Loss of power - no check engine light

[fernando306]

My friends,

My Z has 112k on the clock, I bought it with 84k 3 years ago.
It always pulled HARD, seemed like a lot more than the rated 228hp.

But about a few weeks ago, it simply feels like it has lost 50 HP or something. It is as if I have downgraded from 3.0i to the 2.5i engine. Another way to describe it, is as if I can never push the gas pedal all the way down, but just half-way.

Car starts on a dime, runs smooth. Zero oddities. ECU, zero fault codes. The ONLY fault code it has is from the EWS: "33 toleration of changing code increased with key #3". No idea what this is, and if it could interfere with power!? Sort of like a vallet key!?

I should mention: Vanos was rebuilt 20k ago, DISA valve rebuilt and inspected perfect, no vaccum leaks. New air filter and MAF. New ignition coils. Compression measured between 175psi and 185psi across all six cylinders.

What the heck could this be!?

 

[javis20]

Plugs.

 

[raymond.harper]

Does using the sport button have any effect? Any rattling from the catalytic converter, it could be partially blocked?

 

[fernando306]

Does using the sport button have any effect? Any rattling from the catalytic converter, it could be partially blocked?

Sport mode has no effect.

Cats seem to operate normally, the post cat sensors read a steady 0.75V on both banks.
There's a slight rattle that has been there for at least one year, not sure if it is coming from the cats - but that rattle did not get any better or worse recently.

 

[raymond.harper]

The Cats, and indeed the engine, according to the electronics, are performing within normal parameters, yet there is a problem. https://www.youtube.com/watch?v=kNXh1Lphzr4

 

[enuff_zed]

Fuel pressure? Pump failing or filter blocked?
Did this drop in power coincide with any work being done?

 

[fernando306]

My friend,

Good question about the pump. Just measuring the pressure while idling is enough?

No work was done. Car was running strong, had a blast driving from another state with lots of power headroom. A couple of weeks later, it was simply much slower to gain speed and I feel that there is a drop when you're open wide throttle passing 4k RPM. Nothing dramatic, but you can feel the hesitation and it is as if the engine was downgraded to a smaller one. Car starts and runs smoothly.

I'll get the plugs and O2 sensors replaced. MAF is original BMW with 12k on it. New air filter as well.

 

[Umfaan]

 

[fernando306]

Plugs and O2 sensors.
What you guys think!?

 

[raymond.harper]

The spark plugs are of different makes, not a good sign. Nevertheless, the gap between them looks different so they need to be replaced.

 

[fernando306]

Maybe the picture gives that impression, but they are all the same NGK model. Gap and wear is consistent - all 6 look the same.

Both O2 and plugs are already replaced, plugs are NGK 3199 now.

 

[enuff_zed]

Gap and wear is consistent - all 6 look the same.

But is it the correct gap? Looks quite wide?

 

[fernando306]

Nah! Come on guys... Let's get creative. Haha.

 

[Z4Mariner]

I'm trying to creatively think of what on your engine could reduce power without setting codes. Some sort of restriction of air going in or coming out might cause this. Is your intake and throttle body above all suspicion ? Have you ruled out plugged or partly-plugged catalytic convertors (especially those secondary ones) ?

Proper signal from the downstream O2 sensor(s) only tells that the catalyst has enough capacity to deal with the amounts of excess oxygen or excess fuel it is seeing. If flow is restricted, and the DME adjusts fuel to match the available oxygen, then the downstream O2 sensor can be happy, even though you have less power. If the front end of a cat is blocked and restricting flow, while the back of the cat can still cope with that reduced flow, you might get no code. There is even a recent YouTube video on exactly this scenario on a Honda Element here: https://www.youtube.com/watch?v=SwWcPPjoRwY

Maybe senior forum members and experienced techs can suggest how to test for restricted flow without taking eveything apart ? Data logging MAF flow and comparing the data with another car like yours might be helpful - if the air flow is significantly lower in your car than in its "twin" you would have a clue ?

Wish I had more . . . hope you get this resolved !

 

[Jas- USA]

This will not cost you anything. Remove a cable from the battery for an hour and then reinstall the cable. This should reset your cars computer settings to factory.

Consider changing out your ignition switch. Although I've never heard of a bad ignition switch, causing your issues, I've also never hear of the only code you have, which sounds like ignition switch related.

"33 toleration of changing code increased with key #3"

 

[fernando306]

If flow is restricted, and the DME adjusts fuel to match the available oxygen, then the downstream O2 sensor can be happy, even though you have less power.

This sounds fantastic. I would not be surprised at all if that is exactly the case!

Maybe I can try disconnecting the post-cat O2 sensors and see what happens?

The whole car maintanance is completely up to date. The only thing left unseen are the cats.

 

[fernando306]

My friends,

Took the bimmer out for a longer drive and, she's back to being the peppy punchy car I've known all the way to the rev limiter.

If I were to guess, I'd say the O2 sensor was probably the culprit, as those were original with 112k on them. But I've changed plugs and put a fuel cleaner for good measure.

 

[colb]

Bad Maf can result in the lack of power you are getting.Disconnet the electrical plug on the Maf and the car will resort to factory default settings, see of that improves power, if it does then replace maf with OEM Bosch or Siemens brands nothing else

 

[x-driver]

I'm having maybe the same problem ever since I bought the car half a year back. It's a 3.0i, but feels like 2.5i or less. Above 100km/h it gets lazy. The car has 110k km. Runs smooth however.

The car has new spark plugs. Cats were checked with a camera through O2 sensors holes, they look perfect. O2 sensors look fine. Fuel pump pressure was measured and is ok. Valve cover gasket is replaced, CCV is new. Air intake is ok.

Any other ideas? I haven't checked MAF yet however...

 

[x-driver]

I ended performing a dyno test which showed the car is totally fine I guess I just expected too much.