Porsche developed a mechanical fuel injection system, used versions of it on numerous race cars, and also used it
on several production models in the early 1970s, most famously the early 911, including the iconic 1973 Carrera RS
The big advantage of the MFI system over the other fuels systems of the time was it's instantaneous throttle response,
and it is still favoured today for classic 911 racing.
With todays technology, it is possible to use modern Electronic Fuel Injection systems (EFI), but still it is argued that nothing beats the MFI, both for simplicity, and performance.
The drawback with MFI is finding a good mechanic who can work with this system, and get it tweaked/adjusted to its optimum performance.
In July 2005, after many months/years of searching and researching, I finally took the plunge and bought a 1975 911 Coupe. I was not knowledgable enought at the time to realise what I had just bought! The original 2.7 engine from 1975 would have had the CIS fuel system. However, this car had undergone a detailed restoration around 1995. During that restoration, I was told it had undergone lots of changes.
So, I drove it for a while, figured it was running a bit rich (black smoke, and rough idle) and decided I would read up on the MFI system and find out how to adjust it. Little did I know what lay ahead !
I found lots of useful information about MFI on the Pelican Parts forums, and I needed some special tools to adjust the MFI pump, so I bought those from Pelican Parts in the USA.
I tweaked the idle mixture setting a bit, without much success.
I drove it for another bit, just every now and again, and although it was a fantastic drive, and performing really well, I knew it just wasn't right. It was a bit embarassing sitting in traffic with black smoke bellowing out the exhaust.
I read through the famous Porsche document Check, Measure, Adjust known as the CMA a few times, and decided I'd better get an expert to sort it out for me. Trouble was, I was in the Northwest corner of Ireland, and the closest "god MFI guy" was in the UK. I though about it for a while, and put it on the back burner.
Since I was in motor-mechanic mode, I decided it was time to sort out the 911.
I posted a thread on the Pelican parts forums, about what I intended to do, asking for advice, and got some very good feedback, encouraging me that I actually could tackle it myself, together with suggestions on what I should do, and what I shoudl measure, etc, etc.
I started work. I discovered the MFI pump was the correct pump for the 2.7 engine, so that was a good start
I was also advised to remove the intake stacks and throttle bodies to measure them also. This would mean new gaskets for refitting, so I ordered them, again from pelican.
I removed the throttle bodies, and found they were very dirty. The butterflies and the inner bores were covered/caked with carbon deposits.
After a lot of scrubbing, and a few cans of brake cleaner, I got them cleaned up, and measured as the correct throttle bodies for an S engine, and went through an advised adjustment procedure, using a vacuum cleaner and a synchrometer, to get equal aiflow through all the butterflies, setting the stop positions as required.
I had bought a leakdown tester, so I measured the cylinder leakage across all 6 cylinders. All but one were very good. Jury still out on the reason for that one. Could be carbon build-up preventing the exhaust valve from seating properly.
I got delivery of the dial gauge, so I remove the inlet (top) cam cover, adjusted the valve clearance, and set about measuring the valve lift.
Then I realised my gauge only read to 10.7mm maximum, so it was possible the valve lift was more than that. I was annoyed that pelican would sell a dial gauge which was too small for the task.
After a bit more reading up, I found that I should have been measuring the valve lift at TDC overlap - This is 1 turn after TDC compression, where the exhaust valve is closing, and the inlet valve is opening in preparation for the intake stroke. Specified at 5.0mm to 5.4mm
I found the specs for valve lift for an S cam, and decided I may as well measure total valve lift, as well as the TDC overlap measurement, so I searched and found a Draper 25mm dial gauge on ebay.
While waiting for this gauge to be delivered, I went ahead and refitted the throttle bodies, and stacks.
While under the car to adjust valve clearances & measure the exhaust valve lift, I noticed I had SSI's and I had a 7R case.
Measured valve lift at TDC overlap - Perfect for an early 911 S cam.
Measured total valve lift - close to early 911S cam - still trying to verify this.
So far so good.
Fitted new rev-limiting rotor arm, distributor cap, and new magnecor kv-85 plug leads.
Long time since an update here, so this is from memory.....
I finished the wiring to points, coil & cd box, fitted the hot air supply to the mfi stat, did a quick double check I hadn't forgotten anything
and turned the key.
Next, I adjusted the timing to TDC @ 900rpm.
I contacted a company called Koller & Schwemmer in Germany, who tested them & found they were all opening at too low a pressure
I spent half an hour adjusting the dwell, Something I had never done before on any car !
So, dwell & timing set.
I got the LM-1 hooked up to make sure it was working & got and AFR around 12.8 at idle.
Must say it was much harder to start now without the cold-start hooked up !
I do have two oil leaks from the lower cam covers, dripping down onto the ssi's so I guess I'd better cure those
before I smoke myself out of the garage !
I had an aborted attempt today at adjusting part-load mixture.
So, I hooked up the LM1 with the exhaust clamp & went off for a drive.
Well, I had a good poke around this evening in search of my oil leak(s).
Right, I got under this evening and had a good look at the oil return tubes, and everything else under there. Both return tubes, on both sides had a good coating of fresh oil on them. The #2 and #5 cylinders seem to have a lot of burned oil on the fins - quite black & sticky. I cleaned them a bit, and cleaned the oil return tubes, and also cleaned as much of the heat exchangers as I could get to. I did notice the access holes (for the studs) through the exchangers were very oily, and the bottom surface of the exchangers had a fresh oil coating spreading outwards from these holes. Guess I need new oil return tubes. It does have the collapsable tubes, so I thought mabye just replace the seals, but I don't think I'd be able to get a circlip pliers onto the clips to remove the tubes intact, or is that possible ? I can see the clips & reach them with my fingers. The nuts on the exhaust studs looked quite rusty, so I hope I can install new return tubes without having to remove them. I also have a drip from a couple of the lower cam cover nuts. It seems to be leaking out the stud, but I can't be sure. The studs did have some sort of sealant on them which I noticed when removing the covers.
got some great advice about my oil leak possibilities from the Pelican Parts forum: You can easily fix everything that might be leaking oil onto the heat exchangers with the motor in the car. The first thing to do is to get those heat exchangers out of your way. Drop the whole exhaust system; it will make some of the oil leak fixes easier. Hit all of the nuts with PB Blaster or something for a few days before you try to loosen them.
You should be able to spin the return tubes so that you gain access to the circlips. Use a well padded pair of channel locks or vise grips if you have to. Just put new o-rings in the ones you have and reuse them; they should remain sealed for a good long time. Use some high temp silicone grease on all of the o-rings.
While the return tubes are out, go ahead and reseal the crossover oil return line where it goes into the forward left case. This thing is darn near impossible to work on with the return tube in the way, so take advantage of the fact it isn't. Take the compression fitting apart, then take the fitting out of the case and put some plumber's teflon tape and RTV sealer on the threads and screw it back into the case. The compression fitting doesn't use any sealer, but rather some anti-seize so you can get it apart later if you ever have to.
On the right side, remove the long piece of tin, the forward piece of tin (next to the bell housing) and the shroud screws that go into the oil cooler. Take the "J" pipe off that goes to the tank, and remove the oil cooler. Replace the seals inside of there and remount it. The seals like to fall off when they are horizontal in the car, so "glue" them in with some of that sticky silicone grease you used on the return tube o-rings.
If you have not replaced the thermostat o-ring, do that too. And the breather cover gasket right next to it. Take the oil temp and pressure senders out and put some plumber's tape on their threads, being careful not to cover the openings in the ends. The pressure line to the MFI pump under the temperature sender likes to leak, too, so put a couple of new compression washers on it.
When your valve covers are off, you have an opportunity to seal up the rocker shafts. If they don't already have them, putting in some RSR seals would be a good idea. With any given cylinder at TDC as if you are setting its valves, you can loosen the rocker shafts on it and slide them out into the "dry" areas of the cam towers and put those seals into the grooves. Remember to turn the nut only, not the screw, when loosening or tightening those rocker shafts.
When putting the valve covers back on, don't over tighten the nuts. They have a very low torque value (I think something like 8 ft lbs?). That's why they have the nylock nuts - so they don't rattle loose from that low value.
Make sure the MFI pump is not leaking as well. The baseplates sometimes leak. The oil supply and return lines sometimes leak. If the baseplate is leaking, you have to remove the pump to fix it. I'm not sure that base gaskets are even available; maybe Pacific Fuel Injection or Henry Schmidt has them. I just reuse mine with a healthy coating of silicone RTV.
The pump drive on the forward end of the left cam can leak as well. Yes, it can be replaced with the motor in the car; I've done mine and several buddies'. Take the left rear wheel off. Remove the drive pulley and belt, marking the pulley's orientation (after lining up the "FE" mark on the crank pulley). Remove the forward piece of tin (you have to take the throttle rod off first; it passes through a slot in the tin). From there it is a "simple matter" of prying out the old seal and pressing the new one in. I use a bunch of hooked dental picks to pry the old one out. It doesn't have to be pretty... The new one just presses in with finger pressure. Just make sure it is straight and flush all around. Make sure you line the pulley up the same way it came off; it only uses two of the four holes, and they are not 90 degrees to one another. They are clocked half a tooth off, to allow for that fine of an alignment with the timing marks.
Anyway, that should take care of most, if not all, of your leaks. At least the ones dripping on the heat exchangers. Once you are done with all of that, your tuning efforts will be much more pleasant. So, I ordered a load of O-rings & gaskets.
Today was a good day.
I've been dreading taking off the SSI's, after reading about the possible/probable problems with the studs. I have no heat source, so though I'd stick with the spray-spray-spray method & see.
I've been spraying the nuts with Plusgas for the past week or so. I ran out of plusgas last night so used WD40 instead.
Today I went and sprayed them all again, and thought, I'd try one nut to see if there was any chance the PO had used anti-seize when fitting them.
Sure enough, absolutley no problem. One barrell nut was a bit stiff, but forward & back about 10 times freed it up & off it came.
I stood the ssi up on its end, and about a quarter cup of oil came out
I got brave and decided I may as well take both off. The 4-5-6 side was a bit more awkward. I managed to bend a ring spanner using my bfh, to get at the nuts on #4 and #5. Had awful trouble with teh #6 barrell nut. Not that it was seized, just could not get the hex tool seated properly no matter what way I moved the ssi itself (all other nuts removed at this stage).
I ended up using a different hex bit, with a 1/4 drive small socket that fitted up the access hole in the ssi, a long extension and a ratchet.
From looking up at the engine, without the SSI's in the way, I'm pretty sure the oil must have come from teh time I drove it without plugging the breather pipes. There was a lot fo oil on top of the engine at that time, and a lot dripped onto the floor, so I'm sure it made a mess.
I now have all the various o-rings & gaskets, so I may as well replace them while I have access.
I'm delighted those ssi's came off so easily. I was very apprehensive about getting them off.
Today I got the collapsable oil return tubes out, and got the tinware removed to get at the oil cooler to do those seals.
The more I see the more I am convinced I don't really have an oil leak, apart from the cam covers. It does really look like the oil that got dumped on top of the engine has found its way down by various routes.
I intend to replace the seals & gaskets anyway, for peace of mind.
When I dropped the oil, I was amazed at the strong petrol smell. I've hardly done 10 miles in it, but a lot of idling, while setting dwell , timing, etc.
I put on the exhaust/silencer & fired up last night
I thought I might have to bleed the fuel lines to the injectors, but it sorted itself out after a bit of cranking.
I have a small oil leak at the breather cover. I did renew the gasket but maybe I didnt clean the mating surfaces properly before refitting
No sign of any leaks from the return tubes or cam covers
December 2008 ok, finally all the oil leaks are sorted.
Now, I'm intent on getting the afr sorted at part load. I'm determined to get there before 12 months have passed !!
After a LONG delay, I finally got back to this.
I measured a fuel flow rate from the filter to the MFI pump at 1150ml/30 seconds. Thats fine. Fuel pressure, measured at return from MFI pump to fuel filter housing, measured 0.8bar. Spec is 11.8psi +/- 3 psi
Converting 1 bar = 14.5 psi, thats perfect.
Checked it again a day later, as the gauge was still plumbed in place and am getting closer to 0.65bar.
Still in spec, as 0.65 * 14.5 = 9.43 psi. Spec is from 8.8psi to 14.8psi.
Wonder why there is a difference ?
Next step is to start the engine & see what the pressure is like. Maybe there is a problem there. Hope not.
To Be Continued.....