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Author Topic: how reliable is the MID??  (Read 879 times)

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M-Tek Performance

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how reliable is the MID??
« on: 25 September 2007, 23:51:27 »
drove my dads 2.5 TD Auto down from Hull to Harpenden and back today.

fuel computer says I averaged 46.3mpg at 52mph over 400 miles.

Fuel gauge tells a different story.

It says there are 20 litres left in the tank (its slightly higher than when I filled it up yesterday, and it took 44 litres off me).  My dad reckoned there was about 28 litres in when i filled it up..

I know I should go fill it up and then work it out, but then my dad gets free diesel off me LOL

How much can the MID be relied upon??

This is going to be the deciding point in my getting a TD or not.
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Kevin Wood

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Re: how reliable is the MID??
« Reply #1 on: 26 September 2007, 09:31:00 »
The MID display is only based on a signal from the ECU estimating the rate of fuel flow, not an actual measurement. I find mine is within 1 MPG (petrol) but I'm not sure how a diesel would compare.

I guess the fuelling is more loosely controlled on the 2.5TD due to a mechanical injection pump and injectors so accuracy will suffer. On a petrol model, the ECU knows the injector opening duty cycle and the injector flow rate. Assuming the fuel pressure is OK and the injectors are not clogged it's going to be reasonably accurate.

Kevin
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TheBoy

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Re: how reliable is the MID??
« Reply #2 on: 26 September 2007, 18:13:51 »
MIDs are usually fairly accurate (IF programmed properly!!).  My MV6 is bang on, not really had the tractor running for long enough to say.  A decent motorway run should easily see mid 40s though. Round town is where the MPG dives.

The MID is the engine ECU's interpretation of fuel usage.  Fuel leaks (not uncommon on diesels) will increase consumption more than MID says. Fuel blockages will also mess the figures.
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theolodian

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Re: how reliable is the MID??
« Reply #3 on: 26 September 2007, 18:38:06 »
Mine is about 4% optimistic, but I have slightly leaky injectors.  Was probably pretty close when new.
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