Author Topic: help needed removing trigger points for injectors in lower distributor (M116 )  (Read 934 times)

rutger kohler

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Hi, I want to remove the trigger points for the D jetronic fuel injector system, to clean them, in the lower part of my distributor. I can see the two screws I need to remove but can't get a screwdriver to the back one.  Do I have to remove the distributor to do this, and of so how can I ensure I get the distributor back in exactly the right place?

Following through on this how can the dwell angle and distributor timing be set with a strobe light on the M116 engine.  I can't see a pointer or anything down around the crankshaft pulley as you would on a normal engine.  Am I looking in the wrong place?
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

Benz Dr.

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You will need to remove your distributor. Use a piece of tape or a paint mark indicated to where the rotor is pointed. The bottom of the distributor has a gear that will slide into place and may have to try a couple of times to get it set in the right place.
 
There should be a pointer on the front of the engine. If you have a lot of grease or crud on the front of your engine try to clean that off. We use a de-greaser and a power washer.

Trigger points slide out of the distributor and you can use electrical cleaner to remove any oil film.   
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

rutger kohler

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Hi Don, thanks for that, all clear, but whereabouts on the engine front do you look for the timing marks.  I am looking down from the front, between the engine and the motor towards the crankshaft pulley. It is like Diana's marriage, very crowded!  The engine front is not that dirty but I can't see anything. Should have gone to specsavers?
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

Benz Dr.

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That engine should have a small pin with a pointed end somewhere near the water pump. That's the timing marker.

 I like to clean the timing marks and put some white paint on them so they show up well.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

rutger kohler

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Hi Don, finally found it.  Surely I would need to remove the two drive belts to the power steering to be able to see a realistic reading with the strobe light, with the engine running?

Also is there a Haynes or similar teardown manual for cars with the M116, I need to know exactly where to connect the strobe light for dwell and timing.  Have read some cautionary stories about damaging the transistorised unit by connecting to the wrong place.
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

stickandrudderman

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The front of my timing light has a lot of scars from getting too close to the belts but it is possible to see the marks without removing them, especially if you do as Dan says and use a paint pen to highlight the marks you are looking for.
You cannot damage anything fitting the strobe.

rutger kohler

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Ok I'll give that a go, but just to be absolutely sure what do i cannect the strobe light to plse?
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

Benz Dr.

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Hook positive ( red ) clip to 12 volts and negative ( black ) to ground. If you have an inductive pick up put that around number one spark plug wire. Number one is at the front right corner of the engine as seen from driving position.
Some timing lights have an on off switch that you might have to move into position. Once strobe light starts point it at your pointer on the front of your running engine and see where your timing marks are. I like somewhere around 9-10 degrees BTDC to get all the power from that 4.5   This is more advanced than your specs will tell you but it won't hurt anything assuming it's a USA engine which is pretty low compression anyway.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

Shvegel

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I have avoided D-jet injection like an ex girlfriend but if memory serves the injectors are fired 3 at a time?  That is a huge stumble so unless it is filling on it's face the points are probably fine.

Benz Dr.

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They fire in pairs but not sequentially. D jet works well as long as all of the parts are in good shape but then that holds true for any system. People look at our cars and say they're too hard to work on but it's always about understanding what you're working on. It's very hard to fix anything if you don't know how it works.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

rutger kohler

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Hi, I agree with Don, but it's obvious I have a lot to learn.

Yesterday I drained the petrol (gas) tank, and replaced the fuel filter (Part no 0 450 905 007). Replaced the fuel and ran the electric pump up this morning. Still at 24 psi so I increased the pressure on the 3 way pressure regulator to 28psi. When trying to start the car still popping and back firing so I have removed the distributor and taken out the injector trigger points. 

I was hoping for them to be badly clogged up or a wire off, but they seem to be in good shape. Have sprayed them with a degrease spray and then an electonic cleaner and will let them dry out over night.  photos attached of the trigger mechanism, the first from the top, the second from the bottom and lastly a shot of the side of the distributor showing the model number.

I have marked the distributor inside where the rotor is located, before removing it and also marked the slot where the securing allen cap screw goes.  Have moved the distributor as little as possible and am hoping it will go back in the same place?

It is clear my problem lays elsewhere in the D Jetronic system.  It has been suggested I check the vacuum hose to the MAP for holes however the hose disappears into the back of the engine, how do you get to take the bottom of the hose off?
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

Benz Dr.

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I would add a bit more fuel pressure up to 30 PSI. Tiger points need to be really clean so after you hit them with electrical cleaner open up each set and blow them dry. I would would also check the resistance of the coolant and air temp tensors. If you have the BBB that we often refer to on this site it will have all of the information you need to check this stuff.

The vacuum line going to the MPS can have cracks in it from age. It's possible to reach behind the engine and undo the clamp that holds it on to the intake manifold - I would replace it as a mater of course. The unfortunate thing about these engines is they are very prone to vacuum leaks and they never run well if that's the case. If find that you have to attack each job separately but do it all together like replacing all of the rubber seals on the intake manifold. Not a hard system to learn about but not easy either.   
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

ja17

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Yes, sounds like you have a low fuel pressure problem. Also, if you turn just the key on (engine not running), open the throttle slowly, all the way, you should hear the throttle switch click all the injectors twenty times on a full stroke of the throttle.
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

stickandrudderman

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Whenever I’m presented with the task of getting these running well the very first thing I do is break out the smoke machine and conduct an intake system integrity test. This will quickly expose and leaking injector seals or vacuum pipes and these must be addressed before you can hope to achieve smooth running.

Benz Dr.

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I agree. A smoke machine really finds the vacuum leaks. Many shops have them and should be able to test your system for you.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

rutger kohler

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Hi, thanks for all the suggestions. Today I put the trigger points back into the distributor and got that back onto the original setting, thanks for the advice regarding removal and replacement. I have also checked the resistance of the air intake and the engine water temperature sensors against the BBB specs and they are ok. I also checked the resistance etc on the MAP valve on various pins according to https://oldtimer.tips/en/d-jetronic/72-troubleshooting, and they checked out ok.

I like the idea of the smoke machine for checking the vacuum but at this point will have to locate a garage with one locally.

In the meantime I also think it has something to do with the fuel delivery system.  According to the BBB the fuel pump should be able to deliver 120L/hr or 2L/minute at 2 BARG (30psi). Where would you recomend I connect to the fuel system to check this flow rate, is it ok draining it open ended into a bucket to check the flow or does it have to be at pressure?

Finally it is worth noting that the car was running trouble free until I took it off the road and replaced the front and rear rubbers etc on the trailing or radius suspension arms.  because I don't have a car hoist I had to jack up each side of the car quite high to release the rear springs, one side at a time. I have checked and haven't damaged any of the fuel lines in doing this, however after completing this job I only got a short run in and parked the car.  The next morning large clouds of gray smoke came out of the exhaust but cleared and I did a short run in the car, however the next day the engine really developed the missing and back firing. 

It may be a coincidence, I can't think what might have caused it, however despite having drained the petrol tank already I am going to drain it again and take the tank filter out and clean it.  If it has a lot of crud in it I may take the tank out itself.
1969 280 SL Manual gear shift
1972 280SE 3.5 auto

Benz Dr.

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I would pull the spark plugs and have a look. A lot of poor running can be traced back to fouled plugs.
1966 230SL 5 speed, LSD, header pipes, 300SE distributor, ported, polished and balanced, AKA  ''The Red Rocket ''
Dan Caron's SL Barn

rutger kohler

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Hi, you have hit the nail on the head Don. I never came back because that is what I found was wrong, new spark plugs fixed the problem.  I had a similar problem about a year ago, so the first thing i did this time was to remove the spark plugs and machine wire brush them clean. I assumed this would fix spark plug problems but have since found out, after checking many other things, this is not the case.

Will be straight to new spark plugs the next time.
1969 280 SL Manual gear shift
1972 280SE 3.5 auto