Throttle Valve Switch

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Joined: Sun 31 Mar, 2013 10:06 am
Model you own: w107
Location: Bendigo Australia

Throttle Valve Switch

Post by cjhols » Wed 06 Jun, 2018 10:36 pm

Hi all,
I was wondering whether the Throttle Valve Switch on a D-Jetronic (1973 SLC 450)
could stop your car from starting. If you have read my other post on the Trigger Point Conundrum I inadvertently knocked the wires the TP connector and as they were not the traditionally labelled colours ( on the distributor side) I mixed them up. At the same time, knocked the slides (see the yellow arrows in picture ) on the Throttle Valve Switch PCB. From that time the engine would not fire - at all. Anyway on attempting to right my wrong I have removed the distributor ( to check the trigger point colours), I have completed the ECU check (as best I could with a multimeter) and checked that the engine has spark and is at TDC.
SO.... whilst the trigger points are getting very low (1.8 mm) they still seem to be testing ok (with a multimeter - and yes they still could be trashed).

But I was wondering if the Throttle Valve Switch could also be a possible reason the car is not firing. I tested it with an LED and an Ohmmeter ( see the PDF) and whilst Idle Run contacts seem to be working Pin 17 to 12. The acceleration switch Pin 20 and Pin 9 does not. No movement in LED or Ohmmeter readings. The full load switch also appears not to be working. If I depress the brass connector (red arrow) whilst testing I do occasionally get an intermittent reading.

So is it possible that the throttle valve switch could stop the engine from firing???
Throttle Valve Switch.pdf
Throttle Valve Switch.pdf
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1973 SLC 450
1971 Clubman Mini

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Model you own: w107
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Re: Throttle Valve Switch

Post by TheMadRacoon » Thu 07 Jun, 2018 1:26 am

Another thought: could the fuel pump be off due to ECU not getting an engine run signal? IIRC signal is from trigger points (?) so if ECU isn't receiving signal it turns of fuel pump (relay). This is a safety feature.

Do you hear the fuel pump coming on when ignition switch is on, but not while cranking? Or can you test for it at FRP or at pump itself?

There were some posts on this issue so worth searching for.

Wonder if there IS another safety feature but related to throttle position sensor: ie if it has to be indicating closed for ECU to start engine. Does the djet literature in the Reference Library mention anything like this? I think there is a general desciption of each component and what happens at startup and idle.

EDIT: reread your post and you do say idle run signal working fine, so scrap my second suggestion. Still check Reference Library for explanations though.
1975 350SLC Astral Silver (725) / Blue (2012, 284,900 km - present.... a real Benz, getting better and better)
1988 190E Deep Blue (900) / Cream (2006, 190,000 km - 2007, ~ 215,000 km .... FSH and still spent big $$$)
1974 280E Reed Green (860) / Bone (1993, 316,700 km - 2004, ~490,000 km and still A1)

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