Porsche 911T 2.4 MFI 1972 USA

[BasherBell]

Afternoon all from a very wet and cold UK.
Before Christmas I imported a Bahia red 72 911T from California.it has a permatune cd unit. After one run where it seemed ok I started having problems with firing the car up. Then it would turn over easily but wouldn't start, I thought it could be the CD unit All seemed well apart from apparently not firing up. After a couple of weeks trying In the end I gave up and passed it over to a local Porsche specialist over Xmas to carry out a 12000 mile service. I had no service history at all and this would also serve as a bench mark for it's new history and hopefully solve the problem with starting. So I had it trailered to the garage.

They did the service and said plugs were changed and it started........ I collected it and did a round trip of about 60 miles. Two days later the same problem, won't fire up.

I've just pulled the plugs on the left as they are easier to get to (4,5,6) and they are incredibly sooted . Replaced them with the 3 new plugs of the same Bosch WR5DC+ . The car fired up first try.

So I have read everything on the forum I could find about plugs and heat ranges ( thank you very informative) and I am wondering

1. can plugs really get that fouled in 60 miles ? ( I cleaned 6 a bot just to see what was underneath, when pulled all the same. Can I clean them and learn anything ?

2. If they are fouling so easily should I switch to a hotter plug such as the NGK BPR5ES. Or BPR6ES ?

3. I think I am running rich ( I disconnected the startup solenoid before Xmas) but it seems very complex to adjust this on the MFI . Can it be easily adjuster should I find an MFI specialist and get them to look at it ?

I'm willing to try, just don't want to screw it up more. Very conversant with 912s but 911s with MFI are a completely different beast.

Many thanks

Dave
1965 Porsche 912 Coupe. USA
1972 Porsche 911T 2.4 MFI Coupe. USA
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[tharbert]

The short answer is that in order to get your MFI set up correctly, you must follow specific steps called "Check, Measure and Adjust" or CMA. There's a thread you have to read: Ultimate MFI Resources.

Basically, the MFI system is very good at staying calibrated. The problem is that everything else wears and gets out of spec. So, the trick is to get everything else back in spec. Then, and only then, should you try to adjust the pump.

[tobluforu]

Does it not fire when it's hot, cold or both? MFI cars like to run rich, but there is a whole lot going on in order for these cars to run right. Like stated, before you even start adjusting the mfi, make sure car is in perfect tune, timing adjusted, etc. Then make sure the pump rod is set to the right length, then all the rods are not binding, etc. Then synch the stacks, and so and so on......
There are few shops that will do this for you, best to figure it out yourself, not hard, just time consuming.

[356RS]

Maybe It could be as simple as not enough warm air going through the thermostat. Hose could be damaged or something not allowing the thermostat to get the warm air needed to adjust the fuel leaner for normal warm running conditions. Plugs get fouled and then very difficult to start. Easy thing to check first.

[kltarga72]

If the engine runs great for the first 50 miles I would say that you do not have a major problem. You said you disconnected a start-up solenoid, do you mean the cold start relay? I have a 1972 911-S with MFI and these old Porsches are hard to start without the cold start system in working order. If the cold start system is connected and you pull up on the black handle between the seats to start the engine you do know that as the engine warms up you slowly push the black lever down. Once the engine is warm the cold start (black lever) system should be shut down. I could see this as a possible cause of your problem.

[BasherBell]

Thanks for the replies.
I'm reading through the CMA now.

I disconnected the cold start solenoid on top of the fuel filter assembly as I believe it's causing more problems than solving them I will get around to that later.

I use the cold start lever between the seats and that works fine, it just increases the revs as far as I was aware unless I'm mistaken.

Plugs fouling must be the manifestation of the problem. When I replaced three it started straight up.

Can I tell if the fouling on the plugs is oil or fuel ?

Dave