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C4 996 won't start.


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My 1999 Manual C4 cab won't start. I turn the ignition the lights come up but nothing when i turn to crank.

To add a few things into the mix here's the full story...

My hood at stopped lowering and so i thought i'd check the fuses, the fuse box legend was a bit vague so i checked a few extra to be sure and I had removed the alarm fuse and refitted it (whether this is the cause of the problem or not i don't know but worth a mention). After i knew the fuses were not the cause of my hood problem I left the cat for the weekend. After about 3 days I went to go for a ride and the car would not start.

I've checked all the fuses again. All OK.

Disconnected the batter for 24 hours and reconnected to reset everything. Charged battery.

Checked the fuel pump relay. it works.

swapped the ignition relay. still no joy.

Any other suggestions?

Thanks in Advance,

Paul

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Thanks,

I'll start with those after work tomorrow. I'll get the PDF of the circuits printed out on A3 so i can take a proper look at them.

BTW, I think you have a clutch switch only if it's a USA/Canadian car. Basically when you crank, power goes from ignition switch directly to pin 3 of Start Lock Relay, then from pin 5 to the starter solenoid (when the relay is energized). The Start Lock Relay (pins 2&7) is powered by the DME, which monitors the clutch switch if equipped (clutch switch contacts closed when fully depressed).

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Something I found a couple of days ago. UK might have the switch. It is not just for safety.

CLUTCH "Safety" SWITCH

Here is a post from a user named Gator Bite

"It's not only a "Clutch Delay Switch". A "Clutch Delay" would slow the release of the clutch, and it's usually a mechanical device like a manifold with a fixed orifice to slow the flow of hydraulic fluid from the clutch slave cylinder. BMWs (except M models) use a clutch delay to make the cars easier to drive / harder to stall.

The switch you're talking about does one thing for several reason, one of them overlapping the benefits of a clutch delay. It retards the timing when you press the clutch, and for a short time after the clutch has been released.

1. Retarding the timing reduces shift jerk which makes shifts smoother, but more importantly protects the Dual Mass Flywheel from damage.

2. During take offs, retarding the timing reduces the chances of knock/ping on clutch release. This makes it much easier to launch without stalling (the overlap I was taking about).

3. By knowing when the clutch is being depressed, the DME can widen the range of acceptability in it's misfire detection module.

Here's a quote directly from the Porsche Tech archives: "The program that evaluates misfire is complex. it has to be able to distinguish between deceleration caused by rough roads, potholes, shifting, and other non-misfire causes, and deceleration caused by misfire."

4. By knowing then the car is shifted (watching the clutch), the Torque Control can reduce engine braking during high torque downshifts.

Here's another quote from the archives: "On deceleration with unacceptably high engine braking when downshifting, engine drag torque control (MSR) prevents the drive wheels from locking on a slippery road by slightly opening the throttle valve."

So by removing that switch, you may in fact feel some added sharpness to throttle response when shifting. Because now you have a sharper timing curve. But you will be castrating all 4 of the benefits mentioned above. To summarize:

1. You may experience premature failure of your DMF

2. You may find yourself stalling your car more frequently, and you may find that your car has less power than before, because when it pre-ignites, the DME is going to pull the timing back and keep it back for a while.

3. You may experience a Check Engine Light, and investigation may reveal random misfire codes.

4. You may notice locking of the rear wheels after high RPM downshifts. This is most likely to be noticed on slippery surfaces like rain or snow, and it is likely to cause over steer."

Edited by fpb111
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Hi Frank,

There are two clutch switches. See post #10 here http://forums.rennlist.com/rennforums/996-forum/454057-anyone-else-mod-their-clutch-delay-switch.html

I was referring to the gray clutch switch that clicks when the clutch pedal hits the floor. The sole purpose of that switch is to prevent the car from cranking unless the clutch pedal is fully depessed. I think only USA and Canada cars have it.

The info you posted is about the other switch (black/orange) that's also activated by the clutch pedal (actived as soon as the pedal is pushed). It controls cruise control and timing like you posted. That switch should have nothing to do with cranking.

Thanks

Edited by Ahsai
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Hi Guys,

I fixed it today. it turned out I had put one of the fuses I'd checked back in the wrong slot so there was no power to part of the alarm system amongst other things (fuse E1).

Thanks for your help.

That was easy enough :) Glad you get it sorted out.

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