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1975 450 sl ; 1971 300 SEL 6.3
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Had similar symptoms on 1975 450 sl. See my post “1975 450 SL FUEL INJECTION ISSUES" From two weeks ago.
Problem solved ( simply..after checking ALL components ( temp sensors, trigger points etc) by turning up fuel injection pressure from 26 psi to 30 psi ( spec is 28-32 psi). I note you have tested fuel delivery pressure at cold start valve location ( best place to test) at 29 psi...should be good but if injectors are old and tired, try turning up to max spec of 32 psi)
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,557 Posts
Troglodyte said:
MB, thanx for the tech. info on that.
All I know is (on both a '73 &or a'74) if you pull that connection while the car is running it will die, and will not restart until it is plugged back in.

The C-S valve wiring is, I think, independent of anything else. Unplugging it should give an open circuit to ground so C-S valve should not do anything. I will have to try pulling that plug tomorrow and see if I get the same results :) Pulling the #2 temperature wire alongside the T-T switch could very well stop engine. I will try both :)
Today, out of curiosity, I tested this.

Pulling T-T switch plug made no difference.

Pulling the coolant temp sensor plug that is along side the T-T switch stopped the engine!

Just goes to show how important that TS2 sensor is. Car will not run without it and if it is poorle connected or resistance is out of whack, the engine will run poorly - usually too rich.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Regarding Trigger points and their closing angle.

Another site says 135-165deg closing angle is OK and that 135 is theoretically correct. My MB triggers new out of box were at about 100deg. If you use a dial indicator on the ramps of the cams you can determine what the range of the angle can be. It's been a while, but I posted about the tests I did on that here or on Peachparts. Smaller the angle the better.

Some say that so long as the points open and close, they send a signal to the ECU to start injection for that pair of cylinders. This is true and the MPS then determines the duration of the injection (Or so I have read)

The thing that is not often mentioned, is that the ECU also determines engine rpm from the rate that one set of points opens and closes. As the fiber blocks wear, the Porsche guys figured that the points may start to bounce. If they open and close momentarily, the ecu gets two or more signals. Then it presumably thinks rpms are higher and injects more fuel. Results in rich mixture.

Theory may be right or wrong, but for proper operation, these djets do seem to need trigger points with the closing angle set to about 130deg or less. Several us have cured our rich running problems by adjusting existing or installing new trigger points.

Once automobilist gets his engine running again, this may solve rich mixture problem.
 

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1973 450 SL
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23 Posts
fwiw, my '73 was running as you describe, one of my plug wires was just barely touching the plug, snapped back on and she was smooth as a baby.

Curious (for the experts) I've seen pages of advice about the points but noone mentioning getting a pertronix to replace the blasted thing? Is there a reason behind that I haven't stumbled across yet?

Mine is running 90-95% smoothly and sweetly but has a little miss and a little rough in very small bits and my next plan was the above.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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fwiw, my '73 was running as you describe, one of my plug wires was just barely touching the plug, snapped back on and she was smooth as a baby.

Curious (for the experts) I've seen pages of advice about the points but noone mentioning getting a pertronix to replace the blasted thing? Is there a reason behind that I haven't stumbled across yet?

Mine is running 90-95% smoothly and sweetly but has a little miss and a little rough in very small bits and my next plan was the above.
I believe we did mention it to this owner, but he thought it might add to his problems. Many (maybe most) of us have Pertronix in our Djets.

If you look in the stickies (egv107 section 07.5) or do a search, you will find instructions for, and which Pertronix to buy.
 

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'72 450SL, 107.044-12-000422
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282 Posts
fwiw, my '73 was running as you describe, one of my plug wires was just barely touching the plug, snapped back on and she was smooth as a baby.

Curious (for the experts) I've seen pages of advice about the points but noone mentioning getting a pertronix to replace the blasted thing? Is there a reason behind that I haven't stumbled across yet?

Mine is running 90-95% smoothly and sweetly but has a little miss and a little rough in very small bits and my next plan was the above.
This thread has a lot of references to the FI trigger points (aka pulse generator). Pertronix replaces the ignition points (has nothing to do with the FI).

You may or may not notice an improvement with pertronix (I did not) but I still think it’s a good upgrade. Relatively inexpensive, very easy to do and takes one more variable out of the system. No need to worry about point gap/dwell anymore.


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1973 450 SL
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Sorry, I must have glossed over that in my reading through the thread. From the threads you mentioned I'd decided that was my next step I even found the part number I was looking for and emailed petronix because they're not available but they said they would make one if I ordered it.

Thanks, just similar situations and making sure I didn't miss something.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Sorry, I must have glossed over that in my reading through the thread. From the threads you mentioned I'd decided that was my next step I even found the part number I was looking for and emailed petronix because they're not available but they said they would make one if I ordered it.

Thanks, just similar situations and making sure I didn't miss something.
I think you can get the 1885 Pertronix from a number of vendors. Don't have to go to Pertronix. They also have an LS model that at least one owner here has used.
 

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1973 450SL
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83 Posts
Discussion Starter #69
Will be working on the car this weekend.
It has been suggested by more than one mechanic that I change from the D-Jet to a Megasquirt system. I realize it's not "original" but if it eliminates the D-Jet issues, might be a good thing?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Will be working on the car this weekend.
It has been suggested by more than one mechanic that I change from the D-Jet to a Megasquirt system. I realize it's not "original" but if it eliminates the D-Jet issues, might be a good thing?
You will just move from one technology that few know about to another that even fewer know about. Megasquirt is interesting, but it is for the computer/electronic savvy hobbiest. Those mechanics tell you that because they don't understand the Djet. Which is actually a very simple system. You just need to approach it methodically. For a start, get teh trigger points adjusted. Get someone to send you the tool or maybe someone will adjust them for you. Post here asking if someone can help you with that. Then you see how that works and move to the next step.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I've seen 1885, 1885LS, 1887 and 91887LS (new model with adaptive dwell)?
We know the 1885 works (many of us use that) on 72/73. The post I linked showed one owner that has 1887LS But Pertronix say that is for 74 & 75 model. I would just go with 1885 and hook it up as shown in the stickies. It is inexpensive and works. Just don't leave key switched on for long. I never found a 1885LS.
 

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'73 450 SLC / '74 450 SL / '01 ML55
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Will be working on the car this weekend.
It has been suggested by more than one mechanic that I change from the D-Jet to a Megasquirt system. I realize it's not "original" but if it eliminates the D-Jet issues, might be a good thing?
If you got lots of money it's a good deal for who ever you are paying to work on it
 

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1973 450SL
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Discussion Starter #74
I've got the money to get this running right. While I vastly prefer to keep the original D-Jet, the Megasquirt is in use in thousands of cars, and virtually any decent tuning shop is familiar with it. It also appears that I can keep the car looking "stock", but run a Megasquirt & Pertronix.

Still, as mentioned, I prefer to keep it original. Anyone got the trigger point adjustment tool that I could borrow? Or, might it be feasible to adjust with out the special tool? Or, build up the trigger blocks and machine down to an "original" thickness?

The goal is not to have an endless project car, but to have it drivable and reliable sooner than later. It did spend three years in an outlaw body shop, and I'm exceedingly eager to simply drive it...

All these thoughts and opinions are really appreciated, by the way.
 

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1973 450SL
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83 Posts
Discussion Starter #75
Testing spark. Is there any other good way besides of removing spark plug and visually seeing "good" spark?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I sometimes just use a spare plug, connect it to one or more of the plug wires and ground the plug body. Just make sure area is well ventilated and there are no gas leaks.
The in-line ones they sell in most stores don't fit on out plugs/wires.
You can also use a timing light.
 

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1973 450SL
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Discussion Starter #77
Yep, that's what I thought...
 

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'72 450SL, 107.044-12-000422
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282 Posts
I like removing each plug and checking individually. That way, test every plug in the system.


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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I like removing each plug and checking individually. That way, test every plug in the system.
Good to look at all the plugs, especially after rich running.

But if you just want to confirm that the ignition system is working, using a single external spare plug is quick and easy.

I did that recently. I went to start my SL after having been to doctor. No start. Ooops! Ignition or fuel? Maybe Pertronix fried? It was easy to confirm that ignition was still good using a spare plug. Not so easy to change the fuel pump relay :( (that was the problem)
 

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1973 450SL
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Discussion Starter #80
Still perplexed. Now it looks like no spark... I think I'm going to let the car sit, and move on to another project for a bit until I feel like chasing its problems some more.
 
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