Diagnosing Misfires

[carolinaskies]

I just started using FORScan yesterday trying to diagnose if I have weak coils on my V10 Ford Excursion 03.

I came across the following article http://www.motor.com/article.asp?article_ID=1794 and was wondering is there a way Forscan can be used to gain the data as explained in the article to ID the Mode $06 data?

[FORScan]

I just started using FORScan yesterday trying to diagnose if I have weak coils on my V10 Ford Excursion 03.

I came across the following article http://www.motor.com/article.asp?article_ID=1794 and was wondering is there a way Forscan can be used to gain the data as explained in the article to ID the Mode $06 data?

Sorry, OBD mode 6 is not implemented in FORScan yet.

[carolinaskies]

Is implementation of Mode 6 being worked on?

[carolinaskies]

BTW,

I'm wondering if I can at least narrow down the bank of my engine where a weak coil might exist by looking at O2 sensor values and Short/Long term fuel trims?

Here is a snapshot during one misfire event. I'm wondering if the O2S21 .33v or O2S11 .12v might be indicitive as well as the difference of O2S11.stft and O2S21.stft?

If I could narrow down which bank is having the misfire it might help ID a specific cylinder to target. Or if anyone has an idea what PIDs I could use to run at load that might help indicate the bank in question if not the specific cylinder?

[FORScan]

Is implementation of Mode 6 being worked on?

Yes, along with multiple other features that must be implemented in this program...

I'm wondering if I can at least narrow down the bank of my engine where a weak coil might exist by looking at O2 sensor values and Short/Long term fuel trims?

Here is a snapshot during one misfire event. I'm wondering if the O2S21 .33v or O2S11 .12v might be indicitive as well as the difference of O2S11.stft and O2S21.stft?

If I could narrow down which bank is having the misfire it might help ID a specific cylinder to target. Or if anyone has an idea what PIDs I could use to run at load that might help indicate the bank in question if not the specific cylinder?

PCM detects misfires by tracking changes in engine speed. In case of misfire engine decelerates and PCM is able to detect it. However, Oxygen sensors can be used for misfire diagnostics too. But different types of misfire may cause different readings. For example, injector problems (not enough fuel) will cause lean condition (low voltage), but EGR problems, lack of air or fuel overpressure may cause rich condition. It also should be counted that when PCM works in closed loop (counting signal from oxygen sensors) it tries to fix the problem by adding or deducting fuel (changes so-called fuel trim), so it affects the results too.

If you have problems with fuel or air supply, it will should be noticeable monitoring Long Fuel Trim (LFT) and Short Fuel Trim (SFT) PIDs. If you have fuel supply problems (lean conditions), LFT+SFT should be much greater than 5-8% (+/8% usually considered OK). In case of fuel overpressure (e.g. because of fuel regulator problems) or lack of air (rich conditions), it should be much less than minus 8%. Such kind of problems usually cannot appear and disappear immediately, so they should be noticeable. If everything is ok with fuel trim (LFT+SFT), then you probably should check ignition and compression. In case of these problems oxygen sensor should theoretically register lean conditions. Also EGR problems (EGR valve stuck into open position) should cause rich conditions too.

We recommend you to check the book "Automotive Scan Tool PID Diagnostics", demo version is available on the Google Books (type in google "Automotive Scan Tool PID Diagnostics Google Books" and it will be somewhere at the top). Pages 26 and further tell about misfire diagnostics and oxygen sensors signal analysis. Hope it will give you some new diagnostic ideas.

Also, a recommendation on using FORScan for PIDs analysis:

Use minimum number of PIDs for readings (just ones you really need), because refresh rate directly depends on # of PIDs. So 10 PIDs will refresh 2 times slower than 5 PIDs. It may be important for reading O2 sensor signals that change quickly. In this case we recommend you to leave MISFIRE, O2S11.STFT, O2S11.Volt (these are 2 parts of the same O2S11 PID so in terms of performance, there is no difference if you use 1 or 2), O2S21.STFT, O2S21.Volt.

[carolinaskies]

Thanks for the information.