Learned Collegues:
I've searched the forum for the answer to this, but with only limited success.
Here are the symptoms:
1. I push the cruise control activation button and get the green dash light but when I press the stalk away from me to "set" it, nothing happens.
2. I did a DE at Road America last Friday. While I was driving up to the track, the engine lost power a couple of times...seemed electrical...No smoke, no funny engine noise, just seemed like the DME wasn't listening to the accelerator pedal. If I let all the way off the pedal and pressed again, I got power. I noticed this a couple times on the ride up there and on the track during my lone 20 minute run.
3. One of the guys driving behind me told me my brake lights were on during the whole session. That would explain the cruise not working, eh? So on the way home, I stopped at The Porsche Exchange in Highland Park, IL and picked up a brake light switch. Replaced it in the parking lot. The brake light definitely doesn't stick now. I just took the car out tonight and watched the 3rd brake light in the mirror. It's 100% working right, but still no cruise control.
4. Since replacement of the brake light switch, I have not noticed any loss of power.
5. While I was going to the track, I suspected the brake light switch and was reaching down there while I was driving to see if I could jiggle it or feel something obviously wrong. While jiggling the two wires in back of the brake light switch, the car lost power. Seems to be a connection there.
6. Pressing the clutch also shuts off the cruise. I thought about replacing that switch as well. There is a thread about the clutch delay switch. I thought, rather than replacing it, I'd try shorting it. I shorted the two blades that connect the wires together and moved the switch to behind the carpet just like the clutch delay post said to do. This make the car think the switch is closed. That is the normal position for the clutch being fully up. I'm effectively disabling that clutch delay circuit by doing this. I'm just not sure if that is the switch that affects the cruise control or if there is another clutch switch. Is there another clutch switch I should be looking at?
7. During set-up for the DE, I lowered the brake engagement position one turn with the adjustable linkage in the trunk that goes to the master cylinder. It's not much lower than stock...maybe 1/2" at the most. Helps with heel/toe. The brake pedal still comes all the way up, but it has to travel down a bit more before the brakes actually engage. I don't see how this could cause a problem but the situation started when I started messing with this brake height thing.
So....Could there be another clutch switch that is somehow mucked up? Have I done something to a brake switch? I'm convinced that it's related to one of these pedal switches because the light goes on and there are no other symptoms.
Cruise control was working with perfect German precision just the day before although it has failed to work in the past intermittently. Come to think of it, I have messed with the brake engagement height before too and that may have lined up well with the failure of the cruise before, but it was months ago.
I have a Durametric "enthusiast" fault code reader. Is there some way to tell what's up from that?
Thanks for any experience based ideas on this. Please refrain from posting conjecture. I have been conjecturing in my sleep since this started. Hear you can go blind from that!!!
:cheers:
Wow, can't help much here but I think you're one of the most technically knowledgeable folks here given what you've done already to troubleshoot! I would be at the dealer flashing a credit card already...
Pete:
Thanks, but it still doesn't work!!! It's some little thing, I just know it!
:beer:
If memory serves Porsche's DME programing is brake overrides throttle to avoid the Toyota unintended acceleration thing. So this could explain your power loss and cruise control. I can't recall if there is one switch or two for this.
Interesting tidbit. Maybe this is only for Tiptronic/PDK transmissions? Heel-toe on a manual would be impossible with this, unless the clutch position is factored into things as well.
I have some first-hand experience with the same no-power problem.
First, Porsche's programming in the ECU will idle the engine if you step on the brake pedal while pressing the gas (to prevent the runaway problem associated with Toyotas in the past). As an aside, if you're on the brake before you press the gas, you can rev the engine up while braking, but only up to a certain point -- this allows you to heel-and-toe, but you can't go full-throttle while on the brakes (you can push the pedal all the way down, but you'll only get about half throttle).
So, if the ECU thinks the brakes are being pressed while on the gas, you'll have no power, as you experienced. And, your lowered brake pedal is part of the problem. So, when I lowered my pedal by adjusting the linkage to make heel-and-toe'ing easier, I encountered the same no-power problem. Coming out of certain corners, I'd have no gas for up to several seconds. I finally realized the problem was that the brake pedal wasn't coming up with enough force -- the bumps/transitions in the track were enough to pull the pedal off the brake switch, and the ECU would kill power until the loads changed and the pedal came back up. Readjusting the brake linkage fixed the issue.
So, you might want to try raising your brake pedal by half-a-turn, and see if it helps with the no-power problem. It might also be affecting your cruise control, but don't have any direct experience with that.
No direct experience with lowering the brake on the CS but when I did on my '91 944 I had to adjust the brake switch to match as the pedal actually lowered when the turnbuckle was shortened.
BillC:
Thanks for that! I'd rather not raise the pedal. I like it where it is. Since The brake light is no longer coming on when it's not supposed to. Driving at night really makes it easy to monitor this. I'm thinking there must be another brake switch somewhere that's affecting the cruise and the accelerator although the accelerator has not acted up since I replaced the brake light switch.
I'm gonna check that article again and see if there is anything about resetting switches when you lower the pedal.
Narrowing in on it, at least, I hope so.
:cheers:
