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Help please. My R129 won't start.

Hello again guys.
Sorry for the late reply but not been well enough to get under the car until yesterday.
I've drained the fuel out and it looks like varnish & also there was quite allot of debris that came out as well.
Gonna fit another new fuel filter today if I can but just wanted to ask if there's anyway I can clean the fuel tank whilst in situ.
I've seen some posts online that say it can be flushed using water but that sounds a little bit strange to me.
Also I know its probably a silly question but I'm guessing the arrow on the filter points towards the back of the car.
Thanks again guys, you've all been brilliant.
All the best.
Glyn
Removing the fuel tank from an R129 is a royal PITA , involving use of crowbars etc , even with everything stripped away ; getting at the pipe connectors underneath involves disconnecting driveshafts from the diff , or even dropping the entire subframe .

I know , I had to replace a leaking tank .

Before taking the tank out , I would look at getting one of those endoscopic inspection cameras , the one below at £80 was the cheapest I turned up on a quick search , but you may be able to hire one from a tool hire shop .

You could pull the fuel strainer out of the tank , which leaves quite a big hole , and put the camera in that way for a look inside .

I’d think , though that if you have drained the tank , flushed through with clean fuel and are not getting any more debris , then it is probably OK . You can flush it through a few times using the same fuel , as long as you strain it through a filter before going back in . Even a paper coffee filter inserted into a funnel should remove any particles big enough to cause trouble . And if you filter the fuel before finally using it , you could run the car on it , so not a total waste . A couple of 20L jerrycans would give you almost half a tank .

 
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Hello again everyone.
Thanks again so much for all the help, I really do appreciate it.
I've just changed the fuel filter & put fresh petrol in again and the petrol is coming up through all the pipes attached to the bottom half of the fuel distributor but not through the top part.
I don't know if there's a way to bleed the system or even if that would make any difference.
Also there's a slight buzzing noise coming from the part that's sits at the front off the engine (I've attached a picture) & it seems to lock the throttle linkage when trying to start the car. (I don't know if that's just the way it works)
I've left 1 of the injectors out but there's nothing coming through when I try to start her up
The fuel coming through is all clean & fresh.
So annoying as I know it's nearly there.
Thanks again & all the best.
Glyn.
 

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If what you are saying is that fuel is being delivered to the distributor through the pipes that go into the bottom , but not coming out the top pipes leading to the injectors , then almost certainly the piston which regulates the fuel flow will be stuck . That is presuming you have vacuum and the big diaphragm below the air intake is dropping when you crank the engine over . If the diaphragm does not drop then you have an air leak on the induction side somewhere .
 
Hello again everyone.
Thanks again so much for all the help, I really do appreciate it.
I've just changed the fuel filter & put fresh petrol in again and the petrol is coming up through all the pipes attached to the bottom half of the fuel distributor but not through the top part.

Did you watch the video I linked, particularly about the piston that can get stuck?
 
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Hello there.
I've had the fuel distributor of, cleaned it and the piston moves very freely.
I've watched the video link & it all seems to be working as it should. (Very good link by the way)
I'm running out of ideas at the moment.
As for the diaphragm, it's not dropping when cranking the engine offer.
Should it drop even if the accelerator isn't pressed whilst trying to start her up???
Thanks again guys.
Glyn.
 
Sorry I meant to ask if the 3 holes in the diaphragm should be clear as on mine only 2 of the holes are open. Don't know if that makes any difference to be honest.
Also is it normal when trying to start the car that the throttle linkage is locked as it seems to be controlled by the mechanism that I took the picture off.
Thanks guys.
Glyn.
 
Sorry I meant to ask if the 3 holes in the diaphragm should be clear as on mine only 2 of the holes are open. Don't know if that makes any difference to be honest.
Also is it normal when trying to start the car that the throttle linkage is locked as it seems to be controlled by the mechanism that I took the picture off.
Thanks guys.
Glyn.
this video may help? its part of the throttle actuator mechanism for the M119 and possibly part of the ASR system also. If I got this right it should move as you actuate the throttle?
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Hello there again.
I've been out to the car again today & there is fuel coming through the top of the fuel distributor when I manually push down on the diaphragm.
However it still won't fire up & the diaphragm doesn't go down very much when I press the accelerator pedal when trying to start her up.
Also wanted to ask if it's normal for the mechanism on at the front of the engine (not sure what it's called) that I took picture of to make a buzzing noise.
Thanks again guys & all the best.
Glyn.
 
Hi grober.
Thanks for that. Brilliant link.
That might just be the problem I'm having. 🤞🤞🤞
I'll get out there tomorrow and have a look & I'll let you know how I get on.
Cheers pal.
Glyn.
 
Hi again.
Sorry if this is a stupid question but is that the piece that's attached to the bottom half of the fuel distributor.
Thanks again & sorry if it's a silly question.
Glyn.
 
It appears to be a "drive by wire" system- the throttle pedal is attached by cable to the sender / potentiometer unit at the rear of the engine which signals to the actuator motor at the front only by wire [ this so the ASR system can intervene and modify the accelerator command] --From the actuator motor there appears to be a purely mechanical linkage travelling backwards [UPPER ROD] and then forwards[LOWER ROD] to open the throttle butterfly below the fuel distributor--- the potentiometer idle contacts are supposed to give trouble and cause the car to go into limp home mode
 
Hello there grober.
Been out to the car again today but I'm not to sure where the potentiometer is.
I've taken some pics of what I think it might be but I'm really not sure.
I've got to admit I'm a bit worried about taking the piece of I've photographed.
Thanks again pal.
Take care & stay safe.
All the best.
Glyn.
 

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You are certainly in the right area-unfortunately the video I posted omits the disassembly of the throttle linkage which is a complex electromechanical setup. MERCEDES often don't document "transition technology" very well especially if it only lasts a couple of years. Your problem may well lie with that throttle position potentiometer but such is the complexity of these linkages that even the pros have difficulty with it. I would hesitate to strip the assembly unless you are confident of reinstating it??? Time for someone familiar with that setup i think- this will give you an idea of the complexity

first easy thing to test is whether that throttle is working --ignition must be on!!-- and its a 2 man job 1 to operate the throttle 1 to observe all parts of the linkage operating under the bonnet
 
Hi Grober.
Yeah I know what you mean.
These things are complicated beasts and properly over engineered.
I guess I'm gonna have to bite the bullet as I can't even get the old girl to fire up to get her to a mechanic.
I'll let you know how I get on. (Once I pluck up the courage)
Thanks again for your help.
Glyn.
 
Hello there Grober.
I've been out agai. today & I'm getting fuel through the CIS system and also through the fuel lines when I manually press down the dome on the airflow meter.
Also getting some fuel through the injectors when doing the same.
I'm waiting on a ODB1 reader from the USA but I'm not sure how much information that'll give me.
Do you think it'll tell me if it is the potentiometer before I try and remove it pal???
Thanks again bud for your time and help.
Glyn.
 
If you’ve got some fuel through the injectors now give it a crank over! :thumb: Should at least try and fire :cool:

You may find the air flow meter was stuck and/or the potentiometer has had a few wipes now the plate has been moved :)
 
Sorry haven’t seen the last few posts, I take it you have an electronic throttle? :doh:
 

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