E36 328is Crazy high fuel consumption

[OptiManc]

vsonix said:

It could well be the ECU being dodgy, I think it mightn't be a bad idea to look into it a bit further. The car running well initially indicates possibly all sensors etc could be fine. What would be interesting to do - drive somewhere with plenty of open road for testing economy, then, reset the ECU again, and with the engine as close to operating temperature drive around for a bit, keep resetting and checking MPG1 or MPG2 so you get a rough idea of your consumption at various speeds on the OBC then see when it changes/gets worse, and by how much by. If you can pinpoint a certain amount of time every time, that could be a big clue too...

I must admit I am enjoying this collaborative diagnosis, it's what I love about car forums, BMW ones in particular

Agreed, its great to have such valuable knowledge share, so thank you to everyone who has contributed so far, your efforts are very much appreciated.

I have in the past compared MPG1 and 2 over different speeds. Since it’s an auto, I even switched on the hazards and driven only in creep on relatively level ground, the Range was counting down at its normal excessive rate, however MPG1 from what I recall was around the 40 or 50 mark. Shortly after the reserve light came on I continued to creep to the petrol station, say around 1 mile away, upon arrival the needle was well and truly past half way in the reserve.
So there must be a motion related cause.

[OptiManc]

shouldbworking said:

Interesting read. At this point I think i'd be considering a compression test just to see if the engine is mechanically sound or not.

Can you swap the ECU with another from the same model?

Thats a bit past my abilities now, so have booked her in for a check up tomorrow morning regarding the wiring and I've booked her for a compression test with BM Tec in Manchester for Tuesday 19th.

Out of interest where is the ECU located on the M52? Perhaps it just needs a

[OptiManc]

OldSkoolRS said:

Then snap a branch off a tree and whack the bonnet with it to really show it who's the boss.

Followed by a

[OptiManc]

The telling off didn’t work, however I have noticed an improvement in fuel consumption AND performance if I try one of the following (not sure of the correct pattern exactly as I only came across this last night)
- cold start, turn ignition ON and OFF after a few seconds then start engine again immediately. The fuel gauge is steady, Range static and only drops as the miles climb driven carefully but eventually it returns to being faulty again

- turn engine ON, run for a while and switch OFF before reaching optimum temp (not recommended I know) listen out for fuel tank vent and start engine again. Same result and same outcome eventually

- when OFF but hot, turn ON ignition listen out for fuel tank vent type sound turn ignition OFF and start again immediately. Same result and same outcome eventually

I'm thinking the initial ON and OFF clears a fault, causes a confusion in the ECU which is actually a correction or the charge and voltage going through the circuit a second time helps the data travel around the system better.

Hope ive got this across accurately enough to make some sense.

Had to cancel the compression test for Tuesday due to work obligations.

[OptiManc]

Did some more testing this weekend regarding the OFF and ON theory, initiating the ignition for a few seconds, turning OFF and then firing up the engine means I get at least 5 miles of stability. The fuel gauge doesn’t move, Range is steady, performance is good and MPG1 gets to a nice 22-ish driving casually. Then suddenly it all turns brown again.


I have a compression test tomorrow at 10AM but I’m more drawn to a dicky ECU now, so I will be looking into ECU remapping services which might be able to diagnose faults with the current configuration.

[OptiManc]

Compression tests are in, 174psi from all 6 chambers.

I'm sure its down to the ecu, so remapping is Plan J.

[OptiManc]

Rollcage said:

Have you tried some decent laptop based diagnostic software and a diag cable? Many will give live feeds so you can observe differences during driving/idleing, etc.

No I haven’t actually, I have tried to get engine mod guys to come out and do that but they’ve been reluctant. I've seen the cables online on eBay but have been warned against getting cheap ones and the 'proper' ones seem to fetch into the £300 mark. Spoke to a BMW remapping 'expert' on Friday morning, long story short after describing the issue he said it’s not something he thinks he can solve with software and wouldn’t want to get involve with it!

However, yesterday while driving home it began to smell of melting plastic soon I saw smoke wafting from the engine bay and the temp gauge shot up to the red mark instantly! I pulled up and saw coolant purring out and a water pipe to the front of the engine ruptured (will try and get pics actually). So, got towed home, replaced the pipe immediately after having my tea. Topped up the coolant with just 1 litre of water

Tomorrow she’s going in for a closer look, I suspect a blockage somehow and cross my fingers it’s not a gasket. Wondering though if this could actually be the phantom problem all along and has now finally caused the eventual outcome.

[OptiManc]

OldSkoolRS said:

FWIW you don't need to spend £300 on a cable. I know there are some dodgy ones about, but I went for one that was recommended on various BMW forums and it has proven to work very well. If your recent overheat doesn't lead to a solution, then I'd recommend trying these (no connection to them myself):

http://bmwcables.moonfruit.com/

He even responded to some email questions on a bank holiday, so I got my issues sorted out quicker than I expected. I got the £34.99 version as I need to use the 20 pin underbonnet connector on my Z3 to access all the items, though the OBDII connector under the steering column works for engine errors, resets, etc which would help for scaning whilst driving (with a passenger on the laptop of course ).

Thanks for that, picking her up tomorrow after a water pump and thermostat replacement. Thermo was stuck closed and pump has some play in it.

Will invest in these cables post-haste if the current work hasn’t solved the issue in anyway.

[OptiManc]

Right, shes sprung a coolant leak now . I suspect its either a hose or the rad itself. However, since the thermo and pump were replaced i did notice a gradual improvement in fuel consumption and performance was sharper, not as good as before but certainly more prompt with room for improvement.

But now its somewhere in between, not as bad but not as good as before either.

My theory is that the fault was intermittent due to the faulty thermo, when it would eventually open the system would cool sufficiently and performance would improve. The new kit had, temporarily solved the issue, but now with the rad leak, inefficient coolant level means the same symptoms yet again but this time caused by something else.

Am I right or along the right path at least?

Going to avoid leak stop stuff and look at replacing the hose if thats broken else replace or repair the rad.

[OptiManc]

Leak fixed, was a ruptured pipe.

The original issue hasn’t yet been solved so, I'll be changing the O2 sensors in the coming weeks when I have some time.

[OptiManc]

Afternoon.
Unfortunately no I havent, and still havent got around to changing O2 sensors either due to pressures of work mainly. Also have been driving another car to save a bit of money and frustration, but a plan is a foot to get around to changing O2 sensors sometime in the summer while the weather remains dry-ish.

Will update accordingly!

[OptiManc]

rumple said:

OP I had the O2 sensors go on a 328 I owned, got to be honest it made very little difference to the fuel consumption

Thanks for the heads up, besides those I am all out of options and really dont fancy an engine change. I'll give a go nevertheless, that way I know i've done everything i could try andwont have a niggling voice suggesting O2 sensors.

[OptiManc]

all22 said:

Hi guys just a bit of info for you two thing you want to look is the cam shaft breather vavle and pipes and also look at the temp of the bottom rad hose i had the same prob and it turned out to been both of them conbined but the thing that through ever one that i asked was the car was not overheating but there turned out to be an air lock in the rad and the car was reading nornal temp all the time

Thanks for that, its something I could look into. Do you have any idea what the ideal temp should be for the rad hose? What should I look out for on the cam shaft breather valve, bad fitting from wearing?

Edited by OptiManc on Monday 27th August 15:18

[OptiManc]

Rollcage said:

Doesn't sound like lambda sensors, as the emissions would likely not pass MOT standards.

I still think it's somehow speed related - like on old Ford Kas. Over rev massively at a standstill or in gear, unplug speed sensor and no problem. Makes driving them interesting until the sensor is unplugged!

I had a similar problem like this when I first got it, a scary moment in particular when approaching a roundabout junction 21 on the M62. I'd brake but the car wouldn’t respond much to the braking and continue accelerating towards the roundabout! - turned out to be the floor mats resting on the accelerator?! Managed to stop it by throwing it into neutral.

Now the revs are stable, the only the speed change is that its laboured at take-off and acceleration, certainly no increase in speed.

[OptiManc]

4rephill said:

I still reckon the gearbox management system is going into "limp home mode" intermittently.

(And I know the gearbox itself has been checked out and found to be mechanically ok, but has the electrical management system been checked out?)

You're right the gear management system hasn’t been checked, would the 'limp' mode not display an orange cock symbol on the dash in this case? However, having spoken to mechanics and BMW veterans, their suggestions are that gear management system error would be detected by the diagnostics and changing gears wouldn’t be as smooth and seamless as they currently are.

The O2 sensors were replaced on Friday; an emissions test was done before and after and the results only shy of a difference.

I'm now looking at having it gas converted so that i can contiune enjoying the drive without having to keep one eye on the fuel guage. Not what i want to do but until I find a genuine fix its the only workaround.

[OptiManc]

Rollcage said:

It does sound as if it needs hooking up to a laptop so that live data values can be analysed in the move and at standstill, and then compared to the data given when it is put through an emissions test cycle. Thus should throw up some anomolies somewhere.

OK thanks, i'll have a look for some cables, theres a link on the thread somewhere. Not sure whose laptop I can borrow to precariously position it under the hood while I go for a drive!

[OptiManc]

stevesuk said:

Yeah, the cable I linked to above came with INPA on one of the DVDs (used it to reset my airbag warning light). Just a note to the OP that the software is a bit of pain to get working. I ended up using an old netbook with 32-bit Windows, which is now my BMW diagnostics machine

Thank you chaps. I'll get some ordered and dig out that old HP NC6000
I'll share the results here as soon as they're gathered...

[OptiManc]

Just thought I'd post an update. I haven’t had a chance to do much with the car yet due to work commitments.

However, my brother has been driving the car for a few weeks now and nothing has changed.

[OptiManc]

Thanks for the reply nevertheless 4rephill. What car was this on? I see your point, the diag wont pick up the fault unless its occurring at that time.

I’ve experienced limp mode in my '92 E36 320 and its not that, in the 328 unless you know the car you dont know there is anything a miss but when the 'fault' shows itself the car is laboured, not massively but enough to know something is a miss. With limp mode its like its being forced to clean its bedroom or brush its teeth - it doesn’t want to do it!

the 320 has been scrapped now but i salvaged the transmission ecu so i'll swap them out and see what happens for a period of time but i suspect the issue will go undiagnosed.

[OptiManc]

Just wondering...could the fuel pump be at fault here? Supplying more fuel than required but enough of it is consumed and combusted not to alert the emissions testers, but excess fuel and not enough oxygen being supplied too its causing high consumption and low power output?!