1972 911T with MFI

[Doug Carroll]

HELP. I have a 1972 911T Targa with MFI. The engine was rebuilt by the previous owner, has about 3,000 miles on it, an runs fine. The Problem? This thing sucks the gas, about 10 mpg around town and I drive it gently. Gets about 15 mpg on the highway.

When I first got this car, there was a very noticeable flat spot while accelerating at about 3000 to 3500RPM. To alleviate, I made a slight adjustment in the part load mixture by making it a little richer. The has helped alot. The flat spot is still there but it is signicantly better, hardly noticeable, since the adjustment. Is this the problem with the gas mileage?

I had a 1973 with the CIS engine and it spoiled me for good gas mileage.

Any suggestions for other adjustments?

Thanks for any help you can provide.
Doug

[Tim Walsh]

does your microswitch work?
On the left side of the engine there is a switch that is pushed by the throttle linkage. If that is bad or is maladjusted it will also drop your millage alot since when you're coasting it will still dump gas into the engine.

[Doug Carroll]

Tim,

Hmmm, interesting question. I will check it out.

Thanks very much
Doug

[boyo]

Easy way to check - with the engine off open the hood and see if the microswitch is engaged. If it isn't, it's been disabled. Likely the culprit are the crumbling electronics in the small module in the left hand side of the engine bay.

Search "microswitch" on this board to find replacement options - have fun!

-Boyo

[Doug Carroll]

Thanks for your response. Yours is the second reply suggesting a problem with the microswitch. Will check it out. This engine was rebuilt by a backyard mechanic who could have easily neglected this switch in terms of adjusting, etc.

Doug

[Halm]

Doug, Get your hands on a Gunson Gas Analyser and check the readings. There is an excellent article on this in the Tech section. My mileage was about 16 highway and after an adjustment it went to well over 20mph. We leaned it down 14 clicks and drivability improved dramatically as well.

As for the Microswitch, I doubt it is the cause of low gas mileage. Backfires on over run, yes, but not gas mileage.

[tryan]

same car and i get about the same mpg with a working overrun circuit.

best $20 to go 100 miles i ever spent.

[tobluforu]

Get use to it, these cars love to run rich which in turn sucks the gas

[pwd72s]

As far as the flat spot goes...are you running an aftermarket exhaust? That alone could do it. See? Another search for you...

[Doug Carroll]

No, running a stock exhaust.

Thanks for your response.

Doug

[David E. Clark]

Before I spent a lot of time or money, I'd make sure the easy, lo-cost things are OK. Are the tires properly inflated? Are the plugs clean and properly gapped? Do you need to replace or clean the air filter? Is the timing correct? When was the last time you cleaned the MFI thermostat This contributes greatly to a rich running condition. There are many good threads on this; search "Clean MFI Thermostat." Also make sure the hot air hose from the left heat exchanger to the thermostat is connected and not kinked or damaged in any way. Without this hot air, the thermostat will take a very long time to lean out. Overly rich = poor fuel economy. It might pay to check the easy things before you get into a big project. Good Luck.

David
'73 911E

[Bobboloo]

Go to http://www.pelicanparts.com/techarticles/911_MFI/TipMFI.htm

Download Check, Measure, Adjust. This is required reading before touching anything in your MFI system.

[Burnin' oil]

10 mpg in town? Not bad, not bad at all. I wish my '73 did as well . . .

[Doug Carroll]

Burnin'Oil

You should see some of my responses. Most everyone thinks the car should do better. Perhaps you should pursue the problem for your car.

Doug

[David E. Clark]

I second the check, measure, adjust recommendation. You can find a better (more legible) copy here:

http://www.scatliff.mb.ca/pelican/MFI_Check_Measure_Adjust.pdf

Thanks to poster Derek Murray

David

[Burnin' oil]

I believe that my fuel consumption is primarily related to Webers and uncontrollable and frequent spasms of my right leg and foot.

[Tyson Schmidt]

My '72 T, which I obsessively tuned and adjusted, would get 15 city and as high as 29 highway.

One of the things I found while "obsessing" over my MFI was that the space-cam wore a groove in itsself that made adjustment a moot point. The '71 and earlier pumps had a narrower cam with a roller follower that didn't seem to have this problem. With the '72 and later cars, the follower was more of a ball point device. That, coupled with some surface hardening of the space-cam (or lack thereof) issues caused the wear grooves.

My point is that you may have to break down and just send the pump to Pacific Fuel Injection for a rebuild. Of course, follow all the steps in the Check, Measure and Adjust manual first.

Good luck!

[Doug Carroll]

Tyson, thanks for your reply. Just of of curiosity, what does it cost to have those pumps rebuilt. I have heard it is spendy but have no specifics.

Thanks, Doug

[Tim Walsh]

I've heard you can get them rebuild for anything from $450 to over $1200. Pacific fuel injection might be right in your area even. Give Gus a call there and he'll let you know how much.

[rudy sanchez]

I've spoken to gus before a/b a pump bench test and rebuild. he said it would be over a month until he could test my spare kugelfischer pump. and I'ver heard that a rebuild can take 6 months.

maybe he get's to the porsche MFI pumps quicker... but at over $1k for a rebuild... I found another source. I ended up using a guy in redding, ca who had a 1 week turnaround and price of $350 for the rebuild.

but from what I understand Gus is THE BEST... he just didn't work for our time frame and budget.

paul schuster