Still struggling with my 930. After I found the coil power wire not connected(burned off because the connection was not tight). It solved the no start/die problem but the high/full boost miss continued. I had very high CO reading at idle 8-9%. Reajusted to 3.7%Stock spec is 2.5 +/- .5%. Rechecked and the CO had climbed to over 6%. I replaced the plugs as they were heavely carboned and I assumed were affecting the idle CO reading. I also suspected the WUR but do not have the test gear to check pressures. I took the WUR apart and could not find any thing that was obvious. Applied voltage and the metal strip heated up. The lower and upper diaphram held vacuum. Put it back together and reset the CO to 3.7% . Tested at full boost and no miss. This does not make sense to me. I did not think adjusting the idle CO would make that kind of difference. I am running a 1 bar spring and sport cams and I wonder what the idle CO should be with non stock cams. The high end miss is gone now but it feels a little rough in the mid range under acceleration. Need to purchase the pressure gauge set from Pelican and see what the WUR and delivery pressure are doing. Pumps and filter are new. Any other ideas or knowledge on what the CO should be will be greatly appreciated.

 

It sounds to me that the most likely issue was seriously carboned up plugs, probably contributing to the miss....especially in conjunction with the high CO%. A really rich mixture + weak spark due to carboned plugs = misfire. Get your CO% down to 2.5-3.0%.

It sounds like most of your symptoms have gone away, except for the "little rough" in mid range under acceleration? I personally don't think that's CO related, as you are in the ballpark if maybe still a little high. Generally these cars run better on the rich side, but you could always experiment and lean her out even more to see if your midrange rough goes away. I don't know if the "sport" cam (what is that, an SC?) has any specific requirements relative to CO% that's any different than a stock cam. Sometimes you just have to experiment across the whole range to find what works best, but at least now you're able to get full boost without any miss.

One more thought: If your coil power wire drew so many amps and got so hot to where it burned off, then the wire itself (i.e., the insulation) may be compromised and grounding somewhere, or the internal wire resistance has gone up to where your coil is not firing at full capacity. Just a thought....

And one more thought: You may have already ruled this out, but is there a possible leak in your intake/intercooler system? If so, you will go eye-watering rich when opening the throttle, especially on boost, because of the loss of metered air. The car will miss and bog while on boost.

 

Mark, thanks for your input. I wondered about the coil being less than OK with the problem I found. I haven't thought about the coil wire. Worth a check. The sport cams came from Windward Performace about 11 years ago when I did a rebuild. What happen to Windward? I find a Windward in the Islands selling some Porsche parts but nothing where I bought the cams in Putney,Vermont. The invoice says
"cams sport SC grind for 1979 930. The other problem I have is that I cannot find the timing spec that Windward provided when I did the rebuild. Do you think the SC cam spec would be correct. I plan to do a reseal this winter and need the timing spec. In regard to the CO settings if I go much lower than 3.5 I get alot more poping on decel, which I equate to being to lean. Thoughts?

 

I believe timing for SC cams is usually set around 1.7. Here's a cut-and-paste from a professional cam grinder when I asked the same question on the topic:
"1.7mm is a good setting for the SC in a turbo application. With higher boost levels going back to 1.2 or 1.4 makes sense"
There are so many things that can cause problems. Ignition timing, vacuum leaks, AAV malfunction, boost leaks, WUR control pressures, plug wires, the list goes on....
There is a lot of information on the forum (and on Pelican as well) regarding popping on decelleration. You may want to do a search and review what's been offered. I would say let's get your car running strong and clean through the entire power band, then worry about some exhaust popping later.

 

Mark, thanks again. As I remember I thougth I set timing at .070 or1.77mm. First things first. I what it running right before I take it down.

 

mine are from Dougherty racing cams and the spec was 1.8 to 2.0, he said they should be set at 2.0 but I bought them from imagine auto who said 1.8 to 2.0 with 1.9 being optimum

 

Handy 930,
your cams are not the problem SC grind or not, let's assume the cams are timed properly (would give the car decent power, smooth idle), you either have ignition system issues or CIS (fueling) issues, based on your different CO reading everytime you test, my bet is on the injection system. If you could also give me HC (hydrocarbon) readings it would help alot. You either have intake manifold leaks (possible intake gaskets, injector blocks) or a bad fuel distributor, or combination thereoff. Another possiblity could be the ign. distributor (make sure it works, advance, vacuum, etc.), as for timing, you can set it for around 0 deg. at idle (with vac.) or 35-40 deg. (without vac.) at 4500RPM. This way you can check the distributor (pretty common failure at this age).
Hope this helps
Bernd

BTW
If (I hope your car doesn't) you don't have emissions equipment on your motor, with SC cams/1 bar spring you could set idle CO( 950-1000 RPM) with properly functioning timing at 3.5-4.2 %CO

 

Bernie, thanks for the info. I know the cam timing is not the issue now, but will be taking the engine down for a rebuild this winter and could not find the spec that Windward supplied when I rebuildt 11 years ago. I will keep checking the other components to see what I can find.

 

Will here is the update. The engine continues to run better. My theory. The coil connection started the problem. Carboned the plugs and combustion chambers. Resulted in high CO reading. With new plugs and some aggressive driving the engine continues to improve. The midrange issue is gone. I think the carboned up chambers and plugs were the result of the poor coil connection. The variation in CO was a result of carbon causing an occasional miss fire. I am back to the original position on the mixture control and all seems fine. We will see how it continues and go from here. Thanks to everyone for your inputs. A lesson for me and maybe others.

 

That's good news. Maybe run a tank full of Techron to help clean out any residual carbon buildup on the valves, etc.

 

Mark, that is my plan. Thanks for the help. Where in WA? We spend part time in Port Townsend.

 

Desert country, near the Moses Lake area.

 

I used to live in Selah for a while when i was a kid

 

You're a long way from home, Ken (if Selah was ever considered home, that is). One of my absolutely favorite roads is the old canyon road from Ellensburg to Selah. It just recently got re-paved; great twisties and lots of cops.

 

I lived there from 6th grade to 10th grade my dad worked for the power company and we got transfered about every 5 years.