How did I fix my car ?

Hello - Long time member, though not participating much lately (work work work). Mechanically willing but not always gifted.

My 72T MFI has been a sweetheart for 20y never missing a beat despite infrequent use of late. A few weeks ago it started slightly missing a bit... felt short a cylinder at a specific RPM...
I replaced the distributor rotor and cap out of principle, checked points, looked for plugs to replace my NGK BR7S and could not find any. Nada. Closest I got was BR7ES, seemingly same size but the end connector was not removable (for marine use). Hmm - they fit and clicked in and I had nothing else so put them in and it ran the same, no worse no better. Aha moment, When pulling plug wires I identified 1 dead cylinder... The plug wire end inside the rubber boot was blue from oxydation and broken off ! Dug up an entire spare plug wire from a 911SC (in my old stock, I guess I hoard parts) which looked identical... Vroom - apparently OK... Short lived though as soon after it started missing more, hesitating and smoking on starts, so I decided maybe I was dumb with my marine plugs and put back the original plugs (now cleaned and not very old mileage wise). They were very sooty already surprisingly. Skipping the part where I accidentally disconnected a removable connection near the Permatune, when finishing the plugs, I noticed accidentally one big hose was totally disconnected ! I assumed it was an oily-air return hose of some sort (excuse the technical terms I have no clue what that is ;-)

Can you take a peek at the pic and see the hose behind the arrow - lower one was completely off.. would that hose being OFF explain the rough running and slight smoking? Maybe it's something I accidentally pulled off when doing the plugs wires back there. Just wanna know.. because as of right now it runs PERFECT. And my mechanic just told me he is closing shop.

Oil tank breather hose.

Thank you David, I was close ;-) Would that being off affect running at all ? I'd expect not, just make an foggy oily mess.. So maybe plugs...

FWIW I’ve driven with that thing off for miles and never noticed any issues with it. Does make it smell very much like gasoline though

Greg:

What is the condition of your MFI pump? Has it been fully rebuilt and properly adjusted recently? Your car will NEVER run well with an out-of-spec MFI pump.

Letting the car sit unused for extended periods may cause the MFI “rack” to stick due to today’s piss-poor gasolines.

Assuming the MFI pump is okay (along with the plugs, cap and rotor) the plug wires are the next likely suspect. Get a cheapo multi-meter and measure the end-to-end resistance of each plug wire.

Keep us posted.

Good luck,
Alan
N.J.

Thank you... MFI pump was looked at 12y ago at engine rebuild time, was not rebuilt then - nothing since... I keep using some additives in the gas to lube it. The pump was a thought too but it was adjusted a few years back by a tech who was already old when these came out, he said it responded OK to tuning so possibly OK still, you never know.

I think the issues are ignition. Earlier I had found a corroded plug wire connector and replaced it...
This time I checked all wires for resistance and got some confusing results - 2 wires showed NONE, most showed a number consistent with what I read here (per foot)... I don't understand the lack of reading on 2 of them as the plugs were all firing - maybe not as consistently ?

Also the distributor cap had one corroded spot.. All in all i replaced the cap and 2 wires with more ex-911SC wires for now (that read similar Ohm numbers), cars runs much smoother and revs faster. I ordered a complete plug wire set... still struggling with potential replacement plugs choice (if anyone got suggestions for a 72 T MFI).

Thanks !

For my 911 S cars I use NGK BPR7ES, for a T I use BPR6ES, slightly hotter. The R is for 'resistor' which is the only way you can get them now, it just forces the coil to step up voltage to overcome the resistor, nothing wrong with that. The 'P' is for projected tip which is what you want. I don't understand your point about the tip on the plug, 911 connectors use that tip, unless you have some aftermarket connectors on there, which may be some problem. Correct Porsche wires are solid core copper, therefore have no resistance, all the resistance is in the plug connector. That way all the resistance will be the same regardless of length. I think with correct Porsche type wires and a new cap you'll be fine.

Thank yo so much Ed. I appreciate your recommendations, ordered a set..

The ones I had, the tip was non removable (normally you screw it on - BR7ES -all I could find locally) - it was listed as "marine" not auto. That's why I was worried, but indeed the tip worked. I ordered some BPR6ES, thanks again.