C250TD won't start after alarm went off

[mercedesnut]

Hi, I hope some of you techies can help. I purchased a 1997 W202 (facelift model) C250TD estate 2 days ago and drove it home and parked it at night. Locked it using key fob (ithe type with a large traingular shaped fob with 2 buttons and built-in skeleton metal key. The metal key is only for manually operating the door locks). It was freezing cold (-4.5 deg C) and the alarm went off an hour later. Went out and using the key fob unset the alarm and then locked the car manually (by depressing the lock knob on each door) and using the metal key, locked the driver door. Yesterday morning, unlocked the car using the key fob and tried to start the car, but it won't start. All the ignition lights come on and the starter motor cranks the engine but it won't fire, suggesting that perhaps the immobiliser hasn't disengaged completely and has shut off the fuel supply. Have tried locking and unlocking the car using the key fob several times, but it still won't fire up. The battery may need charging up soon if I continue and so in desperation, I'm hoping that someone can advise. The MB Assist team have offered to help if I pay £184 +Vat for a callout seeing that the car is 10 yrs old! B0110cks to that. The stealer service team couldn't spare a competent engineer who could advise. The incompetent one knew even less than me which is saying something! Can anyone advise please (I'm about to go an get new batteries for the key fob just in case but my guess is that if they were the problem, the ignition wouldn't switch on and the starter motor wouldn't crank the engine, but these are desperate times requiring desperate measures and so I will try most things that don't cost an arm and a leg).

 

[uprightbrian]

Had this happen to my C class estate several years back. After two days of wasted effort a friend solved it. the problem was the fuse for the tail gate wiper which is also the fuse for the immobilizer. Sounds daft I know but it cured the problem.
Hope this helps.
Brian

 

[type49]

Sounds more like a fuel problem than alarm but check all fuses anyway. I think the alarm ones are in the boot. There may also be some under bonnet NS under a cover held on with 4 screws.

 

[mercedesnut]

Have just checked and the rear wiper works OK suggesting that there fuse is also OK. Will check other fuses soon.

 

[mercedesnut]

Finally resolved the problem to a fuel delivery issue. We have a steep drive up to the garage (about 20 inch rise over a distance of 16 ft) and the car was parked facing uphill. It turns out that some (only some) of these C250TDs suffer from fuel running back into the tank resulting in an air lock, hence the starting problem. Rolled the car down and the AA man purged the air from the system and hey presto, 1st crank and it started. He suggested fitting a non return valve in the feed from the tank to the fuel pump (not the return pipe) or cheaper still, don't park the car facing uphill.

 

[television]

This means that you have an air leak in the system, and it could be on the return to tank or around the filter

 

[dieselman]

Fit new clear plastic pipes leading to and from the filter-head. Common fault.
You will probably be able to see the one leaking if you rev the engine hard from idle whilst watching for bubbles in the pipes.

 

[mercedesnut]

Hi Television.
Thanks for the info. Excuse me being dense, but what's the remedy for this? I suppose that the obvious answer would be to locate and fix the air leak (easier said than done I suppose), so should I look at replacing the fuel pipes? Would fitting a non-return valve in the feed pipe from the tank to the fuel filter resolve this or should I do consider this as well as resolve the air leak you mention?

 

[mercedesnut]

Fit new clear plastic pipes leading to and from the filter-head. Common fault.
You will probably be able to see the one leaking if you rev the engine hard from idle whilst watching for bubbles in the pipes.

Hi Dieselman - Thanks for the advice. BTW, is that from the tank upto the filter and back? How big a job is it and are the pipes easy to get at around the tank? I'm not sure whether the original pipes are metal or plastic but I take it that they run under the car to the front and into the engine bay. Regards.