Sudden brief power loss

ZEDonist UK

ZEDonist UK

Zorg Addict
British Zeds
3rd Party Trader
Joined
Aug 20, 2021
Points
63
Location
Cambridge, United Kingdom
Model of Z
3.0 Roadster
Hi all,

Time to ask for help:

I have a 2000 3.0 Z3.

When driving, any speed and any throttle position the car suddenly loses power and almost immediately gets it back again. Its especially noticeable when you’re giving it beans.
It’s as though you quickly stab the breaks before immediately hitting the accelerator again.
The engine revs don’t appear to drop.

I have replaced the vacuum lines
Replaced intake boots and small tubes from F connector
DISA valve rebuilt and seal replaced
Throttle body removed and cleaned

I have an Autel scanner and it shows no fault codes.

The car idles fine.

I can’t hear or identify any air leaks.

Im sure the VANOS needs rebuilding as the car lacks power until higher revs - it’s a bit like turbo lag.

I’m not entirely sure what could cause this so not sure where to start. Hence asking for guidance.

Thanks all
 
If it's a "fly by wire" throttle (which I think it should be on a 2000 model) it's possible an issue with the throttle pedal itself although you might expect a code to throw up. May be worth removing the pedal and applying contact cleaner on the electrical connections.

Tony.
 
Do any dash warning lights flash when the power drop happens? The traction control or ABS lights maybe?

Are any warning lights on all the time?

Two modules can control the throttle. The DME and the ABS. Hence the questions about the ABS and traction as I'm guessing that your Autel scanner does not have BMW software, so can't read the ABD trouble codes?

Oh, and you have to use the 20 pin port under the bonnet/hood if you want to read all the Cars modules. The OBD2 port only connects to the DME and EGS.

There are several options for scanners with BMW software:
If there are no trouble codes in the DME or ABS, then we are looking at engine diagnostics or other things like ignition switches.
 
@NZ00Z3

No warning lights come on

No permanent warning lights

I am using the 20 pin port

I have purchased the BMW-service package from Autel so as far as I am aware I have pretty full access.

I can specifically choose to scan each module.
Interestingly I have the following codes. These codes didn’t show up when doing a global/auto scan (a function which works well on a 2014 Vauxhall).

Module:
“Engine-DME Motor Electronics MS43”
Faults:
“12 DME: Signal, camshaft sensor, exhaust”

“78 DME: Plausability, accelerator and brake pedals”

“27 DME: plausability, signal, brake light switch/brake-light test switch”

Module:
“ABS-DSC Stability Control MK60”
Fault:
“5E40 ABS-DSC: steering angle implausible”

Unable to scan modules:
“ABS-DSC MK20 automatic stability control”
and
“ABS-DSC Stability Control DSC3”


I have cleared all fault codes. It’s getting dark, it’s cold and wet so I’ve gone to hide inside again.
I’ll go for a spin tomorrow then re-scan and see what we’ve got.
 
Does the lights come up on dash like it cuts out for a brief second then comes back to life, if so it's the crank sensor
 
OK the trouble codes make sense.

78 (hex), 120 (Dec), Plausibility Pedal Sensor or TPS. When the DME does not know where the throttle body position or the pedal position sensor is, it just cuts the power to limp mode. Usually the engine light comes on and you have to restart the engine to clear the limp mode.

27 (Hex), 39 (Dec) Brake Light Switch or Brake Light Test Switch. This means you need a new brake switch. Cruise control will not function. It will bring up the "Cog of Death" light on the dash if you have an auto transmission.

Clear the codes and se what comes back after the next power loss event.

For the ABS fault code, you may have to recalibrate the steering angle sensor. Once again, clear it and see if it comes back.
 
Just resurrecting this thread as I think I have the same problem - brief loss of power. It happens at random times at different throttle positions, under load and cruising. For about have a second power is lost and the car slows, then it picks up again and normal driving resumes.

I’m in a 2001 Z3 2.2 manual and have the 78 plausibility of accelerator and brake pedals message on my code reader.

I reset the throttle calibration and it seemed to fix the problem on the next drive, but now it’s back again.

I also have bank 1&2 intermittent lambda sensor errors on the post cat sensors. Insufficient heat output.

Any advice would be greatly appreciated.
 
I’m glad you have.
I haven’t fixed the fault 78 issue yet as I got side tracked with an ECU issue written in a different thread (now resolved).

I’ve double checked all my connectors and given them a spray with contact cleaner but that didn’t help.

Ive swapped the brake pedal sensor which was a right fiddle fart to get at but it did solve fault 27.
 
I can’t find a separate throttle position sensor on the throttle body housing on RealOEM for the 3.0 M54 so I think it’s all built into the throttle body itself.

The throttle pedal position sensor appears to be part 12721712009 and is quite expensive however I can’t see that part number on the actual pedal sensor - see photo
 

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The exhaust sensors probably have burnt out heaters in them hence the code you get. Check for continuity on the heater wires on the sensor, if they are open circuit then they are burnt out and not working.
View: https://www.youtube.com/watch?v=CviauEqXTLk
 
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