Dakota Forumz banner

1 - 18 of 18 Posts

·
Registered
Joined
·
26 Posts
Discussion Starter #1
Hi,

I've been dealing with a P0300 random misfire code for a while, but only when the engine is initially started, or in very cold temperatures. I used a scan tool to check my STFT and LTFT values, and the Bank 2 values are all over the place. When the misfire is currently happening, the STFT B2 value is around 0, but the LTFT B2 value is negative, at -32.8. If I shift into drive, the values immediately move closer to 0, around 1.6 generally. Shift back into park, and the issue is back (engine is shaking, and the LTFT value is very negative). If the engine warms up (about 5 minutes or so) then the STFT value goes to positive 30, and the LTFT value stays around -30, and then they slowly converge until both numbers are very close to 0.

What should I look at for the cause of this, and is my misfire causing the fuel trim issues, or the other way around?

Thanks in advance.

-Nate

The first picture here is at idle, in park, after the engine has been running for about 5 minutes. I left it for about 30 more seconds, and that is when the bank 2 STFT and LTFT values began to converge around 0.

The second picture is before I even started the engine.

2371
2372
 

·
Registered
Joined
·
525 Posts
Excellent description of the issue, with good documentation of the facts. Your bank 2 fuel trims show the engine running very rich when the engine is cold, and as the engine warms up, the issue sort of corrects itself. Check a couple more things. Does the correction start when the engine goes from Open Loop to Closed Loop? Also, does bank 2 sensor 1 O2 sensor show a steady very rich condition when cold -- above 0.8v or line along the top of the graph if graphing. And once the engine warms up and smooths out, does this sensor show cycling from about 0.1v to about 0.9v?

Initially, it would seem you have an injector on bank 2 sticking open allowing excess fuel into that cylinder. Do you have black smoke coming out of the tail pipe? You can also pull the plugs on bank two and see if one (or more) of them is wet and/or sooty. Run the engine only a couple of minutes, with the excess rich condition, then shut it off and pull the plugs. The injector may start to work properly as the engine warms up. If this is the case, try running some injector cleaner through the fuel system.

Keep us posted on what you find.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #3
Thanks for the quick and detailed reply, I appreciate it.

I just had the truck running, and got some new information. The misfire never occurs in open loop, only in closed loop. It doesn't start missing right when the change occurs, but seems to follow the idle speed: at initial startup, it runs fine when the idle is around the 750-800 mark, and then after a few seconds as the rpm's drop down to normal idle, that is when the misfire starts.

When the misfire is occurring, the Bank 2 Sensor 1 voltage was at about 0.190v, and after the truck was running and warmed up with no misfire, the voltage was down to 0.075v-0.115v.

This picture is from when the truck was misfiring, and the shifter was in drive. The engine light started blinking, which I am assuming is from the excess fuel being dumped through the catalytic converters. I drove the truck, and once I was driving it cleared up the misfire, and seemed to run fine.

2373


Thanks for the replies.
-Nate
 

·
Registered
Joined
·
525 Posts
In closed loop, the PCM programs fuel delivery based on a lot of parameters, but especially on the upstream O2 sensors. The PCM intentionally increases/decreases fuel (by a very small amount), and the O2 sensors will fluctuate between 0.1v and 0.8v. Normally, the cycle will take between 1 and 2 seconds to go from low to high to low. If the voltages you're seeing are accurate, the exhaust is very lean, and it doesn't make sense that the PCM is removing fuel (the negative numbers in the fuel trims). If your scan tool has ability to graph, check that way. Also check the voltages on Bank 2, Sensor 1. Your Bank 2 fuel trims are good, so a comparison with those voltages should be a clue to what's going on.

Here's a link to a YouTube video on fuel trims and O2 sensors and their relationship.

 

·
Registered
Joined
·
525 Posts
Sorry, on my previous response, I had bank 2 and bank 1 switched around (it was late!). Bank 2 has the strange fuel trims. Compare the O2 sensor voltages on bank 1 (good) with bank 2 (bad). Also, do you have any trouble codes other than P0300?
 

·
Registered
Joined
·
26 Posts
Discussion Starter #6
Thanks for the correction on your post. We've had some warmer weather here, and the engine code cleared on its own, so I am having an even harder time diagnosing the issue now that it is an inconsistent problem.

I did have another code before though. It was Catalyst Efficiency Below Threshold, Bank 2. I plan to pull the Bank 2 side spark plugs to take a look at them, but if I had a spark problem, or even an injector problem, don't you think that it would present with a specific cylinder misfire, not a random misfire?

Thanks.
 

·
Registered
Joined
·
1,159 Posts
The "random misfire" may be multiple cylinders causing the ECU to flag "random" since it's not tied to just one specific cylinder.

The Catalyst Efficiency error says the downstream O2s are bad, or that the cat is bad. If you haven't replaced it/them, then I'd do that. Or plan on replacing the cats.

Or both.

RwP
 

·
Registered
Joined
·
525 Posts
The catalyst efficiecy error (P0430) makes sense if your engine has been running very rich on bank 2. I'm still thinking an intermittently stuck open injector. So check the plugs for sooty deposits. Also, if the converter is bad, DO NOT change it until you figure out and correct the problem. If you don't correct the problem, you may ruin the new converter.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #9
Thanks for the info. Both the random misfire and bank 2 catalyst code came back at the same time today while driving, and I have not noticed any significant shaking from a misfire at idle, which is new. This weekend I will be pulling the plugs, so hopefully that will point me in the right direction. I will post an update.

Thanks.
-Nate
 

·
Registered
Joined
·
26 Posts
Discussion Starter #10
Just removed all 4 spark plugs from Bank 2, and they all look the same: dry, a little bit of white, and a tiny bit of green on the white ceramic portion. The O-rings on 3 of the coils were bad, so I am replacing those.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #11
While I had plugs out, I replaced all 8. I also checked all the seals around all the coils and replaced as necessary. I started the truck, and its been running better, no misfire code, but I do have the P0430 code. The B2S2 sensor is reading lean still, and the B1S2 fluctuates a lot (between 0.1 and 0.9). Does this indicate that my catalytic converters are failing? I replaced them on a budget last summer, so I got a $250 "Pacesetter" brand from rockauto.com, which I am now thinking may have been my first mistake. The other thing I was thinking of goes back to the leaky injector possibility, but I have a hard time believing that the problem is isolated to only one side of the engine, and moves around between 4 cylinders.

Thanks.
-Nate
 

·
Registered
Joined
·
525 Posts
Ideally, both BxS1 sensors should be fluctuating between 0.1v and 0.9v in a somewhat rhythmic pattern when the system is in closed loop. If the catalytic converters are in good condition, both BxS2 sensors should be much more stable at voltages between 0.5v and 0.7v (not fluctuating much at all). If the an BxS2 sensor is 'following' the associated BxS1 sensor (bank 1 or bank 2), it's an indication that the converter is becoming less efficient. This, by design, is what the PCM is would be basing the P0430 code on -- that the B2S2 voltages are 'following' the B2S1 voltages, instead of remaining fairly stable. However, your description doesn't jive with that. Instead, your B1S2 voltages are fluctuating a lot, and your B2S2 voltages are fairly stable, but at too low a voltage.

You mentioned that you changed the cats last summer. Not to question your abilities, and I'm not sure if the connectors would even reach, but are you certain that the proper connector was connected to the proper O2 sensor?

It's easy to make mistakes. I once replaced my plug wires all together (not one-by-one as is strongly recommended for DIYers), knowing I could figure out the proper tower on the distributor cap because I knew the firing order. It didn't start easily, and ran VERY poorly and wouldn't idle. Turns out I put the wires in based on a counterclockwise rotation of the rotor. Actually, the rotor rotates clockwise, so my engine was running on two cylinders! A quick fix, and obviously the problem showed up right away. Putting connectors on the wrong O2 sensors may not show problems as quickly. ;)
 

·
Registered
Joined
·
26 Posts
Discussion Starter #13
Thanks for the quick reply.

When I replaced the catalytic converter assembly/O2 sensors, I did make sure to put the right wire in the right connecter, but I think you are also correct in saying that the wires wouldn't have reached. Shortly after having replaced everything, I got a faulty O2 sensor code, and had that specific sensor replaced, and then several months later was told by a shop that both bank 2 sensors were bad. The sensors I had initially put in were not good quality and I think this is why, but those cheap sensors have since been replaced by the shop.

When I first bought the truck, several manifold studs were broken, and the manifolds themselves were very loose, causing the truck to run poorly and the intake (and I'm assuming everything else inside) was very dirty. I cleaned the TB very well, replaced the IAC, and ran sea-foam through. Do you think that all the gunk and buildup got cleared through but got caught in the new cats? I didn't think this was the case because I figured that the Bank 1 side would be affected also.

-Nate
 

·
Registered
Joined
·
525 Posts
I really don't have any solid suggestions on what else may be going on. I did have a P0420 on my Dakota (single bank of O2 sensors even though a V6) about 6 or 8 years ago. After reading up on the issue, I decided to risk $25 for a liquid cat cleaner treatment -- check at most any auto parts store for this -- and it solved my problem for about 6 months. The light stayed off and no other side effects. But when the light eventually came back on, I did have the cat replaced. This may clear your P0430 problem, at least for a while, but I don't think it will do anything for your intermittent rough running issue.

Best of luck on getting it worked out. We're available if you need us.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #16
I found my old receipt from when I had the Bank 2 O2 sensors replaced last year, and I checked the part numbers. Turns out that one was a Denso, the other was a Bosch. I replaced both with NTK brand sensors, and the random misfire, lean codes, and low power were fixed. Less than 2 days after driving the truck, I get codes P0161 and P0155, for the O2 sensor heater circuit. My first thought is that the sensors are bad, since both codes are present right after putting the sensors in. Should I try a different brand of sensor, maybe both Denso or Mopar? My other thought is that I have a Flowmaster muffler, and I have heard that low back pressure can foul an O2 sensor quick, but I figured that the issue would be present on both sensor banks then. Is there maybe a fuse that controls that circuit?

Thanks.
-Nate
 

·
Registered
Joined
·
525 Posts
Since those codes did not show up with the previous sensors, I think your theory that both new sensors are 'bad' is reasonable. I suspect that both sensors are working properly as far as reading the O2 content of the exhaust gases -- engine is running fine -- but the heater circuits are different enough to trigger the codes. Both codes indicate the same thing, P0155 for the upstream sensor and P0161 for the downstream sensor. The codes are set if the current is too high, if there is an internal short, or if there is an internal open. (Or if there are wiring problems, but since the codes didn't appear before installation of the new sensors, I don't think this is the case.) I suspect the new sensors' heaters may have a higher resistance, and are drawing more current. I would suggest comparing the resistance in the heaters between the new sensors and the 'old' sensors on bank one. Each sensor should have four wires, two of which are the same color. The two of the same color are the wires for the heater. With the sensor disconnected from the harness, check the resistance on these two wires and compare between banks. If you find the resistance notably higher on the new sensors, I would replace them, but see if the parts store will let you check the resistance of the replacements so that you don't have the same issue with a different brand.

All O2 sensor heaters receive their power through Fuse U in the Power Distribution Center (under the hood) from the Automatic Shutdown relay (ASD relay). Actuation of the heaters is controlled by the PCM. But the PCM controls the upstream heaters as a pair and the downstream heaters as a pair, and turns on the downstream heaters after a short delay so as not to overload the circuits. So I don't think electrical power (fuses) or control (PCM) is at issue here, or you would have problems with bank one also.
 

·
Registered
Joined
·
26 Posts
Discussion Starter #18
oldmarine,

Thanks for the quick reply. I will measure resistance on my current sensors, and also get a new set for bank 2. Thanks.

-Nate
 
1 - 18 of 18 Posts
Top