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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 04-12-2013, 12:44 PM   #21
AK65
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OK, I'm back from out of town and driving on the way back from the airport (freeway driving), I noticed the following. At about 100km/h (65mph), the revs are just over 2000. If I want to accelerate on fairly flat stretch of road, I press on the accelerator. After a very quick initial pick up in revs, the revs start to DROP! All that happens is more throttle just makes the consumption meter hit max, with no appreciable increase in power at all, if anything, a drop in revs and speed. I also notice a vibration seeming to be coming from the rear diff - could this be the guibo? Could this be a power sucker?

I'm just not convinced the behaviour this car is normal, despite what the mechanics say. It's a very subtle problem that doesn't really show itself if you thrash the car at higher revs....

I am racking my brain, but apart from valve timing, which I am assured it isn't, what else could cause a drop in revs when you open the throttle? In the old days when I had a student car, it would be like the vacuum advance wasn't working. I've checked the timing advance though, and it's perfect.

I'm determined to get to the bottom of this though.

And also by the way, I've now got a logged code P0365, which is an exhaust cam sensor (I think). I don't know if that has anything to do with anything.
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Old 04-12-2013, 06:20 PM   #22
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Did you test the cats yet?
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Old 04-13-2013, 12:18 AM   #23
AK65
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When the car was in for diagnostics, they had all types of probes in the tailpipe, and they said the cats were fine. Car has no problem revving, when it gets there. Just crappy torque from 1-3.5 k. Most prevalent in higher gears. It had a boggy stumble at 1.5k in the lower gears which is much better now. But overall, it's performing at about 75% imo.
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Old 04-13-2013, 05:28 AM   #24
jfoj
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Auto trans torque converter bad??

There is a one way clutch for the stator in the torque converter. If the one way clutch goes back, the stator will act as it is not there. The stall speed of the converter will be much lower. Usually this means after 2500-3500 RPM the engine will seem fine, but for dead stop to under 2500 car will feel like a dog.

Highway cruise should feel ok, but acceleration will be be poor until about 3000-3500 RPM.

This will also impact fuel economy.

Any decent mechanic that know what to look for should be able to identify this, however, you may live in a culture of manual transmissions so it may be hard for the average mechanic to pinpoint.
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299
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Old 04-13-2013, 07:38 AM   #25
jfoj
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Just tested this out in my wife's E46 Vert.

Put trans in Sport Mode, start car out in 2nd gear by manually shifting into 2nd gear.

Jump on the throttle from a dead stop and watch the tachometer and see if it jumps up and stays around 2200-2500 RPM before car really starts to move and pick up speed.

If the tach does not jump up to at least 2000 RPM and hang there for a short period until the car moves fast enough for the revs to climb, then likely the stator sprag in the torque converter is free wheeling in both directions?
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

Fuel pump failures - http://forum.e46fanatics.com/showthread.php?t=929501

Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

E46/E39 GM5 Door Lock Info - www.bmwgm5.com

Lower hose fan switch O-ring - BMW #13621743299

Last edited by jfoj; 04-13-2013 at 07:48 AM.
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Old 04-13-2013, 09:20 AM   #26
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Hold up. Stop throwing money at the car and tell that mechanic to stop hustling you. I just had a friend have this happen. I told him the chances that both o2s no matter how old they are will show as both having failed or faulty, is almost 0. Thats like getting 2 flat tires at the same time. If your mechanic is replacing parts based on the error codes, then he needs to be replaced.

The reason why you're still showing as lean is more air than fuel is being deposited in combustion chamber. The reason why is your pre cat o2s are wondering why the maf is lying to it, trying to tell that there's less air being drawn in than there really is. You need to check your intake tubing, the rubber part going from after the maf to the throttle body. It can't be just inspected correctly unless removed. Doesn't cost much but that's your problem

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Last edited by NumbaOneNewb; 04-13-2013 at 09:24 AM.
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Old 04-13-2013, 09:23 AM   #27
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On top of that, everybody that i flashed the euro tune to their ecu told me they notice right away a huge difference from US tune. After updating his car, he told me he felt nothing. I jumped in his car and sure enough, sitting in passenger seat it didn't have that feeling my car has. We knew before the flash he had this big gash right after the maf sensor. I told him get that replaced and thats got to be the reason his car didn't feel fast. He was also showing misfiring codes prior to the flash

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Old 04-15-2013, 02:17 PM   #28
AK65
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Hi

Thought it best to replace both O2 sensors because the one was faulty, and the other had a short on the heater circuit, and got fouled up.

I used the Bosch replacement sensors, which weren't that expensive..

Fuel trim is fine now. No more lean codes.

@jfoj, I tried your test in 2nd gear, and the revs jumped to 2000 pretty much immediately. The highway drop in revs@ 65 and the 1500 rpm sudden drop revs at about 20 mph still persist. I'm tempted to set the valve timing myself. Like I said before, both torque and power are way below spec. 180Nm and 112kW at 6000rpm, are woeful. Also, car seems to perform better when cold. I've also checked for air leaks, haven't found any as yet.

Another point to note is as we are moving towards winter, the engine has started and cut out twice on cold starts on early mornings. So I'll continue to check for air leaks...

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