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

[alex 1993 525i auto]

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.

[632 Regal]

Hi Alex:

http://www.bimmernut.com/forum/5-series-bmw/44445-m50-vanos-tool-drawings.html

http://www.bimmernut.com/forum/3-series-bmw/44200-diy-vanos-removal-installation.html?highlight=vanos

http://www.bimmernut.com/forum/search.php?searchid=44854

Post the prognosis. :)

[alex 1993 525i auto]

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

[632 Regal]

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.

[genphreak]

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!

[alex 1993 525i auto]

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

[alex 1993 525i auto]

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

[alex 1993 525i auto]

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 (http://forum.roadfly.com/threads/12481128-Idle-control-valve-need-resistance-specs)

Would'nt hurt to clean my ICV I guess. I'll post if it makes any difference.

[genphreak]

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?

[ahlem]

crankcase ventilation leaks at the dipstick or breather hose?

[632 Regal]

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?

Yes exactly.

[alex 1993 525i auto]

I checked again TPS and it's resistance is in the specs.

I cleaned the ICV toroughly drawing it in isopropanol for an hour and cleaning it with cotton swabs. It was not so dirty but after the valve was moving freely if shaking the valve. Also its resistance was as per Bentley.

I checked fuel pressure (and pressure regulator) and it's fine. (52 psi) One thing I noticed is that the system doesn't hold pressure as long as it should (loss of 12 psi in 20 min instead of 7 psi) but I don't think it is related. When engine is running, if I depress the throttle the pressure increase then goes back to normal.

I still have to remove the valve cover gasket to see under if something looks weird.

I wonder if the MAF is not monitoring the air flow as it should. I changed the air filter (was not that dirty but was 1.5 year old) when I replaced the camshaft position sensor and it didn’t change anything. The car idles fine, but if I depress the throttle it is like if it was missing air in the mixture (or fuel but pressure is fine, injectors look clean). I can hear a sound like ‘baahh’ when I depress the throttle, and if I depress it fully the engine dies. In Bentley I can only find resistance specs for AFM before 09/92’s E34, for M50TU the only test given is voltage on the harness… which is fine on my car.

Any help in testing MAF (BMW part no. 13621747155, Bosch 0280217502)? I checked like crazy on the net and can't find much on that...

Thanks,
Alex

[632 Regal]

So are we going to finally check the VANOS? Video it or take pictures for the archive.

You already did the MAF check... what's holding you back now?

[alex 1993 525i auto]

Hi there,

You guys were right about timing/VANOS:

The nuts holding the stop plate and diaphragm spring went loose and the spring disk was destroyed, the sprocket on the intake cam was loose on the cam and the chain chewed the tensioner (pic attached, also you can see the 2mm stop disk was being machined by the cam… as well as sprocket) 80198020 This was causing power surge in RPM below 2000 and no-start below 0 oC/32F.

I finished putting together the engine after replacing the upper timing chain, sprockets, spring plate kit, rail guide and tensioner. I did the job exactly as described in the Bentley with all the tools etc. (even tightening the primary chain tensioner to 11 in/lb of torque in the timing setting sequence, as told in the Bentley for M50). I was very cautious as to putting the VANOS back in properly, with the piston fully pushed-in, and with the chain and secondary sprockets turned fully clockwise before inserting with the first matching tooth of the gear and so on.

The car started fine but the idle is now uneven and sometime the engine stalls after starting or when stopping at a red light, or after I give it a burst of gas let’s say from the throttle body (idle was fine before this repair). One good thing is the the power loss below 2000 RPM is now gone; when I take-off it doesn’t surge, it accelerates like before the problem appeared. Still no codes of course…

Upon searching like crazy what is wrong, I found a comment on Pelican website write-up on VANOS installation, dated September 16, 2013: <There's also a BMW tech bulletin on the non-M3 motors that dealt with advancing the timing. So, sometimes if you replace a gasket and don't advance the timing back to where it was, then that might make a difference. That's about the extent of what I know on that issue. The advancing wasn't for more power, it was to eliminate a shaky idle…>

Can anyone find more info on this advance timing BMW tech bulleting? I can’t find anything on the TIS, neither Googling it… Do you think it can be related to my rough idle symptom? Any other ideas what to check beside this? Do you know if I can test my VANOS system without the special tool that I can’t find anywhere? (12 6 410 to simulate the solenoid function)

I drove it for 60 miles or so to see if the problem would vanish but no, still there. I guess I’ll have to remove the cover and check my work… Video attached of the behavior of the engine when idling and running (sound is bad but it can give an idea).

Thanks for any hints!
Alex

https://www.youtube.com/watch?v=X2rjNqQXI4Y&feature=youtu.be

[alex 1993 525i auto]

pics for previous post were not attached properly, here they are:
80238024
Alex

[632 Regal]

Timing can definitely alter the idle. I have no idea about the bulletin though. You did reset the computer?

[alex 1993 525i auto]

Yes I did (1st I unplugged the battery when I saw this uneven idling,then I tried the Shogun's reset procedure, both didn't change it).

[shogun]

Sorry, I do not know that engine, actually have never worked on a M50TU.
What however I would check once more is, that the engines does not get false air, brittle vacuum hoses - even if they look still o.k. from outside - can cause idle problems.
I had a similar problem on my E36 M3 from 1998 with an S52B32US engine. Got a strange noise when starting mainly cold engine for some time. Checked the internet and all showed in direction of a Vanos problem = ticking noise for short time when the engine is started cold.
Never had to install the ordered Vanos repair kit. The problem was a brittle vacuum hose from the air pump to the check valve on the exhaust.

I found this info:
Tech Note The following BMW factory bulletin could have been placed in the TSB section of our catalog, but I thought it would better serve in the TechNote area so I might be able to explain why this pertains to catalytic converter codes and failures.
Although this bulletin is pointing toward BMW secondary air injection fault codes, there is some very important information embedded in here. See Item 8 on Page 3 of the body of the bulletin.
They are making mention of the possibility of cracked vacuum lines going to the non-return valve. They’ve even updated the vacuum line since 11/98! This can be an underlying cause of a lean condition, but worse yet, if a cracked vacuum line is affecting only one or two cylinders (closest to where the vacuum source is), this could result in un-equal fuel distribution. If one or two cylinders is running lean for any reason, there will be left over oxygen after combustion. The upstream O2 sensor will see this oxygen and report to the Powertrain Control Module that a lean condition exists.
This will prompt the computer to increase the injector on time or pulse width across the board because it has no idea that just one or two cylinders are running lean. This condition causes the other cylinders to run RICH! YES, a single lean cylinder or two can cause the overall system to run rich which is a MAJOR contributing factor to carbon and soot buildup. Also, conditions like this can contribute to substrate melt-down due to excessive fuel in the exhaust! See the bulletin below:
SI B 12 04 00 Engine Electrical Systems November 2002 Service Engineering This Service Information bulletin supersedes S.I. 12 04 00 dated July 2000.
[NEW] designates changes to this revision
SUBJECT Secondary Air System Faults
MODEL [NEW] All models with M52, M54, S52 and S54 engine All models with M44 engine produced as of 1/97 [NEW] All models with M60 (3.0 liter) engine produced as of 10/94, M62 engine produced as of 9/98 [NEW] All models with S62 engine [NEW] All models with M73 engine
SITUATION
Customer complains that the "Check Engine" lamp is illuminated and the following fault is set in the Engine control module (ECM/DME):
[NEW] M52, M54, S52, and S54 engine:
Fault code 245 (F5 hex) – Secondary air injection, bank 1
Fault code 246 (F6 hex) – Secondary air injection, bank 2
[NEW] M60, M62 and S62 engine
Fault code 80 – Secondary air injection, bank 1
Fault code 81 – Secondary air injection, bank 2
M44 and M73 engine:
Fault code 80 - Secondary air injection system
CAUSE
Failure within the secondary air injection system.

PROCEDURE
The following diagnostic tips / steps should be followed if the above customer complaint is received:
1. For E36 vehicles equipped with M52 engine prod. 10/95 - 2/96 also refer to SI 12 04 96 regarding Recall Campaign No. 96E-A01.
2. Refer to the OBD II training manual for illustrations and explanation of system operation.
3. Perform test modules/component activation of secondary air system located in the "Service Functions" section using DISplus/GT1.
4. Check operation of secondary air pump using instructions provided in DISplus/GT1.
5. If pump is not operating correctly check air pump relay. For vehicles with M52 engine a modified relay was introduced into production P/N 12 63 1 742 690.
6. If the relay is operating correctly and the electrical connections/wiring to the pump are OK, check the condition of the pump.
7. If the air pump is seized it must be replaced.
Important note: If the pump is seized as a result of moisture (water in pump), an improperly operating non-return valve is the cause. The non-return valve may stick open and allow exhaust gases to condense within the air pump housing leading to a failure of the pump.
Non-return valve sealing / leakage check:
The non-return valve must be checked as follows any time a seized secondary air pump has been replaced due to moisture. Disconnect the air pump feed line/hose (1) at the non-return valve (line from the secondary air pump to the non-return valve).Visually inspect the non-return valve fitting internally for carbon type contamination. (Twisting the corner of a clean shop rag into the valve fitting as shown will assist with this check.) If no carbon type deposits are found on the rag, this indicates that the non-return valve is sealing correctly and does not need to be replaced. If carbon type deposits are found on the rag, the non-return valve is not sealing correctly and must be replaced. Note: A non-return valve which is not sealing correctly will cause damage to the secondary air pump as described above.
8. Check also for cracked vacuum lines going to the non-return valve.
For vehicles with M44 engine the vacuum line P/N 11 73 7 501 180 going to the non-return valve has been improved since 11/98.
For E46 323i/iA and 328i/iA vehicles produced 4/98 - 7/98 see S.I. number 12 04 98 regarding the vacuum hose to the secondary air non return valve service action.
A Non-return valve with a dated code stamping as of 99T075 (arrow) and later is the improved version. date cose explanation: 99=year, T=day, 075=75th day of the year.
Only the improved non-return valves are available from the Parts Distribution Centers.

I found that on Diversified Environmental catalysts technotes.deccats.com/BMW_Vacuum.pdf‎

[alex 1993 525i auto]

Thanks a lot for the info, the M50TU doesn't have the secondary air pump as far as I know, so it may not apply for my car. Anyone ever seen where I could buy the special tool 12 6 410 to simulate the solenoid function by any chance?
Alex

[alex 1993 525i auto]

Ok I got it working fine now!

I did a silly mistake when putting back my solenoid piston, I put it the other way arround... damn I felt bad for 4 days thinking what the hell did I do wrong when putting back the Vanos and redoing the timing... at least I didn't have to open it the cover to find nothing was wrong in there.

This part:11361738495
http://www.realoem.com/bmw/showparts.do?model=HD63&mospid=47404&btnr=11_4855&hg=11&fg=15&lang=enUS

The car runs super well now.
Thanks
Alex

[632 Regal]

Excellent! Glad you got it to work out.

[632 Regal]

pics for previous post were not attached properly, here they are:8024
Alex

Note the chain is 1 tooth off causing the grinding. The thicker teeth align the chain to the sprocket.