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Thread: Low power at low rpm (below 2200 rpm or so)

  1. #1
    Join Date
    Apr 2007
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    Montreal
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    Default Low power at low rpm (below 2200 rpm or so)

    1993 (built 05) 525i auto trans, 257k miles.

    Hi, since a few weeks my car suffer from low power/torque at low rpm. Above 2200-2500 then it then takes off with the good power/torque it used to give.

    When I noticed it I checked for codes with my Peake reader and there was a code for the camshaft position sensor. I cleared the codes and the code never showed up again. I replaced the sensor anyways but it didn’t cure the problem. (One note is when I replaced this sensor the old one came full of metal dust?)

    So I’m wondering what to check as there are no faults stored in the OBD.

    One thing to note is that if the car is idling and I press the pedal to the floor the car dies. Then it starts back fine.

    I’m suspecting either the throttle position sensor (TPS), O2 sensor, MAF or VANOS. I did check the TPS sensor last winter when I changed the spark plugs and the TPS resistance was fine as in Bentley. O2 sensor was replaced 50K miles ago as well as MAF. Vanos piston seal was replaced 3 years ago as well as I upgraded to Spring loaded stopper for the intake cam and the car has been running well since (it cured the metallic taping from the worn Vanos seal). Crankshaft position sensor was replaced at same time. The only sensors I never replaced on this car is the TPS, and also the Vanos solenoid was never replaced (from my ownership = 8 years).
    The Vanos link to that I’m not sure because it is supposed to advance timing at RPM >3000, it should have nothing to do with lower RPM behavior. Unless it is always ‘stuck’ in the advance timing position? Again there are no OBD codes.

    One thing I remember now writing this is that the engine began to have a metallic tapping in the Vanos area a few weeks before the power loss issue. Before that the engine was purring fine.

    I’m planning to replace the valve cover gasket soon so in the same time I’d visually inspect to see if there is anything wrong.

    Thanks for reading and let me know what you guys think!
    Alex
    1993 (built 05) 525i auto trans, 257k miles.
    1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)

  2. #2
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    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
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    Montreal
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    Thanks,

    I went trough all this before (1st for Vanos repair, 2dn for cyl head removal) and I have the special tools etc. and I did follow the procedure exactly and the car started fine right after and has been running well since.

    This made me realize that maybe the secondary chain tensioner went kaput? Which may explain the no power, noise, metal rip on the CPS magnet?

    BTW the 3rd link didn't open-up for me. If you can let me know what's about.

    Thanks
    Alex
    1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)

  4. #4
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    Quote Originally Posted by alex 1993 525i auto View Post
    BTW the 3rd link didn't open-up for me. If you can let me know what's about.
    Yeah I see that, do an advanced search for vanos only in the title.

    I believe your thinking is off a bit, the intake cam advances at low RPM not higher RPM. So by default it should be advanced which is not your symptom right now. Visual inspection for sure especially with noises coming from up front.
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  5. #5
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    Dec 2004
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    Better triple check for vacuum leak in the intake boot... or elsewhere. Anything you've touched or could have gone bad. Esp. underneath the intake manifold- maybe there's a split? Are you saying it conk outs (or stumbles) if you rev the engine in neutral?

    I've seen this happen where the ICV hose connector, that connects to the intake manifold just where it is hard to get to, has come loose (or clip broke so it just works its way out). By far the most common problem on these. If you don't already know this is nicely seated and clipped in, well its the most likely culprit. The ICV hose(s, there are 2 or more) is also known to split, or crack so you have to check that too, and it is deeper and harder to get to. Some remove the intake manifold- the seals are re-usable so its not a bad option even if just troubleshooting.

    Other thing to triple check is the hose to the Fuel Pressure Reg, that could cause this stuff. I've had to replace many of these on M50s, they perish, split crack and fall off- sometimes all of the above, LOL!
    Last edited by genphreak; 10-01-2013 at 08:13 AM.

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  6. #6
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    I tested the throttle position sensor tonight and it is fine, as per Bentley (1.37-3.98K ohms, etc.). Also I forgot to mention that it not always so bad at low rpm, it is like intermittent...

    Thanks for your replies gents.

    On this: ''I believe your thinking is off a bit, the intake cam advances at low RPM not higher RPM. So by default it should be advanced which is not your symptom right now. Visual inspection for sure especially with noises coming from up front.''
    If the cam are advanced at default position (or low rpm), but my Vanos 'stucks' the cam at the 'retard' position, could then be explaining the car's low power at low rpm?

    On the vacuum leaks related stuff I'm pretty sure there is nothing wrong there, I replaced most tubings (if not all) in the last 5 years, I removed/intalled the intake for replacing the camshaft position sensor (and replaced leaky Vanos oil line while in there)l and triple checked that everything was back like it should... and again no change in behaviour before/after this operation. Like I said if the car idles (fine) and I quickly depress the throttle body fully, the engine will stop/conk out like if it was missing air/fuel.

    I will check under the valve cover asap (next week-end or the other next). The car has been running like that since 1 month or more between the ordering of the CPS and now. Whatever wrong if it fails for good then it will be easy to troubleshoot.

    Post any other ideas if you have guys,
    Thanks
    1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)

  7. #7
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    Update:

    Tonight after work the car almost failed to start. After cranking 30 sec. or so it then started and went as before. Later at home I checked the idle speed control valve with my multimeter to see if it could be wrong.

    The idle speed actuator coil resistance values were off. They showed 12, 11 and 24 ohms (between terminals 1-2, 2-3 and 1-3). In the Bentley it says the readings should be 20, 20 and 40 ohms respectively (+/- 10%). But the numbers match with resistance specs of an M60 (12, 12 and 24 ohms +/- 2, 2 and 4). Other tests were fine.

    Any idea about that? i.e. the resistance values are off, they fit with the ones from an M60 (just happens like that?), car stalls when I quickly depress the pedal to the floor or lacks power when I quickly accelerate from low speed/take-off), then it almost failed to start tonight? (It has been raining Yesterday but not today, this morning it was fine).

    I'm not sure about the ICV ohm readings if it shows my ICV is bad. I didn't think a bad ICV can prevent a car from starting. (I checked tonight and it starts when I unplug it, but the idle is very bad of course). When I disconnected the smaller breather vacuum hose, idle was higher at first but it looked like the valve was reacting, like if it was adapting after a 30 sec.

    I'm in doubt if all that can be Vanos related now. I'll check anyways at some point when I have time, my valve cover gasket is due for replacement (is leaking oil, I'll check at same time).

    Thanks for reading,
    Alex
    1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)

  8. #8
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    Just found that the resistance readings are good, there is a mistake in the Bentley, you can check this very detailed post:

    Idle control valve, need resistance specs

    Would'nt hurt to clean my ICV I guess. I'll post if it makes any difference.
    1993 (build 93/05) 525i automatic M50TU (vanos) 263K miles (ca. 423000 km) in Montreal, Canada (bought the car 9 years ago in San Diego, CA)

  9. #9
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    Quote Originally Posted by alex 1993 525i auto View Post
    Post any other ideas if you have guys,
    Thanks
    "I'm in doubt if all that can be Vanos related now. I'll check anyways at some point when I have time, my valve cover gasket is due for replacement (is leaking oil"

    Remember... if oil comes out, air is going in...

    1. So since yesterday, did you fix the valve cover gasket leak?

    2. Another angle:
    Also you need to measure fuel pressure if you have not already- esp. when it is idling badly or under load. Mechanics do this regularly with customer cars as fuel pumps and other upstream electrical faults are common causes of running problems. On three of my e34s, over the space of 10 years, I've had to replace 3 pumps- and they all had running problems before failure...

    3. ... and another,
    On an M20 or M30, a cause of low power is often a stuck valve. On an M50, it is less likely- but it could be a problem. Are the spark plugs wearing/fouling differently?
    Last edited by genphreak; 10-20-2013 at 03:59 AM.

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  10. #10
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    crankcase ventilation leaks at the dipstick or breather hose?

    1990 535im 421,000 miles, 1987 325is, 1989 325is, 1990 m3, 1991 318is, 2001 X5 3.0

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