Brake Pedal Switch

[AMacdonald]

My '97 Alhambra TDi (211,000 and counting!) has an odd problem. Cold starting and running is fine but if I restart when the engine is hot I get several miles of intermittent power loss. After those miles the engine runs fine until the next warm start. The effect is very like the fuel cutoff you get when pressing the accelerator and brake together so I thought it might be related to the brake pedal switch. I had a new black, 2 pin switch in the garage so I fitted it (to no avail) but while I was in there I spotted another, very similar switch mounted just above the black brake pedal switch, in light blue. Would I be right in thinking this switch is related to the accelerator / brake fuel cutoff function? If so, I'll get one and try that.

 

Not sure why the effect only happens for a few miles after a warm start though.

[jccd]

I think the other switch may be to deactivate the criuse control when the brake pedal is depressed, but I'm not 100% sure of that. Can a more experienced member please confirm?

 

Cheers JCCD

[AMacdonald]

Thanks JCCD.

Would the switch exist if the car didn't have cruise? It's a mk1 Alhambra SE TDi.

[seatkid]

The Tdi has 2 switches both wired to the ECU for failsafe operation. One also switches the brake lights. The ecu will trip the cruise control (if fitted) whenever the brake (or clutch) is operated. IIRC If one switch fails, then usually the coil light will start to flash.

 

Check to see if you have any air bubbles in the clear fuel pipe feeding the injection distributor pump when the engine is hot (you will have to remove the engine cover to see this). Usually related to the fuel filter and connections.

 

Other problems may be related to the accelerator pedal - but if that has a (brief) fault, you lose the accelerator function until you turn off and restart.

 

Another possibility is a failing MAF sensor.

Edited July 6, 2010 by seatkid

[AMacdonald]

Thanks seatkid. I think I've always had bubbles in the fuel line but there don't seem to be any more than usual. I've got a spare (used but it turned out not to be faulty last time I had a problem) MAF I'll stick on as well although it doesn't feel like any MAF problem I've ever had and I've had a few (one in a foreign country - THAT was a garage conversation worth hearing). I think I'll take the blue switch off and attack it with WD40 as well.

[seatkid]

Thanks seatkid. I think I've always had bubbles in the fuel line but there don't seem to be any more than usual.

Check the underside of the fuel filter when hot/stood. If it is wet with diesel, the tap may be leaking. I had this, eventually the plastic tap broke off (!!!) and the fuel filter emptied itself and car ground to a halt. I changed the filter and those air bubbles I always had disappeared and I no longer get the odd mysterious missed beats on hard acceleration (which were due to the air)

[AMacdonald]

Fixed it. I forgot the three golden rules of Galaxy TDi fault-finding:

 

1. It's the MAF.

2. Seriously, the vacuum pipes are OK so it must be the MAF.

3. Yes, you only recently replaced the MAF but it's still the MAF.

 

It was the MAF