Question : Adjust of idle speed and mixture MFI
 

I have 1975 911 Carrera with MFI (type 911/83).
I try to adjust idle speed and mixture by the Workshop Manual on 1972.
On Fuel System pages, I found description “see page SF35”, and “shown on SF36”, “see page SF40”.
Unfortunately, I don’t have these pages.
If anyone has these pages, please let me know contents of these pages..
I study about maintenance for my car on this forum from Japan.
Thanks for kindness.

This has what you need.
Porsche 911 Bosch Mechanical Fuel Injection Overview | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article
Download CMA, check, measure, adjust.

Thanks for your advice.
I read the Bosch check measure adjust manual.
But I could not understand.
Because the Porsche Workshop Manual instructs “Check air flow of individual cylinder at 1600-200rpm synchrometer” and Bosch Manual instructs “Start engine and run at 3000rpm”.
I do not know why the idle speed is different.
I want to know the supplementary explanation of the Porsche Workshop Manual.
Regards,
AK

Hopefully one of the gurus will chime in, but here's what I'm guessing you are trying to do. You are trying to synch airflow, do you have a synch? If so check each stack with the synch while its good and warm and at idle. Then raise the rpms to 3000. You do this because you spend the most amount of time around this rpm when driving. Basically you get the stacks perfect at idle, then fine tune at 3000.

Need to match the airflow in each stack. To lower the idle, reduce the amount of air in the stacks. Either close the butterfly's by adjusting the linkage and / or fine tune the idle by using the idle adjustment screws on each of the stacks. When done, check the AFR and adjust the idle mixture if needed.

It's really not that hard if the system has all its components attached as designed by Porsche.

Chris
73 911 E

Thank you.
I'd like to order “STE SYNCHROMETER Type SK” and “Gunson Gastester G4125” for the adjustment work.
I will remove the air cleaner regulator housing from my car.
Then, can I attach the STE SYNCROMETER Type SK directly to each intake pipe?
And I will measure CO using the Gunson Gastester G4125.
If you know other good tools, please let me know.
I am a beginner.
I study car maintenance and English.
I'll be waiting for your kind response.

That device works great, but its only used to adjust the airflow at the stacks, You really don't use it to adjust the co content. Sure the co will change a bit, but its the adjustments at the mfi pump that makes the most difference. There are air bleed screws at the bottom of each stack, you use this device to adjust airflow/idle and thats pretty much all you use it for. After you have adjusted the airflow so the stacks are synched and the car idles around 900, then you can move on to adjusting co with the Gunson. You must make sure the car is in great tune before you take on adjusting the mfi pump. New plugs, cap, rotor, points if you have them, valves adjusted, etc. Make sure the mfi linkage is spot on, the rack rod to mfi pump is 114mm, stacks synched, etc.. You then adjust co last.
Post a pic of your car, engine, etc...

I appreciate your support.
I will try adjusting air flow and mixture.
It is a picture of my car.
Regards,
http://forums.pelicanparts.com/uploa...1484748472.JPG

http://forums.pelicanparts.com/uploa...1484748472.JPG

Looks good and complete. If you have to adjust any of the MFI mixture adjust screw settings. Its very important to keep track of the changes you made...the number of clicks rich or lean so you can undo what you did if need be.

You should be all right just getting the idle down with the procedure described above. The AFR meter takes any guess work out by knowing what the mixture is at the tail pipe when you are done. A little Rich is better than a little lean. Take the reading when the car is fully warmed up as the MFI will enrich itself when cold. That's what the heat tube does on the left

Chris

Great car, needs to be lowered in the front though.

Adjust valves, check dwell and timing and be sure your distributor is returning to its base setting at idle. Don't just start chasing the MFI as the only issue. Good luck and a many miles of driving.
Rusty

As Rusty says, make sure that everything else is ok before touching the MFI.
Start with a complete tuneup, valves, spark plugs, points, timing and dwell.
What doe the car idle at?

OK, it took me a bit but I found it (again.) There are a lot of MFI gurus but when I need to know anything MFI, I look for posts by Early S Man (Warren Hall), Grady Clay, Zeke and David E. Clark (and his Ultimate MFI thread). I certainly hope your idle issues will be fixed with the turn of a few screws. If you find you can't get it to where you want, consider performing "Check, Measure, Adjust" or CMA (download link from Pelican) to bring the system back into tune and, in this process, get your idle back where it should be. Grady coined the term CMA2 for a set of procedures he developed based on CMA that are more appropriate to these now 40+ year old cars with MFI. I've pasted Grady's CMA2 below and here's a link to his original post (Post #24):

CMA2
1) Research, read, ask, plan, and make your own personal notebook/workshop/parts manual. Collect tools and equipment or access to them. Know your starting point; check the oil sump & change the oil, go drive, measure the mileage, and take notes.

2) Air cleaner cartridge. Almost all is done with the air cleaner system in place as it will be used. Have an OE exhaust available. Make it easy to remove sump tank breather and fuel evaporative emissions hose.

3) Compression tests include both cranking compression and cylinder leak test.

4) Ignition: Spark plugs, spark plug connectors, wires, cap, rotor and general proper condition of the ignition system. Check electrical connections and grounds. Check distributor bearing, springs weights condition. Run distributor on tester. Dwell angle, points condition, condition of cam and lubricant. Ignition timing, proper advance curve, and vacuum operation. When complete and timing is set at 6000 RPM, note the timing at idle (with & without vacuum retard if applicable) and static timing.

5) Fuel pressure and flow, new fuel filter and clean the screen in the bottom of the fuel tank. Clean the tank if suspect.

6) Injection nozzles; inspect, test, clean, or replace.

7) Injection timing: If you need to adjust the MFI pump timing, use the opportunity to replace the Gilmer belt and both toothed pulleys. You can save the old ones as road spares. This is also an opportunity to replace the seals at the left cam and injection pump.

8) Camshaft timing and valve clearance. Use this opportunity to torque the cylinder head nuts and rocker arm shaft bolts.

9) Correlation and includes the condition of the throttle bodies. One of the important issues is that all the linkage moves off idle simultaneously. Check air flow at idle and just off idle for each cylinder.

10) Confirm the cold start solenoid doesn’t leak and turns on & off sharply.
Cold start thermo-time switch proper function.
’69-’71 cold start solenoid on MFI pump.

11) Over-run fuel shut-off checked for function. RPM transducer and microswitch.

12) The cold running thermostat must be clean, getting hot air, and functioning properly. When hot, it must be completely shut off.

13) Exhaust emission test; at part load, at idle speed.

14) Road testing, dyno testing and repeat entire sequence.


Good luck and let us know what you find!

I am grateful for your guidance.
My car’s engine stops when idle speed slow down (about 900 rpm) .
I have to use a hand throttle to keep idle high speed (about 2000 rpm) while I waiting signal.
I thought the reason is that mixture too lean.
I read Porsche Workshop Manual and Haynes Repair Manual and Pelican Parts Technical BBS thread.
Then I learned that it is important to synchronize air flow of each cylinder before adjusting mixture.
And I learned more important steps from your reply.
I would like to study more.
When I adjust mixture, which is better, gas tester or air-fuel ratio meter?
Please tell me the item you recommend.
Excuse me, I'm not good at English. I need a lot of time to read your reply.
I apologize for my mistake English.
I will greatly appreciate your further guidance.
This is Japanese thank you.

http://forums.pelicanparts.com/uploa...1484812188.gif

For idle, both will work. What do the plugs look like? I'm guessing its "tuned" up, so if that is the case and assuming everything else mentioned in this thread is kosher, then its time to fiddle with the pump. Do you have the long screw driver and Allen wrench that is used to adjust the MFI pump? If so go two clicks to the left and drive it. Remember to write down how many clicks you went because too much fuel can cause the car to bog and die, to little as well. If you can tell its getting better keep going until it idles, if it gets worse, back off and go the other way. You do not need an afr meter to do this, get it to idle right, then you can buy one if need be.

Thank you.
I have this tool purchased from Pelican parts.

http://forums.pelicanparts.com/uploa...1484835470.jpg

I do not feel the idle adjusting screw clicks.
Is there a good way to feel the click of the screw?
I read “Do not adjust by more than 1 notch at a time” in Porsche Workshop Manual.
I do not know the meaning of one notch.
Is 1 notch of the screw the same as 1 turn?
Regards,
AK

You really need to pull your injectors and check their flow. I spent 2 years chasing similar issues and just last month bought 6 new injectors. My idle would die out as you mention.

New injectors restored the performance to like new. I had previously bought an injector tester and cleaned in ultrasonic cleaner several times but it did not last for a week or two. The problem was poor spray pattern, well it was actually more like a stream. If you don't know the quality of your injectors you need to figure it out before proceeding.

http://forums.pelicanparts.com/uploa...1484838869.jpg

950-1050 should be idle setting. Since it is stalling there, have you checked the microswitch setting or if it is functioning properly?
Until you really understand what you are doing, and that everything else is functioning properly, you should not be moving pump adjustments.
Without following the CMA EXACTLY, step by step, you are going to get yourself in a mess.

For the idle adjust, you need to press lightly on the spring loaded adjuster and turn until you feel it engage, then you can feel each click as you turn it each way.

Thank you for giving me good advice.
I thought that I feel a click every time I turn the adjustment screw once.
Please tell me in a little bit more detail.
At first, do I need to turn the adjustment screw several times until I feel a click?
Does 1 notch in the Porsche Workshop Manual 1972-1983 (Adjustment Instruction) have the same meaning as 1 click?
I have read this thread. But I could not get a feel for click.
Regards,

Its known that the idle adjustment screw doesn't do diddly squat if the main adjustment isn't right. Leave idle adjustment alone, fine tune with that later. Adjust the main rack first, that controls the most amount of fuel. This is the one behind the Allen screw. When you insert screwdriver turn and push very lightly until you feel it insert into the notch, then turn it left. You will feel when it grabs, that's one click, so on and so forth.
RStarga mentioned the Microswitch and is spot on, if it is broken it can cause fuel to shut off when you are coming to a stop sign and not turn it back on at the specific RPM. This happened to my car last summer, disconnect it, then drive it before you go any further.

If you haven't been following this thread, its worth a look.

http://forums.pelicanparts.com/porsche-911-technical-forum/930796-mfi-lean-coming-off-idle-then-rich-again.html

Press on the idle adjust and turn up to 180 degrees in either direction and you will feel it engage. Keeping it pressed and turning you will feel it click, there are about 12 clicks per 360 degrees. The idle is the last final adjustment to do after the main adjust under the hex screw. Make sure you keep a note of any changes made so you can return to the original settings.

Thank you so much for your kind advices.
Your advices are very helpful.
I am starting to fix the trouble of my car following the Bosh CMA manual step by step and your suggestions.
To fix condition for my car by myself, I’ll love my car more.
Regards,