Garage > Mechanicals

280SE woes

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entresz:
Hi all

I'm stumped by a problem with my 1975 280SE. It's a D-Jetronic euro car more specifically.

Recently it broke down. I went to accelerate onto a highway, and it coughed briefly, and then died. I eventually got it to start again - idled perfectly - but again, as soon as I went to accelerate it coughed again and died. What is frustrating is that it's an intermittent fault. I've driven it with no issues after this event, but yet again, it's happened.

I've done the following to try and remedy the problem.
- Replaced alternator - I noticed lights were dimming at idle. It now has a new alternator, and I have adjusted the idle speed up a little as it was a bit low.
- Tried bypassing the ignition amplifier. A mechanic friend of mine who inspected my car suggested this might be faulty. This was terrible as it ran even worse and stalled again only minutes after starting the car. It's definitely not this part playing up. Reconnected it again.
- New points - they were getting a bit old so replaced them
- New spark plugs
- New leads

I also have new injector trigger points (not fitted yet - yet to arrive).

It's running better but instead of completely stalling , occasionally it has a slight flat spot... not quite a misfire, but not far off. Like a hiccup, or as if your foot was taken off the throttle momentarily.

It's also notable that after it broke down, I did notice quite a lot of black soot around the exhaust.

I'm not a mechanic by any stretch but I'd like to try and get this sorted as I'm not prepared to take the car on longer trips... I don't trust it!

Does anyone else have any ideas?

I thought maybe fuel pump? but it's only a 5 or 6 year old fuel pump on it... I'd be surprised if it was already failing.

Would be grateful for any advice!

adamb:
You seem to be really shooting far and wide on the diagnosis.

Upon reading your description of the problem my opinion was also that the number 1 suspect is the ignition amplifier. The earlier ones were weaker than the ones installed on later K-jet cars. Try to find a temporary replacement from somewhere. That should be possible in Australia.

Again, if in any doubt be sure to eliminate spark as the source of problems. It is much more likely to be the cause that the FI.

revilla:
The black soot part quickly caught my attention. That’s an indication of combustion out of balance (rich-lean). The fact that it happens suddenly and intermittently makes me think of the symptoms of a clogged (or almost clogged) filter (main, WUR, or F distributor pressure reg) throwing the mixture momentarily out of wack and then back to normal range. It’s a wild guess based on your description, but how about a batch of contaminated fuel?  (water or else). Happens to us with the small airplanes. How about draining into a container, observing and topping off again to check what happens? That’s a relatively easy thing to check.
Nothing like being next to your car to diagnose, but from far I’d bet on a fuel related issue.  Especially if the black soot gets on the ground too and especially if it’s accompanied by black smoke too (something to check out next time it happens...)
Good luck

mrkozzy:
I've had the same issue for 2 years.
I knew there was something wrong but could not  pinpoint the source.
My problem was intermittent, which is the worst kind.
It's happened 4-5 times and always righted itself after a brief shutdown/cool down.
The last time earlier this year left me stranded and I had the vehicle towed home.
The picture shows what I believe was the culprit(?),
I now know it's called the Throttle Position Sensor. If you look closely you will see 1 of the 4 contact points bent  way out of place. (Cannot fathom how it got there).
I replaced the whole part, although I could've just positioned the brass contact point back from where it came, and so far the problem seems to have been fixed.

* Thanks once again to UTn_boy who helped with the clarification on this one.  ;)

UTn_boy:

--- Quote from: revilla on 28 May 2021, 03:17 PM ---The black soot part quickly caught my attention. That’s an indication of combustion out of balance (rich-lean). The fact that it happens suddenly and intermittently makes me think of the symptoms of a clogged (or almost clogged) filter (main, WUR, or F distributor pressure reg) throwing the mixture momentarily out of wack and then back to normal range. It’s a wild guess based on your description, but how about a batch of contaminated fuel?  (water or else). Happens to us with the small airplanes. How about draining into a container, observing and topping off again to check what happens? That’s a relatively easy thing to check.
Nothing like being next to your car to diagnose, but from far I’d bet on a fuel related issue.  Especially if the black soot gets on the ground too and especially if it’s accompanied by black smoke too (something to check out next time it happens...)
Good luck

--- End quote ---

Bear in mind he has D-Jetronic, not K-Jetronic.  So there is no WUR or fuel distributor. 

I'd be more concerned with your throttle position sensor (what MrKozzy shows) and your manifold pressure sensor, also known as the "MPS".  Rather than taking stabs in the dark, I'd start diagnosing the D-Jetronic system per the manual.  There are several online sources one can go to for D-Jetronic diagnosis directions.  Though, before doing so do make certain that the points dwell, ignition timing, and valve lash are all in good order beforehand.  And make certain that your fuel tank doesn't have trash in it clogging the fuel filter.  Don't rule out a faulty fuel pump and/or fuel pump relay, either.  Just because the pump is only 4-5 years old doesn't mean it's not bad or stopped up with trash.

Regarding the ignition module, properly known as the switch gear, it was the ones made between 1969 and early 1971 that were problematic.  Those had Germanium transistors in them that failed prematurely.  Afterward, they started using Silicone transistors, which was long lived, and is what is  in all W116 cars.  On that note, renew your ballast resistors, ignition coil, and condenser out of principle.  They are not good for the life of the car, and can cause the issues you're experiencing. 

Make sure your sparking plugs are the non resistor type. 

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