MFI Maladies?

Hi guys. I just registered after browsing for a while and learning more from here than any other source- so here goes:
My MFI '72 911 developed an annoying flatspot/ hesitation around 2900-3200 a while back, and still remains in one form or another despite trying everything I can think of. It gets better if you richen the mixture,(idle and/or main) but has to be VERY rich to get wrid of it altogether. I understand that the accelerator linkage to MFI rod is supposed to be around 14.2 cm, but the motor just about refuses to run unless it's considerably greater than that- popping and banging etc everywhere. It doesn't appear until about 20-30 mins of driving under normal temp, but just gets progressively worse until I garage it through exasperation. I've checked all the other stuff(timing/points/dizzy/compression/valve clearance/exhaust etc etc) and it's ok. Any adjustment I make fails to cure that flatspot. Am I missing something vital?. I don't have the MFI manual, and live on the other side of the world from Gus at Pacific. Car's done 89000 miles and came from Arizona to New Zealand a year and a half ago. Surely the MFI's not worn out yet?? I read of someone else having a similar complaint in a '72 T a while back in your column. Is this common? Help!

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'72 911 TE

Are you running the stock exhaust? MFI cars are very sensitive to exhaust system tuning.

Have you been able to check the "part load" and "idle speed" CO content? Also are you sure that you are actualy enriching the mixture to even it out? If the warm up thermostat where dirty or the hose comprimised in some way as the engine warms up to operating temp the fuel mixture would stay rich and the engine would suffer. I have the Blue book, it emphasises over and over to check all the other parameters, Timming, valves etc before playing with the injection system. It sounds like you have verified these other things. It gives this advice CHECK IN THIS SEQUENCE 1. Aircleaner cartridge 2. Compression loss 3. Spark plugs and connectors 4.Dwell angle 5. Ignition timming 6. Fuel pressure and flow 7. Injection nozzles 8. Injection timming 9. Correlation 10. Exhaust emission at part load then at idle speed. Hope this helps some until Warren gets on.

Be sure to check things in the order Mackgoo listed up to the injectors! You need a metric set of Flare Nut Wrenches to remove the injectors ... anything else will damage the fuel lines or the injectors! The injectors are etched with a set or sequence number, and the cylinder number in which they were installed originally, if all are still original. A dealer or approved BOSCH service station can check the injectors for spray pattern, opening pressure, and leak down.

My suspicion is that your correlation (matching the throttle valve opening angle to the pump operating lever angle) is off a bit, maybe a lot!

The MFI pump is not likely worn out, or in need of rebuild, since every sourse I have ever checked says they tend to go too rich when worn out. Flat spots do not indicate a too-rich condition! But, check your sparkplugs again to be sure!

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Warren Hall
1973 911S Targa

Hi Matt,

another NZer. Do you belong to the NZ Porsche Club?

Neil
81SC

I do! I joined a month or two ago but wasn't listed in the last "Spiel" as having joined.

Any other NZers lurking out there?

Cam

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Cameron Baudinet
1975 911S

Cam,

are you in Auckland?

Neil

Yep, and I'm replying about this to your listed email address so we can discuss this without bothering the whole world!!!!!


Cam

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Cameron Baudinet
1975 911S

Thanks guys. I just went for a long drive in the weekend after doing a another full service (great fun of course) and things seem to be a lot better. Only a couple of splutters in 400 miles of driving, and I think I can put up with that. My exhaust isn't stock incidentally, but the problem developed a while after the new system was installed. Sounds great though!
Warren: I removed the injectors and visually checked and cleaned them- are they matched to each cylinder individually via the stamped number? Glad to hear my MFI isn't worn out.How long do they normally last?
To the NZers: No, not in the club yet, mostly due to spending all spare funds on 911 toys (latest was a mechanics stethoscope, excellent....)and avoiding the subs. I'll be there soon! An aside:anyone running 91ULP? I'm sick of the smell of that 96PULP stuff and its seems I don't need it.

Matt, Real glad to hear it is running better! No, I don't think it is a matter of matching the injectors to a particular cylinder in an engine. It's just that all of the injectors in any set are 'matched' to have the same flow capacity within some percentage, and I some how doubt that all engines had the #5 injector in a set installed in cylinder #5, that might be carrying 'German precision' to a paranoid extreme!!!

I don't know what kind of mileage can be expected before an MFI pump would need to be calibrated, but the experts I have talked to say they always go rich to a point beyond where it can be adjusted out to a satisfactory level. So, I guess when sooty, dry, black fouled plugs become a steady problem, you know you are at that point! Keeping engine oil supplied to the pump clean and fresh is the key to a long-lived pump, I'm sure!

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Warren Hall
1973 911S Targa

As far as the 91 vs 96 octane, I am using and will stick with 96. It seems to be reasonable insurance against detonation etc, and who knows what the *real* octane of the 91 is anyway. (By the way, for anyone in the US, that is RON, not MON or an average. I think 91RON = 87 octane in US).

I used 20 litres of race gas for that "feel good" factor a couple of times, even though I know that my 8.5:1 engine has no use or need for it!!

Cam

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Cameron Baudinet
1975 911S

Just a note for the MFI. The blue book makes a big deal about running 87 octane and being able to get the co values in. It bassicaly says" if you are having problems with the Co being too high ask the owner what kind of gas he is using. Running octanes greater than the 87 will cause these problems." these are quotes fro memory.

Ok, so if our 91 is your 87, and the blue book says run it, then I should give it a go I guess. I'll just be a little more alert than usual listening for detonation, although exactly how you are supposed to hear it above that glorious wail and also keep concentrating on the rapidly approaching corners beats me!
If anybody is keen enough to scan some mfi spec sheets, my gratitude would equal that shown to the lowered Honda Civic driver with a scraping Supertrapp muffler and cabin full of spotty teens, who FINALLY ceased swerving and allowed me pass him on the open road yesterday. Kids don't seem to get Porsches, do they?

do you have e mail?

"Kids don't seem to get Porsches, do they?"

Yeah, they think these sewage pipes for exhaust systems and these overwrought body kits somehow make up for their ignorance, not to mention the inherent deficiencies of their rides.

It's a funny thing. You're talking about Rice Boys who are purveyors and sticklers for 'high tech', horizontally opposed fours, and whom (dangerously so) presume that a 1972 small bumper 911 is a relic, and therefore no match for their ‘modern’ Rice Burner; it’s ignorance that becomes arrogance. Shoving performance/technical specs under their nose is an exercise in futility, as is explaining how some engine parts from a dismantled 911 engine could almost be sold in a jewelry store, and how assembled, these parts form a very precise and ‘high tech’ whole. These guys can’t get past the calendar, and the manufacturers know it, which is why these Civics, Integras, Lancers and WRX’s will only go to 100,000kms before the big ‘BANG’.

But it's the hard lessons that they learn from, the harrying from behind when their buzz box is giving them all its got, and then the final, obliterative overtaking move performed at 7,200rpm, and then the smile that finds your face, the smile that is their stupefied frown. It’s the guys in V8’s and Bimmers that (wisely) know to resist the temptation!

Matt, you're just a few hours across the Pacific from me. I'm harassing the Rice Boys over here in Melbourne with my WRX-munching 1974 Carrera, the 1973 (MFI) RS dressed up to at least look like its safety bumper, K-Jetronic stable mates. Both our Islands get the some of the ****tiest fuel available, usually watered down by the fuel stations. Leaded fuel is still available in Oz, but I can’t put anything but Shell Optimax in my tank. My Carrera was tuned to run on Optimax by the previous owner because of the high compression pistons that were installed in the car as part of a 80,000km-old rebuild. Without Optimax, I’d have to restore the engine to its original compression ratio, and even then, the leaded fuel available is not the same fuel as it was when my car was but a spring chicken. With Optimax being the most expensive fuel available due to its premium properties, I know that Shell would dare not risk a thousand lawsuits! Optimax is like the unleaded version of the leaded fuel that our Southern Hemisphere 911’s once knew, albeit more refined, pardon the pun.

Is Optimax available in NZ? If so, I thoroughly recommend that you start using it, because god knows, those Rice Boys are!


Matt Holcomb

[This message has been edited by Matt Holcomb (edited 05-28-2000).]

[This message has been edited by Matt Holcomb (edited 05-28-2000).]

Matt:

Did you just say you can beat a Lancher Evo with your (early) 911?

A rally racer that I know has just gotten a Mitsubishi Lancher Evolution IV, and that thing is a pretty fast little beast, with all wheel drive, and all the techno gismos.

Now that's hardly a rice car, but I very highly doubt you can beat that car with your street driven 911...

I do agree with your statement about most teens being infected with this virus that effects their brains, making them think lots of decals, a loud exaust, and don't forget the huge rear spoiler, will make their car fast. However I'm not going to be as enthusiastic about the hate of most japanese cars, (honda civics, integras and the like mostly) and will just go so far to say a big waste of time, money, and skill (doubt how much of the latter is involved, but that's off subject).

I can see how you like your 911, (you've got one after all, and this IS a 911 discussion board) which no doubt has a lot more character, charizma, appeal and so on, but I highly doubt if it can outperform a Mitsubishi Lancher Evo.

Now as I've said, never seen your car, and do not know much about it, but that Mitsu is not the avarage japanese car, and IMO it would take something very extremely fast to beat it. (Hmm, so was the last generation Mitsubishi Eclipse Turbo AWD, specially when modified, but I guess this is not the place to argue that one).
Ahmet

1.2gees,

No, I was not referring to the Lancer EVO IV, V or VI I understand and appreciate that I would need a 993 Twin Turbo to be competitive against one of those. Having said that, I'd still take a crack at one in my 1974 Carrera. Of course, I wouldn't win, but nor would I lose!

To understand why I wouldn't cower away, you must understand what a Euro spec 1974 Carrera is. For starters, they're about as scarce as a Lancer EVO!

Thanks for that Matt- I had a good laugh. The unfortunate thing is though, I can't be too condemning of the rice burners on account of thinking I was the Road King myself not too long ago. Only we didn't have rice to burn back then; three wheeling Ford Anglias round corners was as good as it got. But as you say, at least the cooker ran on proper gas. I'm sick of this ongoing petrol debate. For the benefit of non Southern Hemispherers, we've been argueing about it for a long long time now. We basically get force fed anything the petrol companies want to offload, and I'm becoming increasingly concerned about the perceived environmental advantages of unleaded. I work at an institution that (amoungst other things)measures atmospheric pollutants, and we see huge levels of residual 'aromatics'(the stuff used to boost octane) in car dense areas. This has gotta be worse than lead- not that anyone is particularly keen on that either, but at least it isn't quite so directly linked to cancer. Besides, it makes exhaust pipes go black and plug reading pretty difficult. The only reason the Ricers put up with it is because those boom box ICE systems drown out the sounds of engine protest. I'll stick with my recently revamped retro original factory mono speaker and leave the real noise to the oily bits, thanks. And no, we don't get optimax to my knowledge. We do get Mobil One, which I've been using to good effect- unless someone smarter can tell me a better oil for my old bus....

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'72 911 TE

About two weeks ago here in Melbourne, several cars pumped water contaminated fuel into their cars at a SAFEWAY pump station, one of which was the owner of a brand new Lexus ES300.

A total of seven cars were damaged that day by the fuel, and of them all, four were towed from the station, including the Lexus.

I can't think of a better advertisement for the Oceania fuel issues, or a worse advertisement for the owner of that particular fuel outlet!

Well in that case...

All I can do is watch you race some real rice burners, AKA the HONDA civic with the (1.6 is it?) small block "4". And the big block spoiler... Well, and the 2 feet wide tip. But than again you wouldn't be competitive against those either, there would be no competition .
Ahmet