Misfire count

[Bain64]

Toby - yea Mode $06 is where I've been tracking the misfires. No misfire codes are being thrown, I'm only chasing the misfires because of the P0430 light that came on (but hasn't been back in a few days now). When I changed the COP's I reset the computer (removed positive cable from battery & jumpered it to negative). LTFT for both banks is around -9%, which affirms the high fuel pressure but appears to be totally manageable (within +/- 25% LTFT). The misfires are about 1-2 per 1,000 rpms and are not noticeable.

Moose- yep I plan to find something with at least 100,000 less miles!

I've never been a big GM fan, but yesterday I realized the Yukon Denali comes equipped with the 6.2l 400+hp motor... I really don't need that motor, only tow a few times a year, but dang I want it anyways, ha... I'm still researching the Expeditions/Navigators too, but honestly they look too similar to the 2003 I already have. They look good, don't get me wrong, but it's not as exciting. There wasn't a really big facelift until the 2018 model year and that's out of my price range.

 

[1955moose]

I wouldn't change the pump, since it's pumping tons. I'd change the fuel regulator. Makes sense with the high pressure. Did you ever smoke the motor for intake leaks? I agree with Toby, in you don't want a shaky or missing motor when your selling a vehicle. It will drop your selling price way down if you do. Sorry your switching sides, but totally understand. Hang out anyway, your experience can help others.

Sent from my N9131 using Tapatalk

 

[Bain64]

Moose, unfortunately the regulator is integral to the pump on the 2003. Unless you're saying I can somehow replace just that part on the pump assembly?

 

[TobyU]

Nothing on the fuel rail with a vacuum line going to it like the older ones? They probably switch it for 03 since that was a lot of the new designs.

 

[TobyU]

I seen that YouTube link on connecting the positive and negative battery terminals once removed from the battery with a theory to discharge the capacitors and everything in the ECM and all that but I found it really does little. All I ever have to do is clear codes on my scan tool and that resets everything and lets me start seeing fresh fuel trims and misfire counts.

 

[1955moose]

I forgot the 03 does have the pump and regulator together. I think I remember seeing it is a separate piece. Problem is with your luck, messing with the pump to get at the regulator, probably would mess up the pump. Since your selling it, don't go crazy on a top shelf pump, I'd settle in the middle, around $100.00 to $125.00. They all pump. Just run the tank below 1/4 tank before you start the job. No fun wrestling with 200 pounds of fuel.

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[John Stephan]

In regards to your P0430. Using ForScan, go to the oscilloscope portion of the tool and graph the O2S1B1, O2S2B1, O2S1B2 & O2S2B2 voltages. What this will show is the activity of the oxygen sensors before and after the catalyst. Ideally at a 1500-2000 rpm range, the front sensors should be switching between .9mv and .1mv with quick succession. Whereas the rear sensors should maintain a steady reading of around .6-.7mv. If you notice that your O2 readings on the back sensors are not steady, but are mimicking the front sensors, your catalyst has failed and needs replaced.

In addition, you can also check the status of a good catalyst using the same scope. Pull the snorkel off just below the air box and stick the nose of a propane torch into the airbox under the air filter. Monitor the scope readings. Both front and rear O2 sensors should peg rich .9mv or even 1v. then watch when you remove the propane, the front sensor should drop first and then the rear should follow suit, but it should be delayed. If it falls at the exact same time, your catalyst is not retaining oxygen and is on it's way out.

If you've had an ignition misfire for a long time, you've been dumping raw fuel into the exhaust, at least until the misfire counter reaches a threshold and throws a code. Once the code is thrown, then the PCM will disable the fuel to that cylinder. Before the code however, the catalyst temperature will get really hot burning up the raw fuel in the converter and it literally melts into a blob. This blob could clog your exhaust which could cause more misfires due to back pressure, but it would definitely cause a low power concern.

I've picked up an app on my phone called Torque Pro, it can monitor OBD2 information on the fly including misfires. I also have an F-150 and found a bunch of posts by a guy named F150Torqued on f150forum.com. It's the same 5.4L 3V engine. He's figured out a lot of calculations to read the hexadecimal output of the OBD2 on the vehicle and deciphered it into easy to read items. Such as raw fuel pressure at the rail, VCT advance or retard readings and everyone's favorite: Misfires.

I still use Forscan for better scan data through USB for no latency. I think my little bluetooth OBD2 reader doesn't have a very good frequency refresh rate.

 

[Bain64]

Thanks for the extra info John, check out my post (#25) on page 3 to see my O2 graphs using the Forscan for iOS app. The bank 2 catalyst looks pretty grimm... That's a good tip on the propane, I have not used that method yet.

 

[John Stephan]

Thanks for the extra info John, check out my post (#25) on page 3 to see my O2 graphs using the Forscan for iOS app. The bank 2 catalyst looks pretty grimm... That's a good tip on the propane, I have not used that method yet.

Haha. Yeah, I'm new so I didn't read through to page 3. I got to the bottom of 2 and jumped to the last page.

Yeah, your bank 2 cat is toast. Funny thing is, I have the exact same problem on my F-150. I bought it with 2 bad COPs which I replaced and it solved the misfires, but it has no power. The cat is done and pretty much plugged up. It's next on the fix list not that my expedition is up and running. Thought I still have an ever slight misfire I'm trying to track down. I'll probably make a new post just to see if there's something I'm missing.

 

[Bain64]

Haha. Yeah, I'm new so I didn't read through to page 3. I got to the bottom of 2 and jumped to the last page.

Yeah, your bank 2 cat is toast. Funny thing is, I have the exact same problem on my F-150. I bought it with 2 bad COPs which I replaced and it solved the misfires, but it has no power. The cat is done and pretty much plugged up. It's next on the fix list not that my expedition is up and running. Thought I still have an ever slight misfire I'm trying to track down. I'll probably make a new post just to see if there's something I'm missing.

Welcome to the forum John!

Yea the cat is toast, but it doesn't seem clogged yet, power still seems good, but I'm sure that's eventually coming for it. My misfire rate is low, something like 1 or 2 misfires per 1,000 cylinder 'events'.