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Join Date: Aug 1998
Location: 1000 oaks, CA, USA
Posts: 9
I think it's the pressure sensor?

Hey there I need help. The other day my 914 started losing a lot of power on the way home from school. I thought a plug wire had come loose so I checked them, and no prob. Then I pulled the plugs, and noticed they were totally black, which makes me think the engine was running too rich. I cleaned them up and tried driving around, total loss of power off the line. today I started it and noticed, that when I gun the motor, black smoke is coming out the exhaust. and still no power off the line. any ideas? If I have to replace the pressure sensor, should I replace the head temp sensor at the same time?

Old 09-17-1998, 12:20 PM
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Join Date: Dec 1969
Location: Dade County, FL.
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Before replacing anything use the Kjnell article to test the components and narrow down the problem. The WORST thing to do is to guess and randomly replace parts. Another part of the FI that can cause all the cylinders to run rich is if the cold start valve (5th injector) is stuck open or leaking. Also make sure the head temp sensor is pluged in and that the vaccuum line from the pressure sensor to the manifold is in perfect shape. When you say black was it sooty black on the metal and light brown on the insulator, or was the whole plug black, wet, and smell of gas. By the way you are right about it possibly being the pressure sensor, I'm just saying there are other (cheaper) possibilities. Also what year/motor is it?
Old 09-17-1998, 01:23 PM
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Its a 73 2.0, but now the motor wont even start, I've got plenty of fuel pressure, (29-31psi according to the gauge), and have spark on all cylinders, checked the fuel injection points, fuel pump, and the coil, and it still doesnt start. Help! I have to get to class tommorow! lol



Old 09-17-1998, 06:09 PM
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By the way, the plugs were really sooty, and my cold start valve is disconected from the fuel line. I used a patch plug on the fuel rail from a 1.7 I live near Los Angeles, and it seldom gets cold enough to require the cold start valve, it was leaking anyway. another one on the list of things to fix when I have enough money, going to college and owning a 914 is hard!

Old 09-17-1998, 06:15 PM
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Sounds bad, see if you can find someone to swap pressure sensors with. Anyone will do, even the 1.7L. Don't forget to check the head temp connection. Also if you have access to a multimeter check the resistence of both sensors.

Also I just remembered, a couple of years ago when I discovered the FI tuning article we tried on a friends 914. At the time we really didn't know what was going on (unlike now of course) and we turned the adjustment screw inside the pressure sensor only about a 1/4 turn but it screwed everything up. I seem to remember the same symptoms as you. The only way we could finnaly start the car was to floor it and turn the starter. Again I would test the sensors, try sucking on the vac line to the sensor (use a vac pump with a gauge if you can) and see if it holds vaccuum. Then try the electrical tests, I'm sorry I don't have any of me notes with me but they are on this site or the Reagade 914 Porche club. BTW is it just me, or the Univ. of Miami, but it seems that the other Porsche owners don't wave back when I cruise campus.
Old 09-18-1998, 09:54 AM
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I tested the resistance of the two terminals on the pressure sensor and here's what happened, between terminals 7 and 15 I got 95 ohms. Between 8 and 15 I got zero resistance, I guess that means its bad, huh? Hopefully the head temp sensor isnt quite as bad

Old 09-20-1998, 09:24 AM
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O.K. here us the site you need to look at www.914fan.net/djet.html From what you tell me it dose sound like the sensor is shot. Between #7 and #15 it should be about 90 ohms. Between #8 and #15 should be about 350 ohms. So check it again, at the sensor, to make sure. Don't try a rebuilt unit, from what I've been told they don't work (at least the ones from Auto Atlanta don't) for long if at all. Ask Pelican about a new or used one, you were right to begin with, it seems the press sensor is bad. Read the rest of the article at Tim's web page it will tell you how to match the press sensor to the head temp sensor.
Old 09-20-1998, 01:45 PM
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