DJet Frustration, Ever play that Whack-A-Mole game at the arcade? Options

[ConeDodger]

Remember that arcade game Whack-A-Mole? You take a hammer and whomp the moles as they come up through the random holes? McMark and jcd914 and me had that kind of day playing Whack-A-Mole with the DJet on Jim's engine (jcd914) in my car...

Recently the engine started running bad. It had a low speed miss and then would go like stink when you got into the advance curve. I have a bunch of new 914 DJet components so I started throwing parts at it. This is a method used by people who aren't mechanics to fix something they don't want to pay a mechanic to figure out and fix. Take a note if you aren't a mechanic - this method is often more expensive then just paying the damned mechanic. So, I replaced the MPS with one that I bought from George at AA a few years back and never really used, I replaced the harness with a Bowlsby harness, I put a resistor in the CHT circuit... Each thing I did made it run better in some ways but often worse in others.
So, I decided that since I was having the Sacramento Porsche Family Reunion today and McMark was coming up, how about having him take a look at it and paying him for his time. Mark was game. He brought his LM 1 Wideband AFR and we methodically went through the tuning process. Here is where the Whack-A-Mole game began. Everything we did would improve it but unmask some other issue. Some things did nothing when they logically should have. We replaced the distributor with a rebuilt one from Rich Bontempi, it ran worse. We discovered that two injectors were not firing. So the distributor was good but the trigger points, which were new by the way, were bad. Swapped in the trigger points from the original distributor and it ran on all cylinders again but still ran bad. Lean, very lean... Then Jim Dupree pulls in the driveway and steps out of his car with an MPS that he pulled off of one of his spares. 30 seconds to plug in the vacuum line and the harness plug and the problem is solved. Turns out the new MPS from AA is bad or badly tuned for the motor. I suspect the later as it will hold vacuum.
So after three hours of Mark's time and lots of parts. The engine - Jim's engine runs very nicely again... Ahhh... the joys of a 30+ year old car (IMG:style_emoticons/default/headbang.gif)

[jcd914]

Years ago, I mounted the MPS to the engine tin (using the coil mount holes) when I set the engine up on jack stands in my drive way to test run it. Since Rob's car had a carbed engine before we stuffed this one in we just left the MPS where it was. At this point I don't remember the order of changes we made by chasing what started as a flat spot at upper/mid throttle.
It would be my guess that it is EMI from the ignition was causing the off idle lean miss problem but I don't know for sure. It may have started when we added the MSD unit (higher & more sparks) or maybe when the plug wires were replaced (routed closer to the MPS) or when the EFI Harness was swapped.
At one point we swapped in a different MPS and it ran great till the next day. Maybe we just laid the MPS in the engine compartment while we went on a road test and then mounted in the same place as the old after road test, thinking we had solved the problem.
Today I tried a different MPS I just happened to lay it off to the side while we were trying to get a mixture reading and the engine ran well, fuel mixture was a tad rich now. Then I laid it on the engine tin and the running went to crap again. Lay it to the side, runs good, on the tin, runs bad. (IMG:style_emoticons/default/WTF.gif)

Sometimes it is just simple things the lead to the problem. (IMG:style_emoticons/default/biggrin.gif)

Jim

[ConeDodger]

Maybe we just laid the MPS in the engine compartment while we went on a road test and then mounted in the same place as the old after road test, thinking we had solved the problem.
Jim

This is exactly what happened that day with Mark. You swapped in the different MPS and we test drove it with it laying off to the side. Then, thinking we had solved the problem, everyone went home and I bolted it back in place on the tin. The next day it sucked again just like before. It never occurred to me to backtrack that one step.
After Jim left today I took a 20 mile drive up through Folsom and back down the Hwy. 50 to Sunrise. It ran great... I am loving it.