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Nissan Primera WP12 - Intermittent fuelling issue

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JammyJayC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JammyJayC Quote  Post ReplyReply Direct Link To This Post Topic: Nissan Primera WP12 - Intermittent fuelling issue
    Posted: 19 Jun 2018 at 11:30pm
Hi guys,

I have the QG18DE engine and my problem goes a little like this:

Started from cold, engine uses more fuel to warm up, then the fuelling settles down once warm. This is the way it should be. Driving as I do the average mpg return according to the OBC is ballpark 58mpg.

Once warm and having been running for around an hour correctly with no problems, it returns to 'cold engine' mode seemingly for no reason. There is nothing to suggest anything is wrong except the obvious increase in fuel consumption (see below).

Started up from warm, the engine assumes 'cold start' mode even though it is up to temperature and remains like that until I intervene. Examples of this are starting up after shopping or getting petrol. Driving as I do in this scenario, the average mpg return according to the OBC is around 33mpg.

I intervene by unplugging the Lambda sensor (Pre cat) and plugging it back in whilst the engine is running. Doing this in scenario 2 sorts the problem, and returns the fuelling to normal. In scenario 3, unplugging and plugging it back in immediately after starting sorts the problem and returns the fuelling to normal.

I'm confused by this as the sensor is giving correct signals from a cold start - it fuels heavily until up to temp then settles down to normal. The fact it's giving a good signal, otherwise in the scenarios above, leads me to believe there could also be an issue with the starting procedure. I don't want to buy a new sensor unless that is definitely the problem. The reason I'm on here is because money is short and I can't afford garage time or unnecessary parts.

If anything needs clearing up please point out. I've done this on my phone so apologies for any errors.

Thank you!

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imckay View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote imckay Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 2018 at 7:36am
The only way to get accurate mpg is to fill the Tank, run to empty, reset the Trip and calculate based on how many Litres you put in to fill it back up against how many Miles you have done.

33mpg sounds reasonable for around Town with frequent accelerating and braking.
40-45mpg on a steady, clear run on a Motorway would be reasonable.

Genuine 58mpg in a large 1.8 Petrol does not sound very likely.

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JammyJayC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JammyJayC Quote  Post ReplyReply Direct Link To This Post Posted: 20 Jun 2018 at 10:54am
It's not the mpg that's my issue, it's what I described above how the fuelling changes intermittently. I only referred to the OBC mpg figures as a reliable way to tell the difference in fuelling.
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imckay View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote imckay Quote  Post ReplyReply Direct Link To This Post Posted: 21 Jun 2018 at 7:08am
The Service Manual has some great Technical Information and Testing Procedures

You want PrimeraP12.zip
See Chapter B Engine, Section EC, QG (With Euro-OBD)
I think Page EC-43 is what you need.
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