Help - stalling 420SEL

1979-1991 280SE, 300SE, 300SEL, 380SE, 380SEL, 380SEC, 420SE, 420SEL, 420SEC, 500SE, 500SEL, 500SEC, 560SEL, 560SEC
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Beamer
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Joined: Fri 14 Dec, 2012 2:59 pm
Model you own: w126
Location: Adelaide

Help - stalling 420SEL

Post by Beamer » Fri 11 Aug, 2017 9:08 pm

After more than 2 years of completely trouble free driving, my 420SEL has decided to develop its first issue - while 600kms from home and with 1,500+ kms to be done over the next week.

The car has started to stall with no warning. There is no spluttering - it just dies immediately (feeling more electrical than fuel related). It has only happened so far when the car is warm. On several warm starts today, it would take 4 or 5 tries to start the car - it will start, but die immediately. It has also stalled half a dozen times while driving - a few times while coming to a stop at an intersection, and also a few times at 110kmh on the open road (in which case it catches again straight away and continues on its after a bit of a hiccough).

Not being at home, nor near a good service/parts centre for a few days, my options are a bit limited.

I have done a bit of googling - am I right to suspect the fuel pump relay? I could probably get one sent to my hotel and exchange it in the next few days, but I'm reluctant to spend the money on a new relay if there is nothing wrong with it. Are there other possible suspects such that this might just be a waste of money?

(The OVP relay is only 18 months old so that shouldn't be the problem.)

Thanks in advance for any help.


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Chris
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Today: 1988 W126 420SEL
Yesterday: 1976 C107 450SLC

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MercMad West Australian
450 SEL 6.9
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Joined: Sun 08 Dec, 2013 2:23 pm
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Location: Perth

Re: Help - stalling 420SEL

Post by MercMad West Australian » Sat 12 Aug, 2017 12:39 am

sounds exactly like a failing fuel pump relay.

could also be a failing crank position sensor too which are notorious for mis-behaving once hot, or any number of ignition related problems. But keep it simple and check the basics first, better to get it checked out than attempt a shotgun approach. Theres always old school merc specialists around.


The engine will run in failsafe old school K-jet mode when the OVP fails / engine KE-jet ecu fails or not even present. In many cases on o2 sensor cars it will actually pull harder too, so it's not going to be that.
MMWA

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Beamer
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Posts: 92
Joined: Fri 14 Dec, 2012 2:59 pm
Model you own: w126
Location: Adelaide

Re: Help - stalling 420SEL

Post by Beamer » Sat 12 Aug, 2017 8:18 pm

Thanks MercMad. The car has been fine today (but covered many fewer kms), so we will press on (another 600kms to do tomorrow) until I can find someone to take a look at it.

Does anyone have any suggestions for a Merc specialist in the Lakes Entrance area?
Chris
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Today: 1988 W126 420SEL
Yesterday: 1976 C107 450SLC

User avatar
Beamer
S Class
Posts: 92
Joined: Fri 14 Dec, 2012 2:59 pm
Model you own: w126
Location: Adelaide

Re: Help - stalling 420SEL

Post by Beamer » Tue 21 Nov, 2017 11:15 pm

To close out this thread, and for anyone else with a similar issue, the stalling issues continued for a bit longer and the car did cut out at one stage on the highway at 110kmh and wouldn’t restart (still a few hundred kms from home). A bit of jiggling of the fuel pump relay in its socket on the side of the road got us going again and all the way home.

My mechanic was not hopeful of being able to diagnose the precise problem so I went ahead and installed a new few fuel pump relay from the forum sponsor. That was a couple of months ago now and I’ve had no problems since!
Chris
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Today: 1988 W126 420SEL
Yesterday: 1976 C107 450SLC

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carina
Maybach
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Joined: Wed 10 Nov, 2010 8:47 pm
Model you own: w126
Location: Tapitallee

Re: Help - stalling 420SEL

Post by carina » Sat 02 Dec, 2017 3:11 pm

It cool how your 420 stays on the roof.......
1991 420se . "Flosshilde".
1982 500SEC "Goldie" .Soon to be Black.
1955 220a Ponton, 'Polly' still getting over the fact I now have a Merc that is 3 years younger than me.

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