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AutoXray data interpretation help......

Discussion in 'The Garage' started by coyle13, Jun 14, 2005.

  1. coyle13

    coyle13 Registered Member

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    I have a '91 Blazer (TBI350/SM465/4.11/33" BFG)that has a wandering idle . I suspect it is a vacuum leak, but I can't find it.
    I have thrown every sensor in the book at it, replaced the intake and throttle body gaskets, replaced all the vacuum hoses, etc. I finally bought an AutoXray to narrow down my search. I ran the following test at 20mph, 2nd gear, in closed loop. I was wonering if someone could help me figure out if these numbers are within range:

    Idle air Mtr Pos-67 steps
    Coollant temp: 181.4
    MAP sensor: 1.17 volts
    Engine RPM: 1375
    Throttle sensor: 0.76 volts
    Integrator: 125
    Oxygen sensor: 79 mVolts
    Battery Voltage: 13.6 Voltz
    Knock Sensor: 28
    Block Learn: 114
    o2 cross counts: 132
    Clear Flood Mode: off
    Learn Control: enabled
    Rich Lean Flag: lean
    Loop Status: closed
    Air Switch Solenoid: off
    Air Divert Soleniod: off
    Battery Voltage Low: no
    Async Mode: off


    Can someone give me a hand in decoding this data? Thanks a bunch.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Well, going here and doing a search for some of these terms will help. If there is a complete EFI dictionary online, I'm unaware of it. Would be nice in cases like these. I know over at thirdgen (link above) you will get a lot of results searching for something like "integrator", so you'll just have to do some reading.

    Some of the stuff though:

    Idle air motor is IAC. Steps are dependent on throttle position, etc. Dare I say "many things"? :)

    Coolant temp is obvious.

    MAP sensor reading is pressure expressed as voltage.

    Engine RPM obivous.

    Throttle sensor is throttle position expressed as voltage. 4V+ is typically WOT, .55V range is typical idle. Should follow throttle opening smoothly.

    Oxygen sensor typical reading is 0-1V, so it's expressed as MV. It's voltage generated by its operation. IIRC, .450V is stoich, but it should bounce low to high under operation. It won't stay steady unless the sensor is bad, or it's cold.

    Batt volt is obvious, although it's what the ECM is seeing, which is typically a bit less than what the alternator is putting out.

    Knock sensor is knock counts. How many times the knock sensor has detected knock. I've yet to see something say what is "normal" here. I'd expect nothing, but mine SLOWLY climbs under operation.

    BLM is here

    O2 cross counts I believe is a measure of how many times the O2 sensor output has crossed over that .450V threshold, basically, rich/lean transitions. (on counts like this and knock, the autoxray "resets" itself after a certain number I believe)

    Rich/lean flag is the O2 switching. (or should show switching, should follow same pattern as O2 voltage reading.)

    Loop status is open/closed loop, once the sensors are in their operating range (temp, etc) then the ECM attempts closed loop.

    AIR switch and solenoid I'm not sure of. That may or may not apply to trucks, I thought they only switched between exhaust manifold or vent to atmosphere, so why you'd need both I'm not sure. It's belt driven, I don't believe there are any electronics in the pump. On a truck, you will likely see things in here ONLY when the vehicle is warming up.

    Batt voltage low is going to be whatever the ECM is set to say is too low. Based on the other volt readings, you are fine.

    The problem with many of these readings is that you need a service manual to know what is "normal" based on the operating conditions. MAP voltage (for instance) is going to vary based on altitude, load, etc., however, at idle, there is going to be a "correct operating range" which could indicate a vacuum leak. Again, this is the stuff that comes out of a manual.
     
  3. nvrenuf

    nvrenuf NONE shall pass! Premium Member

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    <hijack>

    Which AutoXray scanner did you get and from where? TIA! :thinking:

    </hijack>
     
  4. coyle13

    coyle13 Registered Member

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    It is the EZ-Link scanner. I bought it online from a shop up in Washington State. I can't remember the name, but I think it is on the AutoXray web site.
     
  5. coyle13

    coyle13 Registered Member

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    Thanks for the info. I guess I need to get a factory service manual. I have looked on the Thirdgen site, but I wasn't sure what the "normal" range is for most of the parameters and I wasn't sure if the truck codes are any different from the car codes.

    Thanks again.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Car stuff for the most part (TBI to TBI) is going to be very similar. Only physical difference I am aware of is that cars use an inlet air temp sensor that the trucks don't.

    People here have the service manuals, might try a post with a title regarding service manual assistance for your '91, see if someone can post up what the service manual says about poor idle.
     
  7. Thunder

    Thunder 3/4 ton status

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    Block learn 114= rich. Unless you were under acceleration it Should be around 128. Looks like your ECM is may be trying to compensate for a lean condition. I think you are right about the vac leak. Check your TB gasket.
     
  8. coyle13

    coyle13 Registered Member

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    Thanks for the info. I will break out the carb cleaner and eye protection and see if I can find the vacuum leak.
     
  9. RedBrute

    RedBrute 1/2 ton status

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    Check for a vac leak at the base of the EGR valve. Also, spray carb cleaner on the manifold between the TBI and the EGR. Sometimes the manifold can get a hairline crack between those 2 points. Check the spark plugs and see if one or more are showing a lean combustion condition, It may be an intake manifold leak at the cylinder head. Good luck.
     

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