Lose of power

L

LittleZ4

Active member
Question for all you learned folk.
My 2004 3.0 has developed a nasty habit of losing all power, it does cut out but rather just loses all power. Almost like a limp mode but can't even limp......
I can turn it off then back on again and away we go. 9 times out of 10 it behaves after that, occasionally it will repeat the same exciting process of dying in traffic.
Anyone have any ideas what could cause this. It's recently had new spark plugs (no issue with these) and a new injector, again no issue with this. It was misbehaving before these.

I do have a new to me fuel filter to fit, not entirely sure this will completely solve the problem. The car has 186k on the clock.

Any help of ideas would be greatly appreciated
 
Code reader chucks up misfire codes, and fuel codes. I get a screenshot. Also a set of genuine coil packs has gone in at the same time as the spark plugs
 
O/P you advised that with a restart 9/10 times your car is ok after that. Generally, loss of power/stalling totally out of the blue, like you reported is a sign of a failing ignition switch.

Ignition switches are neither costly nor hard to replace.
 
With the error codes being fuel related I'd start with the fuel pump which is a fairly common failure point.
 
At your mileage nothing lasts forever, good suggestions from the others so far. I would look at fuel trims if they are high then it's getting too much fuel to compensate for what it thinks is a lean running condition, usually down to air leaks in the vacuum system from Maf right across the engine to exhaust. Smoke test will find any split or holes hoses you can't find visually. Don't rule out a bad Maf try running the car with the electrical plug to the Maf disconnected, the car will revert to default settings. If it runs better replace Maf with OEM brands either Bosch or Seimens do not fit cheap alternatives you end up paying twice. Certainly change that fuel filter don't be surprised to find it's the original and long overdue for replacement. Ignition switch is an interesting one, given the mileage you have just imagine how many times that switch has been turned on and off wear on the contacts is a suspect with your symptoms, easy to pop a replacement in on the end of the ignition barrel and not expensive. Preety sure you will solve this by working through the suggestions made so far, remember code reader is your friend but not infallible Mafs are known for not setting codes when they fail and because they upset other sensors further downstream can lead you astray and firing the parts cannon at it.
 
HI!

I have a 2004 Z4 2.5 Litre which I got really cheap off ebay.

My symptoms were the car is fine up until you exceed 3,000 rpm which without fail would send it into limp mode - Accompanied by various warning lights - Engine Block / EML / Tyre Pressure / ABS in fact nearly of them together with failing power steering and headlights.

Sometimes you could get it up to 4,500rpm in 2nd gear before it did all of this.

Then you switch off & restart immediately (No need to wait) and everything's OK with all warning lights gone out.

As long as you stay on low revs and everything was fine....

As a matter of course I replaced the Crank Sensor (New Item), Inlet Cam Sensor (New Item), MAF Sensor (Used Item) Oil & Filter, did an Injector clean and Throttle body clean (Spray Carb Cleaner into the Air intake. NOTE - MAF sensor must be removed as carb cleaner could leave a residue on it), Idle control valve remove /test / clean. Vanos Inlet solenoid remove clean test, DISA valve remove /clean /test, vacuum test with my Smoke Machine. (See Youtube Videos on how to test them).

None of that fixed the limp mode problem.

Watching further Youtube videos i saw that the throttle body is not controlled by a cable but it responds to a sensor on the accelerator pedal.

What happens is you press the pedal and the computer counts the number of contacts that are made on the pedal position sensor, 1.2.3.4.5 etc. If one of them is dirty then the computer thinks contact number 5 is number 4, number 10 is number 9 etc.

This signal is then sent to the throttle body butterfly and it moves accordingly and the computer takes note of it's position.

Then the computer checks that the throttle body and pedal position are matching - Which they wont be.

The ECU does not like this as it thinks the throttle is stuck open and therefore sends the car into limp mode for safety.

This will only happen when the accelerator goes past that bad point - Which is why i could get 4,500rmp out of it in 2nd gear but 3,000rpm in 4th gear.

So I replaced the Pedal Assembly with a used item (From some BMW Diesel model- but it worked and so it must have the same sensor in there - IE Does not have to be Z4 specific). The sensor in the pedal assembly is not accessible to be cleaned as it has tamper proof bolts. Then I used a YouTube video to reset the throttle pedal (Something like press and hold for 30 seconds).

This did not work - Still Limp Mode over 3,000rpm.

The other culrpit could be the Throttle body, remember the butterfly in there is operated by a motor which responds to a signal from the Pedal via the ECU. There's a collection of what look like clock wheels to move the butterfly all housed in that plastic cover on the side of the Throttle Body assembly. (I'm not sure if that cover is removeable of if these items are serviceable)

So I replaced the Throttle Body for a used item (£GoodPrice) from Bridgend BMW spares / breakers in Pluckley, Kent. (Not sure If I'm allowed to name drop).

Perfect - Problem solved.

In short the car was going into Limp Mode as the computer did not like the fact that the "Carburettor" was not doing what the pedal / driver was telling it to do. The position of the butterfly did not match the drivers request.

This may be caused by the pedal and / or the throttle body.

The throttle body in reasonably easy to replace.

I saw some videos where they took apart the pedal assembly (There are tamper proof bolts on it) cleaned and problem solved.

For me it was the Throttle body - swapping the Pedal Assembly back made no difference.

NOTE - Don't try to push open / closed the throttle butterfly with your fingers. It's meant to be moved only by a motor, if you force it you'll ruin it.
 
FOLLOW UP - I forgot to mention that this Throttle Body problem threw up a code "28A2 Air Path Monitoring" which I cleared and it's not re-appeared since the throttle body was replaced. I think that's the ECU's way of telling me the Throttle Butterfly is not making sense. The butterfly is on one position (Wrong position) and the MAF sensor is telling it the amount of air going in does not match for the correct butterfly position.

Did also get 29A1 O2 sensor after cat, 2883, 2884 Fuel Trim Bank 1 &2. - Don't know if they're relevant but they've gone as well.
Also got a load of codes in Dynamic Stability Control - All gone .

NOTE- This issue brought up ABS / Traction control lights as the ABS system uses the Throttle position and /or Butterfly position for it's calculations- which would have all been wrong.
 
Interesting, thank you. There are a couple of people who have experienced this recently so this could help them.
I had a similar issue with a 3.0i and arrived at the Throttle Body. Sadly in my case this wasn't the issue and it turned out to be a faulty DME.
 
You must log in or register to reply here.
Back
Top Bottom