Heavy on the gas

[Gavla]

I have a 325i cabrio that i am only getting about 9 miles per gallon, urban driving. Any help?

Also I have just fitted a working OBC that is giving me the incorrect range info, even the (1000 - 1) fuel capacity is out? How do you synchronise this?

Thanks

[Brianmoooore]

Check the colour of the spark plug tips to get an idea if the fuel is being burnt or leaking.
I'm sure the OBC info. is in the wiki somewhere.

[Gavla]

Thanks Brianmoooore, much appreciated!

[Gavla]

Ok so I finally got round to changing my spark plugs. Good result, now getting a reading of 15.7 m/g urban driving. The old plugs were in ok condition but soaked in fuel.

From what I have read up on I could possibly squeeze another 5 - 10 miles per gallon out.

So what next?

Any suggestions / advice would be much appreciated. Thanks in advance.

[Grrrmachine]

http://www.e30zone.net/e30zonewiki/inde ... ch_Running

[Brianmoooore]

Ok so I finally got round to changing my spark plugs. Good result, now getting a reading of 15.7 m/g urban driving. The old plugs were in ok condition but soaked in fuel.

From what I have read up on I could possibly squeeze another 5 - 10 miles per gallon out.

So what next?

Any suggestions / advice would be much appreciated. Thanks in advance.

You were supposed to inspect the plugs, not change them!
What was the colour of the plug tips? All the same?

[Gavla]

Oops! I figured if I was taking them out to inspect them I might as well change them.



Not sure if this photo lets you assess the situation?

Grrrmachine, I did read the Wiki and I do not have a strong fuel smell, not even when I fill her up. Not sure how well they test the mixture at MOT centres however this was not an issue, MOT received beginning March.

Any further advice gents?

Many Thanks

[Grrrmachine]

Grrrmachine, I did read the Wiki and I do not have a strong fuel smell, not even when I fill her up. Not sure how well they test the mixture at MOT centres however this was not an issue, MOT received beginning March.

If you've got bad mpg, the fuels either leaking out of a hole or coming out of the exhaust. A smell test isn't that accurate, so you may want to test the Blue Temp Sensor, as the wiki suggests.

TEST, don't just replace.

[mcbonio]

Looking at those plugs i'd be inclined to replace the rocker cover gasket too.

I had the same problem as you when I got my '87 325i cab. The previous owner wasn't as obsessive as I am, and the car felt sluggish and had poor gas mileage.

I changed and cleaned every item I could on the fuel/air/ignition system right away,

I changed;

Air filter,
Fuel filter
Oil filter
Engine Oil
Spark plugs
New rocker gasket (old gasket was leaking oil into plug holes)
HT leads
Distributor cap and rotor arm

I cleaned....;
Air flow meter (inside flap only)
Idle control valve
Throttle body flap
And all associated tubes, these had oil vapour gunk inside.

After I did this I got a solid 19-20mpg urban and a nice responsive car.!

If I drive conservatively I can even get 22-24mpg urban! I have to drive like an old lady though, 30mph and feathering the accelerator... it's much more fun trashing the derv crew though.. ;)

Good luck!

[Gavla]

Thanks mcbonio,

When I bought the car back in September last year it did go in for a service, oil, filters etc. She starts first time, every time, hot or cold and goes like a bullet. Will look at doing the rocker gasket and HT leads.

If you've got bad mpg, the fuels either leaking out of a hole or coming out of the exhaust. A smell test isn't that accurate, so you may want to test the Blue Temp Sensor, as the wiki suggests.

TEST, don't just replace.

Is it not better to replace? I will test the blue sensor ASAP. Thanks

[Grrrmachine]

Blindly replacing costs money for starters, and could also introduce a new fault into the system.

The Wiki details how to test the Blue Temp Sensor itself, which should take less than five minutes.

[Gavla]

What difference would replacing my fuel injectors make?
The car has an extensive service history and this has not been done. She has now covered 105k miles.

Sorry Grrrmachine I know you suggest not to "blindly replace", however I already have a set of refurbed injectors ready to fit.

[Brianmoooore]

What difference would replacing my fuel injectors make?
The car has an extensive service history and this has not been done. She has now covered 105k miles.

Sorry Grrrmachine I know you suggest not to "blindly replace", however I already have a set of refurbed injectors ready to fit.

Replacing the injectors is the starting point of a 'proper' service.
After 105k miles they are bound to be out of spec. and unbalanced, so any other 'adjustments' are a waste of time until this fundamental determiner of fuel mixture strength is a known, in spec. factor.

[Gavla]

Thank you Brianmooore.

So I do the injectors, I have already done the plugs, I test the blue sensor and replace if necessary and then make sure all readings to and from the ECU are correct / working.

Hopefully hitting 20 m/g after that?

[Brianmoooore]

An E30 325i, driven sensibly hard, and with no long distance stuff should return around 26 - 27 MPG.
There's no closed loop feedback control over the fueling on (most) E30s, like there is with all later BMWs, so the ECU has no idea what the injectors are actually flowing, and can't compensate by adjusting the pulse width. Even with closed loop feedback, the ECU can only compensate for the average flow of the injectors, and not for differences between individual ones.

[Gavla]

Thanks Brianmoooore, I have no idea what a closed loop feedback is but the rest makes sense.

If I can get anywhere close to that mileage I will be quids in!

[mcbonio]

Yeah I really don't get that kind of gas mileage on mine either!

[parkin10]

no i cannot get that mpg ether
early 30s on a run
mid to late teens around town only alot of this is on the cold start though
and mines a 325 tourer auto

[Brianmoooore]

no i cannot get that mpg ether
early 30s on a run
mid to late teens around town only alot of this is on the cold start though
and mines a 325 tourer auto

Short runs on a cold engine will absolutely kill your MPG (and your engine), unless you run on LPG of course.
The auto bit won't help either.

[parkin10]

cannot help having the short runs lpg is on the wish list and as for the slusha box

[Gavla]

So I got the refurbed injectors in today, watch this space.

[mcbonio]

Let us know how you get on Gavla, I'm about to get mine done too..

[parkin10]

watching

[Gavla]

watching

Nothing substantial to report unfortunately. I am getting a few more miles per gallon, as in 1 or 2. She seems to be running a lot more smoothly and acceleration has improved. Maybe just wishful thinking. I have not had a chance to look at the blue sensor or do the rocker cover gasket but will asap.

[Brianmoooore]

I am getting a few more miles per gallon, as in 1 or 2.

You were claiming 9 MPG, and you've upped that by 1 or 2. That's between a 10% and 20% improvement in fuel economy, and you don't reckon that's substantial???????
This is just the first part of getting it to run right - the foundations, if you like. There's much more to be checked yet.

[Gavla]

You were claiming 9 MPG, and you've upped that by 1 or 2. That's between a 10% and 20% improvement in fuel economy, and you don't reckon that's substantial???????
This is just the first part of getting it to run right - the foundations, if you like. There's much more to be checked yet.

Well, when you put it like that...

I will of course update as I progress.

[mcbonio]

Gavla,
You tested the Blue Temp Sensor yet?

[Gavla]

Ok so I have now changed the Blue Temp Sensor.

Initially I thought it had done the trick, the OBC told me I was getting between 15 - 17m/g (up from 10 -11). Then did a round trip to Bicester and the OBC was telling me I was getting 28 - 30 m/g (up from 25 - 27).

Problem is when I got back everything seemed to go pear shaped, at idle OBC dropped down to 7.1 m/g? If I keep pressing reset every time I start driving it gives me readings between 7.1 and 17.

Anyone got any suggestions? Thanks

[mcbonio]

You checked your ignition system? Plugs, Leads, Dizzy cap and Rotor arm.

I changed all of these at once when I got my cab as I got really bad MPG and it stank of fuel at the exhaust. It solved everything right away and totally changed the car, you should be able to do it all with 70 quid and should take 30-45 mins to complete, very easy task.

Try the plugs, dizzy cap and rotor arm first, its unlikely the leads are bad.

That really would be my next move if I were you.

[Gavla]

Plugs already done, will look into doing the dizzy cap and rotar arms. Thanks

[Grrrmachine]

I'm staying off commenting on this thread because you're refusing to co-operate with the good advice being given to you.

DON'T REPLACE THINGS! The point of TESTING the Blue Temp Sensor is to confirm that there's no interruption of the signal from the sensor to the ECU. By just pulling it out and putting another one in, you've done nothing to check the wiring of the blue plug, especially the C191 socket under the injectors which is a known moisture trap. What's more, by fiddling with the plug you've now possibly added a new fault. Did you put the connector back on properly? How do you know, IF YOU DON'T TEST IT!

http://www.e30zone.net/e30zonewiki/inde ... ug#Testing

[Gavla]

I'm staying off commenting on this thread because you're refusing to co-operate with the good advice being given to you.

The car went in to have its clutch slave cylinder replaced so I asked them to check and if necessary replace the Blue Sensor. They changed it.

I have been listening to you and reading the Wiki which has been a great help, thank you. Unfortunately I do not always have the time or necessary tools / equipment to do things myself so have to rely on my mechanic.

[Grrrmachine]

If you pay someone else to do the work, you need to ask them the right questions, otherwise you end up paying 400 quid to have your clutch slave changed. So you need to take the car to someone reliable, who won't just tell you you need parts changing.

If the injectors are new, the fuel pipes and tanks aren't leaking, the ignition system is healthy and the ECU is otherwise ok, then the Blue Temp Sensor is the biggest cause of overfueling on the M20 engine. It needs to be checked properly.

[Gavla]

Grrrmachine you are quite right mate! Now that I know how easy it is to change the clutch slave I will be heading back to my mechanic on Monday for an explanation.

As for the rest, without your knowledge I am perhaps not in a position to to ask the right questions and therefore am learning as I go along and use this forum as much as possible because of the wealth of experience and knowledge from people such as your good self.

[Grrrmachine]

So print off this and tell your mechanic to do it. It was linked to in the Rich Running link I posted two months ago :winkeye:

http://www.e30zone.net/e30zonewiki/inde ... ug#Testing

Or better yet, buy a five quid multimeter and do it yourself.