Ignition timing - Low power

[p27549]

I have my 993 which is 20bhp down on standard power 253 instead of 272. The power dyno graph shows a power drop off at 5200 rpm along with torque drop off, it then kicks back up a little at 5600 rpm. I am in progress of changing plugs and leads but am interested if the second distributor can be out of timing,
Can the distributors be adjusted to change ingtion timing or can a loose belt affect timing between both distributors. The belt is loacted and looks in good condition.
Is there an igntion advance mechanism controlled by vaccuum?
Any clues


Thanks

TIM

 

[Guards Red]

Very much doubt its the ignition timing. The distributors are linked and cannot be adjusted separately and anyhow, the DME sets the timing. As long as the rotors are in the ball park, the DME does the rest. They each do adjust for centrefugal advance and may be worn out or the belt broken that links the primary distributor to the secondary, but my first port of call would be the resonance flap and it's actuator. Is it a varioram? If so, it could also be the actuators for this. Check the resonance flap first, easy to do, turn on the ignition and listen for a loud click from the back of the car. No click means the system is down. make sure you turn off the immobiliser first though.

 

[p27549]

Is the resonance flap fitted to the non vario ram engine?

 

[day1zero]

Yes. I had exactlty the same thing (non vario) the connection was loose. Spotted by Wayne at Chips Wizard. Instant fix....20bhp back !!!

 

[p27549]

Thanks very much for that information. That one i will check out. Is this unit under the throttle housing?

 

[Guards Red]

The vacuum actuator is under the inlet manifold and has a spring loaded diaphragm inside it. The diaphragm is made from rubber and degrades over time and leaks, once this happens it won't hold vacuum and will not move the resonance flap inside the manifold. The system consists of the actuator, a solenoid which acts as an electric valve, a vacuum tank and the ecu which controls the system. The electric solenoid that diverts vacuum to the actuator is on the front of the manifold and is easily accessible. The vacuum tank is under the manifold on the left hand side and is the size of a coke can with a bowl shaped end. Just check the tubes to each of these is in good condition and holding vacuum. If you pull off the connector at the vacuum tank you should hear an audible rush of air to show it was holding vacuum. If the pipes are good, the likely candidate is the actuator itself, about 40 pounds from Porsche.

Good luck.

 

[p27549]

Thanks for all this good information. I actually found the pipe disconnected from the vacuum accumalator. Hopefully the system will now be back working.
I sucked on the the vacuum modulator and the flap opens and closes , with ignition on the solenoid is clicking. Hopefully this is the fix and have relocated my lost horsepower . With new plugs and leads the car should be a pleasure to drive again
Thanks