Got a New Auto Scanner Tool!

vabeachtennis · Mar 31, 2011

Yeah, it's easy to look up the "P0 codes". But what about the "live data" stats? How do I know what the correct "Absolute Throttle Position", "Ignition Advance", MAP, etc. stats are while at idle? I've searched here, is there a source that anyone can recommend? Here are some photos of what I am talking about:

My absolute throttle position was anywhere from 15.7-16.1 this was at idle.

You can see that my IGN ADV went from 17 to 16.5 there's other information like the "fuel trim" , 02si (v), etc. How can I interpret this information? Any help would be greatly appreciated. My wife is laughing at me because I can't figure out my new "toy".

JJacobs · Mar 31, 2011

O2s1 would be oxygen sensor 1. Usually you would see bank 1 (or 2) sensor 1 (or 2, 2 here is downstream) but that doesn't appear the case with that scanner.

Pretty sure the FSM will show a list of expected values for all the PIDs there. You could always google obd2 PID data or similar and see what comes up.

ParadiseXJ · Mar 31, 2011

Did your scanner come with software to sync to your computer?? and a USB cord?

You may be able to get more info that way.

vabeachtennis · Mar 31, 2011

JJacobs said:
O2s1 would be oxygen sensor 1. Usually you would see bank 1 (or 2) sensor 1 (or 2, 2 here is downstream) but that doesn't appear the case with that scanner.

Pretty sure the FSM will show a list of expected values for all the PIDs there. You could always google obd2 PID data or similar and see what comes up.

Yeah, the one photo I left out had that info.

Thank you, I'll have to check that out. I did a google search but I really couldn't find that much information. All that I am basically trying to find out is what those values represent.
For example at idle, my:
Absolute Throttle Position shows anywhere from 15.7 to 16.1,
Ignition Advance shows 17.0,
MAP shows 10.6
ST FTRM11 (%)-3.1

etc, etc,. I'm interested in finding out how to interpret that data. My 1996 4.0 has been having a funny P0300 and P030x lately. This is one of the reasons why I bought the scanner. When the CEL first came on, I reset it to see if the problem would reoccur, 282 miles later it came back on, and after 40 miles it went back off. Now at 180 miles later it's still off.
My idle stumbles, but my gas mileage and performance are good. The misfire almost always happens at 62mph 1950+ rmps and just cruising along. The misfires happened in just about every cylinder except for one.

McQue · Mar 31, 2011

This link has a great article to help you understand how to use the fuel trim info from your scanner.... http://www.motor.com/article.asp?article_ID=1075 you can download the pdf file and get all the pics with it.

If I were you, I would write down the live data info the scanner is giving you when your Jeep is running good, so you can use that data as a point of comparison for when it isn't running good.

vabeachtennis · Mar 31, 2011

ParadiseXJ said:
Did your scanner come with software to sync to your computer?? and a USB cord?

You may be able to get more info that way.

Thank you. My scanner didn't come with software, but it does have a port that connects to the USB so I can get an update if one comes out.

vabeachtennis · Mar 31, 2011

McQue said:
This link has a great article to help you understand how to use the fuel trim info from your scanner.... http://www.motor.com/article.asp?article_ID=1075 you can download the pdf file and get all the pics with it.

If I were you, I would write down the live data info the scanner is giving you when your Jeep is running good, so you can use that data as a point of comparison for when it isn't running good.

Thank you for the link and the excellent idea. I think that I am going to design a spread sheet/database program to track those values.

JJacobs · Apr 1, 2011

vabeachtennis said:
Yeah, the one photo I left out had that info.

Thank you, I'll have to check that out. I did a google search but I really couldn't find that much information. All that I am basically trying to find out is what those values represent.
For example at idle, my:
Absolute Throttle Position shows anywhere from 15.7 to 16.1,
Ignition Advance shows 17.0,
MAP shows 10.6
ST FTRM11 (%)-3.1

etc, etc,. I'm interested in finding out how to interpret that data. My 1996 4.0 has been having a funny P0300 and P030x lately. This is one of the reasons why I bought the scanner. When the CEL first came on, I reset it to see if the problem would reoccur, 282 miles later it came back on, and after 40 miles it went back off. Now at 180 miles later it's still off.
My idle stumbles, but my gas mileage and performance are good. The misfire almost always happens at 62mph 1950+ rmps and just cruising along. The misfires happened in just about every cylinder except for one.

Random thoughts.. the pcm has to learn the profile of the flywheel teeth before it's able to discern enough irregularity to accurately flag a misfiring cylinder. On the stuff I work on, this is indicated by a pid called MP_LEARN and the value is YES when the monitor is ready. It usually only takes a few no-throttle decels from 60 to below 10mph.

Before the pcm gains the ability to flag a miss, the clue is in the fuel trims. An ignition-caused misfire can and will set a lean code. When the miss is happening, the unburned fuel in the cylinder goes down the pipe where its oxygen content is correctly read by the sensor as high, or above .5v and outputs a high voltage. High voltage for any period of time drives up the short term fuel trims.

Fuel trims. The long term trim is a good indicator of the overall system condition. The short trim just tells you what is going on right this second, and drives the long. Say the short trim goes up to 25, or 30 or whatever a manufacturer has chosen. At that point the long trim goes up a tick and the short zeros. The short term can trend down for a while and pull the long back down, or it could increase and drive it up. Rich or lean codes are set when the long term trim exceeds a predetermined number.

I'd be curious to see what your downstream o2 voltage is doing in the midst of this misfire.

vabeachtennis · Apr 1, 2011

JJacobs said:
Random thoughts.. the pcm has to learn the profile of the flywheel teeth before it's able to discern enough irregularity to accurately flag a misfiring cylinder. On the stuff I work on, this is indicated by a pid called MP_LEARN and the value is YES when the monitor is ready. It usually only takes a few no-throttle decels from 60 to below 10mph.

Before the pcm gains the ability to flag a miss, the clue is in the fuel trims. An ignition-caused misfire can and will set a lean code. When the miss is happening, the unburned fuel in the cylinder goes down the pipe where its oxygen content is correctly read by the sensor as high, or above .5v and outputs a high voltage. High voltage for any period of time drives up the short term fuel trims.

Fuel trims. The long term trim is a good indicator of the overall system condition. The short trim just tells you what is going on right this second, and drives the long. Say the short trim goes up to 25, or 30 or whatever a manufacturer has chosen. At that point the long trim goes up a tick and the short zeros. The short term can trend down for a while and pull the long back down, or it could increase and drive it up. Rich or lean codes are set when the long term trim exceeds a predetermined number.

I'd be curious to see what your downstream o2 voltage is doing in the midst of this misfire.

Thank you VERY much for that informative post. If the misfire happens again I will record the "freeze frame" data. What long term trim value is normal for a well running 4.0?

Got a New Auto Scanner Tool!

vabeachtennis

NAXJA Forum User

JJacobs

NAXJA Forum User

ParadiseXJ

NAXJA Forum User

vabeachtennis

NAXJA Forum User

McQue

NAXJA Forum User

vabeachtennis

NAXJA Forum User

vabeachtennis

NAXJA Forum User

JJacobs

NAXJA Forum User

vabeachtennis

NAXJA Forum User

Similar threads