SL500 around idle misfire - what next?

[Alex Crow]

that code 18, it is in the DI (ignition) module isn't it?

if so test 23=>5.0 directs to connect an oscilloscope to the crank sensor pins at the ecu (N1/3, ignition module on inner wing, pins 17+18, the screended crank sensor plug). then crank the engine and compare the trace with 25=>fig2 which shows a regular oscilloscope pattern with alternate up/down spikes above and below 0V seperated by flat line, with one up/down deflection all in one, once per revolution - this is from the magnet.

simply put, if you find someone that can connect and use an oscilloscope, get a trace of the crank sensor when cranking and they should see the trace from the magnet, once per revolution. this will be amongst many other traces/spikes/signals from the regular reluctor teeth bu the oscilloscope operator will know what is what if you relay all the above info.

 

[Nick-V]

Alex, thanks very much for your messages - sorry to be late in replying as I have been away.

I fully understand what you are saying - this will show if we are getting a signal but will it really tell us if the signal is at the right time (if the flywheel etc. was rotated).

Also, I will relay the info that the magnet might be inspected visually as you mentioned.

My next immediate step is the low idle speed...I am fitting a new gear indicator switch shortly as that is showing a fault - I believe idle is raised when in neutral and park - or reduced in drive whichever!.

 

[television]

On cars that had an Idle relay the RPM was increased by 50 rpm in D or when the aircon was turned on, not sure if you have one on that

 

[Nick-V]

No idle relay but I'm told idle revs drop when in gear and are higher in D and P (not due to drag!). STAR reports a fault on the gear selector indicator so it doesn't know what gear I'm in. Hopefully the switch is dead and when the ECU knows about D and P it will raise idle speed.

 

[Nick-V]

Yesterday the gearbox switch (Neutral Safety Switch And Back-up/reversing Light Switch) was replaced for about £60 plus 20 minutes labour. Hooray...idle speed is back to normal.

The switch has 3 pairs of contacts. The two small ones connect to an internal resistor network that tells the EMU which gear the car is in. The old switch was open circuited. The other two contact pairs deal with park/neutral and reversing lights.

"If I was to live my life again" I would resolve all (STAR or OBD) errors including those the "experts" regard as irrelevant such as this switch showing a fault. I've spent far too much money on unnecessary parts and labour and time doing research.

If anyone else suffers from a low idle speed check this gearbox switch !!!

 

[Alex Crow]

wow, good news at last! thanks for the update, and an unusual fault i will remember.
who diagnosed the switch as faulty?

 

[Nick-V]

Star (with the Indi) has been showing the switch as faulty all of this time. I eventually went to see Dennis at the Tooting ex-Merc place (systematic analysis over experience!) who linked the switch and idle fault together as a possible. I did the multi-meter bit.

Thanks for the help here at the forum.

 

[m00n_777]

Nick do you resolve your problem with flywheel magnets ? I have the same issues in m119.970 in w140 500SE. Idle are stable but occasionally missfire and engine stumble. I also have DTC code: Magnets for CKP sensor not recognized. How to check this magnets ? Is that mean i need to replace flywheel or can i repair it ?