps, etc to those cylinders? Does "mis-fire" mean "no-fire" at all?
Sorry if these are "stupid" questions. You've probably checked all this already.

 

[dave6666]

Would a bad/faulty sensor (cam/crank) etc, cause a misfire?
BTW, we missed you last weekend.

Hmmm . . I would think that that either positioning sensor would through off a multitude of codes, most likely not allow the engine to run at all. I am consistently getting these 2 misfire codes. And I memory serves, when I damaged the crank sensor before (I believe it was whooping you in Kentucky on the drag strip), the car would not start at all.

I tried very hard to make it and I was very disappointed that I did not. From the pics, it looked like a great time.

If my memory serves me correctly, the crank sensor determines TDC for starting (hence no start when you damaged it) and the cam sensor is used for timing etc. Simply put of course.

So why would a sensor common to all cylinders (the cam sensor) repeatedly cause an issue with a couple of cylinders exclusively? Does not make sense.

 

[ViperGMC]

I agree, it don’t believe it is the positioning sensors. I am starting to think that it is a global issue. As a sequence of processing, the PCM discovers #4 misfire, then #9 and then gives P0300 random/multiple misfire because it decides that the misfire is happening all over the place. And that is the exact sequence every time, first #4 then #9 and then random/multiple. Most likely a lean condition at some point in the RPM range. A vacuum leak could cause that but it idles fine and usually a vacuum leak is most noticeable at idle. Maybe fuel filter, maybe fuel pressure.

 

[01ACR/VIPER]

Check to make sure the wires are on correctly.I know....sounds stupid but I did my header install and crossed #8&10 wires.It ran but had a backfire and power loss.I also got the misfire codes.When I relooked over the wires and found them crossed I could have kicked myself in the *** for stupidity.

 

[mjorgensen Woodhouse]

Check to make sure the wires are on correctly.I know....sounds stupid but I did my header install and crossed #8&10 wires.It ran but had a backfire and power loss.I also got the misfire codes.When I relooked over the wires and found them crossed I could have kicked myself in the *** for stupidity.

Agreed ^^^^^^^

The real time misfires can be seen with a Dodge star scan tool.

 

[Bandit3]

A lean condition on those cylinders (vacuum leak) will also cause a misfire.

 

[ViperGMC]

Very good advice and I have checked, checked, checked, checked and checked to make sure the plugs were correct. I wish that was the problem. I have an Autotap scanner that allows me so see about 30 parameters real-time, data log and graph the sensor values. It can not show me the cylinder misfire though, just the codes as they are thrown.

 

[Viper Specialty]

2003-2004's are known to have some crank position sensor issues sometimes.

-Check for spark and fuel [which you have surely done]
-Check for wire damage [Ground an alligator clip and trace the wires with the other end to see if there is any arcing anywhere around 4/9]
-Check for vacuum leaks [propane method works well]
-Check for spark plug variance to determine if there is something different cylinder to cylinder. [Change affected plugs anyway]
-Change Crank Position Sensor [check for rust and gunk in the timing windows on the back of the flywheel]
-If all is not OK by now, swap PCM with another 03/04, and see if the problem follows the PCM.
-If it STILL stays with the car, I would start checking wiring with an ohmmeter, and checking those two cylinders with a bore scope for anything odd.

 

[ViperGeorge]

Your signature says you've got 900+ HP to the wheels. Is your engine supercharged or turbocharged? If so you may be blowing the spark out under boost. Quenching the spark is what I believe it is called. I was throwing misfire codes on my supercharged 06 on the track until I spoke with DC Performance. They told me to go with the NGK V-electode plugs (don't remember the heat range off hand) and a 180 degree thermostat. They reflashed PCM to change WOT timer and bring thr fans on at the right temp given the thermostat change. No misfire codes since.

 

[ViperGMC]

I have verified all the easy stuff, wires, plugs, gas, and vacuum leak. I did pull the crank sensor out when I changed the plug wires (could not release the connector so I pulled the sensor). I will recheck but I think it is a long shot. A little background on my setup. I have a totally rebuilt motor and run a supercharger with 15lbs boost with an AEM controller. Every year I have to pass emissions, so I unplug my AEM, plug-in the OEM PCM, open the by-pass to the supercharger and swap back the original injectors. I clear the codes, drive around town till the emissions are ready, get tested and then reverse. That routine has worked fine for the past 3 years until this year. I went on 1 road trip since last year, so I cannot imagines anything mechanic has suddenly changed.

I did do one thing different this year. I got sick of changing the injectors so I got an SCT flasher and thought that I would change the fuel map on the OEM PCM to work with the bigger injectors. I could not get the SCT to do what I wanted. Every time I made a change; weird things went on, even a simple change. No manual or anything available. I don’t tune for a living but I do know how to set up a fuel map, hook up a wide band, log the data and dial it in. I could not figure out what was going on with the SCT and don’t have time to mess with it anymore. I did some research and found lots of unanswered questions, including a bunch by Dan. Did you ever get everything worked out? I returned it to stock but maybe not everything is as it should be. I do have an extra PCM that I had programmed a couple of years ago, but it has a memory check sum error. I think I will get the one in the car or the extra one re-flashed and see if that changes anything.

Dan, you have any suggestion for the SCT???

 

[Doug Supercharged Vipers]

May I ask what spark plug wires are you using?

 

[uvbnbit]

May I ask what spark plug wires are you using?

I think he'd told me he just put in some of AB's (Quality Wires)

 

[ViperGMC]

That’s correct Chip, I have a new set of the quality wires. The odds of 2 bad wires was slim. But just to eliminate that issue, I put an old wire on #4/#9 and no change. That completely eliminates the wires. Did the same for injectors and plugs. I know those are not the problems.


I also changes out the motor, then the chassis, but still the problem persisted. Now I am thinking to change the wife and child, what do you think.

 

[C.Hermsen]

I hope I don't sound too stupid here haha, but are you positive your injectors aren't clogged?
I had the same issue on my 350z, getting fuel, spark, compression and I couldn't figure out why
I was getting a PO304 code for missfire. Sent my injectors to be flow tested and one was only flowing
105cc/min where it shouldve been 550cc. Just an idea.

 

[ViperGMC]

It is not a stupid question. What I did was take out the injectors and had them serviced, in the meantime I put in an old set, no change. When the injectors came from being serviced I replaced them. Still no change. The injectors that I sent for service were fine BTW.

Again, I did the plugs, wires, injectors, compression all the easy stuff. I am looking for something beyond the obvious.

 

[ViperGeorge]

what plugs are you using? Stock plugs WILL quench the spark under load/boost. This WILL throw a misfire code. I'm speaking from experience here.

 

[ViperGMC]

I am not running any boost right now and I tried several different plugs all doing the same thing. So again it is not the plugs or wires or injectors. The car was running fine before I parked it. The setup has been track tested dozens of times. The motor is still very fresh and all the vitals check out fine.

 

[ViperGeorge]

Does the engine throw codes at idle or do you need to run it thru the RPM range? Do you have an A/F meter or fuel pressure gauge? Is your vacuum within range given your mods? Is there any chance you've got a leak at the manifold or head gasket?

 

[britospeed]

How does it run with the AEM? Have you data logged the cam and crank sensors during the missfire? If so how do they look? Have you scoped either sensor to look at the wave form during the missfire?
I'm also guess that you are running a stock MAP sensor that you switched back with the stock ecu and injectors. Are you running a 3 bar with the AEM?

 

[Viper Specialty]

Dan, you have any suggestion for the SCT???

There are many, many things as of late that I have been correcting with SCT, and yes, the system now works like a charm... but a bit different that before, some more items have been added to get things working properly.

I can write you a pretty good starting point for your injectors, and walk you through finalizing it if you would like. It will take a little time, but it will work when its done. I have my car running clean, with Cats, passing NY Inspection, 14.7:1 even in deep vacuum, no issues or errors, on 1000cc's... without having to play computer trickery. It was a task to get done as I found all kinds of table issues early this season, but we nailed them all down and got them sorted out.

 

[ViperGMC]

It idles fine, seems like it may stumble at close to 3,000. A vacuum leak is most noticeable at idle and it does not show any signs of a leak. The I have a wide band on both banks and fuel pressure when the AEM is connected but not with the OEM PCM connected. I have logged the fuel trims but so what. If it is not igniting the fuel or if there is not enough fuel, the O2 will see the same thing “lean”. I am very confident the mechanicals are fine (injectors, plugs, wires, sensor etc) so the only thing it can be at this time is the PCM doing something funny. I can limp the car over to the dealer (if there are open) and get the PCM flashed as long as the don’t start freaking out over all the mods. Does any know if they can flash the PCM removed/pulled from the car??

 

[Viper Specialty]

Nope, they cant.

And the stumble is due to your injectors more than likely... it happens at about 2800RPM and medium throttle, right?

I have to tune it out of any car with injectors it seems........

 

[ViperGMC]

Very astute Brito, I did change back to the OEM MAP sensor. No, I did not gone into details on checking the sensors.

Dan, I will definitely take you up on that offer. I am really beginning to think that the SCT changed something that I did not intend on the PCM that is causing my woes.

 

[britospeed]

What size injector is in the car now with the stock ecu? Are they stock or are they the larger ones that you are also running with the AEM? If they are the larger ones Dan will most likely be able to fix the problem.

 

[ViperGMC]

They are stock. I called Dan and we are going to work on a couple of things. Will let you know.

 

[Qualitywires.com]

I think I have a set of stock injectors that are used and RC balanced. Let me know if you need them. Also on the wires, make sure you can feel/hear the click when you push the wires on the terminals. Sometimes you need to wiggle the boots while pushing on them to get a secure fit.