270cdi revs up and down
10-28-2009, 09:02 PM
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ml 270cdi
270cdi revs up and down
Hello
The engine on my ML 270 cdi, 2004 revs up and down /- 200 rpm when driving in constant speed. This comes and goes as it suits but does not happen when driving with Cruise Control. I have checked the pedal and the wiring. Is it possible that the potmeter is defective because the potmeter does not affect the cruise system ore is this wrong?. There are no fault codes when connecting it to the Star/computer system at the dealer.
I will be thankfull any help with this anoying problem..
JS
The engine on my ML 270 cdi, 2004 revs up and down /- 200 rpm when driving in constant speed. This comes and goes as it suits but does not happen when driving with Cruise Control. I have checked the pedal and the wiring. Is it possible that the potmeter is defective because the potmeter does not affect the cruise system ore is this wrong?. There are no fault codes when connecting it to the Star/computer system at the dealer.
I will be thankfull any help with this anoying problem..
JS
10-06-2014, 11:42 AM
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ML 270 cdi 2004 engine pulse
I have a similar problem that occurs with both normal and cruise control operation. At 2500 rpm on motorway when engine comes under load etc there is a surge of +/- 100rpm. Manually accelerating cures the problem
08-27-2018, 03:42 PM
#4
Hello,
I do experience exactly same problem for more than 4 years I own 2003 ML 270 CDI (W163). Recently I refurbished all fuel injectors hoping this annoying revs up and down at 2500 RPM would disappear if all this was caused with bad injectors and consequently power lack. But refurbished injectors did not change anything except fuel consumption, which improved. A year ago I removed second catalyst - I regret I did so as the the cat was good. Now I am going to remove first cat and install straight pipe or another cat without ceramic internals - let's see what happens.
I measured boost pressure by this annoying rpm play (during steady driving without and with cruise control on) at 2500 rpm (120 km/hr speed) and it was about 10 psi varying slightly sinchronously with rpm-s. Just I touch the accelerator,"revs up and down" disappears, boost pressure goes to nearly 20 psi and the car accelerates quite well - until the next steady regime is established. I have come to decision that first catalyst is (or may be) choked resulting high back-pressure in the outlet manifold and low boost pressure as turbo is, of course, affected. On the other hand, higher exhaust pressure must cause more exhaust gases to enter inlet manifold through the EGR valve and worsen engine performance - kind of magic enclosed circle. I will tie up a vacuum gauge to the EGR valve vacuum hose to find out if rpm-s play sinchronously with EGR valve operation. If it is so, then may "theory" about choked cat will be proven.
I will be back with news.
Dear forum members, as you see the topic starter wrote his post in 2009, next post appeared on 2014 and I found this thread in 2018
So I am quite talking with myself , Anyway, this kind of self therapy makes me happy!
Thanks
I do experience exactly same problem for more than 4 years I own 2003 ML 270 CDI (W163). Recently I refurbished all fuel injectors hoping this annoying revs up and down at 2500 RPM would disappear if all this was caused with bad injectors and consequently power lack. But refurbished injectors did not change anything except fuel consumption, which improved. A year ago I removed second catalyst - I regret I did so as the the cat was good. Now I am going to remove first cat and install straight pipe or another cat without ceramic internals - let's see what happens.
I measured boost pressure by this annoying rpm play (during steady driving without and with cruise control on) at 2500 rpm (120 km/hr speed) and it was about 10 psi varying slightly sinchronously with rpm-s. Just I touch the accelerator,"revs up and down" disappears, boost pressure goes to nearly 20 psi and the car accelerates quite well - until the next steady regime is established. I have come to decision that first catalyst is (or may be) choked resulting high back-pressure in the outlet manifold and low boost pressure as turbo is, of course, affected. On the other hand, higher exhaust pressure must cause more exhaust gases to enter inlet manifold through the EGR valve and worsen engine performance - kind of magic enclosed circle. I will tie up a vacuum gauge to the EGR valve vacuum hose to find out if rpm-s play sinchronously with EGR valve operation. If it is so, then may "theory" about choked cat will be proven.
I will be back with news.
Dear forum members, as you see the topic starter wrote his post in 2009, next post appeared on 2014 and I found this thread in 2018
So I am quite talking with myself , Anyway, this kind of self therapy makes me happy!Thanks
