It all started with a dead battery

[kwikt]

A few weeks ago my battery was stone dead even with battery tender on it. So i jumped started it to move it and it ran fine. I then purchased a new battery and started right up but misfiring. Drove it a few miles and wouldn't clear up. Seemed to be running on 5 cylinders but not. So i began searching and trial error with spare parts. Idle is poor and sluggish with heavy gas fumes and really down on power.

72 911E
Compression 160-170
Leak down 2-5%
Fuel pump flow 1000CC+ in 30 seconds
valve timing spot on
valve lash GOOD
Timing and advance... Good with both Distributors
MFI pump timing good
Disassembled and checked fuel console
Checked fuel pressure 13psi

Replaced ignition coil
Replaced cap/rotor
Replaced with rebuilt CDI
Replaced plugs/wires
swapped MFI pump
swapped distributor/points
Swapped injectors
Even swapped voltage regulator as last resort
Still runs like crap no matter what is swapped. 0 improvement as when started.

[edmayo]

Is the hot air hose hooked to the thermostat, and delivering hot air to it. Double check your firing order.

[kwikt]

Yes firing order correct. First item I checked was thermostat tube. All good. Ed this car finally stumped me in last 38 years of owning it. Got to be something simple like not enough voltage to cdi/distributor. Ideas!!!!

[edmayo]

It may go back to WHY was the battery that dead? So have you checked charging voltage and voltage to the CD box as you said? If the car was running perfectly before the battery died then there must have been something in that sequence causing this. Wth engine running use an infra red heat gun and aim it at each exhaust pipe near the head flange. Look for even temps, need to know if it is one cylinder or all of them.

[kwikt]

Ed I checked for dead cylinders already with my Temp gun close to cylinder head and all seemed uniform on temp but to me it seems like it's not firing hot. I haven't looked to see if there is a purple spark at the plugs yet which would indicate weak firing. I'm also going to check voltage at CDI center pin which I believe is 12v. I swapped voltage regulators thinking maybe voltage but that wasn't it. I checked voltage at battery and while running and all is fine. Really appreciate the input Ed!!!!!!

[Scott A]

Two things that caused rough running for me in the past.

My distributor was off by a tooth. (Tho that was long ago, and I may have fabricated a new memory)

My 16 pin plastic connector had melted, and a short developed.

(The pin connector back in the engine area, on left, near the fuse box)
I had to open the connector to see it.
(It could be 14 pins, I forget the count)
In this case, there was a poor ground at the rear, which caused the car to search itself for another ground.