1981 911 sc porsche fuel pump

[steveclark]

Hey guys I thanks for all the help in the past but I'm still having problems with my car. When I turn my key on the fuel pump runs the whole time and never cuts off is that how its suppose to work. Also car starts for about 2 seconds and dies and want start again. I changed spark and wire had fuel pump checked I fill like its a fuel problem but can't put my finger on it, I live in Lake Charles Louisiana and nobody works on Porsche around here

[psalt]

Steve,

No, that is not how it should be. The fuel pump circuit is complicated, you need to study the diagram, even then it is confusing. The FP should not be running with the key ON and the engine not running. The FP gets power when cranking in the Start position, then after the engine fires, a switch on the air flow meter keeps it running. This is a safety device so if you crash the car and the engine stops, the FP is not pumping fuel over your burning body. Did this suddenly occur or after someone working on the car ? You need to test the circuit and relay to see what is happening. On your car it is further complicated by the rpm limiter and the alarm.

[Discseven]

Steve... there's a 930 FP wiring diagram here. You need to sort out if that is appropriate to your year.

Frederick the Great

Towards the bottom of this page in JB's thread... he posts vid about 930 engine starting but only running for few seconds. Might be some info for your fix in there. In general, that entire thread covers a good deal of 930 ground where engine is concerned.

Frederick the Great


EDIT: Just realized you have WB and not 930. My bad. Perhaps info in links still applies.

[The cap'n]

Sounds like it's starting on the cold start and not the injectors. One major cause of this would be a large vacuum leak. You might also have a sensor plate issue. If the pump runs all the time, you should have good fuel flow, maybe even fuel pressure. Raise the sensor plate for a bries moment with the pump running and see if you hear a "singing" sound from the injectors. If you do, the pressure is likely to be somewhat OK. Get a mirror in the air box and have somebody crank the engine. If you can't see the sensor plate lift, you probably have a vacuum leak. How are the seams (and little screws) in the bottom of the airbox? Grab the top of the box and see if it feels loose. Report back.

The Cap'n

[T77911S]

good advise.

one easy check is the connector on the top rear of the AFM. (what psalt talked about). if that is removed the FP will run all the time.
believe it or not but a bad FP relay will also make it run all the time. the relay energizes to turn the FP OFF.
another thing that is fairly easy is to remove the fuel inlet side to the warm up regulator(WUR) and check to see if the screen is clogged.
also check fuse 18. not likely since it will usually not even run but its easy.


GREAT looking car. nice wheels.

dont let someone work on it that does not know CIS. at the least you are wasting your money. if anything, try a mercedes shop or a volvo shop. you may find an old guy that knows CIS, but ask.


you can fix it with help here but you will need CIS gauges, about $100.

what the capn said. sounds like it is starting on the CSV only. could be you have an air leak, bad cold control pressures mixture could be wrong.