A140 losing power at high speed
05-29-2021, 06:21 AM
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Mercedes w168 A140
A140 losing power at high speed
I've got a w168 A140 petrol from 2000 and trying to figure out why it is losing power.
The problem appears when traveling at the speed of 70 - 80 mi/h (110-120 km/h). It just suddenly looses power. At first it only appeared when traveling at this speed and I let off the gas pedal to apply the engine brake. Once I pressed on the gas again it didn't pick up the pace. My initial thought was that the spark plugs could be at fault but once I stopped the car and restarted it everything got back to normal. In fact when this happens on the motorway I only need to stop the engine and restarting it without stopping the car and everything goes back to normal until I got to that speed again. The car runs fine otherwise, mainly it is used for short shopping trips so this problem never occurs there.
I brought it to a non specialist garage and they made me change the fuel pump and the battery but none of those solved the problems. They were due to be changed anyway but those weren't the problem apparently.
I've read a couple of forum posts about it already and I suspect the MOF. Or the oxygen sensor or the knock sensor or a bunch of other things. So it would be nice if someone could nudge me to some direction.
More questions:
Are general OBDII diagnostic interfaces from amazon compatible with this car? Will I be able to read out the fault codes with any of them or STAR diagnostic is the only available option?
When the car is standing, it doesn't rev over 4000. I've read that other models have a limiter so people can't go berserk screaming their engines in the backyard. Does this model have this limiter or it is something related to the fault initially described?
Thanks!
The problem appears when traveling at the speed of 70 - 80 mi/h (110-120 km/h). It just suddenly looses power. At first it only appeared when traveling at this speed and I let off the gas pedal to apply the engine brake. Once I pressed on the gas again it didn't pick up the pace. My initial thought was that the spark plugs could be at fault but once I stopped the car and restarted it everything got back to normal. In fact when this happens on the motorway I only need to stop the engine and restarting it without stopping the car and everything goes back to normal until I got to that speed again. The car runs fine otherwise, mainly it is used for short shopping trips so this problem never occurs there.
I brought it to a non specialist garage and they made me change the fuel pump and the battery but none of those solved the problems. They were due to be changed anyway but those weren't the problem apparently.
I've read a couple of forum posts about it already and I suspect the MOF. Or the oxygen sensor or the knock sensor or a bunch of other things. So it would be nice if someone could nudge me to some direction.
More questions:
Are general OBDII diagnostic interfaces from amazon compatible with this car? Will I be able to read out the fault codes with any of them or STAR diagnostic is the only available option?
When the car is standing, it doesn't rev over 4000. I've read that other models have a limiter so people can't go berserk screaming their engines in the backyard. Does this model have this limiter or it is something related to the fault initially described?
Thanks!
06-03-2021, 01:44 PM
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A160, С230
Try to swap K7 and K10, they are the same, K10 - rear window defroster relay.
06-05-2021, 10:47 AM
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Mercedes w168 A140
Thanks for the tip! I tried swapping the K7 with the K10 then replaced it with a new one just in case, but it hasn't solved the problem unfortunately.
Since the first post I also discovered that although there are two oxygen sensors in the exhaust there is only one connected without any traces of cable or connector for the other one. Also If I disconnect the remaining one oxygen sensor (closer to the engine) nothing happens. The car works as normal and not even an engine light comes up.
07-13-2021, 02:13 AM
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Turned out to be the fuel pump eventually.
I took it to a specialist garage where they found out that the ecu was remapped so it didn't show some faults. The ECU was set back to its original state then the necessary parts were replaced but the issue still didn't disappear. Luckily there was a problem with the fuel level indicator so the fuel tank needed to be dismounted again and there we found the culprit of the problem. The initially replaced fuel pump (that is also a Volkswagen fuel pump) isn't exactly like the original Mercedes fuel pump. It turned out that it could pull up dirt from the fuel tank and block the flow of the fuel. When the engine was shut off the fuel pump also released the dirt from the filter so next time the car started everything was back to normal until enough dirt accumulated again on the filter and blocked the flow.
Thanks for all the help!
I took it to a specialist garage where they found out that the ecu was remapped so it didn't show some faults. The ECU was set back to its original state then the necessary parts were replaced but the issue still didn't disappear. Luckily there was a problem with the fuel level indicator so the fuel tank needed to be dismounted again and there we found the culprit of the problem. The initially replaced fuel pump (that is also a Volkswagen fuel pump) isn't exactly like the original Mercedes fuel pump. It turned out that it could pull up dirt from the fuel tank and block the flow of the fuel. When the engine was shut off the fuel pump also released the dirt from the filter so next time the car started everything was back to normal until enough dirt accumulated again on the filter and blocked the flow.
Thanks for all the help!
11-10-2021, 10:44 AM
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A160 w168
I've got a w168 A140 petrol from 2000 and trying to figure out why it is losing power.
The problem appears when traveling at the speed of 70 - 80 mi/h (110-120 km/h). It just suddenly looses power. At first it only appeared when traveling at this speed and I let off the gas pedal to apply the engine brake. Once I pressed on the gas again it didn't pick up the pace. My initial thought was that the spark plugs could be at fault but once I stopped the car and restarted it everything got back to normal. In fact when this happens on the motorway I only need to stop the engine and restarting it without stopping the car and everything goes back to normal until I got to that speed again. The car runs fine otherwise, mainly it is used for short shopping trips so this problem never occurs there.
I brought it to a non specialist garage and they made me change the fuel pump and the battery but none of those solved the problems. They were due to be changed anyway but those weren't the problem apparently.
I've read a couple of forum posts about it already and I suspect the MOF. Or the oxygen sensor or the knock sensor or a bunch of other things. So it would be nice if someone could nudge me to some direction.
More questions:
Are general OBDII diagnostic interfaces from amazon compatible with this car? Will I be able to read out the fault codes with any of them or STAR diagnostic is the only available option?
When the car is standing, it doesn't rev over 4000. I've read that other models have a limiter so people can't go berserk screaming their engines in the backyard. Does this model have this limiter or it is something related to the fault initially described?
Thanks!
The problem appears when traveling at the speed of 70 - 80 mi/h (110-120 km/h). It just suddenly looses power. At first it only appeared when traveling at this speed and I let off the gas pedal to apply the engine brake. Once I pressed on the gas again it didn't pick up the pace. My initial thought was that the spark plugs could be at fault but once I stopped the car and restarted it everything got back to normal. In fact when this happens on the motorway I only need to stop the engine and restarting it without stopping the car and everything goes back to normal until I got to that speed again. The car runs fine otherwise, mainly it is used for short shopping trips so this problem never occurs there.
I brought it to a non specialist garage and they made me change the fuel pump and the battery but none of those solved the problems. They were due to be changed anyway but those weren't the problem apparently.
I've read a couple of forum posts about it already and I suspect the MOF. Or the oxygen sensor or the knock sensor or a bunch of other things. So it would be nice if someone could nudge me to some direction.
More questions:
Are general OBDII diagnostic interfaces from amazon compatible with this car? Will I be able to read out the fault codes with any of them or STAR diagnostic is the only available option?
When the car is standing, it doesn't rev over 4000. I've read that other models have a limiter so people can't go berserk screaming their engines in the backyard. Does this model have this limiter or it is something related to the fault initially described?
Thanks!
In my case, the problem was a dirty MAF sensor, which is integrated in the ECU. I had to take it off (takes 10 minutes) and clean it with circuit cleaner and the problem went away.
I could work out that MAF was the issue by reading at the data with OBDII interface (a cheap one bought on the internet), it is worth paying an app like torque, it's only 2/3 euros and it gives you a lot of details that you need if you want to diagnose this kind of issues (STFT,LTFT for example).
If you do the job be careful not to damage the ECU and close it well, because water might leak inside.
Hope this helps
