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Thread: mpg problems, Info please.

  1. #1
    Regular Member blackveccyC's Avatar
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    Default mpg problems, Info please.

    Hi folks, I've been trying to get to the bottom of my over fuelling/bad mpg on my z18xe 2003 75000 miles. Also i get a bad judder on idle which is probably the over fuelling as well?

    I done the whole mpg calculator thing (fill tank up, reset milage etc)
    And 21 mpg came up which is, i think, really bad just easy town driving. Considering i'd been taking my time and no thrashing etc. So the other night i took the plugs out(ngk) and they were all pure black and sooty. From what i gather is over-fuelling, gave them a clean with wire brush.

    Today i tested the CTS for continuity, 1260 at cold and about 600 after running car for 10 mins. So think the sensor is fine.

    SOOOOOO my next thought was have a look at the MAF sensor, had a wee look and it looks like its not a GM one. couldn't see the GM partnumber, Just 450203 nothing else. mayby a cheap aftermarket one causing me the problems??? thoughts? Sorry for long winded story...

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    Regular Member blackveccyC's Avatar
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    Anyone? So am I right unthinking this is a cheap one? Would the gm number be printed on the flat sqaure bit on top?

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    Regular Member luke.oldham's Avatar
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    i had the same problem mate i gave it a full service still no different.then i changed the coil pack and im getting about 27/28 mpg which is very good for my car i was getting 20 mpg if i was lucky. mines a 52 reg same engine code as yours and 80.000 mile. cheers luke

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    Regular Member blackveccyC's Avatar
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    Cheers for that pointer luke, I actually have a proper gm coilpack spare in the shed that I have from an old zafira. Same engine. Same age etc. So will try that tonight and see how I get on. Would a cheepo afm cause these problems though? Thanks again matey.

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    Regular Member jimmyred's Avatar
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    I had similar probs(same engine and year)....was thermostat and CTS failure causing overfueling...not sure about those values, I thought i had read that resistance should drop to 200 ohms but i am no expert! My CTS was working but not over full temp range. Often the two problems could have different causes....the misfire could be coilpack, the overfueling something else. How is the temp gauge behaving?
    Last edited by jimmyred; 8th February 2011 at 17:11.

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    Regular Member blackveccyC's Avatar
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    Replaced thermostat only about a month ago as temp took ages to get up, and dropped when I turned on heaters. Since then the needle on dash gets up and stays about 88.c. Which is why I thought it was fine. The second lower/hot value was only a few mins of idling, think I'll replace the cts as it's cheep enough and will try my other coil pack. Thanks for the pointers. To be continued lol.

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    Regular Member luke.oldham's Avatar
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    Quote Originally Posted by blackveccyC View Post
    Cheers for that pointer luke, I actually have a proper gm coilpack spare in the shed that I have from an old zafira. Same engine. Same age etc. So will try that tonight and see how I get on. Would a cheepo afm cause these problems though? Thanks again matey.
    how does your car run when you unplug the maf sensor think mine nackerd because when i unplug mine theres no change.the car should run crap if its not pluged in.plus been told cheep ones dont last long

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    I have heard the maf theory before but I have also heard that MAF is only used above 2000 rpm and below that its down to lamba sensors to controll fueling.

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    Regular Member Steve01's Avatar
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    I have changed a few things on mine (ZX18E) recently as it has been running like crap! Had a new EGR valve couple of months back, as well as O2 sensor, was better but still not running properly. Last summer I bought a coil pack and MAF from eBay (cheapos). Have put up with it running rough since as my local garage told me it was knackered valves and not worth fixing (117k miles) but last month it was really pi**in me off what with the cold weather etc etc. Thermostat packed in so changed that which helped with the MPG. Thought I would treat it to a service so bought new plugs and a coil pack from local motor factors (Dingbro) coil pack was over 100 quid Was running better but still something not right. Thought I would try the MAF. Got one from Dingbro for 70 quid. Now the car is running like a dream. Wish I had done it all ages ago.
    All of these will contribute to poor mpg I would think so I am hoping it will be much better now!
    Wife wants a new car in the summer and was gonna trade in the Vectra but now its running fine I think I am gonna keep it for my runaround when I not offshore!
    Last edited by Steve01; 9th February 2011 at 01:02.

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    Regular Member luke.oldham's Avatar
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    Quote Originally Posted by Steve01 View Post
    I have changed a few things on mine (ZX18E) recently as it has been running like crap! Had a new EGR valve couple of months back, as well as O2 sensor, was better but still not running properly. Last summer I bought a coil pack and MAF from eBay (cheapos). Have put up with it running rough since as my local garage told me it was knackered valves and not worth fixing (117k miles) but last month it was really pi**in me off what with the cold weather etc etc. Thermostat packed in so changed that which helped with the MPG. Thought I would treat it to a service so bought new plugs and a coil pack from local motor factors (Dingbro) coil pack was over 100 quid Was running better but still something not right. Thought I would try the MAF. Got one from Dingbro for 70 quid. Now the car is running like a dream. Wish I had done it all ages ago.
    All of these will contribute to poor mpg I would think so I am hoping it will be much better now!
    Wife wants a new car in the summer and was gonna trade in the Vectra but now its running fine I think I am gonna keep it for my runaround when I not offshore!
    did you notice better mpg with the new maf sensor.

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