E36 328is Crazy high fuel consumption

[OptiManc]

E38Ross said:

how many miles did you get from that tank? guessing around the 220 mark?

that is truly shocking!

209 and 198...when i filled up at first it said +340 that soon sort itself out! :s

[OptiManc]

Johnboy Mac said:

Wow, 16.3 not good at all but it's the correct figure so there's a fault for sure. Next time when carrying a mpg check, avoid running out fuel as there's no need, just use the trip meter i.e brim the tank, rest the trip, do 150-200 miles and brim the tank gain. Hope, the new coolant temp.sensor does the trick, it's very possible it will.

Thanks Johnboy, i did the empty tank to ensure there isn’t any fuel lingering around inside and the computer making an incorrect assumption of fuel volume. And also at the request of others being so very helpful on this thread.

[OptiManc]

E30M3SE said:

No, that is the air temp sensor.

The coolant temp sensor, there are 2, one that runs the electric fan for the A/C, it's located in the side of the radiator, the one you want is in the side of the head,



part# 14 in this diagram.

Look at this also.

ETA;
if you've already got the air temp sensor then change it, it's the easiest of the lot to change.

Edited by E30M3SE on Monday 28th May 14:47

Nice one E30M3SE! Very nice link, where do you find this lot?
OK, will change air temp sensor first of the shop can get it in today otherwise i'll either wait or attempt the coolant sensor today.

[OptiManc]

Tried to post this last night but the forum was down.

Checked the coil packs on advise of a mechanic but they appear clean.

Have now bought an Air Temp Sensor and Coolant Temp Sensor (so many sensors!) and plan to install Air sensor first tonight and trial it for a week if it seems stable.

I will be resetting the ECU post installation the only way i know which is to disconnect the battery for a while, is that enough?

Brake switch is playing up now but can sort that easily.

[OptiManc]

Manged to get the air sensor in this morning, was very tricky and had to remove a fair few parts to get to it.

Early signs (after 2 starts and 18.4 miles) that there is some stability, however this is what happened with the MAFF and the Cam Shaft sensor so i'm not holding my breath.

Will keep you posted...

[OptiManc]

vsonix said:

hmmm I've had a thought...

The fact that once a sensor is replaced there is an improvement follwed by a decline again makes me wonder if it might be something to do with the ECU... I'm wondering maybe if the car previously had some other intake/M50 manifold/exhaust or similar engine mods, was remapped to take advantage but then original bits put back but ECU left with the remap that is trying to do things that are no longer possible and causing over-fuelling etc. You said you reset the ECU but I'm not sure if that would clear any remapping or not.

I thought that too, however the mechanic and previous owner (second owner from new) confirmed no such mods have been made . However, the ECU update/flash by the mechanic in Jan/Feb this year would have flushed out any remapps.

I'm going to fit the coolant sensor this bank holiday weekend weather permitting, after that if it doesnt solve the problem I'll have to seriously reconsider our future together

[OptiManc]

The air sensor replacement made no difference, coolant temp sensor went in eventually, very tricky position but its in and no difference so far.

Took it into BM Tec in Manchester to diagnose and clear fault codes, no codes to clear mind you. Anyway, they diagnosed it thoroughly and were as baffled as I and perhaps all us on this thread are. They did however say it was the "sweetest" sound engine they'd had in.

Tomorrow (sunday 3rd June) I'll be installing the O2 sensors, after that if the fault is not solved, with a heavy heart I'll have to call it a day...or hold it in parc ferme until I am able try something else.

[OptiManc]

E38Ross said:

so you mean they didn't diagnose it? surprised an indy couldn't do it! really weird as to why it's getting that poor mpg! my much heavier, automatic 728i gets around twice that mpg! 150 miles cruise yesterday sat at 70mph saw the trip computer read 38.1mpg from a cold start!

Thanks for rubbing it E38ROSS!
Correct, they werent able to diagnose it, but they tried for sure.

Danny and I had a chat about his E46 M3, then i looked at Danny and Andy despondently before nursing home my E36

[OptiManc]

E38Ross said:

sorry mate. that's rotten luck they couldn't diagnose!

it's not running on 50k mile old oil is it?

really, really strange....more so by the fact it's running smoothly still.

Let you off.
Nope, oil has been changed 3 times in total, 5w-30 Edge now and plugs have been changed 3 times too, Bosch and now NGK, platinum.

[OptiManc]

E30M3SE said:

Valid point, but I think the OP said the has had recent inspection II, so would assume this it not occuring, but may be the OP could re-check this.

Edited by E30M3SE on Sunday 3rd June 16:27

Correct. Brakes have been checked and theyre working correctly and not binding. Fuel lining also in tip top working order. I wish it were something this simple.

I have '92 320i coupe in the garage, fired that up today, considering getting that back on the road while a solution for the 328ise comes about. Still sounds great!

[OptiManc]

Johnboy Mac said:

Don't want to be sending you off on a wild goose chase but an incorrectly operating autobox, even one with an intermittent fault could cause poor mpg. Do you know if the box is operating correctly?

No I don't, but I discussed this last night with my brother and dad and we had mixed opinions about it. However, my dad recommended I take it to a gearbox servicing station in Tameside so will give them a call on wednesday. However, I'm not holding my breath.

[OptiManc]

E38Ross said:

Whilst its certainly worth a look, having had a thermostat stick open, allowing the car to reach about 25degs below normal temp the mpg was down, but not anywhere near that much.

Sorry for the late reply, I've been a little occupied and sort of getting used to a MK4 Golf I've recently bought till the E36 sorts itself out. Anyway, spoke to a couple of gear box servicing stations and they both said pretty much the same thing, if the gear box or torque converter were at fault I'd feel it and hear it and probably wouldn’t still be going nearly a year later. Never-the-less, taking her in tomorrow for a check anyway.

In terms of the thermostat sticking, wouldnt that cause a rough idle and perhaps even cause it overheat?

[OptiManc]

E38Ross said:

the electronic thermostats are designed such that if they do fail, they fail open....that's my understanding anyway. so basically, it'll run cold and not overheat. still not great but far less damaging than an overheat. mine wasn't running rough either, still silky smooth.....just like an M52 should be. but as said, it was still getting way better MPG than yours and didn't you say your coolant needle is running half way? mine wasn't (1/2 way is from 75 degrees upwards...hottest mine's run was 102 and was still bang on half way though!) ideal operating temp for the M52 is around the 93 degrees mark.

have you found what yours is running at yet? really easy to check.

I submitted that post prematurely, i also wanted to add, i havent driven it for around 3 days, but drove it today for around 15 miles and I was getting between 18 and 22mpg, while the Range was ticking down as the miles climbed up, 1 mile for 1 mile or there abouts very closely. Then eventually it went back to behaving badly again.

@E38Ross thats very interesting, how do i find out what its running at? I know my OBC is locked, i assume i need to unlock it first?

[OptiManc]

E38Ross said:

i'm guessing it's the same for the E36 as it is the E38, as it's also pretty much the same on E92's as well

http://www.meeknet.co.uk/E38/OBC_Unlock.htm

i reckon it'll still be test 7, as said, it's still test 7 on the E92 M3.

Thanks E38Ross, I'm taking it again tomorrow, to go to the gear box garage so will run the process then and report back.

[OptiManc]

tali1 said:

As someone with 20yrs worth of excessive Mpg from short journeys -i never found the cure.
What did the much hyped brim to brim show you? I'm not convinced any of the solutions offered are going to be cause of high Mpg.
Personally , it would be best to take it for a short motorway blast -a mixture of cruising and booting -that may be an easier option.

The brim to brim made it clear there is a fault and its not computer malfunction. I've tried short blasts on the motorway and even dropped a gear to get the revs up.

Took it into the gear box guys today, they said the gear box and torque converter are in perfect working order, but changed the gear box oil anyway.

I am at an end.

[OptiManc]

E38Ross said:

the electronic thermostats are designed such that if they do fail, they fail open....that's my understanding anyway. so basically, it'll run cold and not overheat. still not great but far less damaging than an overheat. mine wasn't running rough either, still silky smooth.....just like an M52 should be. but as said, it was still getting way better MPG than yours and didn't you say your coolant needle is running half way? mine wasn't (1/2 way is from 75 degrees upwards...hottest mine's run was 102 and was still bang on half way though!) ideal operating temp for the M52 is around the 93 degrees mark.

have you found what yours is running at yet? really easy to check.

Right, I managed to unlock the OBC and get more information out about whats being consumed and results are as;
Consumption: 1.5 litres per hour, which I know is excessive, because my bro's V8 4.4/E39 is 1.5/per hour.

I wanted to get the temp as suggested but i wasn’t going to drive it at the time and haven’t since so i don’t have that for now, perhaps tomorrow.

Do you know what the fuel per hour should be around?
As far as I know the thermostat hasn’t failed but I suppose the temp will tell us eventually.

[OptiManc]

Rollcage said:

Poor performance and dreadful fuel consumption sound like MAF issues, but it's been changed you say. Was it for a genuine OE Maf, or an ebay jobbie?

Did you ever get round to changing the oxygen sensors? ( However, the normal emissions readings are a puzzle)

Is it possible that somehow the problem is road speed dependent, in that when stationary the car behaves itself? Something on the induction side maybe?

No it was defo an OEM from bmw specialist, BM Tec in Manchester, £265 if i recall correctly.

Haven't changed the O2 sensors yet because of the emissions being bang on and because they're so ruddy expensive if its not them i'd rather not open them - but having said that i've tried everything else so why not these too?!

Thats an interesting point, yes stationary its fine...its been stationery for nearly 30 mins sometimes and the needle hasnt moved, its been stationary and revved to kingdom come and no noticeable change in needle position, but on the move it starts to slide away. I've looked the induction manifold and from what I can see, stationary and engine off its fine, a bit of build up on dirt but not enough to cause alarm to an amateur like me. Is there a danger in having the engine fired up and not having the air induction manifold connected? I assume I’ll be by-passing the air filter and exposed to debris in the air?

[OptiManc]

lepetitoeuf said:

When I had my Honda ATR, my fuel consumption went from 30mpg down to 20mpg because of a slightly dodgy plug lead. Although there was a slight misfire under load which was noticeable it would run fine at normal speeds.

Thats interesting, my coil packs seem fine to my untrained eye, how did you go about tracking it down to one particular lead?

[OptiManc]

tali1 said:

Autoexpress magazine used to run a feature for readers cars with mystery faults (sorry can't find link) which AA/RAC usually fixed - perhaps give them a call?
Other than that you could go LPG?

LPG is an option however not one i want to consider, not until petrol reaches 200.9p per litre anyway (so next week then!) and it wouldnt solve the problem, except the problem would cost less!

The AutoExpress suggestion was recommended to me by someone else too, when I eventually got round to speaking to the right person, they told me the dont run that feature anymore. I should have just picked up a copy from WH Smiths in hindsight

[OptiManc]

E30M3SE said:

If you haven't got a mis-fire it's not likely to be a coil issue.

Coils can be visually inspected for cracks, and tested by measuring the resistance between the outer 2 pins (there are 3 pins), should read somewhere between 0.4-0.8 Ohms.

Thanks E30M3SE, my coils seem perfectly fine beside a small amount of carbon.

Something that had been nagging at me for some time was the idea of changing the sparks. When I got the car 3 years ago i had a pack of 8 Bosch quad spark spark plugs gathering dust, so i removed the single spark BMW branded ones (with 97k miles on the clock I assumed they were OEM) and upgraded to the Bosch quad sparks and these were replaced like for like during the service intervals.

So last night I down-graded the plugs to twin spark NGKs.

Result; a little bit drop in torque (sensation only not measured) but slightly smoother drive, but ultimately no difference in fuel consumption. However, I had disconnected the battery during the exchange, as I have done during every sensor changes. Resulting in early signs of improvement then after an approximate 10 mile drive the problem would presents itself again – fuel gage needle dropping, range counting down and MPG eye watering.

Disconnecting the battery, I assume is causing a reset or flush of configuration or stored data which is then being collated during running time offering 'normal' fuel consumption results, the data is then possibly becoming 'corrupted' and then resulting in high fuel consumption and poor performance.

Assuming this is correct, I'd assume again it’s the ECU where this data may be stored or used. Therefore, is an ECU replacement beyond the realms of reality? The ECU has been flashed only some months ago, but being from an IT profession I know computers don’t always behave as expected even from a flash or upgrade.