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Old 05-16-2018, 01:19 AM
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Trigger Point Conumdrum

Hmmm (1973 Mercedes SLC 450)
Newbie here - Please go easy :-) I inadvertently unhooked the trigger point connector ( It fell apart whilst trying to clean it -see photo) and in my stupidity may have hooked it up the wrong way. I have simply hooked corresponding colour to corresponding colour (except for the Yellow/blue wire which only has a yellow wire from the distributor - NOT the expected blue).
Anyway, whilst the engine coughed and spluttered for a little while now it won't fire at all.
I'm wondering whether I may have damaged something by mucking around (trying different sequences of connections) ? For eg: a fuse, coil, points or something more sinister.
Can anyone please suggest a 'check list'
of diagnosis so that I might cure this conundrum.
Thank you
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Old 05-16-2018, 08:54 PM
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Search history for D-Jet (D-Jetronic) threads.

There is a US service manual CD that has the troubleshooting steps for the system in general if you know how to use a multi-meter. The same CD also has the schematics.

A paper copy of the M117 cast iron 4.5l service manual would also have all of the above, if you should come across it.

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Old 05-16-2018, 10:29 PM
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it sounds like you just messed up the trigger points that were on the verge of breaking down anyway.

Search the D-Jetroinc forums on Porsches and Volvos, too. Porsche 914's used these during the early 70's; so did Volvo.

I think the Volvo guys came up with a work-a-round or an aftermarket fix of some sort.

The answer is out there.

And don't be afraid of the D-Jet system. If you have a volt meter you can test anything in the system. Parts are expensive, but with a bit of study you can crack the code and troubleshoot the entire system.

And when it works it works great.

A word of warning... If you crank the engine, and the plugs are not firing, and you keep cranking while testing, and then the plugs do fire..... Expect a very loud BANG when all that fuel fires off.

I, uh, saw a guy do this once.
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Old 05-17-2018, 03:45 PM
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There are 5 connectors... I think the worst you could have done was set one pair of injectors to fire constantly (as they are fired in pairs, ex 1 and 5 together).

If you left the key in the "Run" position with it not running though, you may have burned up a ballast resistor or even the ignition box. Check your spark.

Pull one pair from all of your plugs (every other cyl in the firing order). See if it's flooded. Disconnect the coil if you have spark, and crank it with the plugs out and your foot on accelerator pedal, and the pedal on the floor to clear it. You can also try a shot of starting fluid in the intake to see if it fires up on starting fluid, if it's not flooded.
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Old 05-19-2018, 11:22 PM
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I might have just figured out the problem. Correct me if I'm wrong but it appears that someone has wired the trigger points up with the wrong order of

colours - Which means when I was trying to connect the wires from the ECU (Matching colour to colour) they would in fact NOT match. Could you please check the photo and see what you think???
1973 SLC 450
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Old 05-20-2018, 07:51 AM
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I've got a 72 350SL in the shop that is running rich and came across this thread. Thanks
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Old 05-20-2018, 08:10 PM
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Thanks for that,
At the moment i have them connected as you have stated (just in-line for the moment without the plastic connector) but still no luck. Does not fire at all... I checked the trigger points with an Ohm meter by rotating the shaft and it seemed to be working ( O Ohms to Infinity). So I am just about to start checking through what Dr D Jet recommends.
Any ideas would be great though....
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Old Yesterday, 10:23 PM
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one thing to check is the ground connections for the injectors. unbolt them and put it back together.

At starter speed an old fashioned analog multimeter can show you the needle wagging on connections at the trigger points and injectors. A modern digital meter would need to be on a dwell setting to get the same effect.

Follow the trouble shooting workflow in the book and you should be able to narrow it down to a specific faulty circuit and maybe a specific component.

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