JB81

Hi Everybody, I'm completely new to porsche, I bought my first one (1991 carrera4 cabrio) 3 days ago, and I need some help...
the car was originally sold to us market, so it had obc in mph, speedometer in mph etc.etc.
The previous owner changed the speedo to kmh (I live in europe), but now obc does not work (it just shows range of 406 miles, and nothing about trip distance and speed). The cruise control does not work (nothing happens in 4 directions when I move the lever, and the rear spoiler raises up and lowers down manually with the gear in the central tunnel, but does not raises up automatically over 110kmh or down at 70kmh.
I think that all has to do with the change of the speedometer from mph to kmh, then let's go the questions:
- obc on the rev counter: does the imperial obc on the rev counter has to match a mph speedometer? if not, is there any cable I need to check if it's correctly connected?
- cruise control: are there different cruise control between mph and kmh speedos? is not, is there any cable I need to check?
- rear spoiler automatic raise/lower: is there any cable or control unit I need to check if everything is connected properly?

Many many many thanks in advance to anybody can help me diagnosing the issues!

sooner964

Firstly, welcome and congratulations on your purchase! Maybe a picture or two of the beauty is in order?

I don't know about the OBC (my car does not have one), so I can't be very helpful there. My gut tells me the answer to your question is 'yes', but as I do not have that option on my car, I am not really familiar with the functionality and how it operates.

I'm not sure that the cruise control would be affected by the conversion from MPH to KMH, although I suppose it is possible. I will for now make the assumption that the CC system would not be affected by the conversion and let someone tell me that I am very wrong, as I very commonly find myself to be. I do know that there is a speed signal component to the CC system, but I don't know if it is sensitive to the actual units or rather that it is getting a good continuous signal. If the signal is not getting properly converted, then there probably is a direct correlation with the conversion. This would be a good place for Loren to chime in, I think, as he is one of our resident electrical signal wizards. Tore may have some thoughts, too, as he is another electrical signal wizard. But if we momentarily assume (dangerous!) that the conversion does not affect the CC, there are then three places I can think of to troubleshoot. First, check that the associated fuse is not blown. This would be fuse #19 and is a 15A fuse, located in the Central Electric main fuse & relay panel box in the frunk (upper LHS just beneath the carpet). Secondly, the CC system has a microswitch attached to the pedal assembly. It is at the base of the clutch spring & kinematic lever assembly. It has a small metal arm that should keep the circuit closed when the clutch pedal is not engaged (normal driving conditions), and opens the circuit when you engage the clutch pedal to disengage CC. It is possible it is either a) malfunctioned, b) not properly adjusted such that it is not effectively keeping the loop closed when the clutch pedal is not engaged, c) unplugged or has a dirty connector or d) is missing. Also, if your clutch pedal does not come back fully once you release it (it hangs), then the microswitch could remain open and the CC will not function. Third, in addition to the CC microswitch attached to the pedal assembly, there is also a CC cable in the engine bay. The cable attaches to the throttle linkage on the RHS of the metal bracket throttle cable mount. Perhaps the previous owner disconnected the CC functionality intentionally? Are you able to contact the previous owner and inquire as to whether the CC worked prior to the conversion process?

I'm not sure on the spoiler control. I do know that the speed gets translated to electrical resistance and the spoiler control box utilizes the electrical resistance to trigger the raising & lowering based on speed. Maybe there is a different unit based on MPH or KMH? I'm not sure.. about quite a bit, apparently, by reading back over what I've written.

Maybe I've been somewhat helpful?

Spyerx

if your spoiler moves up and down manually, it's something to do with the auto / speed signal.
When you start the car, does the wing symbol (car with little arrow pointing at back) turn on? And when you drive away, does it go out?
Check your clock, ensure all bulbs are functional + ensure all solder joints are good
Then, I would see if you can swap your wing module (on a 91 it should be a grey box about the size of a pack of cigarettes up where the passengers feet are) with a known good module.
I would start there.
Cruise control, not sure. On my car, everything worked before I started removing stuff, but the cruise control was sort of sporadic. It could have been the module or the control system in the engine bay.
OBC, not sure, that wasn't a super common option here

Nikolaus964

I can help a little bit as I also have a US car imported into Europe. Installed a new Rev Counter with KmH (according to PET the Part number for MPH and KmH Rev Counter with ODB are different). That change had no negative effect on the rear wing or cruise control. A few months later I stumbled across a matching KmH Speedo (the one without mechanical trip counter) matching to my Revcounter with ODB and again the installation was flawless without any impact.
My guess is that the conversion Km/H to MPH is only internal to the corresponding dial - hence depending on what you install you see either metric or imperial readings.
Cruise Control could be related to the small microswitches on clutch or brake located in the pedal cluster.
Rear Spoiler should move up at 50mph / 80KmH and retract once you stop the car (i.e traffic light).

JB81

no.

no

I'll do

if it's this unit, I think I found the problem... The plastic seems "melted", it does not look really good...





thanks anyway.