[90MSP]

So had my 330D M Sport for a couple of months (55k on the clock) now and quickly new something was not right. So found and replaced two duff thermostats. But hey... something still not right, MPG is still a bit naff.

So found a P14A7 error.. excessive back pressure from DPF. Took it my local mech who is very good and he forced a regen for me to get the soot down to 4%. However !!.. he found a load more errors.... each glow plug is knackered with five 'open circuits' and one 'short to earth'. This in effect is what led to the DPF error and poor mpg... excessive fuel use.

The car is under 3 month warranty, but I believe these are consumables !.
And the guy who the car before me was an estate agent ... the *&%*&

So my mech has quoted £200 to replace them. Apparently they are £15 each for the part.... is this a DIY job ?

Ta

[Jase 320d]

Im not believing all 6 plugs are dead

Id be looking at wiring or if there's a glowplug controller.


I have never know of 6 to fail by 55k. Gloplugs usually do way over 100k

[danb21t]

I think they are quite difficult to get to, you have to take the inlet manifold off.

As Jase said it would well be the glow plug controller. But in my experience of diesel's so far I can confirm that glow plugs certainly do have a limited life span so not uncommon for them to fail.

I would get them to replace the glow plug controller and push for new plugs if possible. Not really something you would expect to replace..

[90MSP]

Thanks guys, this sounding expensive now... Glow Plug controller !... would that not have it's own fault code ?.... also any idea on how much that is likely to cost ?

[ukbeemerboy]

Originally Posted by 90MSP

Thanks guys, this sounding expensive now... Glow Plug controller !... would that not have it's own fault code ?.... also any idea on how much that is likely to cost ?

Glow plug controllers are around the £85 mark, but I would check wiring first.

[Danny.B.]

I had to change the controller and all 6 plugs on my 330D to get rid of the same problem. Was on about 50/55k miles

[90MSP]

Right, so after a bit of digging I can source a glow plug relay for about £75. Questions is, is this something I can replace myself easily enough ?

[Danny.B.]

Pre LCI - Inlet manifold off
Post LCI - Inlet manifold still on

I wasnt overly confident of not fudging it up so left it to the pros!

[muaythaimadness]

All six were showing as failed on my 335d, BMW replaced the glow plug control unit. Told me that if all are showing as failed it points to the control unit, not the individual plugs

[90MSP]

Just ordered a set of Bosh plugs and a new relay, £130 all in. Will get my indie to fit them for me. Thanks for the input guys.

[Danny.B.]

Originally Posted by muaythaimadness

All six were showing as failed on my 335d, BMW replaced the glow plug control unit. Told me that if all are showing as failed it points to the control unit, not the individual plugs

I was hoping this was true first, glow relay one week. All glow plugs 2 weeks later

[danb21t]

Originally Posted by Danny.B.

Pre LCI - Inlet manifold off
Post LCI - Inlet manifold still on

good to know, thanks!

[Dan-danGT]

We find that most of the time one glow plug has a short to ground and when the relay clicks in it burns out the controller and generally fails all glow plugs in one go. It use to be easy to check them with a amp meter inline, you could connect the glow plug straight to battery + and watch the amp meter read about 20 amps then drop off slowly as the plug warmed up. But now most glow plugs are 6 or 9v which means you can only check resistance

[90MSP]

Originally Posted by Dan-danGT

We find that most of the time one glow plug has a short to ground and when the relay clicks in it burns out the controller and generally fails all glow plugs in one go. It use to be easy to check them with a amp meter inline, you could connect the glow plug straight to battery + and watch the amp meter read about 20 amps then drop off slowly as the plug warmed up. But now most glow plugs are 6 or 9v which means you can only check resistance

That's most likely my situation then. Glad I bought both now, thanks

[doughboy]

Originally Posted by 90MSP

he found a load more errors.... each glow plug is knackered with five 'open circuits' and one 'short to earth'. This in effect is what led to the DPF error and poor mpg... excessive fuel use.
Ta

Why would faulty glow plugs cause low mpg?

They are only used to help cold starting, as soon as the engine is running they have no effect.

[bishbosh]

Originally Posted by doughboy

Why would faulty glow plugs cause low mpg?

They are only used to help cold starting, as soon as the engine is running they have no effect.

The glow plugs are still used when the engine is running. Generally to aid smooth running until the engine has warmed up.

[doughboy]

Originally Posted by bishbosh

The glow plugs are still used when the engine is running. Generally to aid smooth running until the engine has warmed up.

Maybe, but they only run for up to 2 minutes maximum, in which time the pistons and head will only just have started to warm through.

So a faulty glow plug(s) will never affect MPG IMO.

Could be the OP's problem is something else?

[90MSP]

I think it has a knock on effect. Faulty glow plugs / relay means the fuel is burnt inefficiently during the first few minutes of driving resulting in excessive soot buildup in the DPF. This in turn reduces your MPG due to excessive back pressure.

I know, I am going through it. Had my DPF force regened by my local Indie and the soot content reduced to 4%, my MPG has increased by 5mpg as a result. Still have the plugs and relay to do, just waiting delivery.

[nuttallacpw]

Is forcing a regeneration a diy job or a programmed job at a dealer?

[90MSP]

I tried it myself and with the aid of Wynn 'Regen' fuel additive, but no luck. Apparently my mech took my car out attached to his diag tool, ran it at 40mph and 2000 revs until the soot content diminished.

You could have a go yourself, I didn't do the 40pmh bit when I tried.