Technical JTD owners with poor mpg - then read this!

[blackrat001]

Hi all. Well its happened again. Another glow plug has failed so I'm almost back to square one from earlier this year. When I get my man to change it, is it worth doing the heater relay for the plugs as well???

Glad my post has caused so much discussion pmsl.

 

[Shadeyman]

Hi all. Well its happened again. Another glow plug has failed so I'm almost back to square one from earlier this year. When I get my man to change it, is it worth doing the heater relay for the plugs as well???

Glad my post has caused so much discussion pmsl.

Its unusual for glow plugs to fail so often, perhaps you have other issues(plug control module). I've never had one fail in 6 years.

This makes interesting reading. Perhaps an apology or 2 is the order of the day.


Older vehicles are generally equipped with glow plugs that only glow before and during the start phase. They are characterised by the abbreviation GV. Modern diesel cars generally run with GN glow plugs. They are fitted with the innovative 3-phase glow system. This means they glow

1. before the start,
2. during the start phase,
3. after the start and
4. during engine operation (in boost)


Important:

Only GN plugs must be installed in a glow system that was designed for GN glow plugs - GV glow plugs may be damaged in a very short time.​

Glow plugs can show signs of what caused them to fail just like spark plugs can. Towards the end of this PDF document are photos to help you trace the fault so ccompare your failed plug with the photo's, maybe they'll help.​

http://www.w124performance.com/docs/general/glow_plug_info1.pdf

"caused so much discussion" is a serious understatment. :shakehead:​

 

[Argonought]

Hi all. Well its happened again. Another glow plug has failed so I'm almost back to square one from earlier this year. When I get my man to change it, is it worth doing the heater relay for the plugs as well???

It's best to check it first (as per Guide) and replace if found faulty. These plugs are designed to take 12 volts so nothing can make then go faulty other than perhaps being a cheap product (if say previously replaced).

If the error if false (or intermittent) then you should indeed suspect the heater relay.

Also be careful to look for possible contact problems on all plugs/sockets etc.

 

[blcn09]

I can deffinately say one thing has made a huge difference to fuel consumption on both our cars, replacing the MAP sensor. I'm not sure why but installing a new Map Sensor(£20) really did make a big difference. I'm guessing its because the MAP sensor directly effects what the turbo does so some how replacing the sensor gives better control of the turbo resulting in better MPG.

Hi shadeyman, just wondering where you got your map sensor from and what stilo you have?
You said replacing this gives better control of the turbo
Do you mean that you have boost when your meant to?
My boost only kicks in when it wants to
I have replaced boost solenoid and a boost sensor. i am also fitting a new turbo but want to figure out what other parts can be wrong with my car

Thanks, Nathan

 

[Shadeyman]

Hi shadeyman, just wondering where you got your map sensor from and what stilo you have?
You said replacing this gives better control of the turbo
Do you mean that you have boost when your meant to?
My boost only kicks in when it wants to
I have replaced boost solenoid and a boost sensor. i am also fitting a new turbo but want to figure out what other parts can be wrong with my car

Thanks, Nathan

I replaced the MAP sensor on our old Stilo with a non Fiat part. It worked perfectly and was only £28 from a local car spares shop. About the same price on eBay. The MAP sensor directly effects the peformance of the turbo so if your having issuses with it the MAP sensor is the best place to start looking for problems. At £28 each replacing it is the best option but I recommend you check all the pipes in and out of the new boost valve for leaks before replacing any parts.

 

[davethewavec]

Hi all.
I've recently had the poor mpg problem, coinciding with 2 failed glow plugs.
Been reading this interesting thread.
When diagnosing the 2 failed plugs I noticed that the control module has separate wires to each glowplug, a thick wire to supply current to the module, and a set of 4 'other' wires.

This means that the 4 glowplugs must be separately switched on and off by the ecu. And that the ecu can detect the cylinder or glowplug temperature from the resistance of the glowplug. Therefore it is able to adjust the injection timing for each cylinder, and will probably revert to a default (less economical) timing if a plug fails and it can't measure the temperature of that cylinder.

Any thoughts?

Anyway, I,ve replaced the 2 bad plugs this evening, cleared the fault code, and will let you know the effect on mpg in due course!

 

[roy lovelock]

finally some light shed on this old topic, i hadnt noticed lol.
Ive just had another glow plug go, approx 2 years back i had one go and my consumption went out of the window, when i changed the plug it went back to normal, guess what its now gone out of the window again.
Im calling it a day and changing all four this time including the two year old plug and keep the working ones as spares.

 

[davethewavec]

I can't believe it - new plugs, cleared fault code, power-off reset of ecu, and the mpg just has not changed at all!

back to the drawing board and I will have to check maf and map sensors etc. Used to be able to get 60 mpg, but now only 55. (Punto 1.9 jtd)

 

[vladof]

You do realize how small this actual difference is, right? It is less than 300grams of gas for 100 km. This is so small, it could even be explained by a few more overtakes, wind, or simply staying in traffic for half an hour more then usual, over a period of 100 km.

I get anywhere from 35 to 15 MPG and still don't really worry because I know the conditions are different all the time. And I have 2 identical 1.8 Stilos and they act the same.

Unless you measured this distance over a minimum of 100 miles, both ways, no stops, same weight in the car, same speed, same acceleration, this is too small to act upon.

 

[kevuk]

Have you tried the obviouse things first when was the air filter last changed?
And the most obviouse are you running on supermarket diesel it’s a waste of money.
I cover about 1000 miles a week and have noticed supermarket diesel will give noticably less MPG make the car slugish and smoke on acceleration.
The price difference on a full tank of Esso or Shell is less than £1- 00 which is compensated by the extra MPG and a better drive.
I saw a post somewhere that supermarket diesel has a lot less sulpher added and produces a cooler burn which is much less efficent, don’t know how true that is but it makes sense to me.

yes iv heard that aswell about suppermarket fuel and it does make sence