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Discussion Starter #1
Hello everyone, I need some guidance in chasing a P0300 code (random multiple cylinder misfire)
Just did the whole Cajun long tube headers with catted b pipes and uprev tune. Some background info first. Cam position sensor went out at convenience store, would not start,hooked up scanner, cps code appeaared, cleared code, started backfired a few times and then ran great. Had a code for it so replaced sensor. Did the exhaust work and replaced one AF sensor with proper Denso. Also replaced valve covers and gaskets,(leaking horrible!) and new spark plugs. Ngk Iridium 9's. Still triggered code. Replace all coil packs AFTER doing the coil test. Didn't know if they were weak or what so replaced them all. Sprayed carb cleaner on every inch of engine no change.
Starts right up, runs idles well until it comes off high idle. Plenty of power and I will check mpg once I fill up tomorrow.
Several sites said cam sensor can cause p0300. I have a diagnostic tree which says to check fuel pressure first thing? Would not think it would have so much power and also have low pressure. Am in the process of listening to all the injectors to see if they are firing. Dropped a bottle of Lucas fuel injector cleaner to cover all the bases.
This is where I am right now. Two mechanics said drive it until a real code comes up, as pinning it down is like chasing a ghost. So, any and all help would be greatly appreciated!
2004 Armada LE, 162k

Forgot to mention. After I clear the P0300 code, it won't return for a day or so. I drive it to work and back, about 18 mile round trip, no codes. Tomorrow I am sure the code will return, like clockwork. Drive is all stop and go, a few miles at 75mph.
 

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Air, fuel or spark. You have pretty much eliminated spark with new plugs and coils - only thing left there is the battery / alternator and wiring.

Fuel - would be the fuel pump, fuel hoses and injectors. Fuel pressure is hard to test on these without special tools. I replaced my 06 170k fuel pump for $80 and about an hour of time.

Air - would be MAF, air filter, intake, maybe a vacuum leak / cracked hose.

That's what comes to mind except for the ubiquitous "bad ground" possibility. Maybe pressure test the cylinders? Crankshaft sensor?

I agree with your mechanic - 0300 is hard to figure out due to all the possibilities.
 

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Did this happen immediately after doing the Cajun setup?
Have you checked in with Jeff and Joe to see what their thoughts might be on the code?
Are you sure that the o2 sensors were properly placed on the new setup? I believe the original o2 positions flip when you get rid of the 2 pre-cats with the Cajun install.

As far as the timing of the code popping up after reset, some codes are only triggered after certain driving conditions have been met, such as speed, distance, etc... although you wouldn't think cylinder misfire would be one of them.
 

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Discussion Starter #4
Can't recall when exactly the code came up. Have had codes since owning the vehicle in late May. My original thoughts were the codes were because of the cracked manifold and leaking valve covers. Did have an o2 code come up but not come back after replacing the af sensor. I need to get one more set of final data logs to Joe, don't know when i'll get those done. Joe though maybe vacuum leak, but I can't find one with carb cleaner.

Air, fuel or spark. You have pretty much eliminated spark with new plugs and coils - only thing left there is the battery / alternator and wiring.

Fuel - would be the fuel pump, fuel hoses and injectors. Fuel pressure is hard to test on these without special tools. I replaced my 06 170k fuel pump for $80 and about an hour of time.

Air - would be MAF, air filter, intake, maybe a vacuum leak / cracked hose.

That's what comes to mind except for the ubiquitous "bad ground" possibility. Maybe pressure test the cylinders? Crankshaft sensor?

I agree with your mechanic - 0300 is hard to figure out due to all the possibilities.
I was thinking crank shaft sensor or fuel pump/filter. Crank sensor is fairly cheap and easy. What a pain in the bottom this is! completely happy with the headers and uprev...stupid amount of power!
 

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Can't recall when exactly the code came up. Have had codes since owning the vehicle in late May. My original thoughts were the codes were because of the cracked manifold and leaking valve covers. Did have an o2 code come up but not come back after replacing the af sensor. I need to get one more set of final data logs to Joe, don't know when i'll get those done. Joe though maybe vacuum leak, but I can't find one with carb cleaner.
I read where someone else had an issue of the o2 sensors not being torqued in properly after their Cajun install which caused a leak. Maybe worth checking as it would be a simple task.


completely happy with the headers and uprev...stupid amount of power!
Have you tried the 91 tune with 91 octane yet? Muahahahaha! ;)
 

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Although I’m biased towards Redline’s SL-1 fuel injector/system cleaner, using that or any comparable injector cleaner usually doesn’t resolve a P0300.
With vacuum, air and spark ruled out, the fuel system is where I’d look into. Sure an injector may seem to be operating normally, but in order to confirm that, best to actually have the injectors professionally cleaned and tested. A weak fuel pump can also trigger a P0300 since it can’t keep up with what the ecu is demanding it to do.
 

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Discussion Starter #7
Although I’m biased towards Redline’s SL-1 fuel injector/system cleaner, using that or any comparable injector cleaner usually doesn’t resolve a P0300.
With vacuum, air and spark ruled out, the fuel system is where I’d look into. Sure an injector may seem to be operating normally, but in order to confirm that, best to actually have the injectors professionally cleaned and tested. A weak fuel pump can also trigger a P0300 since it can’t keep up with what the ecu is demanding it to do.
One of the diagnostic trees I have says check fuel pressure first before anything else. I've seen though, that testing fuel pressure on an Armada is not as easy as hooking up a gauge to the Schrader valve? Probably in the long run easier and cheaper to just replace injectors? I'll have to check locally and see if anyone does cleaning.
Thanks for helping out! In the back of my mind I can't but help thinking its a bad o2 sensor. I can monitor them through toque, but unsure of what kind of volts to look for and how often it should fluctuate?
Back to the thinking position!

I read where someone else had an issue of the o2 sensors not being torqued in properly after their Cajun install which caused a leak. Maybe worth checking as it would be a simple task.




Have you tried the 91 tune with 91 octane yet? Muahahahaha! ;)
I think the 3 tunes I have are power, valet and theft protection. Not a 91 tune as of yet. Premium is $2.62 here, good price but my other vehicles all take that. I'm not getting great mileage I don't think, but its only 16 mile round trip to work, mostly stop and go. I have a pretty heavy foot:cool:, just can't help myself, that sound, that acceleration, nearly as fun as my SL500!
 

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I think the 3 tunes I have are power, valet and theft protection. Not a 91 tune as of yet. Premium is $2.62 here
Oh I'm talking about just 1 tankful for *&#$ and grins.
You can have up to 5 tunes on there. I opted out of valet mode and had him add in 91 and tow mode tunes.
 

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Discussion Starter #9
This might be something interesting with the o2/af sensors. I filled up the Armada today. 11.81 mpg, not bad for a really heavy foot in stop and go driving and a whole lot of idling in the driveway while I monitor logs. But, today I was idling it and watching the af sensors and here is what I found, it may not matter in the least. Bank 1 sensor 1 is relatively flat at about -.5 volts. The car idles SUPER smooth for 3 seconds when the sensor dips to about -1 volt. Then back to running poorly for about 15 seconds. Bank 2 sensor 1 is at about +.5 to 1 volt fluctuating. Bank 1 sensor 2 is flat line at about -.5 or so. Bank 2 sensor 2 looks like a slow heartbeat with no spikes. Ie, a nice big square wave. Bank 2 sensor 1 is a new Denso. I would not know if bad sensors are causing poor running, or they are reflecting poor running. Any ideas?
 

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Discussion Starter #10
Although I’m biased towards Redline’s SL-1 fuel injector/system cleaner, using that or any comparable injector cleaner usually doesn’t resolve a P0300.
With vacuum, air and spark ruled out, the fuel system is where I’d look into. Sure an injector may seem to be operating normally, but in order to confirm that, best to actually have the injectors professionally cleaned and tested. A weak fuel pump can also trigger a P0300 since it can’t keep up with what the ecu is demanding it to do.
Hello, thanks for your reply. Is this the connector to test fuel pressure? From looking online it appears that checking fuel pressure is not as easy on these as other vehicles? Replacing more parts this week, the fuel system is next for testing if I can figure out the right connector. 51 psi I believe is correct? Thanks for any help.
 

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That isn’t the correct line to test fuel pressure. The fuel line has a push lock fitting, where you’ll need a fuel line disconnect tool in order to unlock the fitting.
 

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From what I remember, it should be located towards the front of the driver side fuel rail.
 

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Discussion Starter #14
Hi all, I don't know how to mark my last topic as solved but it is. If you haven't read it here is a summary:
Cracked manifolds. Did the Cajun long tube headers with catted b pipes. Uprev tune. Replaced leaking valve covers, gaskets and spark plugs. CEL code for AF sensor and P0300 random multiple misfire. New sensors, that problem solved. P0300 still existed. New coils, no change. Changed MAF and crank position sensor. Ended up replacing all injectors. Problem solved! No idea which injectors or how many, but this is the best its run in the 6 months I've owned it. No lousy lumpy idle, no wet coughing after blipping the throttle. Ran like a bat out of hell with the 87 performance tune. Filled up this am with 93 and tried the 91+ tune. Oh dear, what have I done! This nearly 3 ton 4wd suv might be faster than my SL500 Mercedes.
A VERY special thanks to Jeff and Joe at Cajun, they worked tirelessly with my fumbling through issues and suggested new things to try. Very patient with me as I usually work on my Volvo and Mercedes, but the Armada is an entirely different animal.
So, for anyone who needs to replace cracked manifolds, don't even think about getting OEM replacements, just do the right thing, go with Cajun and fugettaboutit.
I'll post some video and times of 0-60 when I get a chance, you will like it!
 

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Thanks for the follow-up. So many people post their issues here and then never come back to post what the solution was. It is unfortunate because then other folks come in with the same issues and don't know what the possible fix is.

Anyway, glad you got it resolved. I have the same setup as you, but I have to say that I am disappointed in UpRev's 91 tune. The 87 tune is excellent, but 91 is not much different than the 87 except for the timing advance. My SuperChips 91 tune gave the 2* timing advance and made the throttle exceptionally sensitive and off-the-line launch was crazy good.

As far as putting the JBA headers/long tubes on, it is a matter of the region that you are in and what you are willing to go through for inspection on whether it is the right thing to do. I did it here in Pennsylvania and finding someone to pass it for the yearly required safety inspection was a PITA. Same goes for our Armada/Titan/QX friends in California. You have to "know someone" to get it to pass inspection. Removing 2 of the 4 cats is a big no-no in many places.
 

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Thanks for the follow-up. So many people post their issues here and then never come back to post what the solution was. It is unfortunate because then other folks come in with the same issues and don't know what the possible fix is.

Anyway, glad you got it resolved. I have the same setup as you, but I have to say that I am disappointed in UpRev's 91 tune. The 87 tune is excellent, but 91 is not much different than the 87 except for the timing advance. My SuperChips 91 tune gave the 2* timing advance and made the throttle exceptionally sensitive and off-the-line launch was crazy good.

As far as putting the JBA headers/long tubes on, it is a matter of the region that you are in and what you are willing to go through for inspection on whether it is the right thing to do. I did it here in Pennsylvania and finding someone to pass it for the yearly required safety inspection was a PITA. Same goes for our Armada/Titan/QX friends in California. You have to "know someone" to get it to pass inspection. Removing 2 of the 4 cats is a big no-no in many places.
We don't have emissions here yet, but there is chance I might be moving somewhere that does, thats why I got the catted b pipes, just in case. Still have the rears.
 
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