Synchronising MFI
 

Tried to synchronize airflow following CMA. No change when turning the airflow screws.... Any advice on how to clean without removing the throttle bodies?
Thanks Ed

Ed,

With the engine at idle, remove a screw one-at-a-time and spray some aerosol carb cleaner in the port.
The engine should respond.
If some don’t respond, squirt some more.
Reinstall the screw and lightly screw it in until it ‘seats’.
Repeat a few times.
Blow in the port with compressed air.

Having the engine at idle tells you if you are getting anywhere and will burn the carb cleaner (rather than have it flood the cylinder).

I’m sure you have already noticed that it is useful to have multi-jointed wrenches (and arms/fingers) for this operation.

Best,
Grady

Thanks! Quickly to the store to get some carb cleaner.
Ed

Ps: a bit too late but happy birthday.

Only cyl 5 responded. Couldn't get easily to 2 & 3..... I'll keep spraying.
Ed

Hard to do with them on the car, not so hard (1/2 day) to remove, clean, set correlation with a vacuum cleaner, reinstall and correlate.

http://forums.pelicanparts.com/porsche-911-technical-forum/277484-mfi-diaries-correlation-last.html

It will rain this weekend so might give it a go.

Do I need a new gasket?

What I don't understand before reading CMA (again) is what the idle setting should be. If I close the butterflies completely the engine will die of O2 starvation. What is proper airflow for idle.

Thanks,
Ed

Yes you should change the gaskets and get yourself some steel M8 wave washers and M8 (12mm across the flats) nuts for the stacks. Don't use aluminum washers because you can't get them out when (not if) you drop one down the intake port! All available inexpensively from our host.

Proper idle setting is three half turns (five half turns for a 2,2). I found that I was reading about 3Kg/Hr on the synchrometer with the TB on the bench, a number around 5 at idle, and up at 9 or 10 at 3000 rpm is typical.

The issue you face is threefold.

1) Most magnesium TB have a deep groove worn in them which causes inconsistent air bypass with the plates closed.

2) Over the years prior owners set the throttle plate angle (particularly on the more easily accessed 2,4 TB) all over the place without following CMA; and

3) The shaft seals can also leak.

What this means is that your airflow may vary all over the place at idle. Once the bores are open it's not such a big deal, which is why I was able to get away with imperfect correlation for so long on a race car (mostly WOT). BUT Grady and Mark Donohue (in Unfair Advantage ) would all tell you that part-throttle operation is CRITICAL to winning races because you must modulate the throttle in the corners.

The problem with imperfect bores and seals is that the changes are variable and unpredictable- one stack warms up and starts leaking, then cools down and stops etc.

Anyway, you want the car to barely idle with all the linkage rods disconnected and the Synchro reading should be equal between all stacks. That is why you use the air bleed screws-- to tune the reading with the linkage rods removed.

In the past I've used pipe cleaners soaked in carb cleaner to clean the bores after spraying into bores also. I've got plastic stacks so I might not have the same problems. Then set all at 3 half turns. Take vacuum readings, average and adjust.
Make sure you have no preload on your rods.
As mentioned above, are you sure they are all closing completely