M50 without legs - low power

[8 POTS]

I've searched and read but have run out of plans, please help.

My 95 525iM (M50 with vanos, South Africa so no cat, O2 sensor or charcoal canister) has a very irritating lack of power, generally feels lazy. Don't want to go into too much detail but have done a number of things to try and eliminate the problem (new filters, checked fuel pump delivery pressure, reset computer, gave it 2 cans of combustion chamber cleaner, new plugs).

Eventually paid someone to read error codes (as stomp test does not work on RSA cars) and got the following: Fuel tank ventilation valve, Knock (Ping) sensor.

Checked fuel tank ventilation, no build up of pressure, and also checked fuel pump delivery pressure, I am thus happy that there is no problem with fuel supply.

So my question is can a ping sensor be faulty and the car is not be pinging, and if it is faulty can it hamper performance?

Any thoughts!

[everlast]

Yes, in theory it could , though I don't know for sure on this particular engine. If the knock sensor fails, the timing for the motor will likely be rolled back to a known safe value, thus decreasing power considerably.

Fix it and post back whether it did develop more power!

[RallyD]

how does one test the knock sensor.
I dropped my timing light and now it is broken.
Usually I would hook up the light and tap the block lightly with a brass hammer to watch timing.

is there another way?

my '91 m50 feels great up to about 1/4 throttle and then it's the same after that. I am leaning towards the knock sensor pulling timing and killing performance.

[8 POTS]

My M50 also feels pretty eager when pulling away (up to 2800rpm) or when using partial throttle, but as soon as you wanna give it some stick things go pear shaped.

It kind of makes sense that if knock sensor is not working engine computer will retard timing by default to protect engine seeing as knock sensor can no longer do it.

Anyway cannot help with testing of knock sensor, but can tell there are two and it seems that the manifold needs to be removed before. My diagnostic man said knock sensor 1, so presume it is one for cylinder 1-3. (please correct if wrong).

Don't know if I will be able to scrape up the courage to remove my cars intake manifold and do repair myself, But if I do I will keep you updated!

[Brandon J]

The non vanos M50 does not have a knock sensor. The knock sensor error code does not mean the sensor is broken. It means it is reading knock or enough pinging to cause a problem.

If the fuel filter is changed, the pump can still be on its way out and not give enough fluel when under load. So, do not rule this out. You could possibly have one common problem or 2 isolated problems. Here is a list of things to check:
1) the fuel line attachments to the engine. At the lower rear, sometimes the rubber and clamps become loose or wear over time and can drip fuel out. The return line can also be affected. The tank pressure can be affected by these.
2) Has the fuel pump ever been changed?
3) Dirt in the tank from bad fuel or fuel pumped from the bottom of a fuel station tank
4) Ignition or vacuum. The knocking could be bad ignition, bad vacuum, or bad fuel. You said you changed the filters, so I will rule out air. Any miss fires or rough running?
5) You engine does sound like it is retarding. A faulty vanos can make it feel sluggish at lower rpms then kick in later. When vanos goes bad, it usually keeps the cams at the advanced, higher rpm power, position.
6) Check for broken rubber intake boot or poor connections.
7) Good Luck!

Oh, for nonvanos M50 owners, there is a way to gain midrange torque in your M50. Advance the intake and retard the exhaust cams. No vanos so no need to worry about physically changing it yourself. I have heard people simply moving the exhaust over a tooth, but since I have not done it, I will not vouch for its accuracy.

[8 POTS]

Thanks for input

As suggested I went over fuel supply again, hooked up a pressure gauge on the fuel line, everything seemed fine with regard pump delivery pressure but working of regulator and hose between regulator and intake manifold was a bit suspect. So picked up seccondhand one and fitted it, also replaced hose.

And car is now much better, pulls nicely specially after 3100 + rpm (vanos). So presume mixture was too lean causing knocking and triggering knock sensor fault code.

Performance still not totally what I think it is capable of, but this probably due to age and neglect by previous owners, old coil packs, minor vacuum leaks etc. maybe will work through all that one day.

But happy for now.

[Brandon J]

Thanks for input

As suggested I went over fuel supply again, hooked up a pressure gauge on the fuel line, everything seemed fine with regard pump delivery pressure but working of regulator and hose between regulator and intake manifold was a bit suspect. So picked up seccondhand one and fitted it, also replaced hose.

And car is now much better, pulls nicely specially after 3100 + rpm (vanos). So presume mixture was too lean causing knocking and triggering knock sensor fault code.

Performance still not totally what I think it is capable of, but this probably due to age and neglect by previous owners, old coil packs, minor vacuum leaks etc. maybe will work through all that one day.

But happy for now.

Great! thanks for keeping us updates.