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Thread: 1.9 cdti 120 poor mpg and flat spot at low revs

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    Default 1.9 cdti 120 poor mpg and flat spot at low revs

    Hi, my 1.9 cdti is returning shocking MPG. Around the town i get on average 32 but then i went on a 30 mile motorway run at 70 with cruise on and it returned 52 MPG.

    I have noticed that it is down on power below 2000 rpm then it just takes off.

    I have already cleaned the boost sensor and egr valve.

    I have also replaced the vacuum hoses with silicon ones ( although the 4mm ones i ordered seemed to be to loose on the fittings so am awaiting some 2mm ones to see if this improves it at all).

    I have also noticed that it takes a while to heat up and is quite inconsistent on running temperatures, its always up and down, I know this would affect the MPG but i cant believe that it would take 10/15 mpg off?

    And finally there is the smell of exhaust fumes in the cabin at standstill and a high pitched whistle at 2500 rpm when booting it that sounds like air escaping, this leads me to suspect that it could possibly be a boost pipe but there is no black smoke out the back at all.

    Any help would be greatly appreciated as I am stumped lol

    Thanks

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    Exhaust fumes in the cabin suggests an exhaust leak somewhere within or near the engine bay - I would check connections to the EGR, especially if they've recently been disturbed by you cleaning it. Also, the flexi-joint in the exhaust (criss-cross metal strands in the section approximately below the oil filter) are prone to splitting and can rise into the engine bay when at a standstill.
    As for the mpg, 32 is low, but then this engine isn't great around town as I understand it - still seems a bit poor. However, 52 on the motorway seems reasonable. There are loads of threads on this site with regards to mpg for people with different driving styles/journey types. I would take a look and you may not feel so bad!
    Not sure on the whistle - could be a boost leak. Check for holes in the big boost pipe from the intercooler to the inlet manifold and the intercooler itself. You will need to remove the intercooler to check for holes unless you have some sort of smoke test unit.

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    Regular Member Slammedorion's Avatar
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    If your heaters get hot then just change the coolant temp sensor. Around £8 quid from local motor factors. ( I've just had a cold start issue with a new Vauxhall sensor hence trying one from Euro Carparts. )

    If they don't get hot then get a complete thermostat housing. Around £50 quid mark from Vauxhall.

    As said above, there's a exhaust leak somewhere which will probably be contributing to your poor lowdown grunt.

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    i am going to clean the throttle body tomorrow as well as check all the boost pipes for splits, could it be possible that the lack of power and poor mpg are related? would an exhaust leak affect the mpg?

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    Did you clean both ends of the EGR valve, i initially only cleaned one side but then took it off again removing the other side (black part with 4x small torx) and it was completely caked, ran great after.

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    is that the solenoid bit that needs to be drilled?

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    The black section is the solenoid - this is the part that actuates the spring-return valve and so has the electrical plug. You need to remove this from the EGR housing to clean out the soot trapped between the two. Also, the solenoid pin itself can become sticky/gritty as it becomes sooted and corroded, which is why some (including me) drill the back of the casing to punch out the moving part. If you haven't already done so, remove the solenoid and clean it out - if once clean the pin doesn't move easily with fairly gentle thumb pressure, then it may be sticking and needs drilling etc. (see how 2s for doing this). It's really an easy job and will save you £120ish for a new EGR, if indeed it is at fault.
    I would do this before anything else too. Get yourself some new EGR gaskets too, to make sure you're not getting exhaust gas leakage from the mating faces.

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