1991 420SE starts and runs as long as starter is engaged??
 

Hi All,

I have got a 1991 420SE (W126) right hand drive that stalled after starting one morning and has been the same ever since,

It will fire up instantly (no misfires) and run perfectly as long as i keep the ignition in the start position, as soon as i let go of the key the engine dies straight away, if i restart it, it starts perfectly and runs but again dies if i release the key!!

It has been to a MB dealer 3 times, the AA have had a look at it twice and the ECU has been replaced, fuel pump relay replaced (and another relay i cant remembe the name of!!) so far and neither has helped at all,

The AA got it running by shorting the fuel pump relay out and it runs fine then, but this cant be a proper solution and might cause other problems,

Can anyone offer any suggestions as to what to check??, I am pretty mechanically and electrically minded and have access to a multimeter and oscilloscope if needed

Cheers

Your problem may be the ignition switch, i.e. it's not providing juice to the ignition in position '1'. You should be able to check that with a wiring diagram and a continuity tester.

Thanks Harry, I was just wondering about that!, any ideas where i might be able to get a wiring diagram from for the ignition?

Cheers

If you're going to be working on the car, you may want to get the shop manuals on CD-ROM. I don't know about the price in the UK. I believe it is about $140 here. Someone else on this list might be able to suggest another source for this information.

I've tried to find a source for the shop cd here in the UK but havent had an luck and really wanted to get this car up and running asap

I think i'll try and get it sorted tomorrow without the wiring diagrams

Cheers Anyway

A few years ago I worked on a car that did exactly the same thing! It turned out that a rodent had chewed through one of the wires to the EZL. It's been a while but I think it may have been the green wire to the TDC sensor? I'll have a look at a 420 as soon as I get to work on Monday to see if it jogs my memory. The funny part of the story is that two days after I repaired the wire the rodent ate through the same wire again!!! I could see where he nibbled at the shrink tubing I installed following the solder repair, but he must not have liked the taste, so he ate through it right next to the repaired section. Let me know what you find.

Thanks for that info, its all usefull to me for tomorrow when i really delve into it!, I will let you all know how i get on

you could look at the website-ebaymotors.com-you will find merc cd repair manuals -i bought one for my car 15 pounds(=21 us dollars).it arrived in 3 days after i ordered and paid for it on-line!:cool: