Low-end torque missing, troubleshooting help requested
I had the car dynoed yesterday and this confirmed what my "butt-dyno" had been telling me: a substantial amount of low end torque and some top end power is missing. Adjusted readings are: 265lb/ft at 1500rpm (should be 295), 275lb/ft at 2000rpm (should be 360). 2000rpm is where the biggest difference is compared to reference values. From there the engine slowly picks up and then there is a significant shift at 3200-3400rpm. At 3400rpm the torque is 369lb/ft which is pretty much what it should be. Top end power is down by 5-10%.
The mechanic running the dyno test thought the torque curve suggested a camshaft position issue. He also noted that the car was running lean at lower rpms. Based on the car's test mode I've also noticed that it seems to run lean at the top end, max readings are 115-120l/h (they were 139l/h a year ago).
The fact that the car is running as it should at around 3500-4500rpm might suggest that there are no significant long term fuel trim issues due to e.g. bad O2 sensors? Any thoughts?
Some background information:
MAF:s are more or less new (VAG Bosch sensors, didn't really make much of a difference when I installed them). Low end torque issues were there both before and after installation.
The fuel pump has been changed recently, but the fuel filter hasn't.
O2 sensors have not been changed as far as I know. CO2 readings were mostly fine, and O2 readings through the OBD corresponded well with the exhaust values.
Cats are functional but the mechanic noted that it took quite a while for them to get heated up.
Inspection II was done a year ago (new plugs, filters etc.), the car has run ~8k miles since then. I haven't checked the condition of the plugs though.
The engine has never thrown any fault codes and it runs ok; it just feels (and is) weak at lower rpms. Idle is steady, the only symptom of something being slightly off (besides the power loss) is that the engine is twitching slightly under light throttle for a couple of minutes after a cold start. Also, the engine vibrates a bit, perhaps more than it should, but this could be due to some more physical issues like e.g. bad exhaust mounts or a tired flywheel?
Last edited by Apeman; 19th September 2008 at 13:20.
I had the car dynoed yesterday and this confirmed what my "butt-dyno" had been telling me: a substantial amount of low end torque and some top end power is missing. Adjusted readings are: 265lb/ft at 1500rpm (should be 295), 275lb/ft at 2000rpm (should be 360). 2000rpm is where the biggest difference is compared to reference values. From there the engine slowly picks up and then there is a significant shift at 3200-3400rpm. At 3400rpm the torque is 369lb/ft which is pretty much what it should be. Top end power is down by 5-10%.
The mechanic running the dyno test thought the torque curve suggested a camshaft position issue. He also noted that the car was running lean at lower rpms. Based on the car's test mode I've also noticed that it seems to run lean at the top end, max readings are 115-120l/h (they were 139l/h a year ago).
The fact that the car is running as it should at around 3500-4500rpm might suggest that there are no significant long term fuel trim issues due to e.g. bad O2 sensors? Any thoughts?
Some background information:
MAF:s are more or less new (VAG Bosch sensors, didn't really make much of a difference when I installed them). Low end torque issues were there both before and after installation.
The fuel pump has been changed recently, but the fuel filter hasn't.
O2 sensors have not been changed as far as I know. CO2 readings were mostly fine, and O2 readings through the OBD corresponded well with the exhaust values.
Cats are functional but the mechanic noted that it took quite a while for them to get heated up.
Inspection II was done a year ago (new plugs, filters etc.), the car has run ~8k miles since then. I haven't checked the condition of the plugs though.
The engine has never thrown any fault codes and it runs ok; it just feels (and is) weak at lower rpms. Idle is steady, the only symptom of something being slightly off (besides the power loss) is that the engine is twitching slightly under light throttle for a couple of minutes after a cold start. Also, the engine vibrates a bit, perhaps more than it should, but this could be due to some more physical issues like e.g. bad exhaust mounts or a tired flywheel?
Rough idle and lack of low end torque sounds like a cam position issue, but I'd start with JClyman's idea and look at other contributing items as well. My suspicion is that there is nothing wrong with your VANOS, but rather that some combination of sensors is sending inaccurate data to the DME and is causing the DME to call for inappropriate cam positions.
What codes were you able to pull from the car? Reset, wait a week, and pull again. Post those and we'll be able to help more. Pretty much guaranteed that you have them, even with no SES (mostly triggered by emissions in the states).
If I were you I'd change the fuel filter. There was another recent post where a guy got an extra ~20L/hr just by doing that. And you just got a new pump...there is a chance that is died early due to stress! I got one online for $23.
Don't underestime the ability of lazy pre-cat O2's to f with your power. I saw you keeping up w/ SleeperE39's power loss thread. Granted he had exhaust cracks so his sensors may have been okay, but it still proves that bad readings from the O2's can rob the power. I got a set from Amazon for $110 shipped a month ago.
8k on air filters? Not too high, but for the price of new why not toss a set in...just to see results.
Were the proper NGK plugs installed at inspection II?
Does your car pass the onboard test for the thermostat operation?
Another recent topic was the power robbing effects of a stuck cooling fan because of a defective fan clutch. Is your fan clutch ok? Search for threads.
Last edited by TMcNasty; 19th September 2008 at 18:28.
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Remember, this is not a USA model so CEL will not be set like it will over there. (Edit: TM- almost any code in USA will set the light, only a few codes set the CEL in EU)
To the OP- you are pulling codes using the OBD port, correct? There are none?
How about any GT1 results?
Definitely reolace the fuel filter, assume air filter is new?.... then look at GT1/other results for o2 and fuel trim.
Thanks for all the comments. The SES light is working, and as I said the car has never thrown any codes (checked with two types of readers including GT1 at main BMW dealer). The last check was after the dyno test, not with GT1 but still through the OBD port.
O2 sensor adaption values were -2.1% and 0%, doesn't sound that alarming to me. Other O2 readings seemed fine as well, basically just what would be expected (pre- and post cat O2 sensors correlated well, no real variation between left/right sensors and and exhaust analysis confirmed the readings). That said, I might still change the O2 sensors if I don't find any other clear causes.
Inspection II was performed at the main official BMW dealer in Finland, so I assume they put in the correct plugs.
Thermostat test has not been run (don't know the procedure), but I get the same readings from the dashboard and from the OBC.
The cooling fan is not stuck as far as I know. Definitely not running all the time and it seems to run as expected when the engine/air is hot.
The car has run 72k miles. Air filters and oil filter have run 8k. I have a time booked next Thursday at the official dealer, so I hope to find out more then. I will definitely have the fuel filter changed, and I've also requested that the vanos solenoid O-rings be changed even if there are no clear indications of malfunction.
Last edited by Apeman; 19th September 2008 at 19:32.
I have a time booked next Thursday at the official dealer, so I hope to find out more then. I will definitely have the fuel filter changed, and I've also requested that the vanos solenoid O-rings be changed even if there are no clear indications of malfunction.
You should ask them to run a full VANOS test. Make sure you are getting appropriate actuation across the full RPM band.
I really HATE suggesting this, but I wonder if you want to look at your CPS sensors. There are SOME reports that these can start to fail and NOT throw codes, yet have symptoms..... worth thinking about I guess.
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