ML270cdi (2003) stalls when revs come down to around 900rpm

wvr

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I Bought a ML270cdi 6 months ago:D, and then my problems started.:confused: My ML270cdi has hard starting and after a long process eventually found out that it is due to low compression (got two different specialists to check):mad::(, this was terrible news but I have had to get over it. I decided that because it still performs really well, I’ll wait until something else goes wrong before replacing the motor with a second hand one:rolleyes:. It recently started cutting out all the time (only when ideling or when I put my foot on the brake, I set the idling up but when I put my foot on the break the idling seems to come down to the default setting of around 850 and then cuts out straight away - if i keep the revs above 1000rpm and drive, she still goes like a new car:(. Could it be the low compression that is causing this because being a diesel, it doesn’t have spark but relies on compression to combust. I’m just worried that if I fit the other engine that it might carry on doing the same thing (other engine comes complete with inlet manifold and turbo and all components so at least ill have spare parts from my old engine)
Has anybody got some advice for me?
Thx wvr:confused:
 
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Alex Crow

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first thing i can think to say is that your scenario is very odd indeed - i find it hard to believe you have compression issues that cause poor starting. the stalling below 850rpm just cannot be because of low compression - no way no how. you would be using more oil than fuel!! and how ould it ever start (starter speed is 200rpm)??

are you SURE it is low compression these two specialist are talking about, and not low fuel rail pressure?
 

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first thing i can think to say is that your scenario is very odd indeed - i find it hard to believe you have compression issues that cause poor starting. the stalling below 850rpm just cannot be because of low compression - no way no how. you would be using more oil than fuel!! and how ould it ever start (starter speed is 200rpm)??

are you SURE it is low compression these two specialist are talking about, and not low fuel rail pressure?

I Left this post for you,,it did not read right for me
 

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quite agree autofix, unless the o/p has just misunderstood the diagnosis from his 2x experts.
 
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wvr

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hi, yes, bosh agent had the car for a week when the car was just struggling to start, but once started ran fine (there was no stalling problem at that stage)they are really orginized and have sll the testing machines to problem solve common rail diesel engines.after checking everything they did the comp. test with results12-17bar(dry) and 15-22bar(with oil).At this stage,car still started ok but had to manually put glow plugs on. did this for 2 months and then she started with stalling problem. I took it to mb, after a week of battling, they did a leekage test confirming leekage through some valves and through to sump in some cylinders. this car has had a lot of people scraching their heads and has become a serious worry.
 
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Alex Crow

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ok, fair enough then wvr, better price up a s/h motor from a breaker. i will fit it for you if you want? just checking though, does it use loads of oil? and if it stalls below 800rpm, how on earth do you start it at 200rpm?? last question needs an answer please.
 
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wvr

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it doesn't use much oil or smoke and has plenty of power. thats the strange thing, about the starting-i was thinking the glow plugs help to ignite the diesel when starting but once plugs turn off, she cuts out. or could it be some idle control unit that is faulty??? i could get by with the hard starting due to the low compression(when cold) if i could just solve the idling problem, and if i could b sure its the same problem, id know its time to redo or replace engine. im just scared i get another engine, put it in , she ends up starting easier but then the idling problem is still there. this situation really sux.
 

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and if it stalls below 800rpm, how on earth do you start it at 200rpm?? last question needs an answer please.

where are you wvr? you need a third opinion on this one. cylinder leakage will mean oil consumpton and smoking, valve leakage will not show 12bar+ when cranking. furthermore this will not cause stalling below 800rpm, many othe things will. if it only stalls below 800rpm when hot and only restarts when cold i suggest a crank sensor for instance...
 
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wvr

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I'm in klerksdorp, (SA). What is the minimal compression required for a diesel and is it critical for the starter to turn the engine at max start speed (like you say 200rpm) when doing compression test?. After the first comp. test i took it to another mechanic who didnt believe it was compression and he says he changed the crank position sensor (R1600 which equals around $160). He says he even tried a part (cam angle sensor) from a c270cdi (newer model) in his shop and it made no difference. I then took it to MB . They picked up (before I told them to do comp. test) injector 1 low voltage and common rail regulator. But both components tested perfect at bosh agents when i had them checked. I recently had the car checked out again and one of the error codes were again synchronisation between crank sensor and cam sensor. Maybe the new crank position sensor just fitted was also faulty (could this happen). There is just too much guess work now. I really don’t know which way to turn at this stage.
Regards
Warrick
 

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the synchronisation code will be logged if it cranks a long time without starting, this can be ignored. really you need a rail pressure test when cranking, the low compression may well be a red herring as this is unheard of in UK, at least in relation to starting problems. the fact that it stalls below 800rpm but restarts at 200rpm is still hard for me to understand.
 
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wvr

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Hi A P
It takes good 20 – 30 cranks with foot flat against the accelerator before she starts, it always had hard starting (that’s how I found out it had low compression) but once it started it ran fine, and when warmed up it started first time. The stalling problem started very gradually doing it once in a while. It then started cutting out when warm, (she idled but once you put your foot on the break to select a gear the revs dropped slightly and then she stalled). This progressively became worse and now once I manage to get her started she doesn’t idle (when the revs come down to "normal" idling speed). If I manage to get it in gear and start driving it drives perfectly with lots of power and no excessive smoke. I know this all sound odd, I’m trying to explain in as much detail as possible. When you mentioned rail pressure, do you think it could be the pump??
Thanks again for your advice so far…
 
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wvr

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alexander patient. I was just reading on the "engine, drivetrain...forum" about cleaning the ERG, could this cause the problem. I posted a new thread there asking the same Q?
thx
 

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if i had this problem i would be moitoring rail pressure on star. it is just possible you have leak off problem at an injector, but stalling below 800 then restarting (eventually) do not quite fit. you can check it your self by removing the litle clips on the injectors and then pulling the pipes out. now simply crank the engine and watch for one injector leaking off far more than the rest. othe pressure faults could be caused by the pump as you suggest, the control valve at the back which some times has split o-rings, or air in the low pressure system. equally you may have no high pressure problems at all, but it is worth checking that leak off...
 
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wvr

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thx, the leak off has been checked, valve at back of rail has been checked, they also checked it with some frequency machine and say it is fine(oring too). this car seems to have had a lot of work done previously even before i bought it, i realized it also has had three previous owners and i suspect a rare, maybe even simple, out of the ordinary fault that no one has touched on. Is there a filter or pump in the tank. another thing i should mention is the oil high used to flash even though the oil wasnt high. About the compression, would u say there are many diesels with 12-18 bar driving around without any problems(the book says 24 bar min. aparantly). In other words, could this b normal for a 180000km engine. would b helpful to find out the compression of a similar engine(similar kilos)that has no problems, then id know. the problem is, no one does a compression test on a car if it has no problems. if you have any records, it would b a great help.
 
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Alex Crow

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never done a compression check on a cdi!! rarely see mechanical problems of this sort, unless they have been through a flood.
 
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wvr

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if only i knew what happened, i see the oil cooler has been damaged and two vanes soldered.maybe there is restricted flow and the oil cooling the piston is not sufficient. all a guess, or maybe petrol was added by mistake. i can get a second hand engine (complete with manifolds, turbo, pumps ect.-only 3 months garentee) for aprox same price
that it will cost to redo my engine(just compression), the advantage is that i'll have spare turbo,injectors,pump ect., disadvantage is it will be an old engine.(with no problems YET!!) any advice???
 
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wvr

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Finally!!!! after 8 months of hell, I found the problem. (ML 270 CDI)

Stalling problem when I put my foot on the break was the ABS pump.
Hard starting was the computer.
Car is running like new.:p

I tracked down the owner before the owner I bought the car from. He said he had the car for 6 months and decided to sell it cause of the intermittent problem that was there from the day he bought it and no one could fix. The person he sold it to (the one I bought it from) admitted there was a problem but he had it fixed (obviously not! which became my problem:confused:). Luckily after a long struggle and when the new cutting out problem started, I finally got it to the right guys (Transport Motor Repairs in Pretoria) and they sorted it out.
:cool:
 

Alex Crow

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we had not forgotten you wvr! so pleased to hear you have it sorted.

any idea exactly HOW the abs pump was stalling the engine?? very odd one that. and have you stopped worrying about that washer? ;)
 

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Pleased that it is fixed and i would love to know what the fault was
 

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