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Thread: Pocket Logger FAQ

  1. #1

    Pocket Logger FAQ


    This FAQ will cover the very basics of:
    • What is a pocket logger
    • Where can I get a pocket logger
    • How do I tune using a pocket logger

    • This faq does not cover STFT (short term fuel trims). I will add that section in at a later date.
    • Consider purchasing an EGT gauge and monitor it's peak values while tuning. Tunes that exceed 900c will lead to melted pistons.
    • Tuning with a pocket logger means you’ll be judging your fuel off of a narrow band O2 sensor. Using a wide band is more accurate, but not entirely necessary.
    • You should probably pay me something for writing up this faq. Paypal: [email protected]
    • You will need a fuel controller in order to affect any change in your fuel curve.
    • I take zero responsibility for any of this. So if your AC flies out your exhaust after following my directions, you can pretty much just bite me [period].

    Okay let’s get started!

    What is a pocket logger?

    Pocket loggers are old school tech and may be considered outdated when compared to some of the logging options we have available to us today such as GReddy Emanages/Stand Alones/and the like. It in no way shape or form controls your fuel or directly, the tune of your vehicle. So why use one? Well, for one, they work. And it's a cheap alternative to paying for reflashes, or custom tunes on your local dyno. Plus at the end of the day, you should have a better understanding of the make up of your tune.

    A pocket logger is normally a hand held PDA that interfaces with the ODBII port on your car. From that port, it can log all sorts of values from water temperature to timing, to the ambient temperature of the air @ the point it enters your MAF. For the most part though, you will only be concerned with 3 values; timing, O2, and RPM.

    Where can I get a pocket logger?

    Hey, good question. So next ask yourself, how much do I want to spend? There are two ways to get a pocket logger (that I know of). You can buy one, or you can make one. I suggest the later, but I’ll cover both.

    If you decide to purchase one, you can do so at What you’ll have when you’re done is 100+ dollars worth of software, a cable and an interface. The PDA is not included, so count on spending another hundred dollars more (maybe).

    Two hundred dollars? I just bought a Thirty thousand dollar car. I can’t afford that kind of money. Whatever. Go wine to someone who cares. So you want to make your own, eh? Here’s what you’ll need. You still need a PDA. Next you’ll need a 9 point serial cable to connect the PDA to the Interface. You’ll need the interface. Lastly you’ll need the tuning software.

    What are all these things, and where can I get them?

    PDA: You will need a PDA running Palm OS software. I believe you need it to be between 3.5 and 4.0. I purchased a Palm M100 off ebay for 10 dollars.

    Hot Synch Cable: The palm M100 synch cable has a 9 point serial cable included. So there!

    Interface. There’s no getting around this. Without the interface, you can’t read the OBDII data. It will run you about 80 dollars from Multiplex engineering. You’ll need part # T16-003. Here is the link:

    Software. Dang, how much will this cost me? Good news. It’s freeware. You can download the software at the end of this link:

    And now either through legitimate purchases or shareware advantages, you should have all the parts you need.

    How do I tune using a pocket logger.

    I will assume at this point that you have familiarized yourself with the software and your PDA. If you haven’t, you should stop now and read this FAQ:

    So you’re ready to log. Or you’re pretty certain at any rate.

    I’m going to assume that most of you won’t be doing this on a dyno, so the first thing you need is room. When you take logs, you do so driving full throttle in third gear from 2500 to redline. So find yourself a flat, smooth open road. If you find a road with a steep incline or decline, or one with a lot of bumps, this will screw up the validity of the log. So again: flat, smooth, open road!

    Next, you’ll need to heat up your car. I suggest warm up your car, then take 3 really good pulls down the street before you start logging. “Cold logs” are useless to you. Set up your logger to read timing, O2 and RPM, then you’ll want to start logging. I suggest you pull at least 3 logs/runs and examine them before you start changing your fuel controller.  yeah you’re going to need an AFC e-mange or something or this is pretty much a waste of time. Didn’t I mention that?

    Pull three logs and go find a quiet place to analyze them. A “safe” goal is to see your O2 values stay around .92 (assuming 91 octane) and your timing should peak around 17-18 degrees @ redline. So for example your log may read similar to the one below (and let’s also assume that this is the average for the 3 runs) *Note: your actual log will have more RPM segments:

    RPM Timing O2
    2500 08 .98
    3000 06 .94
    3500 04 .94
    4000 06 .96
    4500 05 .96
    5000 09 .93
    5500 14 .93
    6000 13 .95
    6500 15 .95
    7000 16 .96

    The goal of a good tune first is repeatability [period]. Making 300WHP doesn’t man anything if it’s a one time deal. In order to do this, we want to stabilize the fuel curve. In doing so, we’ll affect the timing curve. Put that all together and “loosely speaking” it means more power for you.

    In the case above, we wanted our timing to increase steadily past the 3500 mark from around 5 on up to 17 degrees when we’re near redline. The ECU will pull timing back from 2500 to 3500 as it reacts to the boost coming on. After 3500, you should be at peak boost and the ECU will start adding timing. Note: When you're tuning, you may want to lower you boost slightly. This may keep you from knocking. More boost does not alway mean more power.

    If the timing drops, we need to look at 2 things. First, we look at one of the other 2 logs we took to see if it’s a fluke. Second, we look at our O2 value for that RPM segment to see if we were rich or lean at that point. A figure higher then .94 is getting pretty rich and can cause pre-detonation. A figure lower then .91 is headed toward the lean side and means you're seeing knock. Note: The logger does not recognize knock. Knock/pre-detonnation is assumed by monitoring a decrease in timing.

    We want our O2 values to be as close to .92 as possible. As you can see from the past O2 values, we’re running very rich across the board and at 2 points we lost timing because of it.

    Next you’ll want to start adjusting fuel. I suggest you make changes slowly and/or concentrate in one area of your RPM band as you’re getting familiar with logging and tuning. After you change your fuel setting, warm the car back up and take 3 more logs. Then repeat the process until your have a smooth, repeatable tune. For example, an ideal tune might look similar to this:
    RPM Timing O2
    2500 08 .93
    3000 06 .93
    3500 04 .92
    4000 06 .92
    4500 07 .92
    5000 10 .92
    5500 12 .92
    6000 14 .92
    6500 16 .92
    7000 18 .93

    Notice that the timing drops until 3500, then climbs steadily until redline and the O2 readings are consistently on or near .92.

    I'll probably be making edits to this FAQ from time to time. If you see a part you want more information on, or something I've stated incorrectly, please PM me and I'll update it.

    For further information on SAFC tuning:

  2. #2
    Ban Hammer

    drmosh's Avatar
    Join Date
    Jun 2003
    Hybrid Power!

    Re: Pocket Logger FAQ

    This is an update on the Evo X:

    The Evo X uses a CAN based ECU. If you have an older datalogger which does not support CAN you will not be able to read any data from the Evo X ECU.
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