I've been trying to restore full power to a '85 GSL-SE that I purchased recently. I've made some progress and restored smoothness and drivability but the main problem, lack of full power, still persists. At this point I'm starting to think the problem is a weak or erratic spark experienced under high loads.

The car starts easily, runs excellent in the low end and makes decent torque. At WOT the power starts to fade and I can hear a series of "puts" starting when the power goes away. If I use a stock leading coil the power fades at ~4500 but with a MSD Blaster coil it holds until ~5700 before the puts start and the power falls off. The coils are firing and the rotors, cap, and wires are in decent shape. Timing is stock. TPS is in adjustment. New plugs and fuel filter. I've just restored my secondary ports, they work now but only seem to have worsened the condition. The O2 sensor looks ratty and is an unknown. I haven't checked fuel pressure at WOT either.

I'm a professional mechanic with knowledge, skills and equipment. I have access to a hand held ignition scope that I can hook up and observe while driving the car. The thing is that while I am very knowledgeable on internal combustion I am still a rotary novice. I'm not sure the best method I should use to go about observing the ignition waveforms that would make the most sence.

Since the scope is designed around piston engines how should I set it up for the rotary? If I use it in distributor igintion mode, I will only be able to observe one coil and it's plugs at a time, leading or trailing. Then I could go either 2 or 6 cylinder to view all of the plug firings for that coil. If I use its DIS harness and tap directly onto each plug wire I could see all of them at once. But the question is how would I set up the scope to keep track of the wave forms? I'm thinking I should use the DIS harness and set it up as a four cylinder engine. Then I should see two leading waveforms and two trailing. But the scope looks for a positive and negative firing to number cylinders so I don't know what's going to happen.

Is there anyone with rotary scoping experience in the house that can shed some light here before I have to learn the hard way?

Vernon

 

I used an oscilliscope once to check ignition, but never had my hands on a real ignition scope. My guess is that you shoul be able to get it to work in 4cyl mode. Not sure though, because it definately won't look like DIS...

Have you checked the ignitors?
Have you looked for cross triggering?

 

i know fbs are known for haveing marginal stock fuel pumps

 

I'd be more concerned with the leading ign. Trailing ign has little to do with power.