MFI main rack adjustment cannot engage

I asked my mechanic to lean the mixture a little since it has been running rich. The mechanic told me that he could not adjust my main rack because he could not get his screwdriver blade to engage the adjustment screw.

Although I have never done it, I wanted to try it myself. I followed Leslie F. Rice's article on Pelican website and made a small screwdriver out of a 1/8" steel rod about 22" long. After removing the 5 mm Allen screw, I tried to engage my homemade tool. I could insert my homemade tool about 1.5" into the hole but cannot feel it engaging the adjustment screw. With very little force, I could push the tool further into the hole; it felt like I was push something that was spring loaded, but no engagement and no click when turn.

Any advises from the board are greatly appreciated.

do yourself a favour and send it away for complete rebuild incl. the throttle bodies and check/replace the injectors if you do this you will not regret it.

it ain't that expensive and certainly cheaper in long run.
imo


-------------------------
peter kaufmann
'73 911E fully rebuilt to 2.7RS carrera spec.

maybe the adjustment screw has simply been wound too far out and has disengaged from the rack?

It is a little tricky to get the screwdriver to engage the slot. I have the correct tools to adjust the injection, and I have adjusted the main rack quite often, and I still have to "feel around" with the screw driver each time I try. The approach angle and insertion depth are important. The screwdriver can be pushed in too far and seem to bind against something, and even with the correct screwdriver, correct angle, and correct depth I still end up having to slowly rotate the blade back and forth until I engage the slot. If you are using a homemade screwdriver, be certain its dimensions are correct. It is definitely a "feel" thing. Once you have done it once, you'll understand the variables. Take a deep breath, and be patient.

I agree with both above.

It is possible that the screw is now in the bottom of the pump. It is equally possible that your screwdriver blade is too thick.

Try grinding the blade close to knife edge and feel around.

If you are convinced the screw is not there, it is possible to remove the governor cover (the “front” of the pump) without disturbing anything other than the rubber gasket. You don’t need to remove the thermostat or solenoid(s). Be prepared to spill about a quart of oil and possibly your hardware with it. If the screw is out, there is a spring and detent piece that are also errant.

BTW, the P/N for the rubber seal is Bosch # 1 420 206 007.

It is possible that the parts are in the regulator housing (I don’t think they can find their way into the pump housing) and you will need a small magnet to retrieve them. You can’t remove the regulator housing without upsetting the governor settings.

I have reinstalled adjusting screws and gotten the pump back into adjustment. No great mystery.

Best,
Grady

Thanks for the advise. My pump & throttle bodies only have about 40K mi since overhaul, & I don't think they are due for an other overhaul again.

Some follow up questions, if you don't mind:

1. The fact that I can felt the spring, does that mean the screw is no longer there?

2. Grady, when removing governor cover without removing thermostat or solenoid(s), does that mean the thermostat and solenoids stay on the governor cover as the governor cover is removed?

3. Since I have never opened a MFI pump, should I have a mechanic with MFI experience to do it?

4. If yes on #3, do you know one in Los Angeles area (as close to Pasadena the better)?

Many thanks.

robinfly,

Please post some more diagnostic of the current running and what has been recently done as far as diagnosis, maintenance and adjustment. I wouldn’t go much farther without a through CMA and some highway miles.


“The fact that I can felt the spring, does that mean the screw is no longer there?”

If you can feel the spring, probably the screw is still there.
I would try the finer screwdriver blade before you attempt to remove the cover. It is worthwhile to stop by a MFI experienced shop and have them feel around with their tool. I suspect you just haven’t found the slot or the blade is too thick. Search Pelican, this subject has come up before.

Here is an exploded view:
http://www.pelicanparts.com/techarti..._REGULATOR.htm


“2. Grady, when removing governor cover without removing thermostat or solenoid(s), does that mean the thermostat and solenoids stay on the governor cover as the governor cover is removed?”

Yes. Come to think about it, removing the thermostat and solenoid lets the cover clear the cross shaft. Be sure to preserve the gaskets between the cover and the thermostat & solenoid. They determine the adjustment of those devices.


”3. Since I have never opened a MFI pump, should I have a mechanic with MFI experience to do it?”

This is a DIY job unless you can’t turn a screwdriver. Your challenge will be the lower screws on the cover, particularly reinstalling. I have done this on the engine dyno, my mechanics in the car. It may be easier if the pump is loose from the mount.

”4. If yes on #3, do you know one in Los Angeles area (as close to Pasadena the better)?”

There should be lots of choices. Dave at TRE (11046 Chandler Blvd. N. Hollywood, CA 91601, 818-509-2638) in N. Hollywood, John at Otto’s in Venice (707 Hampton Dr, Venice, CA 90291, 310-399-3221), and many more. There are Pelicans in Pasadena who can offer more advice. Try an additional thread on Pelican 911 Technical Forum.

Best,
Grady

You need someone with a working KNOWLEDGE of the pump and show you how to put the correct tool in place, find the slot and what it feels like to engage.

My car runs good for in-town driving at less than 4000 rpm. Acceleration is good till 4500 then the punch went flat. It smokes a lot with wide-open throttle, and smokes even more when starting the engine. Around town I get less than 10 mpg, and highway-local-combine is about 12-14 mpg. It used to average about 12 mpg in-town & 16 mpg highway-local combine. During the last minor service about 200 mi ago (45 days ago), the mechanic hooked it up to a CO tester and said it is running very rich.

I guess the last time MFI pump was touched was about 7,700 mi ago during major service (around 18 to 24 mo ago), but I am not sure. MFI pump & throttle bodies were overhauled during the last engine overhaul about 40k mi ago (might have been 13 or 14 years ago). Pump by Pacific Fuel Injection, and throttle bodies by a place in or near Costa Mesa, CA (can't remember the name).

I drive my car fairly regularly. It rarely sits more than a month without running. I knew the mixture could be adjusted after the overhaul because it still needed smog test back then, and the mechanic would lean it out a lot to pass, then he would set it more rich so it would run good.

I don't race and don't really use its top end performance very much. But I guess I just want it to be all it can be. And better mpg is always good.

Again, thanks for all your help and advise.

If the pump was recently rebuilt, I would assume the rack adjustment to be o.k., or at least close. They don't re-adjust themselves, so unless some one got in there and fooled around with it, I would look elsewhere.

Your poor mileage, lots of smoke, won't run well at higher rpm situation sounds like symptoms of the classic warm-up thermostat problems. Check the paper hose to the thremostat for holes first. If it looks good, and blows plenty of hot air, check the thermostat itself. You can take it off when it's cold, and heat it up to check its operation. The rod should extend further and further out as it warms up. If the rod does not move as it warms up, the internal discs are probably dirty and binding. Pull the whole rod out (being careful of the spring under its cover) with the discs still on it and clean the discs.

If, and only if, none of this is to any avail would I start messing with the mixture screw in the pump.