72 911T 2.4 idles great - dies when driving

[stouff93]

The car sat idle for about 9 months due to a busy schedule and a frozen brake caliper. Now with the caliper rebuilt I tried starting the car and it just popped, farted and would idle but very ruff and then it just wouldn't start at all.

I took the car to a very reputable independent Porsche shop who cleaned out the bad fuel and got the car running, the only new parts were plugs. I drove the car about 5 miles and it ran perfect then suddenly it starting choking as if it wasn't getting fuel and the car died, but I was able to limp the car home. Last night I drove around the neighborhood and same thing, it ran great for about 3-4 miles then starting choking and died. The car has a full tank of new 93 grade fuel and today I let the car idle for 45 minutes with no issues. I could rev the engine to 3k, 4k, 5k rpm without any issues, the Porsche shop did tune the car and in the garage it's awesome. Feeling optimistic I pulled the car out and got 1 mile down the road and it died.


In 2000 I had a new fuel pump put on the car and when I bought the car in 1992 I had a new MFI unit installed.

I'll be calling the shop on Monday but was looking for any insight of what could be my problem. The car idles and revs perfectly in the garage but put it in gear and drive one mile and it dies and that's just driving normal speed. Maybe I just need to let it idle and burn more fuel to clean out the fuel lines, could it be that simple? I did take off and inspect the fuel filter but not much I could really see or tell and reinstalled it.

Any comments or suggestions is appreciated.

Thanks, Eric

[M491Cabriolet]

I had a similar problem with my 1972 911T after it sat for many years. The problem turned out to be that the overflow valve in the fuel filter console was blocked or stuck. This gave an incorrect fuel pressure for the MFI and kept the car from running at anything other than idle, and then died and or backfired loudly. Another problem my car had that affected running was my alternator was totally dead, but that's another story. I would check valve before doing anything else. Good luck (and patience!).

[tobluforu]

My 72 did this and it was the old fuel lines constricting under load. Idled great, I could drive it a tad but then it would just die on me.

[72doug2,2S]

Check the filter in the tank, probably needs to be replaced if you haven't done so already. Not too expensive. A clean tank and new fine mesh (inside tank) filter made a world of difference for my 72.

[curtisaa]

I had the same problem with my 72T . Turns out that it was the fuses. Check & clean ALL fuses & terminals with 1500 sand paper. then make sure the round relay is also clean. I know it sounds too simple, but it works. make sure your inside fan is on and is running. I think it's the #9 fuse. Replace it if it's not working properly.

[FenderBender]

+1 on the Tank filter Mine was varnished shut on my '73.

[stouff93]

Thanks for all the replies, snowing pretty good in the Atlanta, GA metro area so no road tests today. I checked the fuel filter overflow and it was clean. Pulled out the fuel sender since it wasn't working properly and it was coated with junk. Once I drain the tank I'll pull the tank filter, based on the condition of the fuel sender good chance this is the problem.

[RSTarga]

change your main fuel filter too while your at it. It's in the engine compartment if you have MFI

[stouff93]

Here's an update in case any other 72 911 MFI owners encounter the same issue. I confirmed with the shop they had emptied the tank and cleaned the tank filter, kind of wish they had replaced it. I replaced the fuel filter and can now drive the car without dying, but I get alot of popping and backfiring, would this be a too rich fuel/air setting?

Also, is the tank filter metal mesh or like a traditional filter?

[72doug2,2S]

The filter in the tank is a fine metal mesh. It was $10-12 for a new one from Wayne a few years ago.

Do you smell any gas in the oil?

I had a similar problem a lot of stack popping and an occasional back fire, I had the valves checked over again and low and behold the number six was too tight. My NEW mechanic set it and told me to put a few hundred miles on it. Well it's never run better.

The thing is I was just sure it wasn't the valves because I had just had them done -OLD mechanic. Too bad I haven't learned to do this myself, someday.

Since then, no smell of gas in the oil.

[tobluforu]

MFI's like to run rich so all you might have to do is richen it up. Did it run great before all this happened? If so, I would replace the tank filter for sure. Have any of the fuel lines been replaced since 1972?

[stouff93]

Thanks 72doug2, sounds exactly like my engine now. Although I had a tune/valve job less than 500 miles ago it has been over 4 years since the valve job. I didn't drive the car enough and then one of the calipers froze and the car sat idle for almost a year. Wish I could tackle the valves myself, I'd like to learn, but I really want to get the car running correctly. There's always another opportunity. When I run this tank of gas down and I'll replace the tank filter just to have all new filters.

Cudos to all the replies and suggestions, everthing has been spot on.

[berettafan]

fuel pumps can apparently get pretty mucked up as well from sitting.

[stouff93]

tobluforu,
About 4 years ago the car was tuned and ran good, while in the shop it got a valve job and a new permatune unit was installed. Around 1995 I had some fuel leaks and all the rubber fuel line hoses were replaced.

I'll look at some MFI articles and brush up on tweaking the MFI settings, thanks for the insight.

[stouff93]

The fuel system was tested under load with a gauge and the fuel pressure dropped almost to zero under load - bad fuel pump was the diagnosis. A rebuilt fuel pump was installed and the car runs great.

[alexARC]

Just looking through Pelican. I have a similar problem and i suspect the Fuel tank filter.

Does anybody know where i can get a new one?
Could i remove it and replace it by a normal fuel filter between tank and fuel pump?