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  #1  
Old 11-14-2008, 05:39 PM
Lebc888's Avatar
W126 fan
 
Join Date: May 2008
Location: North west Quebec
Posts: 40
Unhappy 420 sel 87 wont start...need help

Hi,

(english is not my first language, please forgive the spelling!)

Few weeks ago, I had the engine of my 420 replaced with a used engine comming from another car.

I took possession of the car at the shop, drove 600 mi and everything was fine for a few days. Then, the car would not start anymore. By spraying gas in the carburator, I establishedd that the problem was that no gas was comming to the carburator.

I replaced (took it in my 560) the fuel pump relay(2)...no start, the Idle relay...no start. At one point, we "pushed" the car inside a garage with a lift. The car started right away (why??). I left with the car and drove 0.5 mile and then...it stoped. Once towed to the garage, we determined that one of the fuel pump was making a funny noise so we replaced it (good chance I have a parts car!). The car started right away and once aoutside, it stoped again. It did not start since.

What should I be looking for next? The snow is comming and I need that car running.

Help...!

Christian
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  #2  
Old 11-15-2008, 10:16 AM
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The problem is that you don't want to just "throw parts at it" until you find the cause (as we say here in the States).

Maybe you have an intermittent crankshaft ignition sensor, but I sort of doubt it. I think their usual failure mode is to go completely dead forever.

If it really is a fuel delivery problem, I think what a mechanic would do is to crack some fuel lines before and after the fuel distributor to see if fuel is getting there, but I don't recommend that you do this yourself unless you really know what you are doing. Maybe you have a bad fuel distributor, but you don't want to replace it unless you are sure it is bad because it is very expensive.
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  #3  
Old 11-15-2008, 04:00 PM
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See if the pump is running while the starter is cranking - you can place your hand on it and feel if it vibrates while a helper cranks the starter.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #4  
Old 11-15-2008, 09:57 PM
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Join Date: May 2008
Location: North west Quebec
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thank you guys for your answers.

Your right, I dont live in the States. But I love my canadian MB and I would be gratefull for any help anyone can give me to put back my very nice car on the road.

From the beginning, I know that it is, at the end, a fuel delivery problem meaning that the engine dont start because there is no gas comming to the carburator. Having a 560 SEC and a 420 parts car, I tried different things, but the problem is still there. When the gas is not comming to the engine, the fuel pump are not working. It look like they dont receive any electricity. When they do, the engine start.

I dont think it is the fuel pump relays because I replaced them using the one of my other working car but it didn't change a thing.

I'm not a mecanic, but I assume that the problem is comming from someting "electrical", a sensor, a switch, a relay...anything that is sending electrical current to the pumps...

Retroguybilly is mentionning "fuel distributor". I will have a look into that.

Any other suggestion will be welcome. I dont have acces to a good MB mecanic, so I am on my own on this.

Bests regards

Chris
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  #5  
Old 11-15-2008, 11:22 PM
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Ignition switch? Good Luck.
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  #6  
Old 11-16-2008, 12:26 AM
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Chris, You should read this thread. MB's are quite complex and there are several things to check. This might help:
300SE W126 Will not start
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  #7  
Old 11-16-2008, 07:18 AM
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Do the most basic test - find out if the pump runs when cranking the starter.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #8  
Old 11-16-2008, 10:50 AM
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pull up a wiring diagram of the starting circuit and figure out what should be getting 12 volts, what is a load. Also check your connections and circuitry.
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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)
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  #9  
Old 11-16-2008, 05:34 PM
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Red face thanks everyone for the suggestions

thanks everyone, I now have a "to do list" for the rest of the week!!


I'll keep you posted...Thanks again

Chris
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  #10  
Old 11-18-2008, 04:20 PM
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Join Date: May 2008
Location: North west Quebec
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Hi everyone,

Here's some additionnal information about my problem.

The source of the problem is electricity comming to the fuel pump and that problem is intermitent. The fuel pumps work fine since thet were tested individually (one was making a funny noise and was replaced by a spare I had)

When the car dont start (like right now), the pumps dont receive electricity.

For an onknown reason, mouving the car (pushing it into the garrage) made it start and on seperates 2 occasions, the fuel pump were obviously working properly...until the car decided not to start anymore (no electricity arriving to the fuel pumps)

Today, I tried replacing the "OVP relay" but the car still didn't start.

Does anyone know where I could find a "starting circuit wiring diagram"?

Thanks again

Chris
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  #11  
Old 11-18-2008, 04:45 PM
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w126 service disc or I can send you it
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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)
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  #12  
Old 11-18-2008, 05:01 PM
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You can also get an alldatadiy.com subscription.

Try a quick check, though.

Pull the FP relay out, and look at the wiring diagram, and identify the plugs on the relay's socket.

Take a piece of wire and bridge 30 to 87. The pump should run. If not, you need to check for 12v on 30 and continuity from 87 to the pump, plus check that the pump has ground.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #13  
Old 11-18-2008, 05:35 PM
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attached is a scan of the start diagram. I have labeled where 12 volts should be, what is a load and I have circled what should be checked. Also check the entire circuitry for conitinuity, opens. Check for voltage drops across wires as well

check connector x4/10

Red=switches to be checked

blue= a load or source voltage

Orange=relays

green=circuitry, everything in green should be recieving 12 volts or have .3 ohms of resistance or less.

http://img237.imageshack.us/my.php?image=startbm1.jpg

larger verison
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1986 300SDL, 211K,Dealership serviced its whole life
1991 190E 2.6(120k)
1983 300D(300k)
1977 300D(211k)

Last edited by Oracle12345; 09-02-2009 at 12:42 PM.
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  #14  
Old 11-18-2008, 07:17 PM
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Location: east Tennessee (southeast USA)
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Quote:
Originally Posted by Lebc888 View Post
Hi,

By spraying gas in the carburator, I establishedd that the problem was that no gas was comming to the carburator.

Carburator? What year of engine did you put back in the car? If it was another V8 out of a Mercedes, it sould be fuel injected, unless.... are you referring to the throttle body?
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  #15  
Old 11-18-2008, 09:13 PM
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W126 fan
 
Join Date: May 2008
Location: North west Quebec
Posts: 40
Hi everyone,

This forum is an extraordinary source of knowledge for me and I am Thankfull to everyone for that.

86560SEL: You are absolutly right, there is no carburator in there. The engine is identical to the one that was remouved (87 420 SEL) and we did spray the gas into the "throttle body". Your comment show how much I need your help!!

oracle 12345 and ctaylor738: thank you for the precious information. This will be very helpfull. I feel (or hope!?!) that we will find the problem soon.

I'll keep you posted

Bests regards

Chris
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