Thread: Crazy fuel consumption readings?!?

Fuel consumption vs zero km travelled will give very high readings. What does the handbook say about how the system works?

What figures do you get if you do a reset whilst travelling on the highway? It takes 1km to get a new reading so it won't take you long.

drive 100km and see what it says

Not too sure on year/spec your P38 is, but mine will do it's calculation over 1km and at 60kmh it'll normally come back around 10L/100km and if traveling at 100kmh it normally comes back around 11.5L/100km. Depending on acceleration/coasting that will change a little but normally on flat-ish ground at steady speed that's what I'll get from a reset.

Cheers
Keithy

Fill it up, run it for a bit, and then refill, and work out that way.
I live in the hills, if I do short trips, I'm up at about 20ltr/100km
I get about 16ltr/100km on longer runs. I have a 98 gems.
Driving harder will obliviously increase fuel use.
But I would work it out manually to get an idea first.

I also have worked it out manually and suburban trips with no crazy acceleration gives 18.5ltr/100.......I do believe this is pretty normal for a Bosch 2000

Originally Posted by p38arover

Fuel consumption vs zero km travelled will give very high readings. What does the handbook say about how the system works?

What figures do you get if you do a reset whilst travelling on the highway? It takes 1km to get a new reading so it won't take you long.

It doesn't really matter at what speed, the figures are mad, crazy high in comparison to what I am used to with mine (mine is a '95 gems and the Mrs is a 97 gems). Had a look under the bonnet and underneath and hers (the crazy one) has pre-cat oxygen sensors where mine doesn't... everything else looks exactly the same. I will do some examples runs tomorrow, (suburbs, highway slow and high way fast) and take photo's to share the experience! Funny thing tonight... when I filled up (carefully and slowly to overflowing) to get ready for a manual calculation over the next few days it only showed as 7/8 full on the gauge.

The craziness I am seeing includes:

1. The gauge seems inaccurate.
2. It seems to "re-set" the fuel gobbling rate to "mad high" at every start up.
3. It then proceeds to wind down the L/100KM figure as the km's increase... but very, very, quickly - as in - it can drop from 40+ to high 20's in a very short trip of less than 3 km's.

The PO used a Faultmate MSV2 (which I have yet to familiarise myself with) and I am thinking that some "dabbling" with fuel mapping or engine management protocols might have occurred.

Is it even possible to do this sort of thing to make a P38 react like this is?

Originally Posted by Eevo

drive 100km and see what it says

We have two P38's... and the first we have had for 10+ years... If I thought taking it for a spin would help, I wouldn't be asking questions here... I would be out driving!

But seriously, I have had it for a while, and put a few KM's on it already just getting stuff done for RWC. On a couple of 50 km trips a week or so ago it did settle to a reasonable rate (high teens) but still jumped back into mad-crazy territory at next start up.

Might have to start checking out how to use that Faultmate!

Originally Posted by Keithy P38

Not too sure on year/spec your P38 is, but mine will do it's calculation over 1km and at 60kmh it'll normally come back around 10L/100km and if traveling at 100kmh it normally comes back around 11.5L/100km. Depending on acceleration/coasting that will change a little but normally on flat-ish ground at steady speed that's what I'll get from a reset.

Cheers
Keithy

My original P38 has never come down to that sort of economy - but has returned close variations on the theme you lay out. It's on gas and so I have never even bothered worrying about if it's a little rich or maybe even overfuelling (which I do not think it is).

The experience with this second one and skimming some of the OBD threads going on at the moment are prompting me to try and get a better handle on it all. 'As if' I am really interested though... sometimes I think we all have a little too much knowledge of the deep dark secrets of these P38's!