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Discussion Starter #1 (Edited)
My 74' 450sl started to rum rough, like it was running on four cylinders. I suspected the trigger points, so they were removed and cleaned. After installing the distributor, the car would not start.

The spark at the plugs Seamed weak, so I ended up changing all the components of the ignition system with new ones. The spark seams fine, but it still refuses to start.

There seams to be pressure in the fuel system after ignition is turned on at least for a few minutes. I have tried to remove the injectors and cranking the engine with the injectors out and there is no fuel coming from the injectors. I have also tried to attach a voltmeter and even a test lamp at the injectors and there is no electrical impulse at the injectors when cranking the engine. When connecting the + terminal directly to the injector, it activates the injector, and fuel is coming, so i guess it is not a problem with weak earth connection?
At the trigger points all four leads closes with the common lead - earth? for 180 deg. However they all connect and disconnect at the same time. I thought only 2 and 2 leads were supposed to connect simultaneously.
I've run out of ideas (and money). Even installed a new (used) Injection control unit.

So if you have any good ideas of how to make my Benz run again please HELP!
 

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2010 Mercury Milan Hybrid, 1993 BMW 325i convertible
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Fuel pump relay or fuel pump would be my guess.

OK, I guess I should go on the record as saying I didn't read all of the original post, then was surprised when people started talking about trigger points, went back and read all of it, and realized it would have nothing to do with the fuel pump.
 

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500SLC #2624. Black on Black.
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My 74' 450sl started to rum rough, like it was running on four cylinders. I suspected the trigger points, so they were removed and cleaned. After installing the distributor, the car would not start.

The spark at the plugs Seamed weak, so I ended up changing all the components of the ignition system with new ones. The spark seams fine, but it still refuses to start.

There seams to be pressure in the fuel system after ignition is turned on at least for a few minutes. I have tried to remove the injectors and cranking the engine with the injectors out and there is no fuel coming from the injectors. I have also tried to attach a voltmeter and even a test lamp at the injectors and there is no electrical impulse at the injectors when cranking the engine. When connecting the + terminal directly to the injector, it activates the injector, and fuel is coming, so i guess it is not a problem with weak earth connection?
At the trigger points all four leads closes with the common lead - earth? for 180 deg. However they all connect and disconnect at the same time. I thought only 2 and 2 leads were supposed to connect simultaneously.
I've run out of ideas (and money). Even installed a new (used) Injection control unit.

So if you have any good ideas of how to make my Benz run again please HELP!
Sounds like your trigger points to me. Have you tried swapping them for a known good set?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Sounds like your trigger points to me. Have you tried swapping them for a known good set?
It could be trigger points, but it could also be something else. It's hard to imagine all 4 sets of trigger points suddenly going so bad that they don't trigger injection at all.

It seems as though the ECU is either not getting a signal from the trigger points, or it is not sending a signal to the injectors to fire. The MPS also comes into it, because it's signal tells the ECU how to fire the injectors to provide the correct amount of fuel.

I would first check all cable and harness connections for continuity and grounds.

Regarding Trigger Points:
If you want to test the points, you could try what I once did. Pull the distributor (noting just exactly where the rotor was pointing!). Set it up on bench. Connect an ohmmeter to the first set of points - Middle pin is ground, so connect other lead to one of other pins. Starting at say 12oclock, slowly rotate the rotor and note just where the points open and close. Do this for each pair. If I recall correctly, the points should close for an arc of about 110 deg depending on how much the fibre cam followers have worn. When they are worn, they stay open too long. You might find the discussion I had on Peachparts useful (PeachParts Mercedes ShopForum - View Single Post - Trigger Points on old D-Jets)

Double check that the cable plug for the trigger points is properly connected. Do the same for the MPS cable and test the MPS as described in the shop manual.

If you suspect the fuel pump is the problem, try jumpering the relay (search here for pins to short) and do a flow test. But I doubt this would be problem.

If injectors fire and nothing comes out that would be a fuel delivery problem, but if they don't fire, it would have to be an electrical problem in the injection system.

Good luck and let us know how you get on.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Let's make sure we are using the same terms to describe things. By ICU do you mean the Switch Gear located in the left fender. This is is different than the ECU which is located on the firewall in the passenger footwell. There is also a relay for the ECU located above the fuse block behind the panel surrounding the fuse block.

Since you have applied voltage to an injector and it sprays fuel we assume you have fuel pressure so it must be electrical.

You can check the ECU relay but I don't know which one it is on your year.

Do you have a CD or M117 engine manual?
 

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500SLC #2624. Black on Black.
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The reason I say trigger points is because he says it was running (although poorly) before they were removed and cleaned, and not at all after.

My logic (and other's might be different) tells me that the only thing that changed between running and not running was trigger points.

Now, that may not be the only problem, or the original problem, but you won't have much luck trouble shooting other issues while the trigger points are parts of the problem.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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I just wanted to make sure we were all on the same page. The readings from the trigger points indicate a problem there so I would agree.
 

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Discussion Starter #8 (Edited)
I do have the manual on a cd. Perhaps I could check at the ECU if the ECU relay is working.
The ignition controle unit in left front fender is brand new. The injection control unit above fuse box is a tested used part. The trigger points are quite expensive and it takes 2-4 weeks to have them shipped from US to Norway. How do I check if they are working as they should or not? I have the kind with a cable coming from the distributor with a 6 pin connector at the end of the cable. One of the pins is not in use. I have measured contact between the pin next to the pin not being used and the other four. There is contact for 180 degrees of turning the distributor and no connection for the other180 degrees. The result is the exact same with all four pins (cables). They are al connected for the same 180 degrees. Is this the correct way of testing the trigger points?

I do believe the problem is electrical since the injector does fire when I connect it directly to the + terminal. When turning the ignition key I can hear the fuel pump running for a second or so, building up the pressure.

Any idea of where to get new trigger points? At Mercedes they cost a small fortune. Anyone have a set of used trigger points that still work for sale?
 

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1973 450 SLC
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My thinking is basic if the trigger points were removed and replaced the car should at least run rough hopefully better...I would double check what you removed or changed to this point...

If the distributor had to be removed from the car to remove the trigger points...double check the distributor was reinstalled correctly. It is a little tricky to get the dist. rotor to line back up with your mark. Check by rotating the engine to see if the dist. rotor line up on the distributor mark and the pulley line up on the pointer for top dead center...otherwise you are from 20 degrees to a week off.
Also, Double check the trigger points cable connection is properly connected

I have nothing else ....:surrender:
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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The trigger points are quite expensive and it takes 2-4 weeks to have them shipped from US to Norway.
Why ship from USA? You may have better luck getting them in Germany? The ones with the pigtail and plug are less expensive and easier to find. Maybe you can find them in stock in USA or Europe?

How do I check if they are working as they should or not? I have the kind with a cable coming from the distributor with a 6 pin connector at the end of the cable. One of the pins is not in use. I have measured contact between the pin next to the pin not being used and the other four. There is contact for 180 degrees of turning the distributor and no connection for the other180 degrees. The result is the exact same with all four pins (cables). They are al connected for the same 180 degrees. Is this the correct way of testing the trigger points?
I described how to test them in my my previous answer. 180 deg for each is not right. Either a problem with points or the way you are testing. Check which pin is the ground. It should be pin 12. Check resistance between that pin and each on the other 4. This is covered in section 7.4 of manual. The resistance should swing between 0 and ∞. You should do this at the distributor plug and at the ECU plug. Also check that you have ground at the ecu plug (pin 12).

Above checks tell you nothing about the trigger point wear - Read my previous post and the link to Peachparts for how to check for wear.

It does seen that you have a problem with the trigger points. But it might just be that they are not properly connected to the ECU.

You didn't say if you had checked the MPS wiring.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,334 Posts
My thinking is basic if the trigger points were removed and replaced the car should at least run rough hopefully better...I would double check what you removed or changed to this point...

If the distributor had to be removed from the car to remove the trigger points...double check the distributor was reinstalled correctly. It is a little tricky to get the dist. rotor to line back up with your mark. Check by rotating the engine to see if the dist. rotor line up on the distributor mark and the pulley line up on the pointer for top dead center...otherwise you are from 20 degrees to a week off.
Also, Double check the trigger points cable connection is properly connected

I have nothing else ....:surrender:
All good points ;)
 

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1975 450SL
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This may sound a bit off-the-wall, but have you checked the ignition breaker points for correct gap? I spent a month chasing around in circles until I checked the points themselves. :banghead:

There was a deposit on the contact surfaces that I was able to clean off by running some stiff paper through them. The dwell angle is important to check, also, and will cause rough running symptoms.

Scott
 

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73 Mercedes 450SL 107044
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Definitive Site for D-Jet Info

Hi,

I am a noob to this forum so I am not sure if this site covering the d-jet has been posted here or not. It was written specifically for the 914 Porsche but about 90% of the info here is applicable to all d-jet systems. It has a detailed troubleshooting section which is very helpful. This is the link:

Brad's '70 914 2.0L

I am new to the R107 but for the past 5 years I have owned a W109 300SEL 3.5 with the same basic engine as yours.

Regards Bill
 
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