mercedes ml270 splutters misses at 1500rpm

[markiotun]

hi could anyone shed some light why my ml270 2002 misses splutters when going slow also if you hold revs at 1500rpm for a few seconds then slowly rev it splutters till it clears had new maf ,injectors checked had it to dealers no code present .it a pain as i dont no what to do next any suggestions would be appreciated thanks.also av problem with abs bas esp dealers say needs new pump esp unit could this be related thanks

 

[BlackC55]

I would still be looking at injectors. Who checked them?

 

[markiotun]

john hogg of sheffield bosch diesel specialist, i had them taken out, and tested on their machine which i was told checks them throughout rev range.also had them tested earlier at firths of rotherham which can only test at tickover ,they read 3.6 3.8 5.6 3.4 2.6 he said this would not cause the problem im having and reffered me to hoggs im mistified been to more so called diesel mechanics as well, getting nowhere fast first merc ive had would not buy another never had so much trouble with any other car,thanks.

 

[Andy Wr]

My Renault van was like that and the problem was sucking in air through a faulty fuel filter housing, an earlier Maestro diesel van had a similar lack of power accompanied by black smoke (unburnt fuel) and it was a knackered diesel injection pump, I fitted one off a Sherpa and it totally transformed it, I had obviously had problems when I purchased it.

Has the problem recently appeared on say the latest tank of fuel or has it been on going for some time ? Have you tried one of the injector cleaner / fuel additives yet ? Checked or replaced the fuel filter, fitted correctly, seals ok ?

 

[television]

What is wrong with the ABS

 

[BlackC55]

5.6 is too high. Should only be a maximum of 5.

 

[markiotun]

hi thanks for your replys, going to see another merc diesel mechanic tomoro who works with merc commercials, hope he can locate problem. put new filter on and diesel filter, will av him check all possibilities will let you no how i get on thanks.as for abs doesnt come on on start up only when you move of after 100yards or so got second hand pump will av that fitted hope that cures it thanks.

 

[Andy Wr]

Please keep us informed if you will.

 

[markiotun]

been tinkering with it tonight think i know were the problem is coming from if i let the air escape out one of the vac pipes then rev it it clears place the rubber pipe back on wait a few seconds its splutters again so its looks like an air problem somewhere anyone got any idea what could be the cause thanks.

 

[psmart]

EGR Valve? From the Vac Pump, you have the EGR Transducer and the Turbo Transducer, both use Vac for control (under electronic command). Not familiar with the EGR, albeit someone like Uncle Benz might shed some light.

Just another thought to remove it from the equation, try swapping the Turbo and EGR transducers around (they are different part numbers, but it will prove if there is fault on the EGR transducer). The EGR transducer is on the bulkhead, looking from engine towards back of car, on centre right, it has 2 vac pipes going in and an air filter (looks like an old fashioned fuel filter) dangling down. The turbo transducer (BPCVT) is on the left hand side, just forward of the round vacuum reservoir ball. Just mark the pipes and swap the transducers around.

 

[markiotun]

thanks for your reply with give it a go tomoro let u now cheers.

 

[Uncle Benz]

Good advice from psmart. If one of the control valves is faulty, swapping them over will prove it. The engine will still have some sort of a fault, as the faulty valve will now be on a different part of the system, but it will certainly point you in the right direction.

 

[markiotun]

hi just swapped the valves over but still doing the same so they must not be at fault

 

[psmart]

It could still be the EGR Valve (the device you changed over was the transducer, it just allows a vacuum to be channelled onto the EGR Valve). You can see your vacuum system here: http://www.detali.ru/cat/oem_mb2.as...GM=716.644&CT=F&cat=06H&SID=80&SGR=010&SGN=01

As you said the problem is cured when you let air into the vacuum, then it would seem likely that its the EGR as I spent a lot of time diagnosing the Turbo side of the engine and didnt come across a misfire.

Try bypassing the EGR transducer by pulling the two vac pipes off the top and connecting them together (the ends of the pipe have an outer rubber sleeving, so only one of these sleevings should allow you to bridge the pipes). If after this change, the engine runs fine, then you have a problem with the EGR valve.

 

[markiotun]

cheers 4 that will give it a go in morn let u know thanks again for your replys they been much appreciated.

 

[psmart]

It occurred to me last night that we may be chasing a bit of a red-herring with the vacuum being disconnected. Make the test so it can be ruled out, but basically by allowing air into the vacuum system, you are in effect disabling the Turbo. As the Turbo vanes are fully engaged into the exhaust stream at tick-over by the vacuum sucking the actuator arm fully down, removing the vacuum would mean the arm remains in its minimum setting. Thus when you rev to 1500rpm, you have less fuelling requirements because less air is being pumped into the engine. Interesting to test this though and see if the misfire occurs at higher revs with the turbo disabled.

Regarding the injector (5.6), it would be possible with a diagnostics system (Star, CarSoft etc) to change the ECU setting for this injector to see if it is directly responsible for the misfire.

Another possibility is an ECU fault (or a general electrical fault given you are having ABS etc errors).

Have you tried driving the car, at 1500rpm up a steep hill to see if the ECU shuts down into Limp Home mode? May indicate if something else is a miss, such as turbo air flow etc.

I cant help much more as its going outside the bounds of what I researched on my car.

 

[markiotun]

hi again thanks for your suggestions as you said if i disconect pipe i lose turbo power. av to switch off engine replace to get it back ,does not miss at any rev range when disconected, also noticed when it misses heavily grey smoke appears from the turbo area could this be a manifold fault or turbo or exhaust.looks like its not going to be cheap any suggestions would be grateful thanks.

 

[psmart]

I'll give some basic info on how the system works. Please excuse the waffle, when I get time Ill try and draw this up properly and put it onto the DIY section.

Basically, you have the standard air inlet (air inlet noise suppressor on left wheel arch with the round vacuum reservoir above) feeding the air filter, which has holes in it to allow a little hot air from the exhaust manifold to enter the air intake, presumably for rapid engine warm up. The output of the air filter feeds the MAS/MAF, a temperature and air mass sensor to let the ECU know what temperature and mass of air is entering the system. After the MAS you have a union with the crank-case breather, fed by an oil seperator sitting on top of the cylinder head (black hand-cream type box). This union allows crank-case/cylinder gases etc to be mixed in with the air stream (it also allows some oil into the air stream). After the union, the air enters the Turbo compressor and is compressed prior to exitting into an expansion box and then into the air-air intercooler (left side). On the intercooler, at the exit (right side) is a temperature sensor and a pressure sensor so that the ECU knows what the final charge air temperature is and what its pressure is. This charge-air then exits the intercooler and is fed into the inlet manifold. The inlet manifold combines Exhaust Gases, where an extra port on the exhaust manifold allows exhaust gases to go through the cylinder head (a
special chamber/hole exists in the cylinder head), through to the inlet manifold side where the gases are cooled in an exhaust gas cooler before going to the EGR (Exhaust Gas Recirculation) Valve, which the ECU opens/closes via the EGR Transducer to mix exhaust gases in with the charge-air. There are some internal regulator vanes inside the inlet
manifold controlled by a Servo Motor/ECU but I havent figured the purpose of these out yet.
On the injection side, you have a high pressure pump feeding a common rail bar, which has a pressure sensor to let the ECU know at what pressure the
diesel will be injected. You then have the 5 injectors fed by the common rail bar and controlled by the ECU.
The whole system is a closed loop control system with the ECU controlling. Basically, on engine switch on, the high pressure pump is indirectly driven by the crank and builds up diesel under pressure in the common rail bar (helped by an electric fuel pump into the high pressure pump). The vacuum pump is also indirectly driven by the crank and it causes a vacuum in the vacuum circuit. As the engine fires (normal aspiration), the exhaust gases spin the turbo (in its minimum setting, it is still spinning, as this engine uses a Variable Nozzle Turbo with a restricted compressor inlet, so it has a minimum spin
speed), the diesel pressure builds up and so does the vacuum. The ECU opens the BPCVT transducer fully, so that maximum vacuum is applied to the VNT turbo actuator, and the actuator arm is pulled fully down, meaning maximum exhaust gases are directed over the turbo turbine blades, which in turn means increased air compression in the turbo compressor and thus the ECU will see an increase in air inrush (MAS) and air-charge boost (temperature and charge pressure sensors at exit from intercooler), so it can thus adjust the amount of fuel injected and control the engine speed etc. It regulates the turbo actuator by the BPCVT to ensure charge-air into the inlet manifold is optimum for the fuel it injects (or viz-a-viz), the RPM it expects and the load it encounters (additional sensors on the engine). The EGR is for emissions purposes and is opened according to the program in the ECU.
The ECU is a computer running a program, and this program specifies via means of a complex 3D map, the minimum/maximum values for example the charge-air pressure sensor should read for a given actuation of the BPCVT transducer etc. Should the ECU encounter a reading which is outside of its map (ie. you disconnect the vacuum from the BPCVT, not
allowing the ECU to control the turbo compression) it throws its hands up in the air and enters an emergency mode, or if the error is serious enough, shuts down the engine.

Many things can upset this controlled loop system, such as:
a) Exhaust blockage - increased back-pressure wont let the turbo spin up fully, thus the ECU will see out of parameterisation errors as well as the combustion process being affected because the expanding gases cant get out of the cylinder fully etc. Depending on how serious, this can cause the engine to run rough before the ECU decides to go into emergency mode.
b) Vacuum - If the vacuum pump or the vacuum circuit has a leak, then the ECU wont be able to control the Turbo or the EGR valve to an accuracy it expects, thus it will go into emergency mode (EM).
c) BPCVT develops a fault, thus wont control the turbo, so the ECU detects this either by seeing an electrical fault on the control lines going into it, or by
looking at the pressure sensor values and seeing that the pressure of the charge-air isnt what it expects for a given signal to the BPCVT.
d) EGR Transducer develops a fault, this is a little more complex because if the ECU decides to re-circulate a given percentage of exhaust gases, it will
re-calculate fuel and air mixture to accommodate, so if the EGR valve/transducer isnt working, then there will be more air in the inlet manifold (as there are no exhaust gases). Other than an electrical fault registering with the transducer, Im not sure how the ECU detects this condition as I didnt do many tests on this area.
e) Turbo/turbo actuator - a fault with the turbo, such as the actuator has a leak/seized, or it goes out of tolerance. If the turbo itself is damaged, you would know about it, either from the big bang and clouds, or a bad grating sound.
f) An intercooler leak or any pipe leak from the outlet of the turbo compressor into the inlet manifold - This will cause a drop in pressure in the system and thus the ECU will detect an out of parameter condition and enter EM.

There are many other conditions, for example if an injector failed, then the exhaust gases produced wouldnt be sufficient to spin the turbo to a rate which compresses air that the ECU expects.

Is there any other information you can add, ie. your driving at X and the car goes into emergency mode (limited revs/speed)?

With you mentioning the smoke around the turbo, this could be the exhaust being blocked or the exhaust clamp broken. With you mentioning the smoke, if you released the clamp on the pre-cat to turbo (even better to remove the pre-cat) you could see if the mis-fire is being caused by back-pressure.

Its best to analyse yourself and when your certain of the problem, only then take it into an Indie/dealer if your not happy with fixing it yourself.

Post up as much info as you can, as besides people like myself, you have quite a few pro-mechanics on the forum who may recognise a scenario and Malcolm who has a lot of experience and access to a lot of technical documents.

 

[markiotun]

hi just to let u know problem was maf sensor, bought genuine one to try everything seems fine now, the two i bought of ebay which were pierburg must not be up to the job, spent £100s on trying to diagnose so dont make the same mistake as me thanks to you all for your time mark.

 

[BlackC55]

After all that it was just an air mass sensor.

Just shows some of the parts on ebay are not what they seem.

WARNING to you all!!