Determining Retard

JHZR2

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There are all sorts of interesting information that can be gained by looking at ignition timing retard/advance. I have scangauges and USB OBD II scanners, but I do not necessarily understand how to read it. I assume when it tells me that IGN is 35 degrees, that is compared to TDC, but it is not clear what the advance/retard is for a specific operating point, load, and use. For example, if I am cruising at 65 MPH on flat ground with no wind, and it tells me 35 degrees or 33 degrees, what is better? What is right? CZan advance go too far? How do I really use this data? It seems that I can optimize on fuel, spark plug life, etc. by looking at this. But when giving a single value number that is "degrees", how do I use it? Thanks!
 
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What you really need is a unit with a data logger funtion so you can compare all the parameters including advance and retard. A scanguage gives no indication if there is any knock detected and if so how much retard is being applied. In the case of a scangauge it is informative only with no direct value. As a rule of thumb more advance is better for fuel economy. Each auto maker sets their own limits when building the software for their specific PCM and vehicle application. My car may only crack 40 on a scanguage for advance but my mazda can crack 50, each maker will be different and not directly compariable. What OBD II readers do you have?
 
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There are just so many variables that determine it. Throttle position, RPM and the knock sensor at least. Advance should increase with throttle and RPM, but be retarded when the knock sensor detects anything. But with emissions stuff now who knows what else has a say in it.
 
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 Originally Posted By: StevieC
I heard that the Spark changes even when a CARB member in California passes gas!
It does - fouls the plugs, too!
 

JHZR2

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 Originally Posted By: TaterandNoodles
What OBD II readers do you have?
I have an OBD2USB device which has a chipset that is compatible with a variety of OBD scanner software packages. I use the freeware packages. Im not opposed to getting a stand-alone scanner or better software, but I do not have a feel for what is really good...
 
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 Originally Posted By: JHZR2
I have an OBD2USB device which has a chipset that is compatible with a variety of OBD scanner software packages. I use the freeware packages. Im not opposed to getting a stand-alone scanner or better software, but I do not have a feel for what is really good...
Are you going to have the ability to reflash your own PCM? The domestics are the best for allowing the end user to change their own data points.
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In Car Operation (Click the image at the right to view a short video.) In car operation is fairly straight forward. Ideally it takes just a few steps: plug the OBD-2 cable connector into your OBD port under the dash and then plug the other end into our OBD2 All-In-One unit. The power light for the OBD2 All-In-One unit will then come on. Then plug the provided serial or USB cable into the other end of the OBD2 All-In-One unit and then the 9 pin RS-232 serial port or usb connector into your laptop. Have your PC turned on and start whatever data collection software you have downloaded, and turn the car key forward to start the communication between your cars ECU/PCM and the PC. You can view your cars sensor data, read diagnostic trouble codes if any are set, and clear the diagnostic trouble codes. Some packages provide freeze frame data, which is all the cars sensor data at the time a particular trouble code was set. Some packages allow data logging for viewing later on with extensive color graphing capabilities. Other packages have built in dynomometer calculations so you can in effect have your own chassis dyno.
Data logging would be the handiest piece in this case. You can document your own wind and air temp etc but the data logger function allows you to have all of the sensor data, coolant temp, advance, intake temp etc. For tuning purposes its the best way to compare changes in engine performance.
 

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I guess I should say that I am not looking to tune anything. I am just looking to see if I can decipher any additional information on exactly how my car is running, and/or exactly how my systems are degrading by monitoring this metric.
 
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 Originally Posted By: JHZR2
I guess I should say that I am not looking to tune anything. I am just looking to see if I can decipher any additional information on exactly how my car is running, and/or exactly how my systems are degrading by monitoring this metric.
I see. Viewing your sensor data is like reading a UOA. Simply looking at only 1 data point does not tell the entire story. It also takes some experience to understand what the entire system is telling you. This can often lead to one wanting to change a parameter to improve the efficiency.
 
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 Originally Posted By: bepperb
There are just so many variables that determine it. Throttle position, RPM and the knock sensor at least. Advance should increase with throttle and RPM, but be retarded when the knock sensor detects anything. But with emissions stuff now who knows what else has a say in it.
I'm not sure if this is exactly what you meant to say. Advance will increase under light load and lower throttle position. If you increase the load and/or throttle position, advance will decrease. Advance "can" be at its highest under deceleration, not all cars are programmed the same. In a vacuum advance distributor the higher the manifold vacuum the more advance you will see. For the highest manifold vacuum you need less throttle, if you increase the throttle you lower the vacuum. Still applies in todays cars. Advance will increase with rpm but at a slower rate and its limited when compared to lower throttle positions. This is basicly for anything below WOT.
 

JHZR2

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exactly right... this is what i am trying to understand... e.g. if there is a parameter that I can extract, say, idle at full temperature, AC on, ignition at -5 TDC, or cold idle, accessories off, +3TDC, if Im getting a different result, can i then discern that something isnt quite right - either a lazy sensor, bad plugs, etc? Patman mentioned in another thread about sparkplugs something along the line of noting a spark retard due to worn plugs during a dyno run, and the data gained from knwoing this prompted him to change plugs, which resulted in spark advance and gained hp. I'd like to be able to read into these things, even if just at a minimal level, as another means of knowing how things are running...
 
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The knock retard (from perfect) is an encrypted protocol. Advance is unencrypted and available on all the cheap scanners. About the best you can do if you can't "crack" the thing is to go 55-65 in cruise control, so you always need some power to overcome wind resistance, and see what peak advance you get on level ground. Then try your proposed change-- eg high test fuel, and see if you log a better number. There are lots of cars out there now programmed to take advantage of high test fuel (or cold air) and using the knock sensors as a regular part of the feedback engine controls. (used to be a save-your-bacon thing just found on turbos.)
 
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JHZR2- I've lately joined the rest of humanity and bought me a laptop... so now I'm itching to hook it up to assorted vehicles. Can you recommend any particular OBDII USB cables? I've seen them around on ebay and such, but haven't figured out how to tell which cables are compatible with which software. What about that open-source software? Which one(s) do you prefer? Thanks.
 
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