RR 2.5 DSE cruise control woes

mcapinha · Nov 13, 2010

Hi all.

The Cruise Control on my '98 RR DSE (manual) stopped working when I exchanged the gearbox, a couple of months ago. It never really bothered me until now and I don't know if it was the gbox blowing up (with the CC on) or the exchange itself, that created the problem.

Things I've tried:
- Ran all the tests in RAVE, everything comes back OK.
- Connected it to Testbook and tested everything (brake position, master switch, steering wheel switches). The only thing that failed was a test that didn't have any identification and the screen just showed "Not present" (could have been some other wording). We couldn't identify what was not present.
- Connected it today to another indy's machine (not T4) and it once again showed no logged fault in the CC. I cleared all the ABS errors, hoping that it could be affecting CC function. Still no luck.
- Took a look around the BECM settings and there was no option to enable/disable CC (I was hoping that it had gotten disabled, somehow).
- Replaced CC conversor, by a used one from another RR, still no luck.

I'm totally out of ideas. Help ?

mcapinha · Nov 13, 2010

Decided to repeat the tests, being more careful

The first test, 1E, is to measure the voltage supplied to the CC converter. I'm measuring 12.7V at the converter and 13.7V at the cigarette lighter. Is this significant ?
Following up with the tests, I checked the wire that goes to the BECM and i'm getting 7ohm instead of 1ohm that is stated in RAVE. Once again, could this be the cause to my problem ? A mere 1V drop ?

Thanks for the input

Datatek · Nov 13, 2010

Diesel? Cruise control is done from the engine ECU direct. It just controls the fueling.

Irishrover · Nov 13, 2010

As Datatek says, on the diesel the cruise is electronic through the ecu instead of vaccum with the V8.
The Becm has the option "Cruise set or not set". I know it makes no difference with the V8 as it's always at "Not Set" and cruise works ok., Not so sure about the diesel if this setting is critical

mcapinha · Nov 13, 2010

Irish, I was hoping to get that doubt sorted too. With the diagnostics tool that I used today I could not find out if CC was set or not. Another thing I expect that may cause problems is having the BECM setup as having an auto box on a manual and vice-versa.

Can someone explain what's the purpose of the Cruise Control converter ? I supposed that it acts as to replace the input from the pedal ?

mcapinha · Nov 14, 2010

I found this in RAVE:

Also, the BeCM (Z238) will deactivate cruise control if the engine rpm rises above 5000 +/ 10 percent, due to the possibility of selecting manual without the use of the clutch (Petrol only).

When my gearbox broke (main shaft gone) I was cruising at 120km/h and the first thing I noticed was the revs spiking up to 5000. I could never be sure if it stopped revving because I pressed the brake or if the CC cut in.

Does anyone know if this "cruise control deactivation" is permanent ? Like an error that is flagged in the BECM and won't clear without T4 intervention ?

Datatek · Nov 14, 2010

mcapinha said:
Irish, I was hoping to get that doubt sorted too. With the diagnostics tool that I used today I could not find out if CC was set or not. Another thing I expect that may cause problems is having the BECM setup as having an auto box on a manual and vice-versa.

Can someone explain what's the purpose of the Cruise Control converter ? I supposed that it acts as to replace the input from the pedal ?

If the BECM is set up for a auto but you have a manual, perhaps that ought to be the first thing to sort out?

Irishrover · Nov 14, 2010

The Becm does not store faults.
You really need to get the Becm settings to be in line with what equipment is fitted to the car.
To do this, ideally it needs to be unlocked and reprogrammed with the correct data.

mcapinha · Nov 14, 2010

This is what I get for not being an english native speaker...
My RR has a manual box and is correctly configured as so.

I will try to get it plugged into a T4 to check if CC is configured as active or not.
If someone can shed a light about the CC becoming permanently disabled after the revs reaching 5.000pm, I would appreciate it.

Datatek · Nov 14, 2010

mcapinha said:
This is what I get for not being an english native speaker...
My RR has a manual box and is correctly configured as so.

I will try to get it plugged into a T4 to check if CC is configured as active or not.
If someone can shed a light about the CC becoming permanently disabled after the revs reaching 5.000pm, I would appreciate it.

I will double check RAVE when I get a moment, but I think cruise disable at 5000 rpm is the same as cruise disable when you touch the brakes etc.
Does the diesel have a cruise convertor? I thought that only applied to petrol?

mcapinha · Nov 14, 2010

Diesel has a conversor, Petrol has an inversor.
Trying to figure out how the conversor works to test it in my workbench.

mcapinha · Dec 4, 2010

It's finally fixed!
After fixing my alternator problems (and a new set of glow plugs) my Cruise Control is working again! I'm guessing that the alternator was on it's way out and producing a low voltage as I was reading 13.7v at the CC. Haven't checked how much it is outputting now, but the CC works!

RR 2.5 DSE cruise control woes

mcapinha

Active Member

mcapinha

Active Member

Datatek

Well-Known Member

Irishrover

Well-Known Member

mcapinha

Active Member

mcapinha

Active Member

Datatek

Well-Known Member

Irishrover

Well-Known Member

mcapinha

Active Member

Datatek

Well-Known Member

mcapinha

Active Member

mcapinha

Active Member

Similar threads