[HELP] Car lost power when AC is on
11-16-2018, 05:43 PM
#1
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2014 E550 4MATIC TUNED - Turbo Upgraded Stage 3
[HELP] Car lost power when AC is on
This issue has been going on for almost 5 months.
When AC is on, Car lost power on acceleration, significantly.
Felt like 30% of HP/TQ power is lost. It doesn't accelerate as fast.
Engine also runs harder and Exhaust sound also changes
It doesn't matter if I set it to bring in Cold Air or Hot Air.
And it won't gain power back after turning off AC.
Car will have to be restarted to gain power back
I was thinking, maybe AC compressor is gone. But it can still bring in cold or hot air.
Any idea if compressor is good or not ? (Since it can still bring in cold and hot air)
Or something else ?
I kept my tune files and I do change tune to tune for testing.
These issues are always there now.
It doesn't matter which tune I put on.
My car is almost at 70000 miles on odometer.
I do have scan tools. I’ll check on timing.
i also have xentry system. I scanned the car. No fault code at all.
The car does have some other issues.
The car will lost acceleration power by 20-30% after driving 35 mins or longer.
And 2 issues during cold start.
During cold start, it has weird knocking (sound like "da da da...") sound coming from the front of driver side. (Some where very close to drive side wheel)
This sound goes with rpm (idle or during driving), It is more noticeable when rpm drop down from 1500-800rpm.
The sound get quieter (or gone) after 15-20 mins of driving.
Also, If I drive out during cold start. Its very hard to accelerate the Car. RPM goes up and I can feel a lot of air been pushed out.
But it is just very hard to accelerate the car during cold start.
If I go WOT during cold start, sometimes P0299 Under Boost code will pop.
All these happened around 5-6 months ago.
When AC is on, Car lost power on acceleration, significantly.
Felt like 30% of HP/TQ power is lost. It doesn't accelerate as fast.
Engine also runs harder and Exhaust sound also changes
It doesn't matter if I set it to bring in Cold Air or Hot Air.
And it won't gain power back after turning off AC.
Car will have to be restarted to gain power back
I was thinking, maybe AC compressor is gone. But it can still bring in cold or hot air.
Any idea if compressor is good or not ? (Since it can still bring in cold and hot air)
Or something else ?
I kept my tune files and I do change tune to tune for testing.
These issues are always there now.
It doesn't matter which tune I put on.
My car is almost at 70000 miles on odometer.
I do have scan tools. I’ll check on timing.
i also have xentry system. I scanned the car. No fault code at all.
The car does have some other issues.
The car will lost acceleration power by 20-30% after driving 35 mins or longer.
And 2 issues during cold start.
During cold start, it has weird knocking (sound like "da da da...") sound coming from the front of driver side. (Some where very close to drive side wheel)
This sound goes with rpm (idle or during driving), It is more noticeable when rpm drop down from 1500-800rpm.
The sound get quieter (or gone) after 15-20 mins of driving.
Also, If I drive out during cold start. Its very hard to accelerate the Car. RPM goes up and I can feel a lot of air been pushed out.
But it is just very hard to accelerate the car during cold start.
If I go WOT during cold start, sometimes P0299 Under Boost code will pop.
All these happened around 5-6 months ago.
Last edited by cocobeex; 11-16-2018 at 10:01 PM.
11-16-2018, 05:57 PM
#2
MBWorld Fanatic!
please define CAR LOST POWER
Do you mean engine crankshaft HP? like it is not as quick to accelerate as before?
or electricl power light the lights dim?
IS this at idle or all engine RPMs?
Do you mean engine crankshaft HP? like it is not as quick to accelerate as before?
or electricl power light the lights dim?
IS this at idle or all engine RPMs?
11-16-2018, 06:04 PM
#3
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2014 E550 4MATIC TUNED - Turbo Upgraded Stage 3
Felt like 30% of HP/TQ power is lost. It doesn't accelerate as fast.
Engine also runs harder and Exhaust sound also changes
It doesn't matter if I set it to bring in Cold Air or Hot Air.
And it won't gain power back after turning off AC.
Car will have to be restarted to gain power back
The power Lost is on all engine RPM
11-16-2018, 07:46 PM
#4
MBWorld Fanatic!
I wonder what the ignition timing is doing when the a.c. compressor is commanded on. If it's pulling back a lot it can cause the symptoms you describe. Do you have a scantool to observe timing? Any stored trouble codes even though the CEL may not be lit?
Speaking of that, am I wrong thinking you've got some mods on your car, including a tune? Any possibility that there is any corruption in the software? But I think you said driveabilty is affected only when a.c. is on.
If the compressor is partially seizing it can drag engine power down. But I'm thinking that the serpentine belt may show signs of glazing or similar effects of heat caused by the belt having to work harder. I guess you've not heard any belt slip or squeal?
Timing and engine speed are changed as needed when a.c. is on. If there was an issue with the throttle body or TPS, etc it seems that this would be noticed at idle and be not when engine speed is increased like when you are driving around. So many Inter-related controls on these cars.
Anyway just some ideas, good luck.
Speaking of that, am I wrong thinking you've got some mods on your car, including a tune? Any possibility that there is any corruption in the software? But I think you said driveabilty is affected only when a.c. is on.
If the compressor is partially seizing it can drag engine power down. But I'm thinking that the serpentine belt may show signs of glazing or similar effects of heat caused by the belt having to work harder. I guess you've not heard any belt slip or squeal?
Timing and engine speed are changed as needed when a.c. is on. If there was an issue with the throttle body or TPS, etc it seems that this would be noticed at idle and be not when engine speed is increased like when you are driving around. So many Inter-related controls on these cars.
Anyway just some ideas, good luck.
11-16-2018, 08:16 PM
#5
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Join Date: May 2014
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2014 E550 4MATIC TUNED - Turbo Upgraded Stage 3
I wonder what the ignition timing is doing when the a.c. compressor is commanded on. If it's pulling back a lot it can cause the symptoms you describe. Do you have a scantool to observe timing? Any stored trouble codes even though the CEL may not be lit?
Speaking of that, am I wrong thinking you've got some mods on your car, including a tune? Any possibility that there is any corruption in the software? But I think you said driveabilty is affected only when a.c. is on.
If the compressor is partially seizing it can drag engine power down. But I'm thinking that the serpentine belt may show signs of glazing or similar effects of heat caused by the belt having to work harder. I guess you've not heard any belt slip or squeal?
Timing and engine speed are changed as needed when a.c. is on. If there was an issue with the throttle body or TPS, etc it seems that this would be noticed at idle and be not when engine speed is increased like when you are driving around. So many Inter-related controls on these cars.
Anyway just some ideas, good luck.
Speaking of that, am I wrong thinking you've got some mods on your car, including a tune? Any possibility that there is any corruption in the software? But I think you said driveabilty is affected only when a.c. is on.
If the compressor is partially seizing it can drag engine power down. But I'm thinking that the serpentine belt may show signs of glazing or similar effects of heat caused by the belt having to work harder. I guess you've not heard any belt slip or squeal?
Timing and engine speed are changed as needed when a.c. is on. If there was an issue with the throttle body or TPS, etc it seems that this would be noticed at idle and be not when engine speed is increased like when you are driving around. So many Inter-related controls on these cars.
Anyway just some ideas, good luck.
This is awesome!!! Very good lead!!!!!
I kept my tune files and I do change tune to tune for testing.
This these issues are always there now.
It doesn't matter which tune I put on.
My car is almost at 70000 miles on odometer.
I do have scan tools. I’ll check on timing.
i also have xentry system. I scanned the car. No fault code at all.
The car does have some other issues.
The car will lost acceleration power by 20-30% after driving 35 mins or longer.
And 2 issues during cold start.
During cold start, it has weird knocking (sound like "da da da...") sound coming from the front of driver side. (Some where very close to drive side wheel)
This sound goes with rpm (idle or during driving), It is more noticeable when rpm drop down from 1500-800rpm.
The sound get quieter (or gone) after 15-20 mins of driving.
Also, If I drive out during cold start. Its very hard to accelerate the Car. RPM goes up and I can feel a lot of air been pushed out.
But it is just very hard to accelerate the car during cold start.
If I go WOT during cold start, sometimes P0299 Under Boost code will pop.
All these happened around 5-6 months ago.
Last edited by cocobeex; 11-16-2018 at 08:24 PM.
11-16-2018, 09:18 PM
#6
MBWorld Fanatic!
I would also check the alternator output voltage while driving to see if it is low. Some of what you said made me suspect the electrical system.
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raja777m (11-17-2018)
11-16-2018, 09:23 PM
#7
MBWorld Fanatic!
Based on your further description, I'm guessing that the a.c. is not the trouble, but it is simply highlighting an existing issue that may be getting worse. It seems that acceleration troubles are mentioned several times, whether in open or closed loop scenarios. Now as you add load from a.c. the trouble is further highlighted. The trouble continues and worsens until you restart (reboot so to speak).
No trouble codes showing, so my guessing mind is leading me to wonder about fuel delivery. Checking fuel pressure may be worthwhile, both at initial startup and after the 30 min drive where acceleration starts to deteriorate. I would also consider checking upstream and downstream O2 sensor voltages as they have a big impact in driveability in closed loop.
I dont have a turbo on my car so I can't point to any particular issues that may relate to that system and/or correspond to the trouble you have. In other words if all this is possibly turbo related I don't have the knowledge to speak to it. I just have a basic understanding of the turbo operation and components.
Also I think it's not good to go WOT at cold start or before operating temp is reached. Some engine controls will automatically limit operability parameters to protect components. Open loop (cold start) is usually a preset program from what I understand until all systems go into closed loop (operating temp).
I dont know if any if this helps, hopefully someone more knowledgeable will add comments too. I tend to nip at the edges of a problem to eliminate things trying to get to the root cause.
No trouble codes showing, so my guessing mind is leading me to wonder about fuel delivery. Checking fuel pressure may be worthwhile, both at initial startup and after the 30 min drive where acceleration starts to deteriorate. I would also consider checking upstream and downstream O2 sensor voltages as they have a big impact in driveability in closed loop.
I dont have a turbo on my car so I can't point to any particular issues that may relate to that system and/or correspond to the trouble you have. In other words if all this is possibly turbo related I don't have the knowledge to speak to it. I just have a basic understanding of the turbo operation and components.
Also I think it's not good to go WOT at cold start or before operating temp is reached. Some engine controls will automatically limit operability parameters to protect components. Open loop (cold start) is usually a preset program from what I understand until all systems go into closed loop (operating temp).
I dont know if any if this helps, hopefully someone more knowledgeable will add comments too. I tend to nip at the edges of a problem to eliminate things trying to get to the root cause.
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11-16-2018, 09:50 PM
#8
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Join Date: May 2014
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2014 E550 4MATIC TUNED - Turbo Upgraded Stage 3
so, I have check Voltage are good.
idle is 11.6-12.3 around.
During driving is around 14 up and down.
Based on your further description, I'm guessing that the a.c. is not the trouble, but it is simply highlighting an existing issue that may be getting worse. It seems that acceleration troubles are mentioned several times, whether in open or closed loop scenarios. Now as you add load from a.c. the trouble is further highlighted. The trouble continues and worsens until you restart (reboot so to speak).
No trouble codes showing, so my guessing mind is leading me to wonder about fuel delivery. Checking fuel pressure may be worthwhile, both at initial startup and after the 30 min drive where acceleration starts to deteriorate. I would also consider checking upstream and downstream O2 sensor voltages as they have a big impact in driveability in closed loop.
I dont have a turbo on my car so I can't point to any particular issues that may relate to that system and/or correspond to the trouble you have. In other words if all this is possibly turbo related I don't have the knowledge to speak to it. I just have a basic understanding of the turbo operation and components.
Also I think it's not good to go WOT at cold start or before operating temp is reached. Some engine controls will automatically limit operability parameters to protect components. Open loop (cold start) is usually a preset program from what I understand until all systems go into closed loop (operating temp).
I dont know if any if this helps, hopefully someone more knowledgeable will add comments too. I tend to nip at the edges of a problem to eliminate things trying to get to the root cause.
No trouble codes showing, so my guessing mind is leading me to wonder about fuel delivery. Checking fuel pressure may be worthwhile, both at initial startup and after the 30 min drive where acceleration starts to deteriorate. I would also consider checking upstream and downstream O2 sensor voltages as they have a big impact in driveability in closed loop.
I dont have a turbo on my car so I can't point to any particular issues that may relate to that system and/or correspond to the trouble you have. In other words if all this is possibly turbo related I don't have the knowledge to speak to it. I just have a basic understanding of the turbo operation and components.
Also I think it's not good to go WOT at cold start or before operating temp is reached. Some engine controls will automatically limit operability parameters to protect components. Open loop (cold start) is usually a preset program from what I understand until all systems go into closed loop (operating temp).
I dont know if any if this helps, hopefully someone more knowledgeable will add comments too. I tend to nip at the edges of a problem to eliminate things trying to get to the root cause.
Forgot to mention, Fuel pump has been upgraded to AMG fuel pump.
And P008A code comes on. 1 out of 20 times on Start up only. (Won't pop up during driving)
P008A OBD-II Trouble Code: Pressure Fuel System Pressure - Too Low
Because this code doesn't pop often, i didn't really take a good look on this issue yet.
I only speculate Fuel pressure sensor might be faulty so far.
I will have to get a log on fuel delivery to find out if fuel delivery is sufficient.
Thanks again
Last edited by cocobeex; 11-16-2018 at 10:17 PM.
