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Discussion Starter #1
Hi!
I know there are a lot of cruise control threads in here, but none that I have found seem to answer my questions.

The cruise on my 91 Turbo R (3-speed) has not worked in the time that I've had the car. None of the buttons on the gearstalk do anything.

I've swapped the ECU for a 2nd hand one that was allegedly OK.

The brake lights (the car doesn't have the 3rd upper light) and speedometer work fine.

How do I check that the buttons in the stalk do what they're supposed to do? I can't see a way of dismantling it!

How do I check the switch in the rat trap?

If one presumes that the ECU is OK, the microswitch in the stalk and the second side of the brake switch would be my prime suspects!

Cheers

Es
 

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Have you looked over the schematic for the cruise circuit? I'm sure there is a relay involved.
 

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1986 RR Silver Spur, 6.8 Liter, custom 700R4 and more to come
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Hi!
I know there are a lot of cruise control threads in here, but none that I have found seem to answer my questions.

The cruise on my 91 Turbo R (3-speed) has not worked in the time that I've had the car. None of the buttons on the gearstalk do anything.

I've swapped the ECU for a 2nd hand one that was allegedly OK.

The brake lights (the car doesn't have the 3rd upper light) and speedometer work fine.

How do I check that the buttons in the stalk do what they're supposed to do? I can't see a way of dismantling it!

How do I check the switch in the rat trap?

If one presumes that the ECU is OK, the microswitch in the stalk and the second side of the brake switch would be my prime suspects!

Cheers

Es
The slight defect that irritates me most about my '86 Spur is the absence of response in the cruise control. Is yours on the right side of the column, as on mine?

I'm going to get into the schematics a bit this morning and try to find a related relay. I've already found the one for the low beam headlights so hopefully it will be fairly straight forward, I'll be following this thread closely!
 

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1986 RR Silver Spur, 6.8 Liter, custom 700R4 and more to come
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The slight defect that irritates me most about my '86 Spur is the absence of response in the cruise control. Is yours on the right side of the column, as on mine?

I'm going to get into the schematics a bit this morning and try to find a related relay. I've already found the one for the low beam headlights so hopefully it will be fairly straight forward, I'll be following this thread closely!

rrtechnical.info/sz/sz80/m8.pdf The only reference I find so far is on page 42 but there is nothing related in the surrounding pages...Is there another resource as detailed as these manuals?
 

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1986 RR Silver Spur, 6.8 Liter, custom 700R4 and more to come
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Those Lucas 6RA relays seem to play a big part in the electrical systems on these cars. I found they are readily available and am adding one to my tool box for diagnostic "swap out" purposes. It's the cheapest part sometimes. The 30amp Bosch relays play a major role too and I've got one of those standing by. Still searching. Flying Spares will rent you their Speed Control Test Box for 100 pounds...ugh
 

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Discussion Starter #6
Hi Guys,

@ Wraithman: on US models (and possibly others with the 3rd brake light), there's a relay in the boot / trunk that appears to be significant. On European models the relay socket appears to be bridged. I'll check mine tomorrow, as I can't recall haing seen that!

I think the micro switches in the stalk can be checked via either the plug for the ECU or a 6-way plug the must be under the steering column.

@ 86BlueSpur: my controls are integrated in the gear shift stalk behind the steering wheel.

Es
 

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Looking at the wiring diagram, this system is very easy to test with a voltmeter or test lamp.
Pin 13 - Engine running and gear selector in drive - 12V should be present.
Pin 14 - Press set/accel switch - 12V should be present when pressing the switch.
Pin 7 - Speed signal, Connect Voltmeter to this pin and drive. I believe that the signal is AC, as you go faster the voltage should increase.
Pin 2 - Ground

If these inputs are good, report back.
 

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Discussion Starter #9
Hi JR2,

That's what I gather too.
Do you know of the pins are numbered on the plug, or what's the numbering convention?

Cheers

Es
 

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Discussion Starter #10
Hi again,
I hooked up a multimeter and checked a few things:

Pin 2: Ground: OK
Pin 5: Resume: 12V when pressed (car driving)
Pin 7: Speed Signal: <1V AC or DC, no significant change with speed. Also checked if it's a variable resistance, doesn't seem so.
Pin 12: Cancel. Permanent 12V, goes to 0V when pressed.
Pin 14: Set:12V when pressed.

I forgot to check the brake switch, which goes to Pin 12.

I take that the speed signal is not present?!
Am I right in thinking that the speedometer gets it speed signal from somewhere else?

Cheers

Es
 

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I take that the speed signal is not present?!
Am I right in thinking that the speedometer gets its speed signal from somewhere else?
Correct.
For some reason, I was under the impression that you had access to the service CD.
Check this electrical connector at the transmission.
29467

I attached the wiring diagram. It's a very simple system. The control unit is the exact same part as 1990's OPEL.

I am in the process of removing my cruise control ECU for repair.
Tomorrow I will try and test my car vehicle speed input and cancel switch operation.
The wiring diagram leads me to believe that voltage should only be applied when the cancel switch is operated.
 

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Discussion Starter #12
Hi JR2,

I do have the CD, and have found and printed the diagrams, but I'm possibly not very good at reading them ;)

I checked and cleaned the connector for the speed sensor yesterday too, but that didn't seem to be the issue.

If the "cancel voltage" is applied permanently, would that possibly indicate that the cruise side of the brake switch is "on"?

Cheers

Es
 

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Discussion Starter #13
I just checked the function of the brake switch on pin 12: when the brakes are applied, the 12V is also cut, like with the cancel switch.

Re. the speed transducer, is it possible that the signal is a pulse of some kind, which is why an AC or DC signal isn't visible on a digital multimeter?

Cheers

Es
 

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Discussion Starter #14
I checked pin 7 again with the frequency function on the DMM, and I get a signal that varies roughly between 200 and 800Hz. It doesn't change 100% consistently though!

Cheers

Es
 

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Pin 2: Ground: OK
Pin 5: Resume: 12V when pressed (car driving)
Pin 12: Cancel. Permanent 12V goes to 0V when pressed.
Pin 14: Set:12V when pressed.
Pin 4: 12V when brake lights are activated.
I have the same results as your posted results.

The backside of my electrical connector is numbered 1->8, 9->15

I checked pin 7 again with the frequency function on the DMM, and I get a signal that varies roughly between 200 and 800Hz. It doesn't change 100% consistently though!
200 - 800Hz sounds correct. I would think that you should have a clean and constant signal.

I ran out of time and was not able to test the speed signal.

You might want to test the signal at "connector 30" on the side of the transmission and see if it changes cleanly with speed increase? It is possible that the wire is poor between 30 and the cruise ECU?

GM Opel/Vauxhall 90247477 (as posted in another thread) is the same unit.


Speed control ECU - question about differing types
 

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Discussion Starter #17
Thanks!
I'll see if I can test the speed signal at connection 30 with the car on a lift and running - easier than trying to run a secondary wire into the car I think.

I took the original ECU out of its housing, and the PCB looks immaculate, which everything covered in lacquer.

Is the speed signal generator also a GM part that can be hap cheap(ish)?

Cheers

Es
 

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Discussion Starter #18
It's me again 😉

Is there a way to test the actuator in the engine compartment, just to eliminate that as a cause?

Also, is there anyone here in Germany who'd be willing to lend me their functioning ECU to check that that isn't the issue? I'd obviously "lend" that person a couple of good bottles of wine in return 😊

Cheers

Es
 

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Conformal coating is on the PCB. You cannot visually inspect a circuit board with the coating and it has to be removed. Only then can you visually inspect solder joints for defects under a magnifying glass.
Defective solder joints are a leading cause of ECU failure.
 

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Discussion Starter #20
Hi Wraithman,

You're right, but my experience repairing other electronic stuff tell me that these joint look OK.
The other ECU I bought was supposed to be functioning, which is why I'm hesitant to send one of them off for repair before I've eliminated all other possibilities.

Es
 
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