MFI Question

[91121]

Hi to all early MFI funs. I've been playing with Bosch MFI for 6 months.
Not reached an end yet. I've checked control rack, rods(air flow at 3,000rpm),air screw at idle(950rpm). I have found sweet ballance, part-lord,idle both, a couple of times. It was very beautiful. after spending all day long to adjust them(part-lord, idle). just like some manual says! disconect pump rod, put some more air, engine stops very soon. push only pump rod, means put only fuel, then idle slightly up then engine stops very soon.
But It chenges when I fire it up next morning! Idle seems to be OK. but power's gone! why?! all the time! That's the reason why I'm still playing with MFI adjustment. 72 T is my mate. I will be very happy to hear from somebady playing MFI like me.

[jeff m]

91121
The hardest part is getting the linkages right. so you're almost done.
There are two adjustments, one for idle and one for running.
I assume you have the tools, a long thin screwdriver and an 8mm socket on a long rod is the best I can descibe them.
It sounds as though you may have only adjusted the idle mixture.
I would suggest richening the main adjustment (check the book it's the oposite direction to the idle) maybe four clicks and stick it on a machine to check co, around 4 to 4.5 should be ok.
Strictly speaking it should be done under load but not many of us have a moble analyser!
Note all clicks on paper so you can return if you mess up! Take your time.
I am also assuming that the thermosatat was checked and that the hose, the 30mm one is attatced, movement of the thermostat is checked by removing the the small trianular plate on top of the pump.
If this is not working adjustment is difficult at best.
Good luck
Jeff

[91121]

Thanks JEFF for your quick reply! I have got the tool for part-lord adjustment as well. and done thousand times, and also checked and cleaned thermostat too with removing the small traiangle plate on the pump. It's working propary. I guess the part-lord setting is very close to the point according to reading plugs and its pulling on the high-way. I have no idea why the setting changes on next morning. Please advice.
NAOTO

[ChrisBennet]

It's part-load, part-load adjustment.

[Tyson Schmidt]

The MFI system is very dependant on intake air temperature for proper adjustment. That's why the '72 and'73 models had thermostatically controlled intake air. The MFI rack only knows throttle position, rpm, and (sort of) engine temp. It can't measure intake air temp, so it has to then regulate the air temp coming in so it can be as accurate as possible.

I'm assuming that you had the air cleaner off while making the adjustments. This will throw the mixture off after you reinstall the air cleaner set-up because now the pre-heater will be warming the intake air and throwing off the mixture. You should try to do your final adjustments with this system in place.
It also helps to blast the car around the block and then retest. Sitting there running for long periods isn't the best way to tune the system since it doesn't match the normal driving conditions.

Also, with the engine idling and being revved for long periods of time standing still while you adjust it, the Mfi thermostat has had plenty of time to heat up all the way. But starting from cold and driving off, it may not ever be getting hot enough to come off the cold-running position. So my suggestion is to check the condition of the hoses that supply hot air to the MFI thermostat, and the condition of the left side heat exchanger.

[tryan]

take your throttle plates out, clean them up and set them to spec. make sure are the linkages and bleeds are 'spot on' . (old mb diesel linkages are cheaper)


make sure both thermosat ( inner and outer ) lines are intact and the exhaust has the proper mfi riser.

invest in a co sensor and get the part load setting dialed in. you will not be able to run at 3% with todays fuel. try 5% or so. lead free fuel makes reading the plugs a thing of the past.

when you get that set, get your idle setting. you will have to comprimise between a good idle and good starting characteristics.

make sure the flapper in the intake snorkle is working properly. check the overun microswitch is set and working.
the cold start fuel solenoid on top of the fuel filter is working when it is supposed to.

i had a wicked flat spot at about 2700, so i richened part load up two clicks. i still had a hard time starting the car hot , warm or cold. one of the injectors was dribbling and after replacing all of them she now starts disgustingly well. runs a tad rich , but i change the oil quite frequently.

i gave the injection tools away when i was done. when your pump starts to grow hair, that means you are playing with it too much.





tom

[91121]

Oh Lord! Thanks CHRIS. It's part-load. I need some adjustment too.

[91121]

Hi TYSON,thanks for your advice. I am making the adjustment with these system in place. I have doubted pre-heat box? once.It's located between air-cleaner and left heat-exchanger. controls intake air temp. I cleaned it up and working properly now.
and I checked thermostat, replace the cover on the top of pump. It's leaned out completely.

Have you experienced that your MFI setting changes after adjustment?

[91121]

Thank you TOM. Yes! I may be playing with it too much!
I have taken throttle plates out clean them up and set them to spec. also all the linkages and bleeds been checked to the manual spec, using air-flow meter. microswitch,cold start fuel solenoid and the flapper in the intake snorkle as well.
I haven't checked CO value yet. she starts well anyway.

Does these adjustment need a night to settle down? I am struggling still becouse I have experienced very sweet run with my MFI once. Just one night dream?!

Or another problem?! My hands are dirty today too.

NAOTO

[KOJI]

Hi Naoto.
Where are you living Naoto? I'm living Tokyo,Japan and enjoying to drive 73-911E that has MFI.
I understood your difficult situation because I had similar problem.
It turned out to be worn throttle bodies on no.4 and 6 cylinders. I had poor idle and severe flat spot above 2500rpm. I made thousants of adjustments and tried to find good compromised point between idle and part load. I could set reasonably good running condition once but next day engine did not idle or accelerate beyond 3000rpm(miss fired).
Every couple of hours adjustment i was resonably satisfied but it didnt last long.....
I got used good condition T/B. It was installed on June,last year. After several adjustments my engine run perfectly.
I think it isn't exactly your case but I'd like to share my experience.

Koji
911E(73) colored green.

[tryan]

spray wd-40 or carb cleaner around the pivot bores on the throttle plates to see how bad they are leaking. use a sensitive tach and see what kind of increase in rpm you get. you could buy koji's and send them to eurometrics for a rebuild to minimize your downtime.

or you can try to set the idle mixture right off idle if the throttle bushings are worn. an a/f ratio meter might help.
check your injection timming also.

i'm also due to have the pump and plates ( and motor ) rebuilt.

you guys must have the coolest rides in town.

[91121]

Hi TRYAN. Like you said,throttle plate leakage may be a suspect. I will try!
actually throttle body is not shining like a new penny, must have some worn.
but I could give synchronizaiton to air flow at 3000 and idle barely. I can live with it.
I guess I'm almost there. will take a time.
Thanks TRYAN, your suggestion helps me a lot!