Ultimate MFI resources thread

[David E. Clark]

Fuel Injection Troubleshooting Chart (From # 1 in the list above). Posted here for educational purposes.

Page SF28:



Page SF29:



Page SF30:

© Dr. Ing. h.c. F. Porsche A.G.

[Don Z.]

OK, so here's my silly question. Supposing one had a '74 Carrera. And suppose that Carrera SHOULD have had an MFI system, but because it was sent to the US, it has a CIS system. And suppose that engine was needing to be rebuilt soon...

Where would I go to find all the parts I'd need to convert it to MFI? I figure if I start collecting now, when I get to the rebuild, I'll have what I need...

It would be nice to have a checklist...

[Grady Clay]

DonZ,

I’m working on that.

Best,
Grady

[David E. Clark]

John Cramer's MFI/CMA mnemonic aid:

Any
Competent
Porsche
Driver
Tracks
Faster
If
Brakes
Come
Smoothly

Translates to:

Air Filter
Compression
Plugs
Dwell
Timing
Fuel pressure
Injectors
Belt (MFI pump timing)
Correlation
Smog


__________________
John Cramer

Gotta Love it!

Don Z

PM sent ...

[David E. Clark]

Exploding Diagrams for 1972-1973 MFI system. (From # 10 in the list above). Posted here for educational purposes.

Porsche Spare Parts Catalogue, page GR 1-7, 2/5:


Porsche Spare Parts Catalogue, page GR 1-7, 2/5.1:

© Dr. Ing. h.c. F. Porsche A.G.

[David E. Clark]

This essay was stolen from the middle of this thread:

MFI, 1972 warm-up issues (combined).

It was written by Grady Clay and deserves repeating here as a wonderful foundation for new MFI owners and as a reminder for those more experienced with MFI.


So long as you are patient and don't have 10 thumbs. you can do this. Slow is good. No one will do it as patently as you. Most don't want to pay $100/hr for an expert to go slowly. If nothing else, you gain the knowledge and experience to properly communicate with the pros (if you can find one).

...

The slippery slope you could go down is as follows: You clean the grime out of the thermostat (the device that Milt is talking about) and get it working properly. Now the engine hardly runs at all. You then think the plugs were fowled from the dirty thermostat and do a tune-up on the ignition system uncovering some "while you are there" issue. And so on with the engine not running well. All the time it turns out that the PO had adjusted the main mixture to compensate for the dirty thermostat. There are many possible scenarios but they lead to the same result -- you get lost in the system. Many professional mechanics have been bit by this also.

What to do?

Porsche developed a system for addressing MFI; it is called Check, Measure, Adjust (CMA). The emphasis is on Check and Measure before you Adjust.

The original CMA covers this sequence:
Porsche lists the Check Sequence as:
1) Air cleaner cartridge
2) Compression loss
3) Spark plugs (spark plug connectors)
4) Dwell angle
5) Ignition timing
6) Fuel pressure and flow
7) Injection nozzles
8) Injection timing
9) Correlation
10) Exhaust emission test
a) at part load
b) at idle speed

You should study the CMA document and ask questions. It is designed for the professional mechanic who is already familiar with the system. CMA was written in about '68 and assumes all the parts are new. While we have the benefit of 20-20 almost 40-year hindsight; none of the parts are new any longer. You are about to practice geriatric mechanic.

While CMA gives you most of the steps, it doesn�t tell you exactly how to do them. These few cryptic words are chapters in a 300 page book.

In fact it is so much more I call it CMA2. Following is an outline; 1 to 14. I'm going to address each one separately as an individual project. In practice there is considerable overlap. In chasing an elusive problem, you may go through the complete sequence many times.

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.


I'll go through the sequence one step at a time and everyone can chime in and keep it on the straight and narrow.

For now, your mission is to gather information, change oil and go drive.
Pelican and some others are full of good archival material. Do some searching and download the relevant stuff. Start yourself a "Personal Car Specific Manual"
notebook.
Your first oil change on a dry sump 911 will be an enlightening experience -- read up.
Aside from the fun, this driving has an actual purpose. You want to get everything "settled in" with highway and spirited driving. This is the only way to get good accurate compression and cylinder leak tests. You also want to carefully measure your fuel and oil consumption under controlled circumstances. Note the color inside the exhaust tip.


Don't let this seem like it can overwhelm you. Mere mortals can do this.

Automotives 101:
An engine has three basic systems; air/fuel, electrical, and mechanical. For our purposes the air/fuel system can be divided as fuel supply, high pressure mechanical fuel injection, cold start/run enrichment, and air metering. The electrical can be divided as 12VDC supply, high voltage ignition, and low voltage control circuits. The mechanical system has three basic functions; power generation, power transmission and the necessaries. Power generation has to do with the sealing of the combustion process, getting the air/fuel into the combustion chamber, and getting the combustion products out. Power transmission gets the power to where you can use it and includes the piston, rod, bearings, crankshaft, etc. The necessaries let everything happen and include valve actuation, oil system, engine cooling, etc.

The bell rang -- end of class.

Best,
Grady

[David E. Clark]

This came up in another thread so I thought I'd post it here:

(From # 2 in the list above). Posted here for educational purposes.

Factory recommended MFI part load co2 settings:

Note: most people find that their cars run better with 6-8%. I'm not recommending this amount, just passing on what I have read and noting my personal experience.



Copyright Dr. Ing. h.c. F. Porsche A.G.

Here's the page out of the factory manual supplement -- says the same thing. Posted here for educational purposes.

Copyright Dr. Ing. h.c. F. Porsche A.G.

[David E. Clark]

Tyson Schmidt posted this explanation of why MFI cars run rich at idle but get leaner when they are driven hard in this thread. I thought it concisely explained a question that many of us have about our MFI cars.

Originally posted by Tyson Schmidt
MFI actually gets leaner under load, since it really has no way of measuring load other than by throttle position and rpm. That's why they run so well under acceleration when set very rich.

You have to set them rich while free-revving so that they are not too lean under load. So if they are set to be a little rich under load, they are really rich under all other conditions, especially during warm-up.

MFI engines will run very well with overly rich mixtures compared to carbs or EFI, since the injection pressure is around 250psi, resulting in excellent fuel atomization. And I suspect that they likely clean the plugs off more efficently under acceleration due to the leaning out effect I mentioned earlier, so they keep running relatively well with too rich a mixture that carbs just wouldn't tolerate.

Then if you delete the fuel shut-off during over-run feature, you are dumping a lot of fuel during over-run. This is actually fine, so long as you don't do a lot of deceleration with your foot off the gas, such as compression braking in every gear, or down long steep grades.

If you delete the fuel shut-off, then you need to change your driving habits to using the brakes, not the engine to slow the car down.

[David E. Clark]

I just found this Service Circular listing the "final CO-specifications" for the 1972 911 models. Nothing new, but in the interest of getting all the information in one place ...

(From # 2 in the list above). Posted here for educational purposes.

Copyright Dr. Ing. h.c. F. Porsche A.G.

[David E. Clark]

(Porsche Product Information Circular P250, from # 4 in the list above). Posted here for educational purposes.


Copyright Dr. Ing. h.c. F. Porsche A.G.

[louielargo]

...

[MJHanna]

OK, I stumbled on to this tread thanks to Dave’s signature link. I’ve been reading and have the tools on order but an lost on the “protractor” Pelican does not list it, is it really necessary ? Or what are we using instead of it?

Thanks for creating this tread.

Mark
Who knows he is going to have to work on his 69S MFI at some point.

[David E. Clark]

The protractors are now almost impossible to find and, if you somehow manage to find all three, the directions for their use are - I'll be kind - not easy to follow unless you were trained by the factory in the late 60's. This is why Porsche came out with the 28 April 1972 Product Information Circular "P250" (two posts above) which simplifies the correlation procedures. There are a few guys that still know the old ways, Grady Clay and John Cramer for example, but from my experience if you follow CMA and P250 to the letter you'll be fine.

[David E. Clark]

Here is some fairly technical, but nevertheless valuable, stuff. These pages give some additional insight about adjusting the internal partial load adjusting screws (especially the first two pages). Note the statement "no adjustment is generally provided in the field for this operating mode on Porsche systems" on page 15. It appears that Porsche thought that these adjustments were beyond the capability of most repair shops (and certainly a backyard mechanic) so they never included this information in the Factory Service Manual or CMA. Apparently, Bosch has discussed these adjustments in their technical manuals, especially MFI Pump Test Instructions VDT-WPP 711/1B (ref Section 3.0 Inspection & Repair), but this instruction is next to impossible to find! If you have access to this document, please share!!!





© Harold T. Glenn, Glen's Diesel and Gasoline Fuel-Injection Manual, pages 15-18 (1973). Posted here for educational purposes only.

For more information about these adjustments and other internal mysteries of the MFI pump, follow this thread.

[jcge]

Link to a post with MFI nomenclature, exploded drawings & service parts lists


Some interesting MFI documents

[Flieger]

How to repair and tune RPM transducers for the engine braking fuel shutoff circuit:
For MFI Gurus. . .and friends of Warren . . .

[Robert Karow]

Hi Everyone,
I have been battling with a cold start problem on my 1972 911 T. I am sure the answer is somewhere in all of this literature but I am having trouble finding it. The problem is that when I get in the car cold and start cranking the engine it takes probably 5 to 10 seconds before anything happens, and then it starts to sputter, pop and fizzle and shuts off a few times before it's good to go. I have sent my injectors off to supertec to have them cleaned "again" and the only other thing that I can point to is the cold start valve. Everything that I have read says that the cold start doesn't do anything until its a very low temperature though and I am in Florida. Any ideas?

Robert Karow

[David E. Clark]

I've decided to try to update and make the MFI Message Board Index easier to use until the Pelican wiki is functioning. The separate posts are so that I have room to add additional links later.

The link is here.

What do you think?

[Rusty 356]

I recently delivered a very nice runnng E with an S engine to a very nice guy in Alabama. Today he called me and is having a problem. To much power at foot off the throttle. The coil sping that returns the fuel system to idle broke. The sping goes on the cross throttle shaft and one end hooks into the stack and the other around the throttle arm. Where can one find these springs? Also for all you guys with MFI, it only has to fail once and you are into the wall, full throttle with no retrun. Change that damn little spring. I noticed also that my 72 S motor has the same small hole in both stacks so would recommend the coil spring on both ends of the cross shaft. Part number and source appreciated.

[313green]

For your listening pleasure, here is a funny sound from my '72 911T 2.4. It is coming from the air intake. Listen carefully to the end of the video. Some of the friendly pelican forum people think it's MFI related....

YouTube - 911t motor sound