W126 500 SEL starting problems.

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neilrr

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Someone I know who is getting a 500 SEL back on the road has run into an issue with the car starting. Below is the email he sent me. I do not think it's EZL related. IME they either work or they don't work.

Anybody come across this before?

Whilst the re-commissioning work has been on going the EZL has been showing signs so of failure unfortunately. Failing to start the car anymore than once over the course of a couple of hours. and despite another new coil pack and then also an NSS to cure it not starting in park, another symptom it developed. My mechanic and I have concluded the EZL is definitely on its way out.
 
An update.

I actually just had a play with it and did several starts in a row and it seemed to gradually find it more difficult especially after having run for a while. It’s almost like it finds it harder the hotter the engine temp.

Having also just done some research I am going to double check the spark plugs and then perhaps a new air valve sensor and fuel accumulator. Although I did just have all pumps and filters changed.
 
I hope that his mechanic is better at diagnosing problems than he is. They should both go back to basics.
 
Another thing that can cause all sorts of gremlins on cars of that vintage is the OVP relay - an easy swap if you have a spare one handy to try . Fuel pump relays can cause intermittent problems too .

As Al says - basics : plugs , leads , dizzy cap , proper fuel delivery & check for vacuum hoses off or other leaks on the induction side .

Fuel accumulator might cause loss of fuel pressure over time when
Standing but in itself shouldn’t prevent immediate restarting, and after standing for a while car should still start once fuel pumps pump fuel up . Fuel delivery/pressure can be checked ( with cold engine ) by loosening pipe from fuel distributor and getting assistant to momentarily turn on ignition ( with something to catch fuel in ) .
 
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I've recently had an issue with my 420 SEC, which was very reluctant to start, especially when cold. A new fuel pump relay cured it. £17.50 from eBay, with a two year warranty, or £80+ from M-B.

By the way, I would recommend changing the vacuum hoses. The full set is still available from M-B for about £100. Changing the injector seals will be beneficial as well. I recently did both jobs and the idle and performance were much improved.
 

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