Finally getting around to CMA on my MFI

[declang]

Hi folks,
After a long time thinking about it, having a few half-hearted attempts, deciding I'd get someone else to do it, deciding no, I'd rather do it myself, etc etc , I'm finally getting around to sorting out (or trying to sort out) my MFI all by myself, so I'll be asking some daft questions on here over the next while.
My intention is to get it as good as I can, then get an expert to tweak it the last little bit, so it will be as good as possible.

I have a '75 2.7 on MFI. (Yes, MFI)
It was converted from CIS to MFI by the PO during a rebuild. I have a big stack of parts receipts, but other than that have no detailed info on what was actually done during the rebuild.

My reason for tackling the CMA is very rich idling.

Lots of black smoke on idle, very rough & slow idling.
Seems to run a bit rough under 3500rpm until it gets warmed up.
Once its warm, its goes well, but still doesnt like pulling in low revs, say from 1500 to 2000 rpm, its like a flat spot - If I keep revs above 2k its very good.
I've also noticed on a longish drive, fully warmed up, after sitting in slowish moving traffic, say 45/50mph, when you accelerate again there is a good bit of dark black smoke from the exhaust for a few hundred metres/yards, but then it stops again with no noticable smoke until the next slowish traffic, then same thing again under acceleration.

So far, all I've checked is the thermostat and airflow at each stack. After reading the thermostat thread on here, I took it all out & cleaned it, put it back together but no noticable difference. I do have warm airflow from heat exchanger to the stat, verified after a drive.
I haven't removed the panel from the pump to check if its fully operated when hot.
I did use a synchrometer to equalize the airflow across the individual stacks, but in my haste I just reved the engine by ear, I didn't do it at 3k rpm.

I also dived in & tried adjusting the idle mixture on the pump (without doing all the necessary CMA steps ). I thought it had a little effect but its still very rich. I *think* I remembered the number of clicks and put it back to where it was, but no guarantee I got it right !

Another thing I do have to sort out is the throttle linkage. There is a bit of stiffness in going back to rest position. PO seems to have added a long coilspring stretching towards front of car, secured near the mfi pump, to pull the linkage (crossbar) back into the off position at no throttle, but it still seems a bit stiff. (any pointers on removing & cleaning this bar ?)

I've been reading and reading the various MFI threads on here and got some great info.
So, I need to start at the beginning.

I've invested in a leakdown tester, so once I figure out how to use that I'll check the cylinder leakdown figures.
I have new plugs and new Magnecor kv85 leads.

To check & set my ignition timing, should I simply get it warmed up and adjust the throttle to keep 900rpm while I adjust the timing, adjusting throttle to keep 900rpm ?

(As an aside, my hand throttle works but does not stay in position - I have to hold it or it will fall back down again - I assume it should stay where I put it, and this is simply adjustment of the lever itself ?)

When I get to the stage of checking CO at part load, I'm a bit lost. Do I need to secure my gastester somehow and drive it to get it under load, as per the CMA, or is there a different way to do that ?

From what I've read I need to get the part load correct before going near the idle mixture, as part load has such a big influence over it.


All pointers, suggestions and advice on things to look out for are most welcome.

Thanks,
Declan

[911st]

Wow, it has been a long time lets see if I can remember something about this and get you into more trouble.

The mfi system can not think or sense air flow like cis, efi and even carb's. Thus, everything has to be in its designed position to work.

Thus, if you exaust has been changed, air filter dirty, timming off, not getting heat to the thermostat. It will be off so fix all this stuff first.

If this thing has been sitting for some time they can gum up and have some issues. I took the covers off mine and used carb leaner in it. There is a lot of oil in there and it should be primmid with oil befor a restart.

If it is not indesed correctly when installed or the drive it installed, it will still run but may have a stumble someware in the rpm range and other problems. I had mine 180 deg off. it had a stumble around 4000rpm.

Next you need to get the linkages right.

As to ballancing the throtle bodys, the main goal is to make sure they are ballanced at idle and off idle when the slack is taken out ot the system when they come off the stops. Thus, you can ballance them at idle, then just advance the idle a bit and use the linkages to ballance it. Go back and make sure it is stil ok at idle.

You do not have to go all the way to 3000rpms for balance.

Next check the linkage to the mfi pump. You want the pump to be all the way closed or just off the stop at idle. Some times you can play with this linkage to add more fuel. If it is not clear where the pump is fully closed, snap off the linkage and check it's range of motion.

Next, the thermostate can be a problem. If you took it apart and put it togeather wrong you are in trouble. You can test it to see if it operarates by heating it in watter or carfully with a torch or heat gun.

On my car I went to headers and took this off, made a plate with an adjusting screew and used this for an easy external adjustment. Not recomended.

If all this did not work, you can now start adjusting the pump.

It is best to test this under load in some manner. If you can add a wide band o2 sensor to your system you can use this. Drive the car on the freeway, get to cruse speed and get your reading. Then adjust the pump untill it is right.

There is an adjustment allen screew on the front of the pump. Turn off the car, remove the screew (watch for oil to come out) there is a screw in there that curns with clicks. This thing should be very sensitive to adjustment.

As to the black smoke, it should be from running to rich. There is also a lot of oil in the mfi pump. If worn, it migh be possable for oil to pass through to the fuel.

The best thing to do is send the pump to Guss at Pacific Furl injection to have it serviced and bench calabrated. There are springs on a cintrifical device that works to determing the position of the space cam (fuel map). If they loose there tension, the pump will advance to fast and make it to rich to soon as the rpms increase.

Please check this against other advice, it has been a while and I made up this approach after taking eveything apart and seeing how it works.

Good luck.

[72911]

Was the complete system installed by the PO? If it was there is an enrichment solenoid and it acts directly on the control punger rack. The energizing circuit for the enrich solenoid is controlled by a thermo-time switch in the breather cover.The enrich solenoid moves the control rack BEYOND FULL POWER SETTING (read rich) for starts. It sounds like you are running very rich.

[Grady Clay]

Declan,

Whoa hoss, we don’t want the cart before the horse.

We need to try and figure out what the engine is. What cams? What MFI pump? What throttle bodies? What distributor advance curve? And more.

A possible indicator of the cams is to measure the cam timing of both cams. That is easy to do during a valve adjust. More tedious is to measure the profile of an intake lobe. It is more work to remove the chain covers.

The MFI pump model is on a plate on the outboard side of the pump. The Bosch number will be in the form “0408 126 xxx” and are in the CMA booklet.

The only definitive way to tell the throttle bodies is to remove them and measure the ports. Thil will also let you measure the ports in the heads. All you need are 12 gaskets; six 901.108.391.01 (or .02) and six 901.110.191.00.

You can get a good measurement of the distributor advance curve by measuring the advance every 500 rpm from idle to 6000 rpm.

Once we know the basic structure of the engine, the cranking compression may give an indication of the compression ratio.

While doing this, you can do more of the basic CMA tests; check the MFI pump timing, cylinder leak and much more.

“Once its warm, its goes well, but still doesnt like pulling in low revs, say from 1500 to 2000 rpm, its like a flat spot - If I keep revs above 2k its very good.”
This may be due to the tuning but it might have 911S cams (basically a 911/83 Carrera RS 2.7). Those are not CIS. They don’t start to ‘breathe’ until the 4000 rpm to 7300 rpm range and have little performance below 3000 rpm.


With the engine running very rich, I suspect the oil may be diluted with unburned gasoline. This is very dangerous for the machinery. I suggest you change the oil very often until things settle down.

Best,
Grady

[72911]

Whoa hoss, we don't want to over react here let's be practicle please. I thought Mr Declang wanted rational advice, but maybe I misunderstood...so please continue with your $0.75.

[rs911t]

Originally Posted by 72911

Whoa hoss, we don't want to over react here let's be practicle please. I thought Mr Declang wanted rational advice, but maybe I misunderstood...so please continue with your $0.75.

Rational advice might include knowing which MFI pump. They don't all have the enrich[ment] solenoid controlled by a thermo-time switch in the breather cover. Cold start enrichment is controlled via air from the heat exchanger in the later pumps.

[72911]

Ah, I can see Mr, declang is in good hands and I will lurk about and see what his issue really turns out to be...(I definately will not have 6000 posts in five years with this attitude, ha!)

[rs911t]

Declan,

First things first, the rest of the engine must be in good working order before tackling the MFI system. That might be problematic in your case, since as Grady mentioned you don't know what's in the engine - cams, dizzy, ports, etc. I'm far from an expert in these matters - my MFI is also rich at idle, but doesn't smoke as you describe - but I'll chime in anyway. Someone is bound to jump in at some point and straighten us all out (probably Grady). 911ST mentioned all the following, but you need to these correct[ed] before messing with the pump.

Adjust the valves and do a leakdown test.

Get the engine HOT and use the hand throttle or helper to maintain idle and 6000rpm while you check the timing.

The linkage geometry needs to be correct. Requires Porsche protractors and I've never done it myself, so can't be much help. If they're sticking you can pop the caps off the ball joints and apply some grease. If the sticking is in the throttle bodies they probably need to be rebuilt.

Balance the stack airflow, as stated early.

CMA says to set the part-load mixture before moving to the idle. Yes, an LM-1 with WB02 sensor stuck in the tailpipe is a great tool. You can find CO-to-AFR conversion tables via Google. Enlist a passenger to read the LM-1 output, then you can pullover, make adjustments and continue the road test.

Then tune the idle mixture.

Injectors? You can have those tested for correct opening. I did and found mine were essentially dribbling fuel constantly. Replace them if bad.

No doubt a few dozen critical points I'm missing. Lots of info on the board, maybe find a Pelican or Early S Registry member in your area that's done this before.

Good luck!

[eapcpa]

7211

Ah, I can see Mr, declang is in good hands and I will lurk about and see what his issue really turns out to be...(I definately will not have 6000 posts in five years with this attitude, ha!)

Look my friend, Grady did not mean to dis you but MFI is a special beast. You don't go in and start making adjustments. There is a specific manual written called "Mechanical Fuel Injection check, measure and adjust" that is the bible for beginning to understand poor running and tuning of MFI systems. Grady has 6000 posts because he has a lot of experience and has given great advice over the years. You would be wise to read what he has to say. If it ruffles your feathers to be asked to slow down and take a measured approach then you need to grow some thicker skin. The MFI group is very interested in gaining a better understanding of this system because they have become very expensive to purchase parts for and the original knowledge base of technicians is dwindling slowly. If you would like to just lurk fine, if you want to add to the discussion that is fine as well. If someone disagrees with you don't get pi$$y. It would be wise to anyone just starting with MFI to read the Ultimate MFI thread and print out some of the manuals. I have two three ring notebooks with all of those pages inside them. One on my workbench and one in my office (or bathroom) just kidding. Just cool down and take a deep breath. Isn't that better. Now back to tax returns for me, my clients are calling. (screaming) Hey, I don't make the tax laws I just follow them.

[356RS]

Listen to Grady, he is a wealth of information.

[declang]

OK Folks.
I'm inclined to follow Grady's advice about figuring out what spec engine I actually have.
(Absolutley nothing to do with the fact that Grady is my surname !)

I'll be home tomorrow afternoon & will get a start on that & report my findings.

The PO told me, twice, that SC cams were used. Didn't make sense to me, so I questioned it & was told yes, definitely SC cams. I presume that probably means S cams ?

Thanks for the replies so far.
Declan Grady

[Grady Clay]

Declan,

I guess this means we need to pay serious attention to the cams. I don’t think The CIS cams from a 911SC will work with MFI. Obviously it will run, abet poorly and way too rich. It will be interesting to see what actually is there.

You are going to need a dial indicator and the little “Z” holder (P207 ) to measure the valve lift at ‘overlap’. This determines cam timing.

Depending on what all the components are, you probably will need to make a decision as to how to best bring the collection into a configuration that will run properly. MFI requires the proper SET of pieces to match the particular ‘space cam’ in the MFI pump or vice versa. The choices are pretty much limited to T, E or S. Not bad choices.

Best,
Grady

[72911]

You don't go in and start making adjustments.

To suggest (if you have a start solenoid) checking an easy source of rich running is not an adjustment, it is a quick check. I have complete confidence in the advice here but don't agree with "Whoa hoss" in response to a very easy quick check. I have also studied MFI and am by no means an expert, but I thuroughly understand the pricipals involved here. I am sure declang would know if the start solenoid was installed and if it is/was could eliminate this troublesome piece quickly and move on to more suggestions. This easy advice was up to declang not someone else to decide what was appropriate. To make a suggestion like this and then the next suggestion is to remove the throttle bodies desrves the real "Whoa hoss".

[eapcpa]

This easy advice was up to declang not someone else to decide what was appropriate. To make a suggestion like this and then the next suggestion is to remove the throttle bodies desrves the real "Whoa hoss".

I agree if we are talking factory installed MFI, but, he is dealing with a 75 2.7 MFI converted by prior owner from CSI. Therefore you have a completely unknown platform to work with. It would be wise to document what pistons, cams, throttles and pump you have. As you know, with MFI you must be certain of the underlying state of tune before attempting any adjustments or you can get way off very fast.

Cheers

[declang]

Hi folks,
Had a quick look and found the following :

MFI Pump is Bosch # 0408 126 019 which is correct for 2.7 according to CMA manual. (Porsche No. 911 110 254 00)
It also has numbers 472R and 928 stamped onto the PUMP body near the Bosch ID plate.

Only other numbers I can see are on the end of the thermostat housing.
1 425 500 007
1195 226

(I noticed the CMA refers to the 2.7 as the 911SC, mabye this is where the confusion about my "SC cams" comes from ?)

On the fuel filter, there is a solenoid on the top, with fuel lines going to each of the 6 intake stacks, but there is no electrical connection to the male spade terminal on the top. (see pic below). I did find a matching cable with female spade connector which looks like its the right length to fit on there. Can't remember disconnecting that at any stage though)

Solenoid number is BOSCH 0 330 106 004

I'm thinking this might be the "cold start enrichment" solenoid, so I guess I should just leave it disconnected & insulate the loose wire.
I have never had a problem starting.

Cheers,
Declan

Edit: Pics


Right stack, showing fuel feeds from solenoid


Left stacj showing fuel feeds from solenoids

[Jeff Higgins]

You are right, declan, that is the cold start enrichment solenoid. The disconnected lead goes to the thermal-time switch located on the breather cover. The other connection on that thermal-time switch goes down to the starter solenoid. When you turn the key to start the car and the starter is actually cranking, that wire feeds power to the thermal-time switch, which in turn feeds power to the cold start enrichment solenoid. Until the thermal-time switch heats up, then it opens the connection and quits feeding power to the solenoid. When that solenoid is tripped, it sends fuel directly to the stacks to prime them for starting.

The fact that the car starts easily when cold, without this system connected, further indicates the very rich idle and low speed condition you have already diagnosed. There has to be a lot of fuel coming from somewhere to start a cold engine, and if this circut is disconnected, it can only come from one other source.

Sounds like you have a copy of CMA. Also sounds like the motor has the correct 2.7 pump. That's only a part of the system, however. Unfortunately, there is no way to tell what the rest of it is without doing as Grady suggests. You could run all the way through CMA and see where that gets you, if you feel encouraged by finding it has the right pump. Might be worth a shot.

[declang]

Thanks for confirming that Jeff.

Since the car does run so well when warm, I am tempted to assume it has all the correct bits & run through the CMA to see how it pans out.

I went through my big stack of paperwork and found lots of interesting bills, from piston rings to valves, crankshaft regrind, b/e & main bearings, etc, to lots of smaller bits & pieces from reputable suppliers, so in my mind it looks like the work was done with due care & attention; but no mention of cams, so thats still a mystery.

- Would a non-mfi camshaft have the gear on the end for the mfi drive belt, or am I clutching at straws ?

Next hurdle is I intended using a "gunson gastester pro" for some of my measurements, but reading the paperwork it's not recommended for CD ignition systems. (It takes a feed from the ignition coil 0V for dwell & rpm measurements.)
Does that mean I should invest in something like an LM-1 ? (good euro:dollar rate at the moment and I do like the idea of logging the data )

How would I go about checking the cams ?
I figure the gauge that Grady referred to above would somehow measure the cam profile, but I've never done anything like that before, so am a bit lost on it ; Is it as simple as rotating the camshaft by so many degrees, and noting the gauge reading, and then correlating all this data to give a profile of the cam lobes for one camshaft rotation ?


Cheers,
Declan

[Jeff Higgins]

Declan, your left cam has to have the extension poking out of the front of the cam tower, or there would be no way to fasten the drive pulley. Any cam profile can be supplied with that extension. Turbos have it as well, but it drives something else.

It would be unusual to find that extension on an SC cam. Some guys hop up their turbos with SC cams, so it is not unheard of, however. But, there are some other compatability issues that make it pretty unlikely you actually have SC cams. SC cams go into four bearing cam towers, where the 2.0-2.7 liters had three bearing towers. So unless it has also been converted to four bearing towers, there is no way to put SC cams in it. The cam bearings are actually larger in diameter in the four bearing towers as well, leading to yet another compatability issue. The seal on the front of the left cam, where it pokes out through the tower so the pully can be fastened, is only made in the proper size for three bearing towers. It is too small in its O.D. to press firmly into a four bearing tower, and will leak like hell. A custom seal holder needs to be made, that will hold a turbo pump seal in the hole on a four bearing tower. Henry Schmidt at Super Tec makes them, by the way.

So, working our way through this (somewhat) logically, it is clear there would be a number of problems in fitting SC cams. It is clear the original 2.7 CIS cams could not be used; the left one lacks the MFI drive. Some one had to buy some cams for this thing. The logical choice would be "S" cams. Three bearing, with the pump drive extension. And, best of all, original spec for the 2.7 RS. Which is where the "019" pump came from. With the "due dilligence" displayed in finishing up the rest of the motor, would it be a stretch to assume the correct cams were ordered? They had to be replaced anyway. They had to fit three bearing towers and have an MFI drive. That leaves the "T", "E", and "S" as readily available, off the shelf choices. Some one would have to had put a great deal of extra effort into fitting anything else. I know; I just finished a 3.0 on MFI, with four bearing towers. I've been through these headaches.

So, at this point, I would make everything right per CMA and see where you are. Yes, an LM1 is a great tuning tool. Get one if you can. I could not have gotten mine running properly without one.

[Grady Clay]

Declan,

The dial indicator and “Z” bracket are the normal tools for checking and setting the cam timing on a 911. Porsche specifies the valve lift at Top Dead Center Overlap (TDC overlap same as Z1 overlap). This is where both valves are open as opposed to TDC Compression where both valves are closed.

The specification for the MFI 911S (and Carrera RS 2.7) cam is 5.00 – 5.40 mm with the desired value 5.20 mm. You can easily check both cams with just the intake valve covers off. This should be a good clue. Yes, it is as simple as rotating the engine to Z1 and taking a reading.

To measure the profile the measurement is just repeated at sequential angles of rotation.

Your feeling ‘no power’ at low rpm may just be the ‘S’ cams exacerbated by the super rich condition. Once the mixture is correct it will ‘scream’ at high rpm but will never perform like CIS or DME at 2000 rpm. That is what a 2.7RS is all about!

Jeff is correct. If the engine will start cold without the cold start solenoid valve functioning, the system is way too rich. After we do ALL the other stuff, we will get there. Remember the oil change.

BTW, there is a cold start enrichment solenoid on earlier MFI pumps (’69). It is a second solenoid just below the shut-off solenoid. It operates directly on the rack in the pump and forces it full rich – richer than the engine ever runs under other conditions. It is useful to use in place of the cold start solenoid valve on top of the fuel filter console because it eliminates the second fuel circuit (fire safety). You can retrofit the two-solenoid governor cover to the later pumps.

Please post the part number for the pistons & cylinders. That will be invaluable info.

You are correct in that only MFI cams have the extension to drive the pump. However, other cams have two threaded holes in the end and you can mount a separate (custom) extension to drive the pump.

I’ll let others who have first-hand knowledge advise on the current crop of exhaust analyzers. I too like data acquisition.

Best,
Grady

[declang]

Jeff, thats great info. thanks

As it turns out the PO was not the person who did the rebuild. It was the Previous-Previous-Owner.
I did come across some printouts of email communication in the file between PO & PPO and it stated "Sc cams" so I'm guessing at S cams, with a simple typo. The PO, being non techy, passed that info on to me as SC Cams, and confirmed that when I queried it.

Some of the restoration photos show an immaculate rebuilt engine, which leads me to believe it more than likely was done correctly.

I think I'll have to order an LM1 and do the full CMA then see how it works out.

Now to discuss with my accountant (swmbo !)

edit: cross posted with Grady's post.
Grady, thanks for that explanation. Makes sense now.

Considering the temperatures here do not get very low, would I need any cold start enrichment ?
Lowest temps would be around 5C or 6C ( roughly 42F ) - would that require the cold start enrichment ?

I cant find any invoices for P's & C's, so don't have part numbers. Are cylinder P/N's readable with engine in car ?

Cheers.

ps. oil change done about 30 miles ago. Most money I ever spent on oil !