Reliability of early fuel injected 911s

jyocca · 07-19-2006, 01:21 PM

I'm leaning toward purchasing an early fuel injected 911. Maybe 1970 to 1973? Before I go this route it would be great to hear from those who own these early 911's and what type of mechanical isses are common. I would like to own a reliable driver that isn't expensive to keep on the road. Or, would I be better off with a mid 80's motronic?

Thanks in advance for any advice/suggestions.

John

zotman72 · 07-19-2006, 01:39 PM

Oh boy, now you have done it. As an owner of an early MFI 911, two CIS 911s and one Motronic, I think I can respond to your question. First off, are you at all mechanically adept? Or alternately do you have a MFI savy Porsche mechanic in your general vicinity. As you are going to become good friends with him. Most of the original MFI pros are near retirement these days. MFI works great when everything is spot on, and runs wierd or worse, plain terrible when things are whacked. Expect lousy gas mileage but excellent throttle response. Reliable maybe but inexpensive, not hardly if things need to be replaced. Nothing brings more thrill to a 911 pilot than an MFI engine on sound. All that said, the later 911 fuel delivery systems are more recent for a reason. I like my wife's Motronic system quite a bit right now.. Get a 80s Carrera. YMMV

TRE Cup · TRE Cup's Garage

69-71 injection has mag stacks- as such they heat up and pre heat the air getting sucked in. Terrible in traffic- the car starts running richer and richer , popping/ farting with loss in power. Porsceh recognized this and went to plastic stacks starting in 72. Better but not perfect as the cars would not meet upcoming emissions. Porsche usa models started with the CIS injection with the 73.5 T, then all the models till the 84 DME carrera.
The rest is well covered by Zotman72's post- he is right ; a dme carrera engine is the best all around way to go> especially when fitted into a 73 down chassis!

randywebb · 07-19-2006, 02:31 PM

But... if it has MFI on it stock, then removing it really kills the value of the car.

MFI is claimed to have the fastest throttle response of anything*

- and to run fine for years once it is set up correctly.

*Prob. includes stock EFI, but not performance tuned EFI systems.

jyocca · 07-19-2006, 02:56 PM

Excellent feedback. Thank you.

A local Porsche mechanic I just spoke with recomended a 1973.5 CIS if I was to buy an early 911. Are these engines well regarded or are the '80's carreras still a better bet?

tsuter · 07-19-2006, 03:54 PM

Sounds like you're a credit card mechanic thus....buy as new as you can afford.

pwd72s · 07-19-2006, 04:09 PM

Yup, you have to be a bit of a kook to love the early MFI cars....I'm a bit of a kook. FWIW, my MFI has given me zero trouble since it was set by a man who understands MFI...but then it never did give me much trouble, he just tweaked it a bit. I'll never get over the thrilling sound of those stacks as the revs go from 5,000 to 7,300....

On the other hand, Boxster owners tell me they like their cars...

TRE Cup · TRE Cup's Garage

Well- here in lies a sleeping problem: CIS has been out there on the cars since 73.5. How many miles the car has experienced will usually determine how well the gasoline related parts of the injection performs well. For example, Replacement fuel distributors do not grow on trees any longer- Bosch is getting stupid money for a replacement IF they are available for the particular model- if not, then you get to update to a later CIS system. Sure there are ways to repair what you have on some of the components, but lets face it the stuff is getting used up. So, practically speaking the latest motronic/ DME makes the most sense.

I am sure i will get flamed here , from various owners that keep their cars in the best shape- that's ok- their cars are the exception to the "rule" due to the better upkeep and attention to details

randywebb · 07-19-2006, 05:28 PM

That's a good point, and the '73.5 is the very oldest CIS you can buy...

"1973.5 CIS if I was to buy an early 911. Are these engines well regarded?"
- I am a known CIS hater... CIS is a hydraulic'ly operated FI system that ws created in the early 1970's and replaced by modern electronic computer controlled FI systems (EFI) in the 1980s. Yet CIS is not MFI either. Instead, it is designed to give good fuel economy and emsissions performance by 1970s standards. It is not about sports car performance at all and the engine will not behave like a real sports car motor.

The earlier MFI system uses direct mechanical linkages to operate & control the FI system. It was the next thing after carbs. Reread Paul's comment re aural thrills.

"or are the '80's carreras still a better bet?"
- Now we are into EFI, aka DME systems. These are able to track and compensate for, a variety of environmental parameters as well as info about the engine. The 997 uses an evolved version of DME and the 1984 version on the Carrera was the first one. The only problem is that you have to buy a big ol' heavy Carrera to get one (or do a motor transplant into an earlier car).

So... I would prefer a Carrera to an SC or to a 1975-77 "mid-year, 2.7L engine'd" car. The '74 had CIS but is light enough to make the think twice. If you got a Carrera, you could always rip out some of the heavy luxo-crud...

But the engine is just part of the car. Also, I'm not you...

What do you value in a Porsche? Do you want the ultimate stipped down, primal sports car experience? Then get something earlier than a '73.5. The '72 is special because of the oil tank location. The '70-'71 have the road racing transmission with its superior shift pattern. The '73 is the last before the dreaded CIS ruined all our fun. Or you could get a short-wheelbase car and have fun spinning.

The other side of the 911 spectrum is the heavy, luxo-bloated cars with their giant bulbous safety bumpers. These are ok for a starter 911 until you are ready to move on to the real 911s. You can put a big heavy audio system in it, add some curb feelers and pretend you are in really well designed LeBaron.

So there is my completely objective, unbiased opinion.

BAPhotowerks · 07-19-2006, 06:36 PM

My MFI has run fantastically for the 7 years I have owned my '70E, without so much as a tweak besides fuel and air filter maintenance, correct plugs, and expensive gas. I don't have any experience with the negatives listed here or the storied ones that drove most owners (backwards) to carbs. Maybe I'm one of the lucky few...

Sure it can pop and fart between 3300-3600, but it is occasional and usually in traffic, plus I do the same! Great note about traffic/induction pre-heating and the switch from mag to plastic; I always wondered but figured it was a weight thing, along with the airbox.

BA

pwd72s · 07-19-2006, 06:39 PM

And NOW...we get to consider the current political push to 85% ethanol fuel. Should that happen? Most any Porsche out there today will make a nice moorage anchor for a sailboat...

Zeke · 07-19-2006, 08:39 PM

Quote:

Originally posted by jyocca
I'm leaning toward purchasing an early fuel injected 911. Maybe 1970 to 1973? Before I go this route it would be great to hear from those who own these early 911's and what type of mechanical isses are common.

John

Things to look for: Worn throttle bodies/plates, dirty or otherwise not peak performing injectors, dirt in the air correction ports, worn MFI pump drive gears or belt, dirty thermostat, and the various electrics associated with the system. If these things are all in good shape, the car will be reliable. It's a good system and the mileage is not that bad if it's dialed in. In the upper teens. If you can keep your foot out of it.

If I can tune an MFI to just close, not perfect, almost anyone that can do carbs and such will be able to keep the system running well. However, it the motor itself is not up to par, the system will not work well. So, do a thorough pre-purchase inspection (PPI) for compression and ignition health, not to mention the rest of the car. Not very many affordable cars come with all these things in top shape.

jluetjen · jluetjen's Garage

My MFI runs great and a "professional" MFI mechanic hasn't looked at it in generations! The most commons problems that I've seen from watching here for more then a few years seem to be...

1) Worn throttle bodies which then leak air around the throttle shafts. Often the cause of popping and farting on over-run and deacceleration. Apparently more common in E's and S's because of the increased overlap causing pulses in the intake which wear the shafts. Easy test, with a warm car at idle, try shaking the throttle shafts, if the engine start to miss, you've got leaky throttle bodies.

2) Clogged or gunked up thermostats. Possibly a knock-on affect of the the above situation, especially if fault 3 has occurrend.

3) Thick-headed mechanics who know nothing about MFI. They routinely increase the richness to make up for the leaks, which then causes fouling, poor transitional running, etc. etc. etc.

That being said, with the help of the folks on this BBS, and some focused investment (when it's time to get the throttle bodies refurbed, it's time), you can set it up. Mine was mal-adjusted by the previous owner and I was able to tune it back to a happy state just using my "seat of the pants" dyno and a notebook.

Don't dismiss MFI just because of the "conventional wisdom". If "conventional wisdom" was always right, lemings wouldn't swarm off of cliffs and there wouldn't be any "real estate bubbles".

PS: So far I haven't seen any issues with running the 10% Ethenol mixture being sold here.

Type911 · 07-20-2006, 05:29 AM

All good advice given here.

If you can find a car w/ the MFI set up properly & components in good condition you should expect decent reliability.
I would not shy away from a good MFI car. Will this be a weekend fun car, or a daily driver ?

Drive an early CIS car, then drive an
early MFI car...the choice will be obvious

Jim Richards · 06:13 AM

If you're hooked on the looks of the early cars (I know I am!) and want the reliability to make it a daily driver, I'd look for one that has been properly converted to a later engine with DME (3.2L or 3.6L) as Dave from TRE mentioned. If you want an early car that's stock, then I would not shy away from one with MFI. I'm sure you'll find them to be reliable, and no more expensive than any Porsche to keep on the road, albeit a bit harder to start in cold weather. By the way, where do you live?

MikeR90S · 07-20-2006, 07:29 AM

I'm not an MFI expert though I love the way they sound. I do know my way around CIS pretty well, having driven a '74 911S for the past decade +. I would avoid 73.5 CIS cars (these were T's by the way, 73 S had MFI for the whole year). The 73.5 CIS has a lot of peculiar parts that went away in '74. '74 and on are pretty similar and parts are available. I just put new injectors in mine after 32 years and 180k miles. CIS doesn't have the raw performance of MFI but makes for a very good driving car. I disagree that CIS is not a sports car injection system. Unfortunately the 74's and SC's are really the only CIS cars to consider. 75-77 have too many problems IMHO.

If you like early small bumper cars best (I know I do), then consider an E or a T as well. Early S prices are through the roof with E's close behind. A 72 or early 73 T has MFI and is pretty much the same as an E (140hp?). A 70/71 2.2 T with Webers is great too. I've had a '71T with webers for 10 years and its been great too.

Superman · 07-20-2006, 08:39 AM

I REALLY want to drive a tuned MFI car. Sure, certain custom EFI systems may very possibly have equivalent throttle response and perhaps even better. But not by much. And MFI was powering these cars thirty-five years ago. Finally, the famed '73 RS with MFI is still considered to be one of the most responsive automobiles ever produced. It's handling, braking and throttle response is legendary.

I REALLY want to drive an MFI car.

pwd72s · 07-20-2006, 11:20 AM

Super, could this be a hint?

I hope one of the Seattle boys accomodate you. I try to avoid the big cities and clubs gatherings these days...

SandyI · 07-20-2006, 11:41 AM

I've put nearly 30,000 miles on my '69 911E in almost five years. Otto does all the service on my stock MFI. Have had zero problems. Zero farting and backfiring even when driving in the heat of L.A. summer traffic. Throttle response is AWESOME.

Tom F2 · 07-20-2006, 11:57 AM

I've owned 2 73.5 cars. Both were/are wonderful. It's easy to fit the 2.7 pistons and cylinders if you ever have to get into major engine repairs, and these make for a great driving car. Also, gas mileage is good, for a 911. I also owned an MFI T and a '66 with Webers. Neither was nearly as easy to live with and fun to drive as the 73.5 cars.

The Motronic engines are definitely better, but may be out of character in the early car. Plus, it's nice to keep an old machine running around in something like the configuration in which it was made. Not that I haven't thought about putting a 3.2 in my car...