Jazz GD CVT Economy

[JackH]

Having previously had a manual GD that used to average around 48mpg, we’re quite disappointed by the overall economy of the late 1.4 DSi CVT we recently acquired.

We filled it up last night and it’s only managed 36mpg on a mix of mainly motorway / A road work. Computer was showing 40mpg. I would have expected a genuine 45mpg plus in the manual driven in the same manner despite it revving higher in top gear once you’re moving.

A recent gentle run through the country that would have always seen that 48mpg from the manual resulted in 40mpg.

So... given we were led to believe there would be minimal differences in mpg between the two, I’m wondering if the current one has an issue.

One observation is the ambient temperature reading is blank but the sensor for this is purely for information purposes and has no input into the fuelling?

Tyre pressures have been checked and are as they should be.  The car has only covered 27k from new and I suspect has spent the bulk of its life to date being driven sedately so would it benefit from some injector cleaner in the tank and an ‘Italian Tuneup’?

Car has full main dealer history and so I’m presuming it would have had new plugs at the last service at 26k.

Anything else to check? I’ve read that the CVT box sometimes needs recalibrating if the battery is disconnected but it all seems to work as you’d expect / doesn’t ever labour the engine due to too high a ratio or be revving excessively.

[Kenneve]

Hi JackH
Have just checked the readout on my Mk3 CVT and for just over 15000 miles it shows an average of 52.0mpg over all sorts of motoring.
Obviously the in car readout tends to be a bit optimistic, but maybe only around 2mpg.
As I recall it, my previous Mk2 cars were not much different, so I would suggest that your car needs looking at.
I tend to get a bit twitchy, if the average readout gets much below around 48-50mpg.

[JackH]

Thanks for the heads up

Today I am going to do the following:

New NGK plugs
Fuel additive (I have some Sea Foam and I’m not afraid to use it!)
Clean the EGR (not detected any hesitation though so suspect this is fine).
Disconnect the battery and do the ‘rolling start’ recalibration for the CVT.
Check all wheels are rotating freely when off the ground to ensure no sticky calliper issues.

Other than maybe changing the ambient temperature sensor (as before, I don’t believe these have any fuelling input but want the readout to work whatever), I’m not entirely sure what else to do / check given the FMDSH indicates it’s been serviced annually having usually covered around 2.5k in between visits.

Run it at slightly higher tyre pressures than recommended as some do?

It seems to drive as well as it should whatever but may have to consider getting something else in the longer term if this is the kind of MPG we can expect from it.

[JackH]

Would the lambda sensor be throwing on the EML if that wasn’t reading 100%? I believe that’s a possible cause of poor MPG.

In the absence of a gauge on the dash, is there anyway to check what the temperature engine is running at? Engine temperature sensor / thermostat a known issue on these? (I’m probably clutching at straws as it idles nicely once the initial raised RPM warm up is out the way but worth consideration).

[Kenneve]

Not sure of the age of your car, but I assume you will be changing 8 spark plugs, not 4.

On a gentle countryside run I would expect the best part of 60mpg, in fact on a recent run from Solihull to Stratford-on-avon, (about 17 miles and we drop around 80mtrs) I managed 62.2mpg, although the average speed I guess was only around 30mph due to heavy traffic.

If you have a multimeter that reads temperature, then get the engine warmed up and then ticking over whilst pressing the sensor against the cylinder head. I'm only guessing, but would expect it to read at least 75c

[guest5079]

The engineers on the forum might disagree but if the Lambdas ( there are TWO) were out the MOT should have picked it up. On the MOT cert it gives a min and max for the Lambda and if yours is in parameters I would guess they are OK! Of course with the official let out about MOTs it does depend when your
 MOT  was done. It is easily checked if you have a friendly garage that will do a gas test for a few pounds.

[JohnAlways]

Hi Jack H

A Honda GE has only 4 spark plugs, usually iridium and last for 70,000 miles (not needed then in your case).
It may just be it's had such a gentle life it's still tight.
I would check the air filter yourself to see if it's pretty dirty, very easy with just a couple of clips to undo. Choked air cleaner element will kill economy. As you're checking for seized calipers I don't think there is much else. Interesting that you feel there is a common issue "Engine temperature sensor / thermostat a known issue on these" unless that was a question. No issues there that I'm aware of or read about. You have played about with the controls to make sure the ambient temperature isn't just hidden? Sounds like it is a tight engine from the way you describe it's former life, run in lower gears for a bit and see if that helps (4th instead of 5th, 3rd instead of 4th) etc

[JackH]

Hi Jack H

A Honda GE has only 4 spark plugs, usually iridium and last for 70,000 miles (not needed then in your case).
It may just be it's had such a gentle life it's still tight.
I would check the air filter yourself to see if it's pretty dirty, very easy with just a couple of clips to undo. Choked air cleaner element will kill economy. As you're checking for seized calipers I don't think there is much else. Interesting that you feel there is a common issue "Engine temperature sensor / thermostat a known issue on these" unless that was a question. No issues there that I'm aware of or read about. You have played about with the controls to make sure the ambient temperature isn't just hidden? Sounds like it is a tight engine from the way you describe it's former life, run in lower gears for a bit and see if that helps (4th instead of 5th, 3rd instead of 4th) etc

Hi... as per title it’s a GD.

Air filter is fine. There was a question mark at the end of ‘Engine temperature sensor / thermostat a known issue on these?’ and asked it having experienced MPG issues on VAG TDIs in the past when these failed.

Ambient temperature is a permanent readout just above the odo/tripmeter on the GD (or at least the ones we’ve had).

It’s an auto so whilst yes you could run it in manual mode, I’m not entirely sure that’s the issue as it starts, revs freely and runs as you’d expect.

[JackH]

Not sure of the age of your car, but I assume you will be changing 8 spark plugs, not 4.

On a gentle countryside run I would expect the best part of 60mpg, in fact on a recent run from Solihull to Stratford-on-avon, (about 17 miles and we drop around 80mtrs) I managed 62.2mpg, although the average speed I guess was only around 30mph due to heavy traffic.

If you have a multimeter that reads temperature, then get the engine warmed up and then ticking over whilst pressing the sensor against the cylinder head. I'm only guessing, but would expect it to read at least 75c

It’s the very last of the GD models with the 1.4 DSI engine so yes... eight plugs.

No heat function on my multimeter unfortunately. Is there anything like VAGCOM (VW OBD diagnostics lead / application) available for Hondas? Something along those lines would usually give you access to data like engine temp etc.

[JackH]

The engineers on the forum might disagree but if the Lambdas ( there are TWO) were out the MOT should have picked it up. On the MOT cert it gives a min and max for the Lambda and if yours is in parameters I would guess they are OK! Of course with the official let out about MOTs it does depend when your
 MOT  was done. It is easily checked if you have a friendly garage that will do a gas test for a few pounds.

MOT was in October and it stood for quite a while before we got our hands on it, but yes... excellent idea. Will see if the chap who does my MOTs can book it in for an emissions check.

Found some articles on lambdas in general that suggest removing them and soaking them in petrol for 8 hours would loosen up any deposits and give them a nice clean.

[JohnAlways]

Sorry JackH i was looking by your name "My Honda: GE 1.4 EX" so I thought a GE. Apologies

[sparky Paul]

Sorry JackH i was looking by your name "My Honda: GE 1.4 EX" so I thought a GE. Apologies

Yes, that's where all this GD/GE business gets confusing - late mark 1 cars like mine are GE too.

Is there anything like VAGCOM (VW OBD diagnostics lead / application) available for Hondas? Something along those lines would usually give you access to data like engine temp etc.

Yes there is, Honda dealers have their own system HDS, and you can buy a Chinese clone - it's a lot dearer than the VAG-COM interfaces though, about £90 last time I looked. These diagnostic tools can be very useful indeed, but I'm holding off buying the Honda one until I need it.

If you want to read engine fault codes, temperatures and other live engine sensor data only, one of the generic ELM327 type OBD2 USB cables or bluetooth adapters will do that, and they are only a few pounds.

There will be an inlet temperature sender for the ECU. Not 100% certain on the Jazz, but they are usually completely separate from the dash outside temperature display.

It sounds like you have checked all the obvious, and as neddy says, I would be very surprised if there's a lambda problem if there's no EML on and exhaust emissions turn out to be good. They don't normally fail unless contaminated by something, for example an engine burning oil or head gasket failure, etc.. Unless something shows up on the emissions, I would leave them alone for now.

It's definitely worth a look at the EGR valve. They can fail without significant symptoms, and on a car which has done little mileage,  it's possible that it has been tootling around town all its life. It's worth a quick check and a clean out with some carb cleaner - nothing oily.

Also check for sticky calipers, as you suggest - it's the first thing I go to if there are any mpg worries. Feel the centre of the wheels after after a good run, see if anything unusual is going on. Fronts may become lukewarm or 'aired', with the two sides even, and the rears should always feel cold.

[olduser1]

Best to run it for a couple of weeks , as regards fuel additives I would only use Redex - Wilco's have an offer on 4 bottles at the mo.

[JackH]

Sorry JackH i was looking by your name "My Honda: GE 1.4 EX" so I thought a GE. Apologies

  No worries 

[JackH]

Changed and gapped the plugs but they didn’t look that old / dirty.

Sea Foam now in the tank. Took the EGR valve off and found a bit of carbon so soaked with brake cleaner and gave it a good tap before refitting. I’ll be surprised if this is a factor as haven’t felt any sudden drop off in power like we did in the manual one we had when that needed a clean, but worth a try.

All brakes nice and free.

Not had a chance to take it for a run yet so we shall see. As much as it’s not likely to be the lambdas I’ll give them a clean when I can next borrow a ramp to go under it.