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Thread: 2003-2004 Mk4 Golf 1.8T low MPG when cold.

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    2003-2004 Mk4 Golf 1.8T low MPG when cold.

    Is there any tests I can run to see why my car seems to be getting bad MPG when cold. I'm not getting any misfires everything seems fine. Just I'm getting 5-15mpg till the car has warmed up?

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    Benevolent Dictator Uwe's Avatar
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    When you first start the car, it's getting 0 mpg. Then it runs "open loop" for a while until the oxygen sensors heat up enough to actually produce readings. You can monitor the whether they're on-line or not in MVB Group 030. Meanwhile, the engine management runs an intentionally rich mixture while also running the secondary air ijection system for the first (roughly) two minutes after a cold start to try to get the CAT lit off as fast as possible. And this time of year, with cold ambient temperatures, there's lots of pumping losses from the thick oil until it warms up. Bottom line: If your fuel consumption is reasonable when the engine is warmed, I wouldn't worry about high consumption when the engine is cold -- that's normal.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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    i checked 30 and on cold start was 000 run for 20 secs see it go to 100 then back to 000 then the bits went to 100 then back to 000

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    Benevolent Dictator Uwe's Avatar
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    That should be the sensor heater bit. What about the Sensor Ready and Control Active bits? Did you click the link in my previous post?

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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    This is where I'm getting a bit lost.
    I only checked channel 30 and only run the car for a short time say 1 min.

    I did look at the link, and was not sure on it to be honest, what I was looking for.
    I guess I only have a 1 bank system, also was unsure on the channel 30 reading. 000 would mean all off. were 100 would mean sensor heated but not ready or active? yet say 011 would be all on ready and active?

    Question is, if I run channel 30 for say 10 min engine running. what should I get if all is ok?
    Also what other channels should I check, and I will test in the morning?

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    Benevolent Dictator Uwe's Avatar
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    What you're looking for is to see when the ready bit comes on and when one of the control active bits comes on. Until then, your engine management is running open loop..

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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