MFI Help?

[aerocrosby]

Just got my '72 911T back on the road after a restoration and need some MFI advice. I had the engine out for detailing and then professionally reinstalled and the MFI all set up including an exhaust analysis. All checked out good. The car starts easily but when cold - it bucks, misses, pops, backfires, and generally runs like crap until it is fully warmed up. (over 180F oil temp) Then, it runs absolutely perfect. My mechanic, who is about 100 miles away from me, suggested some fuel injection cleaner through a few tanks of gas but that has not helped. Next week I am going to drive to his shop and we are going to remove and check all the fuel injectors for proper function. If they all check out good - I don't know what to try next.

In the meantime - anyone have any ideas what might be wrong? I hate to start throwing money at the MFI system like replacing injectors at $200 a pop when there might be something simple I am missing. I also don't want to spend $3500on PMO carbs either.

By the way - before I pulled the engine for detailing and oil leak fixes, I had none of these symptoms. The changes I have made while the engine was out were:

SSI exchangers
Dansk stainless muffler
MSD ignition w/ Blaster II coil
new premium plug wires
new plugs

Thanks very much for any help or ideas!

[frogger]

My guess: Check the preheat line (paper/foil tubing) both from the left heat exchanger to the underneath (left) side of the engine tin, and from the top (left) side of the engine tin to the thermostat on the MFI injection pump. It may have been knocked off or damaged.

[FenderBender]

+1 on the preheat line and make sure the thermostat is clean.

What Plugs? People have had problems with Platinum plugs.

Just my 2 cents

[1972_911T]

Originally Posted by frogger

My guess: Check the preheat line (paper/foil tubing) both from the left heat exchanger to the underneath (left) side of the engine tin, and from the top (left) side of the engine tin to the thermostat on the MFI injection pump. It may have been knocked off or damaged.

This would cause the oppasite to happen it would run good when cold but crap when its warm as the thermostat fails to get upto temp properly. It sounds to me like your pump needs setting up properly also check for air leaks with carb cleaner. What you describe is what heppens when an MFI engine is running too lean.

Steve

[frogger]

If it's backfiring out the exhaust, it could be very rich on start up. Bucking could be a symptom, too. Popping, I'm not sure about, as I know it happens on lean conditions. Perhaps rich, too?

Anyway, when the engine gets hot, ~180 degrees, the ambient air at the thermostat housing (recall it's open on the underneath side) is plenty hot, which should lean out the engine even if the paper tubing is damaged / disconnect and let it run correctly. (edit) I had experience with this recently. It took much longer for the engine to lean enough to drive well. Essentially until it was up to full operating temp.(end of edit) If it's too lean at start-up, it's only going to get worse as the engine warms. Still, I could be wrong, but it is a couple of minute effort to make sure that that's not the problem.

[304065]

Follow the link in this thread for more about the hose.

MFI thermostat data. . . and distaster!