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Old 01-14-2007, 03:51 PM
Registered User
Join Date: May 2006
Location: West Paducah, KY
Posts: 44
420SEL No Start - Sometimes

I bought a 89 420SEL at a salvage yard that looked like it had a future and drove it home. When it starts , it hits immeidately and runs fine. When it won't, it does not hit at all. I put in new plugs and monitor the fire with a timing light when cranking and it is triggering the light. I do not know alot about the fuel pump circuit. When it runs the fuel pumps hum. When it does not, they come on momentarily. Do they shut down when pressure is built? I jumped the relay 30 and 87 and the fuel pumps ran. Still no start, Smelled gas. When it starts, it starts for days. When it does not, it will then start on a random day. Flooding? Any ideas? Thanks, Al

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Old 01-14-2007, 06:58 PM
Registered User
Join Date: Nov 2004
Location: North central Texas
Posts: 2,588
One of the two pumps may be bad. If you have a amp meter you can measure the current of each pump.
If not, use some series resistance (resistor, length of thin wire...) in each pump's brown lead and measure the voltage drop across it. Compare the two.
It WILL run with just one pump if the bad one is not inline.
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Old 01-15-2007, 04:54 PM
just-n-time's Avatar
Registered User
Join Date: Feb 2006
Location: Louisiana266 Maloy Rd winnfield71483
Posts: 804
Cool NO start problem

Sounds like you maybe having trouble with the position sensor found at the fly wheel upper left looking up from bottom hard to get out, perhaps some one can tell you if there is a test to check it I just changed mine not to long
ago.I have a 90 mod 420sel.look up some of my post on how I changed the unit,it fixed my no start problem and after much reserch and checking other electrical components it is doing very well. j-n-t
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Old 01-15-2007, 06:00 PM
Registered User
Join Date: Aug 2006
Posts: 141
No Start

During your next no start condition unplug the coil wire from the dist cap and insert a sparkplug into the wire,Have someone crank the car while you watch the plug for spark. (If no spark check crank sensor and EZL and coil)
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Old 01-16-2007, 10:28 AM
david s poole
Join Date: Mar 2005
Location: dallas
Posts: 1,822
just replace the sensor,if it's not bad today it WILL be bad tomorrow or next week.

David S Poole
European Performance
Dallas, TX

"Fortune favors the prepared mind"
1987 Mercedes Benz 420SEL
1988 Mercedes Benz 300TE (With new evaporator)
2000 Mercedes Benz C280
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