My average MPG has dropped from 38 to 28!

[daznkel]

As above according to the IPK, which I understand not to be as accurate as a brim to brim test, the average weekly mpg has dropped on my ZT CDTi. Average about 400 miles a week.

Now, the car is regularly serviced, by myself every 8K or so (Last one 1.5K ago) and gets a monthly shot of STP injector cleaner. Tested the MAF and it seems to be ok. It has been 160 remapped by Phil-T4 and still drives well, with no noticeable loss in power/response, black smoke or boost loss.
When Phil flashed the 160 a few months back, injector 3 was slightly overfuelling. I cant remember the exact figures, but he said it was ok.
I renewed the top boost hose earlier in the year and at that time the EGR was not significantly coked up. I have never removed the inlet manifold and cleaned it yet. The car is currently on 152K ish.

What would be the best course of action?

I am guessing, Clean or delete the EGR,
Remove and clean the inlet manifold,
Injector leakback test.

Any help, much appreciated.

[clf]

Originally Posted by daznkel

As above according to the IPK, which I understand not to be as accurate as a brim to brim test, the average weekly mpg has dropped on my ZT CDTi. Average about 400 miles a week.

Now, the car is regularly serviced, by myself every 8K or so (Last one 1.5K ago) and gets a monthly shot of STP injector cleaner. Tested the MAF and it seems to be ok. It has been 160 remapped by Phil-T4 and still drives well, with no noticeable loss in power/response, black smoke or boost loss.
When Phil flashed the 160 a few months back, injector 3 was slightly overfuelling. I cant remember the exact figures, but he said it was ok.
I renewed the top boost hose earlier in the year and at that time the EGR was not significantly coked up. I have never removed the inlet manifold and cleaned it yet. The car is currently on 152K ish.

What would be the best course of action?

I am guessing, Clean or delete the EGR,
Remove and clean the inlet manifold,
Injector leakback test.

Any help, much appreciated.

Have you checked the temperature of the coolant using the OBD? Mine increased around 30% when I fitted the top hose mod thermostat.

[klarzy]

How often doyou rest the mpg figure. ?

[daznkel]

Originally Posted by clf

Have you checked the temperature of the coolant using the OBD? Mine increased around 30% when I fitted the top hose mod thermostat.

It has an in line stat fitted in the top hose already. Although, it maybe just me, but in the last week or so, seems to have been taking longer to get to temperature.

Originally Posted by klarzy-dials.com

How often doyou rest the mpg figure. ?

Usually every couple of weeks. Also generally drive the same routes each week.

[klarzy]

Do you reset it when stationary....

[daznkel]

Originally Posted by klarzy-dials.com

Do you reset it when stationary....

Yes mate, usually before I set off. Just checked, the last reset was over 800miles ago, so about 2 weeks normal driving.

Why would it make a difference?

[clf]

Originally Posted by daznkel

It has an in line stat fitted in the top hose already. Although, it maybe just me, but in the last week or so, seems to have been taking longer to get to temperature.


.

Has the ambient temperature been much lower recently? I doubt this, however that could explain the longer temp times. But in saying that, the top hose stat may have failed also. For the cost and effort it would probably be the easiest 'repair'

[daznkel]

Originally Posted by clf

Has the ambient temperature been much lower recently? I doubt this, however that could explain the longer temp times. But in saying that, the top hose stat may have failed also. For the cost and effort it would probably be the easiest 'repair'

Not really, maybe a couple of degrees in the last couple of days. The stat that is fitted, was there when I bought the car 32K ish miles ago and is the one that sits inside the tophose. I only know its there because I had a squeeze around for it, when I bought the car. But as you say, for the cost, it is probably worth eliminating.

[first-things-first]

My ZT auto diesel averages around 37 MPG on my usage - about 50 / 50 urban and faster roads. If I sit at around 70 I have seen 45 MPG.

Colder weather hits this by around 3 MPG. I have a working OEM stat.

The EGR and manifold were cleaned by me. I had a fair bit of gunk, but not excessive as some have had - about 5 - 8 mm of gunk.

Cleaning helped responsiveness and smoothed gear changes a bit (they are now almost seamless - before would slightly feel the jolt of changes). MPG not really different.

FBH will affect MPG as it uses fuel.

[daznkel]

Originally Posted by first-things-first

My ZT auto diesel averages around 37 MPG on my usage - about 50 / 50 urban and faster roads. If I sit at around 70 I have seen 45 MPG.

Colder weather hits this by around 3 MPG. I have a working OEM stat.

The EGR and manifold were cleaned by me. I had a fair bit of gunk, but not excessive as some have had - about 5 - 8 mm of gunk.

Cleaning helped responsiveness and smoothed gear changes a bit (they are now almost seamless - before would slightly feel the jolt of changes). MPG not really different.

FBH will affect MPG as it uses fuel.

My weekly drive is about 50/50 also and I regularly saw 38-40mpg. (Manual transmission). I could sit at 85 on a longer journey and easily get 45mpg.

I think an EGR/manifold clean up and new inline stat will be the first port of call then.