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1973 450SL
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Discussion Starter #1
As I slowly make progress on my '73 SL, we've come up against a pretty bad rough running, black smoke situation. I'm NOT a mechanic, but do have a young friend who is a Nissan tech, VW tuner guy that helps me out frequently.

The car was not run for several years, other than to load and unload from my trailer recently.

Symptoms: starts quickly, but idles & runs rough. Pretty high amount of black exhaust.
What we've done so far:
  • New spark plugs, plug wires, cap, rotor, points, coil, ballast resistor.
  • Compression tests fine: about 120 across all cylinders.
  • Fuel injectors were tested and ultrasonic cleaned. One was bad, replaced with new.
  • Vacuum hose appears good between intake manifold & valve & distributor.
None of that seems to have helped, or made any difference.

Seeking assistance, bright ideas?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Two things. Check that trigger points are not worn (They probably are). Test the temperature sensors and make sure they are properly connected. Read Comprehensive Guide by Proctologist in EGv107 Djet section. VW/Nissan and even today's MB mechanics are not likely to know anything about these old Djets :)
 

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1973 450SL
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83 Posts
Discussion Starter #3
Ah, I overlooked that guide. Thank you...
 

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1973 450SL
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Discussion Starter #4
Well, we checked the trigger points, appear to be like new. Checked both coolant temp sensors, test ok. Still running very rich... My modern mechanics are struggling with the D-Jet, and can't figure it out... 🙁
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,557 Posts
Well, we checked the trigger points, appear to be like new. Checked both coolant temp sensors, test ok. Still running very rich... My modern mechanics are struggling with the D-Jet, and can't figure it out... 🙁
Did you check the angle that each set of trigger points stays closed? This is only easy way to test if the fiber rubbing blocks have worn, short of removing them and measuring with a caliper.

The contacts always look good (except sometimes they get oil on them). You can test the closing angle yourself even with distributor installed. Just hook a meter up to the ground pin (center pin on old style, not sure on ones with external plug.) and each other pin. With cap off, put a piece of stiff paper under the rotor. Rotate engine slowly using a wrench on the PS pulley (pull up on belt if it slips). Mark points where resistance changes from zero to infinity and back for each set. Measure angle after removal with protractor. Some used other tricks, like an old CD or something instead of stiff paper.
 

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1973 450SL
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Discussion Starter #6
We'll give that a shot. Thanks again...
 

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1973 450SL
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Discussion Starter #7
What values are we looking for?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,557 Posts
What values are we looking for?
Something less than about 140 deg. If you see numbers like 160+ there is a problem. My new set were down around 100 deg, I think but you won't see that with used sets.
 

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'73 450 SLC / '74 450 SL / '01 ML55
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What values are we looking for?
So, I got a little sister up in Snohomish.
Listen to Mr. Graham. He forgot more than he knew, 110 - 115 degrees is doable, and that is from his Peach Parts connections. I had "No" hot start issue at all after that was put into practice.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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110 - 115 degrees is doable,
It is, but he would need Norbert's tool to reset them. Seems Norbert is not shipping them at present but they can be made or someone may loan one.First thing though, is to measure the closing angle.

I suggested doing without pulling the distributor. Not as easy to rotate. But at least the timing doesn't get disturbed. Maybe pulling distributor, checking trigger closing angles, adjust if needed and then reset timing would be better. Automobilist is not doing this himself, so would need to advise his mechanics of timing numbers as well. Also how to not get the distributor back one tooth off ;) BTDT.
 

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1973 450SL
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Discussion Starter #11
Thanks, good info.

We lost basic timing when we pulled the distributor to check the trigger points, due to my error. No big deal resetting to TDC. I tried getting the open/close angles, but couldn't get the crank to turn via turning the power steering pump, while also holding multimeter. Too much belt slip. Will try again with someone turning crank bolt.
In the meantime, I vacuum checked the MAP: fine almost no loss.

Started checking fuel pressure, and seems very little, almost zero at fuel pressure regulator. Good pressure at pump 28+PSI, but pressure drops after fuel filter considerably. Will see if local NAPA has a new filter. (The one Pelican sent me has incorrect fittings)

I am determined to get this running and running very well. At this point, it starts, but very rough & smelly. Ragged.

My mechanic has limited availability due to his full time job, and honestly, I want to learn to do this myself as I plan to hold this car for a long time. Plus it would be very cool to fix something that has him baffled...

Ed
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I tried getting the open/close angles, but couldn't get the crank to turn via turning the power steering pump, while also holding multimeter. Too much belt slip. Will try again with someone turning crank bolt.


Started checking fuel pressure, and seems very little, almost zero at fuel pressure regulator. Good pressure at pump 28+PSI, but pressure drops after fuel filter considerably. Will see if local NAPA has a new filter. (The one Pelican sent me has incorrect fittings)
To turn engine over with PS pulley, you need to pull up on the belts on the underside while turning the nut. It usually works just fine. Turning the crank nut is another thing, at least on my car. I would pull the distributor before doing that.

When you measure pressure at the regulator, where did you put the gauge? You know it has to be on the rails? Best place is on the line to the cold start valve . The pressure after the FPR will always be almost nothing because it just returns fuel to the tank.
 

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1973 450SL
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Discussion Starter #13
Checked it on cold start valve hose. Gauge showed zero. Will try the trigger point measurement again. Thanks, it's appreciated...
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Checked it on cold start valve hose. Gauge showed zero. Will try the trigger point measurement again. Thanks, it's appreciated...
Do you hear the pump run? If you turn ignition on and off a few times and your pump runs, then, provided fuel lines are connected correctly, it is hard to see there being no pressure at all on the fuel rails. Could be lower, but zero? Unless there is a big leak down through FPR or back through supply line or through injectors or cold start valve into engine. If you go to section 7.4 of manual, there is a section on how to test fuel pressure leak down.
 

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1973 450SL
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Discussion Starter #15
Installed new fuel filter, tested good pressure at the filter output.

After copious head scratching, and one good shower of unleaded premium, I discovered that the mechanic had installed the fuel feed / return lines in reverse. The car appears to have started and run rough & rich solely on unregulated fuel pump pressure... Reconnected the fuel lines properly, but now no pressure after the pressure regulator. Next I'll check pressure after the damper, but before the regulator. (Should have done that first, I know...)

Onward...
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,557 Posts
Installed new fuel filter, tested good pressure at the filter output.

After copious head scratching, and one good shower of unleaded premium, I discovered that the mechanic had installed the fuel feed / return lines in reverse. The car appears to have started and run rough & rich solely on unregulated fuel pump pressure... Reconnected the fuel lines properly, but now no pressure after the pressure regulator. Next I'll check pressure after the damper, but before the regulator. (Should have done that first, I know...)

Onward...
Hopefully your lines are now connected as shown in diagram in manual and this post: 1975 450sl Fuel Supply issue, what now?

If you have no pressure after regulator and damper that is how it should be. That fuel is returning to the fuel tank.

Measure again at the cold start valve. You should see 30psig there.

If not, double check the fuel line routing.
 

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1973 450SL
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Discussion Starter #17
Fuel pressures all test ok.
We removed the distributor and tested trigger points. Unfortunately, they all pretty much measured the same: 160 degrees... Any bright ideas on what to do now?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Bright ideas??
Those 160deg closed angles may not be your problem. So long as the points open and close once and send that signal to ECU, the angle should not matter. However, I read early on that Porsches with similar injection had trouble, especially at higher rpms. The distributor bearing are probably a little worn. This may cause the worn points to bounce. In other words, send more than one open/close signal to the ECU. Then you get more fuel injections than needed and a rich mixture.
Even if this is not your problem, you should do something about it. There are trigger point repair kits available from Bosch. Need some soldering. Then there is Norbert's tool that allows the points to be adjusted by bending. Not a real repair, but will extend the life and get points back to where they may work better. Someone here may have the tool or at least a drawing. Norbert said he was not shipping at present. Otherwise, maybe someone has a spare set they could sell or loan you.
 

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1973 450SL
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Discussion Starter #19
Don't feel any play in the dist shaft. Really solid feel.
Appears then that the only real fix is the Bosch repair kit.
To clarify, you're not saying the existing 160 degree measurement is the core problem?
This is a very vexing issue...My mechanic has somewhat lost interest, so up to me to solve.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Not saying one way or the other. If I had car here, I would check a lot of things. AAV not sticking, timing properly set and centrifugal advance working , temperature sensors meet specs, MPS meets specs and adjustment screw has not been tampered with, harness connections all good, plug and injector wires connected properly. Check plugs to see if they all show richness. Fuel flow after regulator to spec, Pressure gauge reading correctly (high pressure would not help) More, I am sure, but I have had a long day.... I would adjust or replace the trigger points.
Read the comprehensive guide, the EFI training manual, section 7.4 & 7.5 of manual. Nothing complicated about Djet, but it is 'different'.
 
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