W124 CE300 24V – non starting

[optimusprime]

Grober i did a check and i cant find a fpr for the 12 valve engine . We dont know for sure if it is a 24 valve .

 

[dimits1]

Thank you both for the input. very much appeciated !!!

Optimusprime, do you suggest that the MAS is been damaged because I bridged the OVP relay? If that’s true is the supplied voltage exceeded a certain threshold supplied by the alternator say 13-14V, which I don’t think it happed as I had a mustimeter attached to the battery and it never went above 12.7V, or you think that I fried every electronic on board?

Gobler is your suggestion to replace the MAS as measuring the pressure is very difficult as I don’t have the pressure gauge to do so? Saying that I would expect that the engine will start with the primed fuel and then continue to run with the run pump. I’m not sure that the pumps are variable speed adjusted by voltage to meet the required pressure, hence the low voltage 7-8VDC after prime. If that’s the case then this means that the pressure during prime is achieved and the pumps are running slower to meet the required pressure. In either case the car should start.
Could it be something else?

 

[ray_hennig]

the knob that’s on top in both 0 and I positions

That's purely to lock/unlock the module. No other purpose.

The MAS relays are pretty reliable. I haven't replaced mine in more than a quarter of a century.

RayH

 

[dimits1]

Thank you Ray. Im not convinced that the MAS is faulty but I have no way to check. I am planning to replace the fuel pumps as they are noisy and the car stopped running after I fill it up with petrol.
Saying that I have both spark and fuel but it does not want to start.

 

[dimits1]

to add to the investigation, I have tried easystart spray, not easy as the intake is at 90deg to the air intake, but the car did not start.

 

[grober]

The fuel supply output pressure from the pumps is a constant flow /pressure feed-return loop-the amount of fuel supplied to the injectors is taken from this loop by the injection system control system. I was not suggesting the fault lies with the MASS just describing its function. To trouble shoot these systems requires monitoring the basics - fuel supply and ignition voltages in real time with the appropriate instruments-diagnosing obscure faults remotely is nigh impossible- most mystery problems occur when assumptions are made that certain basic functions are working/fitted properly when they are not.

 

[neilrr]

Check for spark on all leads.

 

[dimits1]

Thank you Grober for your help and I absolutely agree with you, that assumptions lead to false diagnosis, big f**s

Thank you for confirming what I was expecting that the pumps are constant flow constant pressure. This means that the voltage should not drop to 7VDC when they are on run mode. This will increase the current from approximately 11 Amps to more than 20 Maps. This indicates malfunction pump or a faulty relay, with the latter being unlikely as the pump has one relay for both run and prime functions.

In your expert opinion, shall I concentrate on the fuel supply? What will be the fuel pump pressure?

Hello Neilrr. That’s a good point. I did check one spark plug and the distribution cup, lead, ETC. I will do that.

 

[alexanderfoti]

What is your main battery voltage doing at crank? I suspect it is also dropping down past 10V, as I would epect, so explains your lower voltage reading at the pumps.

If its not running on easy start, the issue is spark related, not fuel!

 

[grober]

These cars have EZL ignition units- if the problem is ignition related then this may be the source of your problem- they cant be repaired-just replaced-and they are very thin on the ground now

 

[ray_hennig]

These cars have EZL ignition units

I hope it's not the EZL.

If you have a spark, I think the EZL is OK. Can't be 100% sure but my experience is that these either work or don't.

But do make sure that your HT system, from coil to plugs is 100% 1st class. If you want the best, get it all from MB. Even the leads can be made up by MB. I have my doubts now about the quality of aftermarket Beru leads and Bosch caps. Just my recent experience.

Good hunting.

RayH

 

[zipdip]

Well I have no input on this problem but as I have eaten my wheatabix this morning I have read this whole thread and seen this forum at it's very best with a few old hands dusting off their grey matter and trying to solve a new members problem.

 

[grober]

Wayback Machine

 

[optimusprime]

Just an idea go and select the gears a few times and see if it starts then

 

[dimits1]

Thank you all for the input. I did not had the time to try what you suggested but I will send an update as soon as I do. hopefuly this comming weekend!!


Thanks

 

[optimusprime]

This might help sometime