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Kit

MPG?

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Hello.

 

Just wondering what mpg people are getting from their E34’s?

 

My late touring started out as a 520i and did around 27/28mpg on a mixed run. Having changed the engine to make it a late 525i I’m getting 29/30 (with esso supreme 99 and driving very sensibly). So around 420ish miles before the light comes on and I have to fill up - note the rear end and manual box is still the original 520 setup. 

 

The internet stat-sites say I should get closer to 35 and up to 40 mpg on a clear run with a b25tu.

 

Wondering where I’m losing out? Car is very well looked after and the engine is running sweetly and there is no sign of fuel leaks on the drive or on components that are easy to see.
 

Thanks in advance.

 

Kit

Edited by Kit

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Sounds about right to me. I’m usually mid to high twenties with a 525i auto. I’m convinced I could get 500 miles out of a tank on the perfect run though usually it’s more like 430-450.

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535i Auto.

 

On a motorway economy  run ( 60ish) 26-27 MPG

 

Combined town / country driving - 18-19 MPG

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An m30b30 powered e34 does up 30mpg driving at 60 mph on the motorway on reality I get a reliable 26 to 28 mpg average depending on how many short journeys I do. I try to do none. 

 

30 mpg sound great that 500 miles from a tank.

 

I filled up once from ran out of petrol empty and it took 75 litres. I had to push it onto the forecourt. 

 

If you think an e34 is bad on fuel try driving a range rover with a petrol v8. 

 

You might get more mpg with a taller final drive gear ratio. The 520i used a 3.91:1 which is great for acceleration but it will hurt fuel economy.

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8 hours ago, Hogie said:

535i Auto.

 

On a motorway economy  run ( 60ish) 26-27 MPG

 

Combined town / country driving - 18-19 MPG

 

4.6 V8; similar figures, perhaps 28/29 on an economy run, otherwise 16-19 depending on how heavy my foot is.

 

I've never ever seen 30mpg in the 4.6 but I could swear I did in the 540i/6 I did, maybe 32/33 on a long eco run.

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Hopefully be popping into End Tuning in Birmingham on Saturday, hoping his chip will make the most of the 99 octane I put in.

 

Will report back once I get an idea of what it’s done, hopefully it helps make the most of what I’ve got and leads to a mile or two extra mpg if I’m lucky.

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Does the late m5x engine have a knock sensor? If it does then your ecu should automatically adjust ignition timing. That's all higher octane fuels do really they allow more ignition advance. The energy content of the fuel is the same as 95 RON.

 

 

Edited by bm0p700f

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12 hours ago, bm0p700f said:

Does the late m5x engine have a knock sensor? If it does then your ecu should automatically adjust ignition timing. That's all higher octane fuels do really they allow more ignition advance. The energy content of the fuel is the same as 95 RON.

 

 


The internet tells me there is one on the M50tu’s, so perhaps it won’t effect it however this is an extract from the first email I got back from End Tuning a while ago on the subject…

 

‘The older engines and ECUs were set up to handle as low as 91 octane, and they weren't as clever as modern ECUs which usually have a bunch of different tables, some for high octane and greater efficiency with backups they could switch to to lower octanes.
The older ones had to be "gentle" enough to run without issues on lower octanes and that leaves a fair bit of slack’.

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91 octane fuel has never been on sale in the u.k. 

 

In the USA 91 AKI/PON octane is equivalent to 95 Ron fuel sold here. So it's not clear what o1 octane means. 91 octane Ron fuel was sold in Eastern Europe at some point. 

 

However the Compression ratio of the engine needs to be high enough to make more ignition advance useful. It probably is not in your engine. It's made to run safely on low and higher octane fuels. 

 

Since your engine has a knock sensor the ecu should be advancing ignition timing as far as the programming allows. Back in the 90's 95 ron fuel was common so bmw would have loaded tables for that too. 

 

What engine mapping can do is maybe improve how the engine fuels in response to throttle changes. You may notice that. Getting more mpg for the car would require engine changes I.e making it more efficient.

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Changing you final drive ratio for 3.64:1 from 3.91:1 would make a  difference to fuel economy. That would reduce engine speed and the engine breaths/burn fuel more efficiently at 2000 rpm than it does at 3000 rpm. 

 

That were would could spend your money. The stock tune is pretty good. BMW spent alot of money and time doing it. 

Edited by bm0p700f

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On 14/09/2021 at 09:29, Kit said:

 

 

The internet stat-sites say I should get closer to 35 and up to 40 mpg on a clear run with a b25tu.

 

 

 

:lol: Never in a million years. You *might* get early 30's on a run. 40 is fantasy. 

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So it looks like it what I thought it would. Improved throttle response. And your happy so that good too. 

 

Surely there is someone round Colchester way that does this given you had engine change done in leavenheath.

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32 minutes ago, bm0p700f said:

So it looks like it what I thought it would. Improved throttle response. And your happy so that good too. 

 

Surely there is someone round Colchester way that does this given you had engine change done in leavenheath.


To be clear my main goal was a better driving car, the mpg was a hopeful bonus extra based on reviews I had read. 
 

I originally come from Derby and was visiting family in Birmingham after a visit home, so fitted it in.
 

In truth after doing my research he was the one person I wanted to do it. For me it’s a lot better than the stock tune.

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An old car has a worn engine. That invetibably is not going to perform as well as when it was new. Perhaps the remap adapts the map to the state the engine is currently in. 

 

 

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41 minutes ago, bm0p700f said:

An old car has a worn engine. That invetibably is not going to perform as well as when it was new. Perhaps the remap adapts the map to the state the engine is currently in. 

 

 


I get the impression you don’t like the idea that an aftermarket chip can improve on what BMW created, I suggest speaking to Enda himself as he’s been doing it for 30 years or so and can explain in more detail why and how he can improve things. As I understand it having a more specific setup over a more general one has created a better e34 for me. 


Obviously engines lose power over time (my donor happens to be a low mileage, one owner example that was very smooth and quiet beforehand) and if BMW didn’t factor that ware in - it’s very handy to have a cheap solution to improve it now.

 

As someone who is very oem focused this is an exception I’m pleased I made.

 

Edited by Kit

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The standard BMW map is very conservative for two main reasons, these being warranty and emissions. To that end, the ignition timing isn't as advanced as it could be and the fuelling isn't as generous as it could be. This is down to making the catalytic converter work as good as it can - both a leaner mixture and slightly retarded timing make the exhaust gasses hotter. Manufacturers like BMW started this around 1987 with the E32 and facelift E30 with Motronic 1.3, both cars being catalyst prepared with the Lambda sensor plug in place on the engine loom regardless of whether the car actually had one. The first GB spec BMW's to have one was the 1990 24v M50 E34 followed by the 1991 E36.

Old emissions tests consisted of a car on a rolling road in a cell, started from cold and driven for a set distance and the collected exhaust gasses being measured. The cold start element meant a bit of 'Peter paying Paul' which is why they run pretty lean when hot.

Remapping a car like this E34 is just giving the engine what it really needs for maximum efficiency. Bizarrely, remapped cars are often more economical because they aren't working as hard. A 525i is better on fuel than a 520i for example. 

 

*A properly maintained BMW engine with 100'000 miles is probably just as powerful as a new one. 

 

 

Edited by Sir Anthony Regents-Park

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Having just (finally) having filled up I can get some sense of the mpg post chip.

 

Not an exact measurement as around half of the fuel was used pre chip but I am seeing a difference.


It did 310 miles using 44 litres over mostly very sensible motorway driving, so an average of 32 mpg.

 

Will report back after a full tank of mixed use but the difference with the cars new engine and chip vs my old stock 520i is marked in more ways than one.

 

Maybe all the hassle and expense was worth it!

 

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