[Unkle Munkle]

Hi all,

Had my 1.8 for a while now and love it. It's quiet, refined and drives beautifully. Going from the 159 1.9 JTDM, I expected it to be less economical but the trip says 24mpg which is pretty poor for a relatively modern petrol engine. The 159 returns 40mpg no prob.

It's recently been serviced, had a cam belt and a new thermostat and runs like a dream. Is this just the norm or is there anything else I can be checking?

I do notice the occasional smell of fuel at the rear of the car (outside). However, it recently flew through its MOT and this would have been flagged. I can't see any obvious leaks when it's running. Hopefully the trip computer just isn't that accurate.

The fuel gauge seems to drop an eighth of a tank every time I start the engine!

I love, love, love the car. It's almost more of a pleasure to drive than the 159!

Thanks in advance...

 

[scottyf]

Its low.

Average early 30s mpg.

on a run mid to high 30s
town I used to clock about 27-28

On lpg I average 24-26mpg.

But petrol should be circa low 30s.


Put it in perspective. I did Birmingham to bristol 90mph+ on lpg for 190 miles and got 24mpg on lpg. Id expect at that speed petrol would be 28.

Id say yours is running rich.

 

[Unkle Munkle]

Its low.

Average early 30s mpg.

on a run mid to high 30s
town I used to clock about 27-28

On lpg I average 24-26mpg.

But petrol should be circa low 30s.


Put it in perspective. I did Birmingham to bristol 90mph+ on lpg for 190 miles and got 24mpg on lpg. Id expect at that speed petrol would be 28.

Id say yours is running rich.

OK, I though it was just cars with carburettors that ran rich! How do you rectify an injection car that is supposedly running rich or how do you investigate/check/rectify?

 

[scottyf]

injection engines rely on feedback from sensors such as Lambda, Map , Maf and a multitude of other sensors tthat get fed into a map or table of what amount of fuel to inject and open at a desired fuel pressure.

So saying that lets start with the basics.

Check things mechnically. Start looking at the air filter. clogged fliter means less air also means less fuel injected but it means you'll open the throttle more to get the desired power.
Also check tyre pressure. If the brakes are binding etc.

Once those are okay things like checking the maf and lambda need checking. Now you'll need a copy of multiscan to check those. so check the first few things and report back.

 

[Unkle Munkle]

injection engines rely on feedback from sensors such as Lambda, Map , Maf and a multitude of other sensors tthat get fed into a map or table of what amount of fuel to inject and open at a desired fuel pressure.

So saying that lets start with the basics.

Check things mechnically. Start looking at the air filter. clogged fliter means less air also means less fuel injected but it means you'll open the throttle more to get the desired power.
Also check tyre pressure. If the brakes are binding etc.

Once those are okay things like checking the maf and lambda need checking. Now you'll need a copy of multiscan to check those. so check the first few things and report back.

OK. Good call. Will check these things tomorrow and see what's what. I've also heard that an ECU reset is possible but not sure how this is done.

The car had a faulty thermostat and I know that this can affect fuel consumption but this has now been changed. I wonder if the car has 'set itself' to compensate for this and is still running the same way. Long shot, I know!

 

[Unkle Munkle]

Would it also be worth trying a second hand Bosch MAF or is it likely to be the lambda (or both) that causes the issue? That is, if the air filter is clean and tyre pressures good. Can't imagine a problem with the air filter as the car has regularly had its service items replaced and it's only done 48,000 miles. How easy is the air filter accessibility to check it?

As I say, the car idles beautifully and drives perfectly. Perhaps I'm creating problems in my mind but the mpg readout on the trip computer is definitely at 24mpg :-(

I don't want to rock the boat if it risks ruining how it feels!

 

[ransoman]

Would it also be worth trying a second hand Bosch MAF or is it likely to be the lambda (or both) that causes the issue? That is, if the air filter is clean and tyre pressures good. Can't imagine a problem with the air filter as the car has regularly had its service items replaced and it's only done 48,000 miles. How easy is the air filter accessibility to check it?

As I say, the car idles beautifully and drives perfectly. Perhaps I'm creating problems in my mind but the mpg readout on the trip computer is definitely at 24mpg :-(

I don't want to rock the boat if it risks ruining how it feels!

What year of 156 is it? It could well be a sensor but depending on the year it could have up to 3 oxygen sensors.

 

[alfizta]

I also own a 156 1.8 TS (my 2000) and always got what the book says. best 43 mpg, lowest 26 mpg.

 

[ExBrick]

Ignore what the computer tells you, work out your mpg from fuel used and distance between top-ups of a full tank. And go from there. Mine does ~33ish in reality compared to ~37 on the computer.

 

[Unkle Munkle]

What year of 156 is it? It could well be a sensor but depending on the year it could have up to 3 oxygen sensors.

It's a 2003 '52 plate - a pre-facelift model. The trip says 24.3mpg. I do approx 21 miles each way to work on a mixture of roads but don't often get stuck in traffic. Half is on dual carriageway.

My father-in-law has a Snap-on scanner (very expensive piece of gear) for diagnostics etc but the 156 doesn't appear to have the same plug-in socket as the 159. Guess it's because it is older.

I can check basic things myself but wondered if there was a definitive guide to checking things out that could be causing such poor mpg. It's a shame as the car drives and idles beautifully. You can't even feel it idle when sitting inside (if that makes sense). Would love to check if there are any problems for peace of mind but I suspect it's not going to be straightforward... :-(

 

[scottyf]

That's because the 1.8 is a peach of an engine.
Do a brim to brim calc and come back. Computers can over / under read.

 

[gazza82]

Would it also be worth trying a second hand Bosch MAF or is it likely to be the lambda (or both) that causes the issue?

Not really as you have no idea if the 2nd hand MAF is any good. Two things I found to affect fuel consumption the most are lambda(s) and thermostat/temperature sender. (that's not ruling out a lead right boot!). Putting a non-standard lambda in can be a pain .. use Bosch, avoid NTK.

That is, if the air filter is clean and tyre pressures good. Can't imagine a problem with the air filter as the car has regularly had its service items replaced and it's only done 48,000 miles. How easy is the air filter accessibility to check it?

Ah. You'd be amazed how many invoices say "new filter" when it's obvious the cover hasn't been removed .. TS filters are a PITA to work on as the bolts tend to snap off .. and once the top cover fails to seal properly, that can cause issues.

As I say, the car idles beautifully and drives perfectly. Perhaps I'm creating problems in my mind but the mpg readout on the trip computer is definitely at 24mpg :-(

I don't want to rock the boat if it risks ruining how it feels!

Don't try comparing a TS petrol with a diesel .. diesel will always win!!

My father-in-law has a Snap-on scanner (very expensive piece of gear) for diagnostics etc but the 156 doesn't appear to have the same plug-in socket as the 159. Guess it's because it is older.

Should do .. it's behind the fuse box cover on the right side of the dash! Its a standard EOBD connector on that 156 and the 159. Although not all cars are as "standard" as they should be when it comes to diagnostics .. MultiEcuScan (MES) is still the preferred diagnostic on 156s.


To reset the ECU properly you need MES. You can leave the battery disconnected but it doesn't clear all the "learned parameters" ..


And like the temperature gauges in the 156, the MPG computer can be misleading .. I do the brim-it, drive it, brim-it calculations .. my 2.0 has been up to the high 30s before now. I regularly get low 30s even with "spirited" driving ... how else do you in an Alfa?!? :biglaugh:

 

[Unkle Munkle]

Not really as you have no idea if the 2nd hand MAF is any good. Two things I found to affect fuel consumption the most are lambda(s) and thermostat/temperature sender. (that's not ruling out a lead right boot!). Putting a non-standard lambda in can be a pain .. use Bosch, avoid NTK.



Ah. You'd be amazed how many invoices say "new filter" when it's obvious the cover hasn't been removed .. TS filters are a PITA to work on as the bolts tend to snap off .. and once the top cover fails to seal properly, that can cause issues.




Don't try comparing a TS petrol with a diesel .. diesel will always win!!




Should do .. it's behind the fuse box cover on the right side of the dash! Its a standard EOBD connector on that 156 and the 159. Although not all cars are as "standard" as they should be when it comes to diagnostics .. MultiEcuScan (MES) is still the preferred diagnostic on 156s.


To reset the ECU properly you need MES. You can leave the battery disconnected but it doesn't clear all the "learned parameters" ..


And like the temperature gauges in the 156, the MPG computer can be misleading .. I do the brim-it, drive it, brim-it calculations .. my 2.0 has been up to the high 30s before now. I regularly get low 30s even with "spirited" driving ... how else do you in an Alfa?!? :biglaugh:

Some good points there and obviously appreciate the diesel 159 will always be more economical. I think I'll take the trip computer with a little pinch of salt and do my own calculations as you say.

Can the air filter be removed from the top of the air box? Apart from snapping screws, is it fairly easy to check / change the filter?

I don't want to go changing parts on a whim so I'm wondering if the scan / diagnostics will show or indicate a faulty lambda or MAF. I've no idea about what they should be doing or reading on such equipment to be honest but any guidance or tips to go by would be greatly appreciated!

 

[Unkle Munkle]

I have also read a lot about the temp gauge reading 90 degrees regardless of outside temp. When I got the car, the guage hardly moved so I replaced with a decent quality thermostat. The temp gauge generally sits at 70 degrees when driving along now. If standing still, it will climb to 90 degrees and the fan will come on as it's supposed to when it reaches temperature.

Could something as silly as the temperature sensor/sender be causing issues with mpg?

Probably clutching at straws with everything as it will no doubt require further investigation at some point and end up costing money! As I say, it's frustrating as the car runs and drives like new!

 

[Unkle Munkle]

Have checked the air filter and, as expected, it's like new! However, one of the screw mounts for the lid of the air box has broken so it doesn't quite seal properly. Would this cause enough problems to cause a drop in mpg?

Tyres fine.

I think my next step is to take it to a local Alfa specialist and get some diagnostics run to see if it's all in order....

 

[rgwm]

If its really running at 70C, then that could well be contributory to any fuel consumption issues you have.......it should read at 90. Again a test with multiECUscan could reveal whether the sensor is telling the truth and the gauge is faulty, but if the gauge is accurate then your new thermostat seems to be faulty.

 

[Unkle Munkle]

If its really running at 70C, then that could well be contributory to any fuel consumption issues you have.......it should read at 90. Again a test with multiECUscan could reveal whether the sensor is telling the truth and the gauge is faulty, but if the gauge is accurate then your new thermostat seems to be faulty.

MDZ Italtec changed it for me npand they said it was running at the correct temperature despite what gauge says. The guage wasn't moving hardly at all before the thermostat was changed.

There is a temp sender though too isn't there? Could that be the problem?

 

[gazza82]

Worth changing the sensor in thermostat housing. Gauge should float up and down as it is actual temp not average like a lot. Mine was better after a new sender.

I can usually get 380-440 miles from a tank before I panic and find the next fuel pump. My 2.0 runs further on Nitro+ too.

 

[alfizta]

I have had full open thermostat in the past in winter and never had such a bad mpg. So your 156 issue might not just be the thermostat.

 

[ransoman]

Have checked the air filter and, as expected, it's like new! However, one of the screw mounts for the lid of the air box has broken so it doesn't quite seal properly. Would this cause enough problems to cause a drop in mpg?

Tyres fine.

I think my next step is to take it to a local Alfa specialist and get some diagnostics run to see if it's all in order....

If the airbox isn't sealing properly then it can damage the maf as unfiltered air can get in. Run it for a tank with the MAF unplugged and see if you notice a difference. you may need to reset the ECU just to get it to idle with the Maf disconnected though.