Idle / Cold Start

[JK McDonald]

Hey Hkp7 - The Aux Air Valve is electrically in parallel with the Fuel Pump. Both the AAV and Fuel Pump receive their power at the same time from the Fuel Pump Relay (XVII). The Cold Start Fuel Injector only receives +12v when the starter is being applied. The Cold Start Fuel Injector ground is through the Cold Start Temperature Switch on the very front of the Thermostat housing. If during the start mode and the engine water temp is warm - the Cold Start Fuel Injector receives +12v power but no ground is available.

On top of the Thermostat housing (toward front) the Fuel Injection Computer Engine Temp Sensor (Temp II) is used to determine the engine water temp for the Fuel Injection pulse width calculations – and – (toward rear) a dual element temp sensor is located for the Over Temp Warning Light (small prong) / Temperature Gauge (larger prong).

Hope this help,
Michael

[Hkp7]

I was curious, not counting the cold start injector, isnt there two stages to the fuel pump running, such as cranking and operating? I thought there was a stage that only ran during cranking and if that is so, maybe that stage is sticking. Shot in the dark. The car runs really rich when the problem is there (stinks). Worse comes to worse, I am swapping jetronic and if its not the problem, I will just have a spare.

[JK McDonald]

Your are right about the fuel pump having two modes of operation - if you count one mode as being the initial no engine RPM moment that you turn the key from "OFF" to "ON" and before you select "START". The Bosch fuel injection computers all have a brief 3 - 4 second pressurization cycle to compensate for any internal leak down issues while your car is parked.

When a Porsche is not running the system fuel pressure should be statically held between all of the shut off fuel injectors and a screw-in check valve on the output side of the fuel pump. Of course once the engine starts and the key returns to "RUN" (RPM sensed) the fuel pump now has a steady power source.

When my car has not been driven for over a week or so - I usually turn the ignition key from "OFF" to "ON" several times to re-pressurize the fuel rails before trying to start the engine. I know that my fuel pump check valve leaks down a bit. I just haven't changed it out yet.

If the Cold Start Injector is not leaking, make sure your O2 sensor is good. The O2 sensor should be generating a continuous (1 second duration) square wave output that swings from approximately 0 to 1 volt. Each side of the square wave tells the Fuel Injection Computer that the exhaust is lean (0 volts) or rich (1 Volt) then tweaks (slightly increases and decrease) the pulse width of the primary 8 injectors. This ongoing automated air/fuel mixture adjustment always swings back and forth while trying to maintain the ideal 14:1 ratio.

Michael

[Hkp7]

It is quite possible I found my problem. The temp sensor that was sent to me was part number 928 606 201 01 listed for 78 to 88 and the temp sensor in the book is part number 928 606 125 01 listed for 80 to 84. When I checked the temp sensor resistance at operating temperature it read 50 ohms. The book says it should be 250 to 390 ohms.

[Hkp7]

update, 928 606 201 01 is the sensor for the guage, my mistake. But my temp sensor is still reading incorrectly. Mrmerlin, you stated in the past that the sensor should be getting 6 volts, mine gets 12v and the connector is grey like the book says, aav is black 12v and the cold start inj is blue, thermo time is brown like the book says. What voltage do the injectors run at? The connector is the same as the injectors, maybe i have an injector running at 6 volts?

[Hkp7]

Just wondering if someone with an 80 to 84 could disconnect their coolant temp sensor, turn the key on and read the voltage between the two connections on the plug and tell me what they get? Book says nothing about what the voltage should be. Thanks, Bill.

[Hkp7]

When I turn the key to the on position, i dont hear the furl pump kick on, isnt it supposed to even as early as 84. Is it starting with no fuel pressure or low fuel pressure and sending the computer into lymph mode when cold?

[Hkp7]

Found out today, my air flow meter is not for an 84.

[Mrmerlin]

whats the part number that you need for the airflow meter??
And please add your car info to your signature click on user CP at the top and then click on edit signature

[Hkp7]

mine is a 0 280 213 015 and i need 0 280 203 015

[Hkp7]

Got a wiring diagram, checked continuity between time temp switch plug and the aav ground and found open. Removed part of harness and found ground connection was made at the A/C idle control valve on the crossbar. There is no ground on that valve, it is held in place by rubber. Moved the ground to a threaded hole in the thermostat housing, started car, started off at 1100 rpm then after about 20 seconds, the aav closed and brought the idle down to normal. What a workout, I have a lot of experiance in the mechanical field but a couple hours here and there at night makes it difficult when working a full time job. I have had a lot of suggestions to check the aav and bought two others to try to swap out. I guess when I had voltage to the valve, I was right, but I had no ground. This car would idle as high as 1500 rpm and surge. Glad thats over. Well now its on to the next project. Thanks for everyones help. Bill.

[MPDano]

Originally Posted by Hkp7

Got a wiring diagram, checked continuity between time temp switch plug and the aav ground and found open. Removed part of harness and found ground connection was made at the A/C idle control valve on the crossbar. There is no ground on that valve, it is held in place by rubber. Moved the ground to a threaded hole in the thermostat housing, started car, started off at 1100 rpm then after about 20 seconds, the aav closed and brought the idle down to normal. What a workout, I have a lot of experiance in the mechanical field but a couple hours here and there at night makes it difficult when working a full time job. I have had a lot of suggestions to check the aav and bought two others to try to swap out. I guess when I had voltage to the valve, I was right, but I had no ground. This car would idle as high as 1500 rpm and surge. Glad thats over. Well now its on to the next project. Thanks for everyones help. Bill.

Welcome to the Club. I also had an issue with my AAV in the past.

[Maleficio]

I'm really enjoying this forum. I'm an electrician on F/A-18C fighter jets, and our conversations about fixing gripes on the jets sound exactly like the conversations I've read in this forum.

Very cool.