911 warm stall

[fish57]

I have a 1987 911.

When warm it starts to buck like crazy, then stalls completely.

After an hour it starts again but it takes 30-45 minutes of driving to do this.

2 weeks ago had complete tune up but it did no good

Any ideas ?

[Loren]

If you haven't lately... replace the plugs, wires, cap, rotor. Change the fuel filter and check the fuel pressure. Adjust the valves. Check for intake or vacuum air leaks.

Unfortunately any of these could cause your problems - so you just need to eliminate them one at a time.

[jrose]

If you note that the engine is running rich (black smoke, etc from exhaust) when the bucking begins, you might want to check your head temperature sensor. Just an idea, of course, but those things do fail.

[jrose]

Just another thought that has occurred to me. I've also seen ignition coils fail when warm but work OK upon initial start-up. Do you have spark immediately after the engine stops running when warm? If not, you might want to try substituting a coil known to be good. Also, back to my first thought on this problem--the head temperature sensor or sensor II as Porsche calls it--when the engine is thoroughly warm (when yours seems to die), you can disconnect the sensor plug in the engine compartment and check the sensor's resistance to ground with an ohm meter. With a fully warmed engine, the reading should be about 90 ohms. A working temperature sensor's resistance will go from high (making the mixture rich) to low (leaning the mixture out) as the engine reaches normal operating temperature. If yours remains high when warm, you have a faulty sensor. Hope his helps.

[Greg]

I have heard a bad ground strap can cause electrical problems that develop when the car is hot.

[aak5454]

Based on my experience with early 911s (pre'73), I would look closely at fuel delivery. Given that it take an hour to restart, you may be delivering too much fuel to the car and/or something is overheating. I don't know much about the sensors of that type of car so not able to suggest much there.

Also, I am assuming you have experienced this over more than one tank of gas. Crappy/old gas could cause something like this as well.

[HenryV]

I have a 1987 911.

When warm it starts to buck like crazy, then stalls completely.

After an hour it starts again but it takes 30-45 minutes of driving to do this.

2 weeks ago had complete tune up but it did no good

Any ideas ?

<{POST_SNAPBACK}>

Clogged fuel filter?

When the engine is cold, the fuel mixture is enriched (choke), hiding the problem. As the engine warms up the fuel mixture is leaner, exposing the problem.

This should be most noticable when you are higher revving (with a warm engine), e.g. on the freeway or accelerating - do you notice a loss of power?

[magcuda]

under the drivers seat next to the DME is the DME relay. I would change it just because they fail.

[My87Targa]

check your catolitic converter mine collapsed and caused my car to do the same thing, oh and rotor, cap, plugs, and wires

[MobileWrks]

Put a set of fuel gauges on it. Sometimes the Fuel pressure regulater goes bad on the carreras. Also does it puff any smoke upon start up???

Jimmy @ MobileWorks 408-580-7919

New members to this forum......Thanks Ed!!!

[tadk]

I have a 70 911T that had a similar problem. It would run and then buck and die. I found it to be a clogged fuel filter. After the car sits for awhile the fuel leaks back into the line and lets the car run and then cuts out. I changed the filter and never had another problem. I had alot of sediment in the tank because my grandfather had the car stored for some time. Hope this helps.

[89Carrera]

My car has a similar but not identical problem. My 89 Carrera bucks when warm. It feels like the engine is cutting out or running on less than 6 cylinders. The problem exists only when coasting on a light throttle. There is no hint of a problem when the car is accelerating. Oddly enough the problem also disappears at exactly 2000 rpm. The problem occurs above or below 2000rpm. I have owned the car for 10 years, it now has 96k miles and has been well maintained. I have spent a bunch of money at some great Porsche shops and none have been able to fix.

Work done so far:

Replaced: injectors, DME relay, cams reset, valves adj, spark plugs, ignition wires, distributor cap & roter

Tested (parts swapped): Ignition coil, air flow meter, temp sensor, motronic control unit, air box

Other Tests: compression test (160-175), fuel pressure, engine vacuum leak, injection and top end fuel system clean, engine "leak down" test (all cylinders are 2-3%), cylinder head temp, exhaust cylinder temp (1 cylinder runs cooler?), exhaust back pressure, exhaust analyzer indicates lean mix below 2000rpm, heat exchanger, battery, DME pickups, air flow meter, altitude sensor

[Loren]

My car has a similar but not identical problem. My 89 Carrera bucks when warm. It feels like the engine is cutting out or running on less than 6 cylinders. The problem exists only when coasting on a light throttle. There is no hint of a problem when the car is accelerating. Oddly enough the problem also disappears at exactly 2000 rpm. The problem occurs above or below 2000rpm. I have owned the car for 10 years, it now has 96k miles and has been well maintained. I have spent a bunch of money at some great Porsche shops and none have been able to fix.

Work done so far:

Replaced: injectors, DME relay, cams reset, valves adj, spark plugs, ignition wires, distributor cap & roter

Tested (parts swapped): Ignition coil, air flow meter, temp sensor, motronic control unit, air box

Other Tests: compression test (160-175), fuel pressure, engine vacuum leak, injection and top end fuel system clean, engine "leak down" test (all cylinders are 2-3%), cylinder head temp, exhaust cylinder temp (1 cylinder runs cooler?), exhaust back pressure, exhaust analyzer indicates lean mix below 2000rpm, heat exchanger, battery, DME pickups, air flow meter, altitude sensor

Is the cold start valve leaking fuel (not closing when the engine gets warm)?

[Daryfury]

It's the crank sensor.