Throttle Valve Switch

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cjhols
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Throttle Valve Switch

Post by cjhols » Wed 06 Jun, 2018 9:36 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???
Regards
Peter
Throttle Valve Switch.pdf
Throttle Valve Switch.pdf
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1973 SLC 450
1971 Clubman Mini

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TheMadRacoon
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Re: Throttle Valve Switch

Post by TheMadRacoon » Thu 07 Jun, 2018 12:26 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.
Emad,
TheMadRacoon
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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cjhols
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Re: Throttle Valve Switch

Post by cjhols » Thu 02 Aug, 2018 10:43 pm

So I finally got the car to run. Still don't really understand how? cleaned 2 plugs and adjusted the gap on 1. Problem is you have to have the throttle full on to start the car and then it will only idle for about 30 seconds. I've tried to adjust the air screw but whilst it fixed the idle rpm it still eventually stalled.
Could it be the throttle switch not adjusted properly ( I had to take this off to fix it)?
Or could it be the points not adjusted properly. It is idling at 5 Degrees BTDC but I can't adjust it anymore towards TDC as the stopper bolt stops the distributor moving?
1973 SLC 450
1971 Clubman Mini

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TheMadRacoon
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Re: Throttle Valve Switch

Post by TheMadRacoon » Fri 03 Aug, 2018 7:45 pm

Cj... this sounds similar to how my 350SLC behaved prior to putting in a reconditioned MAP Sensor.

If you can get it to idle, pull off the hose between manifold and MAP Sensor (at manifold end) and suck on it... if no change in idle then MAP Sensor might be kaput.

This tip courtesy of Mercmad when he helped me a few years ago.


(sorry, I havent re-read your previous posts on this so you may already have ruled this out)
Emad,
TheMadRacoon
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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cjhols
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Re: Throttle Valve Switch

Post by cjhols » Sat 04 Aug, 2018 3:41 pm

Just an update
I got is running but roughly. I first thought it was spark but now I think it might be some of the injectors not firing. I pulled the leads of each one at a time as it was running and only 3 altered the RPM (in fact it stalled). I wouldn't have thought that it would have run on 3 cylinders though???.
So now I'm trying to check the voltage at the injector plug ( while it is running) but I'm not sure what voltage you should have there? I can't test the good ones because it stalls.
Then it could be the trigger points - From the Black wire to Y/Red and Y/blue I'm getting roughly 2.4 to 3.0 Volts but from the Black wire to the Y/ white and Y/Green i'm only getting .036 Volts. so maybe it is my trigger points?
:Doh:
1973 SLC 450
1971 Clubman Mini

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Chai
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Re: Throttle Valve Switch

Post by Chai » Sun 05 Aug, 2018 8:33 pm

The throttle switch sends an "at idle" signal to the computer, and you've tested that.
Each of the 4 contacts at the trigger points sends the computer signal for a pair of injectors. So the odd number (3) of 'working' injectors is strange.

The contact gap is checked via the dwell setting, which needs to be checked with the vacuum pipe(s) disconnected from the distributor (some cars have one and others have 2 vacuum pipes - mine has one). The vacuum pipe retard the engine advance - and is not-retarded when the air-conditioner is switched on.

Have you checked the manifold pressure sensor (MAP) by sucking on the vacuum pipe when the car is running - even if roughly? This is most critical to the proper running of the car as a vacuum leak here will cause the engine to run over-rich and very rough.
Chai
1974 450SLC

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cjhols
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Re: Throttle Valve Switch

Post by cjhols » Mon 06 Aug, 2018 8:29 pm

Well,
Another update. It turns out that the 4th injector was receiving a signal but was not firing - at the moment only 2 sets of injectors fire. I will have a look at that later. Yesterday if I disconnected the black wire off the trigger point connector I could get the alternate injectors to fire (don't ask me why) but not all 4 sets together. Today I tried taking the black wire off and it stalled (and this is what I assumed should happen in the first place). The interesting thing is that I can swap colours around in the female socket - the ecu side with wires from the T/P (eg; green for yellow) and the injectors continue to work but only 2 (again don't ask me why). So it seems like it is the socket and not the T/P wires that are determining what injectors fire.... I have included a picture of the working sockets (with the yellow arrow) and the shambles of a colour code that some dipstick rewired on the T/P and caused all this confusion.
Thanks
IMG_0772.png
trigger markup.JPG
IMG_0772.png
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1973 SLC 450
1971 Clubman Mini

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Chai
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Re: Throttle Valve Switch

Post by Chai » Tue 07 Aug, 2018 9:34 pm

As some of the photos are "no longer available", here's some information that may help (or not).

I confirm the wiring colour codes for the cables to the trigger are correct for the one picture still available in your latest post.
Here's another picture showing both the five (original) yellow wiring colours and the pin numbers on the plug at the other end.
20180807 Trigger points wiring colour codes.png
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Chai
1974 450SLC

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Chai
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Re: Throttle Valve Switch

Post by Chai » Tue 07 Aug, 2018 9:35 pm

20180807 Trigger points wiring colour codes.png
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Chai
1974 450SLC

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cjhols
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Re: Throttle Valve Switch

Post by cjhols » Wed 08 Aug, 2018 5:38 pm

Hallelujah,
After a seeming eternity I found the fault. Nothing wrong with the ECU or TPS or the TP. Two wires at the base of the joining connector (ECU and T/P) had frayed to the point that they were just holding on. I re-soldered and away it went. Well 7 of the 8. In the process I found that Injector 1, whilst receiving a pulse and having the correct resistance must be stuck - I will work on that next. But a big thank you to all of you (Chai et. el). It goes to show how such a small thing can cause such a headache.
Signing off ( for a little while at least )
Peter
Thank you
1973 SLC 450
1971 Clubman Mini

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