Boobs, baby boobs?
Ahem, the BMW M47 engine fitted to the Freelander TD4 is a lovely piece of kit, decent power and economy and quite refined for an oil burner. Unfortunately it's also fairly cold blooded, and can take a while for the coolant to warm up and supply heat to the cabin.
This is why a fuel burning heater (FBH) or a ceramic heater is fitted to many models (depending on year and spec) to assist in getting the coolant to temperature when (baby) it's cold outside.
Sadly an older Webasto FBH can be a little fickle these days, often ignored in terms of servicing and because it's hidden away behind the front bumper, some less enthusiastic owners are probably oblivious to its existence.
My Freeby does have a FBH installed, easily identified by the exhaust pipe poking out of the front near side (UK) bumper, but through the winter it didn't work. I didn't feel like laying in a cold wet gutter trying to fix it so now we are moving to spring and warmer temperature I decided to get busy.
Firstly, a brief explanation on how the FBH should work.
There is a temperature switch mounted behind the lower front grille, normally open at temperatures above 5 centigrade and closed below that. One side of this switch has 12v supplied to it when the engine is running (from the Freelanders instrument wiring), and when closed this 12v represents a "go" command to the FBH.
Once the go command is received, the FBH starts its ignition checks and if all is well starts pulsing the fuel dosing pump which is located in the rear offside (UK) wheel arch. To clear some confusion, this pump doesn't run continually, rather it pulses every second or so providing a small squirt of fuel. Easily checked if working as it will make a clicking sound.
With regard to the ignition checks, as it runs on diesel there is a glow pin within the FBH, apparently a good one should read 0.4 ohms when cold, and when the FBH is lit and running the same glow pin is then used for flame detection, when it should read around 0.8 ohms. Not a lot of difference but it makes a world of difference to the operation.
The FBH also checks operation of the water pump, but I haven't had to check that yet so haven't got the info.
On my particular FBH, I removed the temperature switch to check and found it to work when placed in the freezer, but mine has a black plastic body. There is a revised one with a green plastic body that works over a wider temperature range, so that will be what I put back in. I checked I was getting 12v to the switch so I know the car is sending the go command.
Shorting across the connectors made the FBH spin up its combustion fan, and then it ran for just over 4 minutes before stopping. This means there is something wrong with fuel or ignition.
So a quick look under the rear wheel arch and I found a lump of rust that was supposed to be the dosing pump.
At the same time there was a used one for sale on eBay so I sniped that at the last minute. Once arrived I checked its operation with a cordless drill battery and it did indeed work, so I applied a coat of hammerrite to help protect it from the tin work. Yellow paint because it looks jaunty (ok, it was all I had).
Testing on the car and the FBH still didn't work, according to some research if it fails to fire after 4 minutes 5 seconds (as mine), it indicates a glow pin fault.
So bumper off again and checking the glow pin resistance I found I had 0.6 - 0.7 ohms when cold. This is out of spec so it won't start the ignition process.
There was a "fix" posted online where a 5w lamp was wired in parrallel with the glow pin. Apparently this helps bring the resistances back in spec and also provides a visual indication that the glow pin is working.
I tried this but it did not help, still locking out after 4 minutes 5 seconds.
So looks like I need a new combustion unit, these cost approx £160 so for now, because of the rising ambient temperatures, my FBH repairing is on the back burner (ho, ho). I'll still check over it now and then if I find new info, but I have better things to spend the money on for the summer (like getting the air con working).
Come August I'll return with some aplomb.
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