MFI Running rich at low and high rpm

I have read the Pelican MFI Article and the "check, measure adjust." It still runs too rich. I've done all the suggestions there and what I have found on this board including the warm air thermostat, which is working perfectly. The car is running so rich that after about 50 miles the plugs (set to specs) are carbon fouled. I have even plugged the enrichment line from the fuel filter. For the first 30-50 miles the car runs perfect then the carbon fouling then lots of backfiring in the exhaust. All the plugs look the same: a thick dry layer of soot. It appears the two mixture adjustments don't work, I continue to turn them in the direction that leans them out (and yes I am turning them the right way) and nothing happens even after turning them over 20 clicks! I fear the MFI system is worn out. Any ideas of how to trick the system into running leaner? I guess what I am getting at is how to get more air and less gas into the combustion chamber. I know I need to get the pump rebuilt, but I would really rather drive the car while warm weather is here and possibly rebuild it this winter. So, any ideas?

Kurt V
72 911E

When my pump was rebuilt turn around time was less than a week.

Mackgoo, where did you get your pump rebuilt?

Kurt V
72 911E

I think it was H&R, he is in the back of the 911 hand book. His name is Hanz. I live on the East coast, He's in NY so I decided to go with him instead of Gus.

hello

On the early pumps you have only 6 cliks either way. If you do to much you have to rebuild it. later pumps have a stop.

Before doing anything with the pump you have to make the basics.

Check coldstart fuel enrichment. Check throttle flaps and base regulator rod lenghts. check ignition. Check Pump FE

One way would be to choke the fuel inlet but this will generate cold start trouble and it isn´t propper work just a kind to pfusch around or find out what.

Grüsse

Kurt,

I don't remember what all yiu did during your recent removal adventure, but did you remove the MFI system from the engine? And, how does the engine run now, compared to pre-removal? My suspicion is that you have the correlation between throttle body angles and pump off by a significant amount, such that the pump control angle is 'advanced,' compared to what it should be. That is just about the only thing that would have 'INSTANTLY' caused your rich running problem since reinstalling your engine!
------------------
Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 04-15-2001).]

Warren, I guess I should have stated that this problem existed before I pulled the engine. I was hoping that with the engine out I could more accurately set the throttle bodies and hopefully cure the problem, but it appears the problem is in the MFI pump itself. Guess I just need to bite the bullet and send the pump in for a rebuild.

Kurt V
72 911E

i would imagine you have checked the pump timing.? are you getting hot air up the hose to the thermostat? is the pump lever up against it's stop at idle? did you check the pump rod length? are you using an exhaust gas analyzer? what are your readings at idle and at 3000 RPM? 6-8% on both is the top end of the scale where it runs well with good transition. they don't like to run too lean. the orig. factory settings were quite lean. must have had better gas back then.

John, I'm not using an exhaust gas analyzer, but I have checked everything you mentioned except to see if the pump hits its stop. I'll check that tonight. The weird thing is until the plugs foul the car run absolutely perfect, with the exception of running extrememly rich.

Kurt V
72 911E

i would highly recommend the use of EGA. at least have a shop check it to see where you are. it's hard to ear-ball these things. check idle with the pump lever at it's stop, and at 3000 rpm.

John, I try to do as much as I can. I know I can get a Gunson EGA for around $125.00. People in my british car group swear by this tester when they are prepping for emissions testing, especially those in England. Do you have any experience with Gunson? What do you think about me trying it myself?

Kurt V
72 911E

Try disconnecting the enrichment selenoid on top of the fuel filter. Also check the rod length from the MFI pump to the linkage. It should be 114mm center to center.


Kevin Kipta
72 911T/E

Kurt V----Could you tell me where I can get more info. on the $125. EGA. I have never heard of this unit. I have 2 MFI cars and would like to have one if they are any where near accurate. Thanks

Eurotech, you can find Gunson testers here: http://autoexpertproducts.webjump.com/
Kurt V
72 911E

Hello

The best is you get a portable 12 Volt gas tester so you can test under load.

I sugest to hang out the coldstart enrichment complete. Also very important is never toech or even carry the MFI Pump on that "yellow shining holder". This is barometer and normaly pulling on that thing will enrich fuelmixture. Those things where set very acurat, 0,01 mm is it. Maybe a slight tap back.....Those Pumps needs watch like precison.

And use a small mirror in conjunction with a strobe. Flash to FE on the crank pulley and look if your pump has the mark up too.

How is you Powerband. Do you have top end untill the neeedle hits the limiter ?

If you have Bosch Plugs replace them with NGK. Use 964 units for testing ( 3 electrodes AFIK BPR 6 ES)

And check if yo didn´t mix up the fuel hoses. Swaping intake to outlet will give many head scratches.

Grüsse

Kurt V Thanks for the link!!!!! I am going to buy one.