993 engine firing at the wrong time

[911TE]

I hope anybody ever had the same problem and know how to solve it!
I just did a complete engine overhaul on my 993 and put a new LWF (964RS, 993RS) instead of the DMF in.
Unfortunately I didn`t check if the timing ring cutout is in the same place relative to the positioning pin as on the old DMF.

Now my engine is running really slow in idle (400rpms) and is nearly not reacting to the throttle, also the exhaust is getting extremely hot.
In flashing the belt pulley with a stroboscope I see that at idle the firing point is around 15 degrees after TDC!
(I guess it should be around 5 degrees before)
What could be wrong?
The ignition point is not adjustable with the distibutor, the timing impulse only come from the TDC-sensor at the flywheel.

Anybody ever heard of different timing rings on LWFs?

I really don`t want to take the engine out again!

Unhappy Sebastian

[alexmurp]

hello did you check the belt in the distibutor could have broke or jumped a tooth ive installed light weight flywheels and never a problem but did break my belt by turning the engine over with a wrench and the distributor got caught on the dist cap hold down clip put the engine on tdc by the flywheel notch and take both dist caps off and check the that the rotors line up with the notches on dist housing alex..

[d_boyce]

Sebastian,

It's very easy to bend the sensor ring on the LWFs when mating the transmission to the engine. I'm referring to the ring of teeth that is read by the crank position sensor. There are 2 teeth missing on the sensor ring that allow the ECU to determine TDC. If any of the teeth are knocked out if place beyond about a millimeter this will cause an eronous 'missing teeth' signal which results in the timing being off.

The quickest way to test it--if you have the equipment--is to connect a scope to the crank sensor, turn the engine over and record the signal from the sensor while the engine is cranking. If the flywheel's sensor ring is bent, you'll see the signal drop. The signal has to stay above about 3 volts.

If it's bent you may be able to use a hammer and dolly to repair it.

Good luck on this.


-doug

[911TE]

Just found the problem. My LWF has the two missing teeth in a different location, so the DME thinks TDC is at another place than it really is. Bad Luck! I had to pull the engine and gear-box again to change the Flywheel!
Fly-wheel is from a GT2, so beware and always compare the timing ring from your old flywheel to the new one (In relation to the pin!)
Would have saved me a lot of work and money!