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Discussion Starter · #1 · (Edited)
Hi there guys,

every 1-2 weeks I have the strange problem, that the idle speed of around 580rpm suddenly drops to <400 (around 350), illuminating the "Check engine" (because of the drop, I assume) and stays there, if I would not switch the car on/off again.

Sometimes one, but occasionally 3 restarts are necessary for the car to return to normal idle speed. Having done that, I can drive around all day long...

Also the car shutted off 2 times, instead of the 30 times or so the engine rpm has just dropped.
Apart from this, the car drives fine, no other problems can be observed.

All this appears during warm-up of the engine before reaching normal operation temperature and usually after having the car parked over night.

What I have done so far:

  • Measured the throttle positioning sensor for continuity.
  • It passes the idle check, but fails on full-load (no continuity).
  • Cleaning the Idle Speed Actuator. Haven't yet checked squezzing the hose between it and the air meter. Will do tomorrow.
  • Checking resistance of the Coolant Temperatur Sender. It reads 300Ohm with the car just beeing driven and 3700 Ohm after sitting over night in cold weather. 3,7k Ohm equates 12°C so this one should be fine.
  • Unplug the EHA on warmed-up idle. No change observed
  • I tried to measure the milliamps of the EHA during start-up, but my adapter seems to be a malfunctioning, as I am measuring no current at all. Will work in this one
BTW the PCME (Powertrain control module engine) gives the errorcode "Mixture control rich".

Any opinions so far? Ideas what to check next?
 

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You should do a diagnostic, either with the On board if available, following the procedure you will find on the Aussi forum, or pluging Mastercheck.It could be so many things, start bu the simple, check if the OBD has recorded something.
 

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Discussion Starter · #7 ·
The cars of these years dont have OBD. Only from MY96 in Europe.

And there is no one with the Mastercheck within a reasonable distance.
Furthermore I think it would display the same error as the on-board diagnosis.

The DIP gives me "Mixture Control Rich (tested today).

Given the blink-code 2.3.4.4 (Mixture control rich), the manual says: "Adaptive Lambda pre-control reduces EHA current more than -5 mA). The EHA is on the output-stage of the PCME, while the Lamda sensors are on the input-stage side.
Will measure the lamda sensor(s?) as well.

But I doubt if this is really the reason for the occasional sudden drop of the RPM during the warm-up stage.

Will also check for corroded contacts.

Currently I am preparing the car for the painter to rectify the typical galvanic corrosion problems these ones face...
And the leather cusions up front will be redone :)
 

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The cars of these years dont have OBD. Only from MY96 in Europe.

And there is no one with the Mastercheck within a reasonable distance.
Furthermore I think it would display the same error as the on-board diagnosis.

The DIP gives me "Mixture Control Rich (tested today).

Given the blink-code 2.3.4.4 (Mixture control rich), the manual says: "Adaptive Lambda pre-control reduces EHA current more than -5 mA). The EHA is on the output-stage of the PCME, while the Lamda sensors are on the input-stage side.
Will measure the lamda sensor(s?) as well.

But I doubt if this is really the reason for the occasional sudden drop of the RPM during the warm-up stage.

Will also check for corroded contacts.

Currently I am preparing the car for the painter to rectify the typical galvanic corrosion problems these ones face...
And the leather cusions up front will be redone :)
Potentially steering off topic but has anyone looked into Mastercheck > OBD2 adaptors? I have a Raspberry Pi in my MX5 which feeds into the OBD2 port on board. Would be great to be able to set one up to monitor my Turbo R too.
 

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Discussion Starter · #9 ·
You can rewire the Mastercheck to use a OBDII plug. But that wont work for your Turbo R, as it does not have this plug.

From MY92 on these cars had a round Mastercheck plug, which was used to read fault codes with the Rolls-Royce "Mastercheck" scanner. Very hard to come buy today... an alternative is the Omnicheck scanner. But that does not work for a Motronic 1.3 and Mastercheck (already tried it on my 93 Turbo R), only with Motronic 3.3 from MY94 on.

The PCME sends some data via simple voltage signals to the plug. Instead of using the Mastercheck, you can read certain sensors with a multimeter - or a rasberry. E.g. the turbo pressure can be calculated from it. (Btw that also works on Zytek cars, they use the same PIN).

A friend of mine made a tutorial for it. But its all in german ;)

Can you also work with arduino? Or use a rasperry as a multimeter and logger, attaching a display to it?
 

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Bentley plug is not standard, it's not 36 pins like Mercedes for example.


Lambda has a life period around 80/ 100.000 km.


Engine light ON is a sign
fuel consumption upper is a sign
Bad iddling is a sign
Loss of performance is a sign


How many kilometers has your car ?


Oxygen sensor is indeed on possibility, you should dig the topic
 

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I'm not familiar with your particular model but most rich mixture problems with fuel injection are similar regardless of the make of car.
The first and easiest thing to check for would be a vacuum leak at the air intake and along all the narrower hoses or a clogged breather hose.
A vacuum leak at the inlet manifold gasket is another possibility, vacuum leaks an the inlet manifold gasket are easier to check by squirting water on the joints before the engine has warmed up as warming often causes the metal to expand and temporarily seals the joints.
A vacuum leak at an injector seal or dirty injectors is another thing to look out for.
Poor fuel delivery due to a clogged fuel filter or weak fuel pump can also cause a rich mixture as the ECM tries to compensate.
Check also that the throttle body is clean.
Dirty oxygen sensors are another possibility as is a dirty mass airflow meter, I presume there's a separate sensor on each exhaust manifold but I'm not sure. If the air filter is clogged that wouldn't help either.
Good luck tracing your fault, hopefully it's something as simple as a leak on one of the intake or vacuum pipes.
 

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You can rewire the Mastercheck to use a OBDII plug. But that wont work for your Turbo R, as it does not have this plug.

From MY92 on these cars had a round Mastercheck plug, which was used to read fault codes with the Rolls-Royce "Mastercheck" scanner. Very hard to come buy today... an alternative is the Omnicheck scanner. But that does not work for a Motronic 1.3 and Mastercheck (already tried it on my 93 Turbo R), only with Motronic 3.3 from MY94 on.

The PCME sends some data via simple voltage signals to the plug. Instead of using the Mastercheck, you can read certain sensors with a multimeter - or a rasberry. E.g. the turbo pressure can be calculated from it. (Btw that also works on Zytek cars, they use the same PIN).

A friend of mine made a tutorial for it. But its all in german ;)

Can you also work with arduino? Or use a rasperry as a multimeter and logger, attaching a display to it?
Ah okay thanks for the info. I will check and see if there is a plug, you never know!
Feel free to link anyway, I will do my best to translate !!


Yes could work with arduino or a pi. It would be great to pair it with a modem and gps and have it upload my trips, no display needed then! Combined with some OBD style stats it would be really cool
 

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Discussion Starter · #13 ·
Issue solved. The TPS at the throttle body (one position wasn't detected) and the potientometer at the mixture bridge were faulty..(Bosch rebuilded it).
 
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