Help - Diagnose No Fuel - D-Jet 1973 450SL - Mercedes-Benz Forum
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#1 (permalink) Old 07-25-2010, 03:23 PM
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Help - Diagnose No Fuel - D-Jet 1973 450SL

I've tried to search for a thread like this, but haven't found one. Now I'm planning on doing this a second time, towing my car from a mechanic that won't work on the car. This time the car won't start. I drove it to the shop running, and now it seems to get no fuel. I thought it had no spark until the shop guys showed me what gumout in the air intake does. It definitely sparks. Since I'm going to have some time while waiting for AAA, I'd like to spend it usefully trying to diagnose teh fuel problem I seem to have. I fugure I should start at the tank, and move forward. I don't even know all the components on my 450SL, and conveniently left the haynes manual in the trunk of the car. All I've done so far is swap relays per Rowdie's recommendation.

1) Gas in the tank - I assume I've got it because I'm on the mark above the R, and the idiot light is not on. I'm still planning on bringing a can of gas anyway. Just thought if this one - I had over a half tank whne I filled up, and I think I remember a "phsst" when I last put in gas... could my tank my under big vacuum... add heat making my fuel pump work extra hard?

2) Fuel pump: Can I verify this is working by just disconnecting the hose, and checking to see if it spews some gas on the gound when I turn the key?

3) That vibration thing back there connected to the view pump. Could that be a problem worth investigating?

4) Fuel line to the front of the car. Is this next? Where's a good spot to check for fuel flow (if I make it past checking the previous items)?

5) Do I have a fuel accumulator on the d-Jet? (don't think so, right?)

6) Fuel ring/manifold thing. This seems easy to check. I assume I can disconnect one of the hoses to see if gas is getting to the top of the injectors.


I'm making the assumption that the fuel pump could be the culprit right now, but really have no clue.

So with limited time, are there easy check points to diagnose the different parts of the fuel system?

Here's a list of items that German Star appears to have for my 1973 10704412007016. Are all of these easy to check?

A) Cold Start Injector | 0000713437 | All to 1975 | $239.00
B) EFI Control Unit | 0005452632 R | All to 1975 | $645.00
C) Fuel Distributor | 0000740313 | All to 1979 | $465.00 - Where is this?
D) Fuel Filter | 0000927601 | All to 1975 | $19.00
E) Manifold Pressure Sensor | 0025422817 R | All 450SL to 021762 | $295.00
F) Fuel Pump | 0010917101 R | All to 1975 | $329.00
G) Fuel Pump Relay - German Star shows only parts for 380 and 560 SL? Huh?
H) Fuel Sending Unit - German Star shows only 450SL from 034421. Does this mean my 10704412007016 has none?
I) Injection Nozzle | 0000783423 R | All to 1975 | Fuel Injector $62.00
Warm-Up Regulator - German star makes it look like the don't offer one for before 1976. Do I not have one?


Next, I have to decide where to have the car towed. MB Dealer? Or my friend of family who didn't really want to work on it in the first place? Or my garage to do it the cheapy way, which also seems like the most handy. I like learning about the car, and it seems to keep me from running back and forth to shops that don't want to work on the car.
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#2 (permalink) Old 07-25-2010, 05:36 PM
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As first quick check, disconnect the hose leaving the fuel pressure regulator, and run a longer piece of hose into gas can. Turn the ignition on & off a few times without starting the engine - you should get a good flow of gas into the can .

To check the flow, you need to jumper the fuel pump relay and then let pump run for 30sec. You should get 1 litre of gas.

If you push a piece of clean hose down into the fuel tank through the filler, it should back out wet if there is gas in the tank.

You should be able to hear the pump run when you turn the key. If not, first check the fuel pump fuse. If that is good, try swapping the relay.
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#3 (permalink) Old 07-25-2010, 08:57 PM
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MBGraham:
I was looking for a picture of the Fuel Pressure Regulator, and realized that German Star doesn't have one listed for our cars, just 380s and 560s. Is the fuel pressure regulator something that GermanStar simply doesn't have on their web page for our cars? Or might it be named something else for our years?

Sorry to be such a noob. AND THANK YOU FOR YOUR HELP!
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#4 (permalink) Old 07-25-2010, 09:47 PM
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Yes you have a Fuel pressure regulator and it is not the problem.
I am quite a bit older than you and I can hear the fuel pump come on.
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#5 (permalink) Old 07-25-2010, 09:59 PM
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Originally Posted by rowdie View Post
Yes you have a Fuel pressure regulator and it is not the problem.
I am quite a bit older than you and I can hear the fuel pump come on.
Sounds like I should make sure I'm getting power to the fuel pump and then buy a new one. Anyone have one for less than $329? :-)
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#6 (permalink) Old 07-25-2010, 10:00 PM
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C) Fuel Distributor | 0000740313 | All to 1979 | $465.00 - Where is this?
H) Fuel Sending Unit - German Star shows only 450SL from 034421. Does this mean my 10704412007016 has none?

Warm-Up Regulator - German star makes it look like the don't offer one for before 1976. Do I not have one?


.
C) No fuel distributor on D-Jet
H) this has nothing to do with fuel delivery

You don't have a WUR

Have you checked your trigger points? If your trigger points aren't working your injectors won't open.

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#7 (permalink) Old 07-25-2010, 10:06 PM
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Originally Posted by Fotografa View Post
C) No fuel distributor on D-Jet
H) this has nothing to do with fuel delivery

You don't have a WUR

Have you checked your trigger points? If your trigger points aren't working your injectors won't open.
Thanks for verifying. I didn't think my d-jet had a fuel distributor. I guess I shouldn't rely on German Star's price list to teach me about my car. :-)
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#8 (permalink) Old 07-25-2010, 10:18 PM
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Originally Posted by Fotografa View Post
You don't have a WUR

Have you checked your trigger points? If your trigger points aren't working your injectors won't open.
Checking Points:
I thought everyting under the distributor looked OK when I pulled off the rotor and that cover that goes around it. That's as far as I got into the points though. The car was running when I brought it in, so I was assuming the points were probably OK. I think the emissions get a little sloppier after warming up, but I figured that's well beyond my basic starting issue now. The starting issue seemed a little intermittent. First week I owned the car there were two instances that it took 5 tries to start the car. Then after sitting for about two weeks in the garage, I probably tried a dozen times, opened the air filter, tried, put it back, tried and it started. That's when I decided I should start the car regularly to keep it running. Then I had it just in front of the garage a few days ago (while putting some stuff in garage attic), and the car would not start. I started mucking around, pulling distributor cap and rotor off, scratching them with sandpaper to no avail. Then I just tried it maybe 15 or 30 minutes later and it started right up. It seemed to be starting reliably, but I knew I should get someone to look at it. So while picking up my wife's Jeep from getting a new radiator, I figured it would be easy to swap cars at the shop, not needing a ride from my wife. I even showed the guys at the shop how I think the distributor needs to be replaced, and I felt it wasn't getting a spark. I was pretty confident in my simply diagnosis... until they shot gumout in the air intake and the engine sparked.

I'm guessing that this is the type of intermittent failure you could see in a fuel pump. Maybe?


BTW: What is a WUR?

Last edited by Fonzi; 07-25-2010 at 10:19 PM. Reason: What is a WUR?
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#9 (permalink) Old 07-25-2010, 10:36 PM
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I'm referring to the trigger points, for the EFI, not the ignition points. They are also in the bottom of the distributor, but not accessed by removing the dist cap. As the dist spins they are triggered to open the fuel injectors.

WUR = warm up regulator.

Still, like other's have said, best first thing to check is that your fuel pump is pumping.

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#10 (permalink) Old 07-26-2010, 07:04 AM
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Quote:

I'm guessing that this is the type of intermittent failure you could see in a fuel pump. Maybe?


BTW: What is a WUR?
Don't go throwing parts at it. New D-Jet fuel pumps cost more like $800. The one you have seen is possibly a rebuilt.

You need to either learn all about the Bosch D-Jet ignition and fuel injection system, OR try and find an independent that knows how to work on the Bosch D-Jetronic engines. (Early VW, Porsche, Volvo, Jaguar and others used similar system).

The engine for the '73 450SEL in this link is same as yours - sections 7.4 and 7.5 cover injection and ignition. There is a section on diagnosis including trigger points, except they call them "release contacts" (Section 07.4 040-10 for M117 engine using standard voltmeter). The attached pdf calls them "sending contacts" ??

For general info, this link may help, and I have also attached a troubleshooting pdf.

It could be that you may just have a loose connection to the trigger points or even a bad ground for the injectors on the top rear of the engine under the air cleaner.

Try to check everything systematically, starting with fuel pump (you can hear it run when you first turn key on, but only for a few seconds, then it cuts off until engine is started). As mentioned before, if you hear nothing, check the fuse first!
Attached Files
File Type: pdf Troubleshooting.pdf (147.8 KB, 205 views)

Last edited by MBGraham; 07-26-2010 at 08:27 AM.
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