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  #1  
Old 08-04-2007, 09:04 PM
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1975 Mercedes 450 SLC, Model 107 – No Start

My wife has a 1975 450 SLC, Model 107 VIN: 107 024 12 009837 and it will not start. It always started fairly easily until recently. We took it out for a drive and as we returned it started acting as if it was out of gas and I barely got it in the drive way. I put in 5 gallons from a can & it would not start. I let it sit for a couple of weeks and tried again and it started, sounding as if it was “flooded”, smoking etc. – I removed the air cleaner and was checking to see if I could see if something was wrong and it started running fine. So I drove it around the block about 10 – 12 times and finally drove it to a service station and filled it with gas. About 3 miles one-way. It started fine and I drove back to our home, on arrival it started smoking and sounding like it was “flooding” out – again I barely made it in the drive way. I then had it towed to a Mercedes repair place (or so they claimed) and they said they could not find out what was wrong ($200 bucks and at this point it would start but really ran very rugged – smoking etc). I had it towed to a second shop (again a so called Mercedes shop) and they said they couldn’t fix it for less then several thousand dollars! At which point I had it towed back to my driveway. Now it will not start at all. Has plenty of spark at the plugs. I pulled the plugs and they are dry - not wet from gas. I do know my way around cars but I have never worked on a Mercedes and I do not have a manual. Can anyone start me down a path to troubleshoot this thing?

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  #2  
Old 08-04-2007, 10:12 PM
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First check the fuel presssure.

Then check it has not jumped time, cams or ignition.
Pull the valve covers and roll the engine over and check the notch/vee on the front cam towers against the TDC mark on the crank pulley ( O/D )

BTW Welcome to the forum...and, are you in the Witness Protection System, like a lot of others here ?.

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  #3  
Old 08-05-2007, 07:53 AM
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If this is a 1975 model, it should have D-Jet injection, which is not exactly my strong suit. But your problems suggest either a fuel pump or fuel pump relay as the cause of your no-start.

The pump is back by the RR wheel. Have someone crank the engine and put your hand on the pump to see if it's running. Assuming it is not, make sure it has a good ground. Then pull the fuel pump relay out and jump pins 30 and 87 with a piece of wire. If the pump comes on, replace the relay. If it doesn't, replace the pump. You can also do this test by running 12V directly to the + side of the pump.

If the pump is working, then you're off my map. I think the next test is to turn the ignition on, open the throttle, and listen for the injectors to click. If they don't, then I think you look at trigger points in the distributor.

Beyond that, do a search on D-Jet and you will find lots of posts on how the system operates, and troubleshooting.

Good luck
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Chuck Taylor
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'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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Old 08-05-2007, 09:15 AM
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The manual is easy, call 1-800-for-merc on Monday. The CD should set you back about 30$.

Between now and then, if you're handy with a multimeter and have a fuel pressure guage that can read 32psi, notes in dozen other threads here at mercedesshop should give you a good idea of what's up.

Yours is an M117 4.5l cast-iron v8 that has a transistorized ignition system (hopefully) and a D-jet (d-jetronic) fuel injection system. That should be enough keywords to help you get by.

To expand on DK's comments, to hand crank the motor to check the cam/crank alignment, you need a 27mm socket, a small extension rod (like 3") and a long breaker bar. But like he said, hold off on that until you check the more easy things, like fuel pressure and basic ignition timing.

-CTH
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Old 08-05-2007, 10:36 AM
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Thank you for such a speedy response - I can now get started. I’ll let you know how it turns out.
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  #6  
Old 08-05-2007, 11:23 AM
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It will help if you google D-Jet and get a basic idea of major components and how the system works. Whatever you do, resist the temptation to start adjusting the mixture at the control unit!
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Chuck Taylor
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'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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  #7  
Old 08-05-2007, 12:31 PM
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Update: I checked the timing with a timing light and it is fine. The fuel pump feels like it is working & I can hear each of the injectors clicking (using a long screwdriver as a stethoscope) when the engine is cranked. I am now off to purchase a gage to check the pressure on the rack. I also intend to pick up a new fuel filter just in case that may be the problem. Thanks for the input.
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  #8  
Old 08-05-2007, 04:29 PM
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It's sparking and you hear the injectors ticking but that doesn't mean they're delivering fuel. If your fuel pressure regulator isn't holding the pressure in the rails, the fuel is just running from the pump to the tank. There are so many things that can be the cause, you need to find out:

1) Is there pressure in the fuel rails?
2) Is fuel coming out of the injectors when they open?
3) Are you SURE you aren't flooded? The D-Jet system can very quickly flood an engine that isn't starting. If your plugs are dry and you've been cranking it a while, then you do without a doubt have a fuel delivery problem.
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  #9  
Old 08-06-2007, 01:48 PM
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Update: Purchased a fuel pressure test kit and installed it in the middle of the rack (a hose connection to what I believe might be the cold start injector – no fuel rail diagram and no actual test point that I could find). The following events take place.
  • Turn the key on, fuel pump starts, and the pressure goes to 32 psi. Pump stops and pressure drops back to 0 psi in +/- 4 seconds.
  • Crank the engine and the pump keeps pressure at 32 psi. Stop cranking and the psi drops back to 0 psi in +/- 4 seconds.
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  #10  
Old 08-06-2007, 05:20 PM
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Another Update: I have pulled the injectors (Still attached to the rack), put newspaper under each side and turned the ignition on / off to cycle the fuel pump. Pressure goes right up to 32 psi and drops back to 0 psi within 3 seconds when the pump shuts off. However, the newspapers are dry under all the injectors – not a sign of gas! The CSI is not in the system at this point (gage hooked to that hose). So where else might I be loosing the pressure if it is suppose to stay a 32 psi? Will this keep it from starting? Or should I be looking elsewhere?
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  #11  
Old 08-06-2007, 07:06 PM
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Update 3 – OK, I tried cranking the engine with the fuel injectors still out and on the paper. Had 32-psi fuel pressure when cranking. After cranking for several times and for at least 30 seconds at a time – still no gas from fuel injectors – paper absolutely dry! I then put everything back together, pulled the distributor and check & cleaned the trigger points. Reinstalled, checked timing, tried to start – nothing. Do I now assume I need an ECU? Or what does anyone suggest (I already had a suggestion my wife didn’t care for).
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  #12  
Old 08-06-2007, 09:22 PM
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Well, as I said, if you were getting gas out of them you'd be flooded after all this cranking, but since you're not getting gas:
You said you heard the injectors clicking. This sounds like they're opening, but all plugged up. Yes, all can plug up; and it's possible whatever is plugging them is causing your regulator to malfunction (see addendum below). So your ECU isn't the issue. If you want to make sure an individual injector is getting power (just as a test), put an LED on the wire and crank; if it doesn't flash reverse it and try again. No pulse from the LED would indicate failure (maybe use an LED that also helps determine polarity, but brown is ground. I suggest an LED because you should be able to see that strobe, a bulb may not be as obvious). Pull an injector off, clean it out by squirting carb cleaner into the top and see what crud comes out. Soak them overnight in carb cleaner if need be. Test to see if it opens (WHEN IT IS DRY!) by giving it 12V, polarity doesn't matter; it should open.


Also: You definitely need a new regulator. Although you should be able to start... my fuel rails can hold the 30PSI required for a LONG time.
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  #13  
Old 08-10-2007, 12:14 PM
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Wrap-up: As it turns out there were two major problems with this vehicle. After pulling cleaning and checking each injector, the car still would not start. I then moved back to re-checking ignition spark to the plugs. I pulled the coil wire and distributor cap, fixed the coil wire at about ¼ inch from ground and cranked the engine. I found sparking only lasted about 3 seconds during cranking. I fixed this problem by replacing the ignition module with one from a junkyard 76 Mercedes. Even with a very strong spark the car still would not start. I then started tracing wiring to the major sensors – starting with MPS & TS2. Upon checking the MPS I found two wires open / broken. Upon repairing these wires, the car started on the first crank. Although I had to adjust the idle down, during a test-drive of the vehicle around town and the open road it ran fine. Thanks to all for help / suggestions offered.

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