W124 M104 3.0-24 starting issues

[Benzsc1]

Hi all,

Right where do I start with this??

My 1992 300CE-24 will not start now as has been dead for some time so you know I have been process eliminating the fault by swapping parts from the 300-24 saloon which I know runs!

Initially I diagnosed it to be fuel incorrectly so after swapping the FP relay OVP ECU and fuel and air metering unit (Overkill I know) I carried out further test now bear in mind the car has been in to one of my pals grages but he is a classic car specialist I am talking MG's jags that sort of stuff and he reckoned that when he checked the spark it was nice an blue.

So last night when I change the OVP The last part changed in the list above upon removing the plugs which had previoulsy looked dry following several cranks of the engine are now getting wet with fuel?

Re-checked the spark which is yellow and IMO weak! The leads cap and rotor have all been swapped from the other running M104 (Or M103.5) if you like to call it that.

My qeustion is have any of you got some advice as to where to check next I am guessing swap the coild over and see if that the cause but I am also curious to know what else could cause a weak spark on the ignition system?

I am technically competent being a mechanic and garage owner in a previous life but I do not have all the tools I used to have mainly diagnostic equipment

Any help would be greatly appreciatted (And apologies for the long post I am know for going on a bit )

Regards

Si

 

[Ian B Walker]

Have you checked the coil, if the earth is lose it will cause weak sparking.

 

[Benzsc1]

Hi Ian,

Thanks for your response. Not yet but I will check this tonight the earths on the nearside shock turret have been cleaned but I guess I need to get a multi meter on there really.
Do the coils on these go on a common basis I must admit I have never had to change one on mycars or other I have worked on? I have owned the CE since 2002 and it never let me down other than routine maintenance its been a gem. So I would hate to see her go to waste rotting on the drive way

 

[Ian B Walker]

Not common, thinking onwards, what about the secondary engine management unit bolted to the passengers wing. Has the heat protective paste behind it dried out?

 

[Benzsc1]

Right Ok I had read about this on previous posts before joining this forum. I am going to be honest I was not aware a secondary ECU existed.

So I will need to check this. Is the paste something that is main dealer specific and will re-applying the paste potentially cure the issue? (I am presuming this is similar to the silicone gel used to mount some control modules (Mainly ignition modules) on other cars? Or is it likely the unit will be fubarred and require a replacement.

Also where exactly does it mount on the passenger wing.

I appreciatte the help and TBH feel slightlty embarrassed asking I have owned this car for so long and am usually ofay with solving these type of issues

 

[mazza]

Right Ok I had read about this on previous posts before joining this forum. I am going to be honest I was not aware a secondary ECU existed.

So I will need to check this. Is the paste something that is main dealer specific and will re-applying the paste potentially cure the issue? (I am presuming this is similar to the silicone gel used to mount some control modules (Mainly ignition modules) on other cars? Or is it likely the unit will be fubarred and require a replacement.

Also where exactly does it mount on the passenger wing.

I appreciatte the help and TBH feel slightlty embarrassed asking I have owned this car for so long and am usually ofay with solving these type of issues

The only item that is fixed to the inner wing is the ignition module..isnt it??

Benzsc1-- I also read your thread from the other forum...you said you cleaned the crank sensor (sits on top of crank pulley)..mate, that sensor is for diagnostics only...the ignition TDC pulse sensor is actually located close to the starter motor by the flywheel. Usually these work fine even if the engine hasnt been cranked for a while.. Did you change all the HT leads? and if so...did you guide them back to the correct cylinder?

By null, shot with DMC-TZ3 at 2009-09-25

mazza

 

[Ian B Walker]

Thanks Mazza, I couldn't remember the name of the item.

 

[Benzsc1]

Hi Mazza, firstly thanks for the info Yes I am now aware of the sensor being on the rear of the engine near the starter. I will have to look at swapping the ignition control unit over to see if that works.

TBH I just think if there were a fresh pair of eyes on the car the fault would get diagnosed in minute! This job has just turned out to be a bit of a mind bender for me!

Thanks again

 

[Benzsc1]

Right chaps the ignition module and coil have been swapped.

The only other two components I can now think to swap between the cars are the crank sensor at the back of the engine an d the EZL unit? Has anyone else got anymore idea's? BTW the rev counter is dancing around a bit when I am cranking?

Any help at this point will be really appreciatted.

Simon

 

[Vlad]

I think I'm right in saying that the EZL units on the 300-24v models are a known weak spot and that they break down with age......I'm sure somebody else with more knowledge will be able to chip in with more info.

 

[mazza]

Right chaps the ignition module and coil have been swapped.

The only other two components I can now think to swap between the cars are the crank sensor at the back of the engine an d the EZL unit? Has anyone else got anymore idea's? BTW the rev counter is dancing around a bit when I am cranking?

Any help at this point will be really appreciatted.

Simon

Hi Simon

If you are getting spark on piston 1, your crank sensor should be working ok..as its sending (TDC) signal to the igniton module... THE EZL unit is for ignition advance and retardation (depending what petrol you are using) UK stays on (S). there is one sensor (air temp.sensor) that is connected to the EZL which retards the ignition when temp is above 25deg c.

I really cant see the problem being the EZL or air temp sensor.

I know you changed the fuel distributor unit from the working car...but..any chance that the problem may be caused by lack of fuel pressure from the pump/fuel filter. The injectors require 50PSI to open and work properly.

dont despair mate...KE J IS A BIACH...and thats why we love it...lol

mazza

 

[219]

Since you have both fuel and a spark , I'd investigate the vacuum pipe under the fuel distributor : this awkward to see 'U' shaped pipe sometimes comes off and kills all vacuum in the inlet manifold , which will stop the engine from running despite both fuel and spark being evident . If there is no problem with vacuum then the flap at the top of the throttle body will not sink to allow air in when the engine is being cranked over ( remove air filter and compare this with your running engine to be sure ) .

 

[Benzsc1]

Cheers guys,

Still at it I removed and cleaned the oil caked TDC sensor and still no joy then I pulled out plug three to check for a spark and got nothing??almost like she is weakly firing on some cylinders only and that how is sounds when your cranking there is a tiny amount of combustion and the suggestion it might try to fire but no where near enought to inspire any confidence.

Pontoneer its interesting what you say about the vacuum I will check it out now!

Cheers again

 

[Benzsc1]

Right still no resolve and I am quickly losing the will to live on this one!

The vacuum pipes look ok (Pontoneer just to be clear where abouts on the manifold does the U shaped pipe connect) I really can't think what else it can be other than on the off chance one of the parts I have fitted has inadvertedly failed. I must admit the OVP has only been swapped I should really check for dry joints on both relays.....

Something interesting I should mention is when I removed the original ignition module the paste under the plastic sheet was dry only in one area and had discoloured to a brownish black in an area slightly larger than the size of a 50 pence piece and on the inner wing where the module seats the the area i mention above was seating on a section of bare metail the paint had somehow come away??? Now I have fitted the other module from the saloon W124 straight on to that bare metal section I am now wondering whether that has something to do with my problem?

Its just got to the point I am not sure what else to swap maybe I should actually swap the TDC sensor. Diagnosis if difficult purley because since I gave my workshop up the diagnosticve equipment I had is in storage which I guess at this point I should really go and retrieve.

Hey ho onwards and hopefully upwards (Providing the ash cloud does'nt prevent me)

 

[Benzsc1]

Right after some thought and some time to rest after nearly throwing the towel in!! (as if I really would )
I am now going to swap the TDC sensor from one car to the other. If this does not work then its time to start checking the loom. I am certain that loom should not be affected by the quality issues on the later 124's I have already removed the loom from it plastic enclosure that runs along side the cam cover and after removing some of the insulation tape the loom looks ok on that section no splits or brittle wires although there are some rather strange looking but possibly factory original?? connectors that are a translusent brown colour I must admit it does not look typically Mercedes but then again these connectors seem quite permenant if you know what I am on about....

Still we shall see I will get a resolved tag on this thread I promise. I Must have thios car running for summer!!

 

[mazza]

BTW the rev counter is dancing around a bit when I am cranking?

Any help at this point will be really appreciatted.

Simon[/QUOTE]

Hi Simon

I could be wrong but!!!! if the tachometer (rev counter) is dancing around. Doesnt that mean that the TDC pulse generator is working fine and is receiving magnetic pulses from the flywheel?

I still think that your TDC sensor is working fine.


mazza

 

[Benzsc1]

I thought the rev counter took its feed elsewhere TBH but I could be wrong?? The Rev counter has been dancing around sometimes its rising up to about 1000Rpm other times it just sits on nothing barley moving......

TBH Mazza I hope it is the sensor otherwise bar going out and buying new parts in terms of hardware I have been through it all...

We shall see BTW thanks for the help and advice its been a great help so far. This site has some good members and a great depth of knowledge

 

[mazza]

I thought the rev counter took its feed elsewhere TBH but I could be wrong?? The Rev counter has been dancing around sometimes its rising up to about 1000Rpm other times it just sits on nothing barley moving......

TBH Mazza I hope it is the sensor otherwise bar going out and buying new parts in terms of hardware I have been through it all...

We shall see BTW thanks for the help and advice its been a great help so far. This site has some good members and a great depth of knowledge

Hi Simon

No worries mate!! Its a strange this one..

mate! while you're checking the TDC sensor...give the Coolant temp sensor a good going through as well...just wandering if the coolant temp sensor is not working or giving false resistance...the first sensor to be energised by the ECU is the COOLANT TEMP SENSOR.. its takes a reading of the engine temp..and if its cold start temp (less than 95deg F)..it sends a signal to the ECU and ECU activates the cold start injector for extra fueling I believe this also gives way for the idle speed valve to open to increase air flow.

give it a go mate...it wont hurt

mazza

 

[Benzsc1]

No worries will Do mate oh and Happy Birthday BTW

 

[Benzsc1]

Update: Swapped crank position sensor (Not the TDC diagnostic sensor as i incorrectly referred to above) and still nothing she is trying to fire but I think only on a couple of cylinders. the plugs were sopping wet when I removed them following a few attempts to fire her up so dried them off and let the remaining fuel evaporate from the cylinders re-installed plugs and re-tried still the same. The last thing on the ignition I can think of is the insulating plate that sits behing the rotor arm as i have heard cracks in this can cause tracking howver I cannot visably see any cracks??

My next port of call is check the entire vacuum system has anyone got a diagram of the various vacuum connections??