Low on power – One bad Dizzy?

[Sam 69 Gulf]

I have a stock 90 964 c4 with the exception of a primary muffle bypass.

I have noticed recently the car seems low on power/torque – specifically low in the RPM range. Above 4K it is still Ok but at around 2500 rpm it pretty much dies when you floor the throttle. There is definitely not the response I used to get or would expect from a 3.6.

The car has just had new caps and rotors, clutch and valve set…..

Has anyone experience with the impact of loosing half (or a percentage) of the twin spark. I am hoping something simple like one bad coil, coil lead etc to one set of wires…..

Any input is appreciated
Sam

[Oracle]

Maybe too lean/rich?? Have you connected the Hammer or Hammer-like to get the error codes? That would be an easy and cheap start point.. Maybe someone in your area has the tool.

good luck!

[deoxford]

Sam,
You can test this by removing one coil pack plug at a time, if the car dies that is the bad coil.
same for the dizzy

[bazar01]

Check the dual dizzy belt.
Unplug one ignition control unit at a time and see if it runs
Check the airflow meter plug connection
Do a resistance test on the cylinder head temp sensor
backprobe the O2 sensor

[tshih]

To check the drive belt of the twin distributor just unplug the primary (one closest to the fan) and see if the engine will run. Be careful (45000 volts in spark wire!). The secondary set of plugs will fire the engine if the belt is still working. Or you can manually remove the cap and rotors and see if the belt is still there and 2 marks and rotors line up correctly after setting the engine at #1 TDC.

[Steve@Rennsport]

Pull the lower distributor cap and see if the rotor will spin freely,...

Thats the easiest way I know to see if the belt has snapped.

Do you have a vent kit on there????????

[Sam 69 Gulf]

Vent Kit - no, no no - I just open the windows when the passengers complain...

OK, you have me - what is a vent kit!

Thanks
Sam

[Steve@Rennsport]

Sam:

The vent kit is what Porsche retrofitted on on 964's to help prevent premature failures of the distributor drive belt from excess ozone.

Its rare to find a car today that doesn't have one, but it happens from time to time.

Look for the white rubber tube doing into and out of the distributor body.

[Geoff_91Targa]

I have purchased two different 964s with a broken distributor belt. In each case they ran so well, the owner didn't realize there was anything wrong. If you are running easy, it's not really perceptible- if you are running hard, there is a noticeable loss of power, and you can usually hear a slight pinging (detonation).

If you pull your left distributor cap, you'll easily tell by a freely spinning rotor that the belt is broken. If that's the case, note which terminal is excessively burned, and you'll know which cylinder has been impacted. Pull the plug and you'll have some indication of how much damage was done.

The 91 that I presently own, had a broken belt for 10,000 miles without trashing the engine. I could tell this by the fact that the Porsche dealer that serviced the car at 60,000 miles replaced the distributor caps. (I had the invoices). I bought the car at 70,000 miles, the belt was broken, and the left cap had 5 shiny unused terminals, and one that was burned. The engine seems no worse for the wear.

The distributor can be repaired with a belt replacement. Brumos Porsche in Jacksonville typically stocks the belt. Pelican Parts may also have it.

[ischmitz]

Another way to test for dual spark is to pull the connector to one of the ignitors at a time and then try to start the car. If I does not start with only the left or only the right one plugged in you have an issue (coil, belt, ignitor). I do this every once in a while as a quick and simple test. No tools required.

BTW: The ignitors are the small black modules mounted on the heatsink on bracket that holds the coils. Simply pull the spring clip and pull the plug.

Cheers,
Ingo