Misfire After Header Install

[5pntslo]

So, about a week ago I installed long tube headers, using o2 extensions for the front and deleting the rear o2 sensors. Flashed the car with a new tune and it ran good. However after a cold start, the car gave me a P0300 code, I did a crank relearn which seemed to solve the issue, for about a day. In the morning I started the car up, from another cold start and got another misfire code. This time I was advised to to a KAM reset. Once again the code went away for about a day. The code is back once again! Im stumped as I have researched on multiple forums and haven't found anything for my situation. The car itself feels fine and doesn't really sound like it is misfiring. The code always comes on after the car calms down from a cold start, then the light stays on. I don't have any vacuum leaks, and everything else is connected properly. Could this be caused by the o2 extension harnesses? If so could I connect the front o2 sensors without the harness? Could this have anything to do with the IMRC valves or the tune itself since I have the rear o2 sensors unplugged? Any input would be appreciated, I'm hoping somebody has been in the same situation as me and resolved the issue.

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[Zelek]

So, about a week ago I installed long tube headers, using o2 extensions for the front and deleting the rear o2 sensors. Flashed the car with a new tune and it ran good. However after a cold start, the car gave me a P0300 code, I did a crank relearn which seemed to solve the issue, for about a day. In the morning I started the car up, from another cold start and got another misfire code. This time I was advised to to a KAM reset. Once again the code went away for about a day. The code is back once again! Im stumped as I have researched on multiple forums and haven't found anything for my situation. The car itself feels fine and doesn't really sound like it is misfiring. The code always comes on after the car calms down from a cold start, then the light stays on. I don't have any vacuum leaks, and everything else is connected properly. Could this be caused by the o2 extension harnesses? If so could I connect the front o2 sensors without the harness? Could this have anything to do with the IMRC valves or the tune itself since I have the rear o2 sensors unplugged? Any input would be appreciated, I'm hoping somebody has been in the same situation as me and resolved the issue.

My guess is it's O2 sensor related. I'd check the tune to make sure the rear O2 delete is in it for one.

Are you able to flash back to stock and run it on that for a bit or do you have an intake that requires a tune? That would be another way to test it. P0420 doesn't come on right away for headers on a stock tune.

 

[5pntslo]

Would it be safe for the engine to run on a stock tune with headers? I used to have an air aid intake but I am currently using the stock intake.

 

[Zelek]

Would it be safe for the engine to run on a stock tune with headers? I used to have an air aid intake but I am currently using the stock intake.

Nothing unsafe about it for what you need it to do. It just throws a code after you drive it for a while for P0420 Catalyst System Efficiency Below Threshold. Even when that code is on, the car runs, but just runs really rich.

I've done this method to pass inspection before and just flashed my tune back on when they were done. Different car, but it worked. The only time this wouldn't work is with the tune only based intakes. You'd need two tunes in that case.

 

[5pntslo]

Does anybody else have any input, like I said, the light only comes on after a coldstart when the engine has calmed down to a normal idle. Is this simply the tune? Has anybody else had an experience like this?

 

[Raiders3342]

Having the same issue after installing Kooks catless long tubes and getting a new tune. The car has constant misfires at idle during cold start until it reaches operating temp (above 180 degrees). Just wondering if it ended up being a tune issue, an O2 sensor issue, or something else?

 

[18 Smoke]

Having the same issue after installing Kooks catless long tubes and getting a new tune. The car has constant misfires at idle during cold start until it reaches operating temp (above 180 degrees). Just wondering if it ended up being a tune issue, an O2 sensor issue, or something else?

Did you also delete the rears. I had this happen twice after my Kooks catless install. I reinstalled the rear O2 with MIL/CEL eliminators. Never happened again

 

[ManBearPig]

Does anybody else have any input, like I said, the light only comes on after a coldstart when the engine has calmed down to a normal idle. Is this simply the tune? Has anybody else had an experience like this?

Unfortunately I don’t have any helpful suggestions, but I have not had this issue. I wouldn’t think it’s the tune though. I don’t even have my rear o2’s plugged in. They are turned off completely in my Lund tune butbeven on the factory tune all I get is a cat inefficiency code. No misfires, no crank relearn needed.

 

[ugstang17]

While adaptive learning of the S550 ECU is generally capable of correcting for the relocation of the O2 sensors (further down stream generally than the stock location) on most added aftermarket LT's, I personally believe it is not fool-proof. The initial misfire code could be seen because the O2 sensor does not sense the standing wave in the time frame the ECU is initially expecting it to be and therefore also trips a crank trigger relearn. Before contacting the tuner, save yourself some time and inspect for leaks in the exhaust. After you have taken the time to do that, then contact them with the problem. Be prepared to datalog the startup so that they can see what is going on when the P0300 pops up.

Misfires are detected down to the cylinder by the O2 sensors (lead sensors) based on firing order. The ECU knows the length of time required for the exhaust standing wave from each cylinder to reach its respective bank lead O2 sensor. When this changes the car is thrown off. It may only be a matter of allowing the car more time to detect the change and correct for it. Or it may require adjustment in the data in the tune that addresses this.

Contact your tuner.

 

[drive_55_not]

Misfires are detected down to the cylinder by the O2 sensors (lead sensors) based on firing order. The ECU knows the length of time required for the exhaust standing wave from each cylinder to reach its respective bank lead O2 sensor.

Uuuuhhh, What?

.

 

[ugstang17]

^^^ Read Greg Banish's Book 'Advanced Tuning'.

There is a delay between the time the exhaust gas leaves each cylinder and reaches the O2 sensor. The ECU knows the firing order and also knows the time it takes for that exhaust sample to reach the sensor. There is a delay factor though few ever realize that unless they study it. So the sensor knows which cylinder's exhaust arrives and how long it should wait to expect it after stroke four (exhaust stroke) of that cylinder's four stroke cycle. If the sample is burned but the O2 does not see it in time (because the O2 sensor is now further down stream and adaptive learning has not corrected for it or still is trying to learn and correct for the change) a misfire could be seen and trigger a CEL. Intake air and exhaust moves through the system in standing waves. That is what you feel when you place your hand up against your exhaust pipe. The exhaust is not smooth, it fluctuates..hence the term standing waves as I have come to understand it.

 

[drive_55_not]

^^^ Read Greg Banish's Book 'Advanced Tuning'.

No need to,, Here's how the FORD Misfire Monitor circuit werks.

Page 19:

http://www.fordservicecontent.com/ford_content/catalog/motorcraft/OBDSM1505.pdf

Misfire Monitor

The input to the Misfire Monitor is the signal from the crankshaft position sensor and timing wheel. The signal is acquired and processed by the PCM and provided to the Misfire Monitor as individual tooth period measurements. The Monitor uses the tooth period measurements to calculate crankshaft acceleration signals for misfire detection. All misfire processing is performed in software (separate chips are no longer used except for some vehicle lines that may still be using older style PCMs.)

Hope that helps

 

[ugstang17]

^^^ Appreciate that thanks. I was aware that crank trigger was involved but that it only provided position data for piston one on TDC compression stroke. Thanks for the 411.

However keep in mind that it is the O2 sensor that detects a missfire in the event of situations such as spark blowout. THe COP can be fully operable but misfires can still occur that can only be detected by unburned mixture which is detected by the O2 sensor as a higher than normal O2 content or lean condition due to no combustion taking place similar to a conditions where too little fuel will leave too much O2 in the exhaust due to stoich. (14.7 aka L1) not being met. So the O2 sensor still plays a role, and its position with respect to where the ECU software constant says it is can cause issues if Adaptive learning isn't capable of correcting properly for the new O2 location.

 

[velocity550]

Did you also delete the rears. I had this happen twice after my Kooks catless install. I reinstalled the rear O2 with MIL/CEL eliminators. Never happened again

Are those still working for you?

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