MFI / CMA revisited ...
 

I'm a newbie to this Forum but not to the early 911 (current is a '69 911E), but could use some precious advice :

Problem : Car is hard to start, idles correctly at first and engine will accelerate to @ 4K RPM before completly warmed-up, then will not accelerate beyond 2,5K and when fully warmed will not idle at all.

CMA Check-list :
NEW 1) Air cleaner cartridge
* 2) Compression loss
NEW, all leads checked 3) Spark plugs (spark plug connectors)
Cheked, OK 4) Dwell angle
Checked, OK 5) Ignition timing
** 6) Fuel pressure and flow
Checked, all OK @15bar 7) Injection nozzles
Checked, OK 8) Injection timing
Checked, OK 9) Correlation
*** 10) Exhaust emission test a) at part load; b) at idle speed

Questions :
* I have a leak-down tester and compressor that I use for the annual on my airplane (Cessna 177RG). The question is: what is the recommended test pressure ? (for aircraft engines it's 80psi) and I'm going to have to make an adaptater since aircraft plugs are not the same size.

** I bought and installed a new fuel pump and filter with no effect. Only after (!) did I run the simple fuel delivery test and got only about 20cl in 30 seconds... Well, the culprit was quickly un-masked : fuel pick-up cloth screen was completly clogged.

*** Please recommend a cheap/effective portable gas analyser that I can use to dial in my MFI.

One last question : I tried to adjust the main enrichment screw on the rack but could'nt 'feel' the screw. I removed the enrichement solenoid to have a look : How in the h*ll can you expect to access the screw when the lever is smack-dab right over it ! ? ! ? There just is no way to go straight through the access hole and expect to engage the screw slot ! What gives' ? Am I missing something here ?

Thanks a 1,000,000
M Chartier, '69 911E, Paris, France

Describe 'hard to start'.

Do you you have to crank it over for a long period of time before it will start? If so, the cold start device is not functioning.

If you find that the cold start system has been disabled inspect it very carefully before hooking it back up. I think your car would have the cold start CS nozzels in the airbox so there is a good chance they have been disabled intentionally due to the fire hazard.

It sounds like the thermostat may be working since the car is leaning out (engine speeds up) as the car warms.

How did you set the timing if the car wont run past 2500RPM? Timing needs to be set at idle and then at 6000RPM. Im assuming the points are set?

The main adjustment screw is about an inch behind the allen bolt on the front of the pump. You need a specialized tool to remove the bolt and then another tool adjust the screw.

Hi M Chartier. Sent you a PM. I'm going to be near you this week and may be able to give you a hand...

<<<Do you you have to crank it over for a long period of time before it will start?>>>
Yes, that's the problem. I have disabled my cold-start device along time ago, so I am used to having to crank a bit more in cold weather. Having said that, my garage these days is @ 60F so not that cold.

>>>It sounds like the thermostat may be working since the car is leaning out (engine speeds up) as the car warms. >>>>
I agree - it appears that the thermostat is ok since I have cleaned and R/R it.

>>>>How did you set the timing if the car wont run past 2500RPM? Timing needs to be set at idle and then at 6000RPM. Im assuming the points are set?<<<<
You are correct : I have not been able to check timing @6K, nontheless I am sure that it is "close enough" for now. Points were set with feeler gauge and double checked. I know this is not as good as dwell, but again close enough to get it running through-out the rpm range.

<<<<The main adjustment screw is about an inch behind the allen bolt on the front of the pump. You need a specialized tool to remove the bolt and then another tool adjust the screw.>>>>
Well it is normaly an inch away but when you insert the 'special' screwdriver you merely are pushing on the lever until it contacts the Control Rack Head (have a look at page SF 16 in the Factory Porsche Workshop Manual)

I should add that I have not yet re-started since cleaning the fuel pick-up strainer but I am now getting 1 liter in 30 seconds per the factory test specs. This is quite probably my problem although I would like to get the low-down on the en-richment adjustment, leak-down test (using aircraft type dual gauge tester) and a proper Analyzer.

1).With these cars and all the things that people ad and take off, timing can be set by ear so I do not think that this is causing your prob. If the car cranks and fires, timing is close.
2)Have you checked the MFI pump timing? If not make sure the marks are aligned. The car will still run if not, but if it's way off then this "might" be a prob. It sounds as if it's the thermostat though.
3)But it could also be the fuel lines. I had a problem where the car would start when cold, it would run, but after a few minutes, it would conk-out and not start no matter what I did until cold again. I gave up after weeks of messing w\it and brought it down to shop. Within 1 hour I was called and was told that the fuel lines were shot-Fixed (under car from pump to tank). You may have to drain the tank and replace screen.

4).Do you have the hose that connects from the pump to the exhaust hooked up?
5). Make sure the rod that runs from the rack to the pump is the correct length.
6). Take a small screw driver and shave it down w\a file and it will fit right in hole that is covered w\allen screw. Do not worry about idle adjustments just yet.
P.S. Good luck

My suspicion is that your PRIMARY PROBLEM is a rusted gas tank and supply line through the tunnel ... and all of the other issues are secondary until your fuel pump can put out a liter of fuel in 30 seconds or less at the inlet line to the fuel filter/cold start housing ...

The fuel tank should be drained and removed [remove the fine bronze filter screen at the outlet fitting] ... and cleaned & sealed with a slosh/seal product such as what is commonly used for light aircraft fuel tanks.

Blow out the fuel line in the tunnel with compressed air ... to see if any rust particles are still clogging the fuel flow! Replacement of the line may be necessary to achieve the specified fuel output of 900 cc - 1000 cc in 30 seconds!

After the fuel supply issue has been resolved, you can proceed with trying to address the starting and other running issues ...

I totally agree with Early_S_Man : there is no doubt that the fine mesh strainer on the fuel pick-up was definently restricting fuel flow. That is now corrected and I am getting about 1lit in 30 seconds. I have not yet put things together, since I removed all the injectors for testing and I need to replace all the rotted rubber fuel lines between tank and pump tommorrow, but I suspect that the clogged fuel pick-up was the main culprit.
* * *
I found the answer to my own question about leak-down testing : use 100 psi and the difference is the % (ex : 90psi/100psi = 10%).
* * *
I still am concerned about how to get to the main rack head erichement screw : direct access is blocked by the lever of the enrichement solenoid, hence it is immpossible to directly access it through the access hole. Having said that, it IS possible to get a screw driver blade on it after removing the enrichement solenoid, albeit, at about a 30° angle.
What's the deal on this ?

bump

Definitely sounds like it would MFI related if the engine temperature has a big influence on how it runs. With that said, double check you used the correct timing marks on the lower pulley to set your base timing--it's easy to pick the wrong ones. I had an idle/low speed running problem one time until I noticed the ignition timing was terribly wrong...

If you could post a picture of the adjustment location that is causing you grief, it might be easier to give suggestions on how to "succeed" in tinkering with it.

Did you have the car running well before?

Good luck!

Before adusting the rack, make sure the rest of the system is working properly. While you say and believe that your timing as set by feeler gauge and at idle is "close enough," then you will have to believe me then, that your MFI part load adjustment is also close enough.

The amount of adjustment you can make on the part load is not going to cure the problems described in the first post, IMHO. Once you lose that adjustment, you will be in left field.

Do they have left field in France? Maybe the Left Bank. Either way, you will be out there.

I thought the French were boycotted . Just kidding . He must be allright , he owns an early 911 .

Kurt Williams

Well gentlemen : Chalk one up for CMA (Check Mesure Adjust) and what I call RTFMi ! (Read The F*cking Manual - idiot !)

After needlessly emptying my wallet of a couple hundred $$$ for a fuel pump, fuel flter, ignition coil and testing my injectors, dozens of hours dismantling the MFI, injectors, distributor, plugs etc., as well as not using the ole Porsche for almost a year (!) my problem was a clogged fuel pick-up: number 6 in the CMA list !

So now that I'm up and running, I now need to 'fix' everything I screwed-up !

Moral of the story : RTFMi ! or more politecly correct : CMA.

Thanks for the input guys !