944NA 1983 vacuum line diagram and altitude switch
06-02-2011, 06:48 AM
#1
5th Gear
Thread Starter
944NA 1983 vacuum line diagram and altitude switch
Dear all,
I'm working on a bad (cold) starter, and carrying out the required checks.
When measuring CO% during (cold 20°C) starting I see that there is very little enrichment at cold running. The A/F-ratio during cranking not measured yet, but expected to bee not rich enough, causing the bad starting. The engine runs fine when warm, with correct CO% etc. For this reason fuel pressure is not measured yet.
First suspect: coolant sensor, but it reads approx. 2.5kOhm at the ECU connector at approx. 20°C; no mass connection, no wire problem. Does anybody has a specification (resistance vs. temp) of this sensor?
All other ECU inputs outputs seem to be OK as well (after I corrected the throttle stop, so now the idle contact of the TPS works as well, unfortunately no influence on cold start)
CO% was generally a bit low, but re-adjustment did not have any influence on the bad starting next morning.
I have two issues that are not clear for me: 1) "vacuum" hose routing and 2) altitude switch.
1) "vacuum" hose routing (944NA, 1983, without canister purge system)
What puzzles me is the way the extra air for the AC is controlled. One side of the extra air solenoid valve is connected to the manifold, but the other side is not connected to anything! So when the AC is operated, extra air is dragged into the engine NOT PASSING THE MAF!! I doubt that the Porsche engineers wanted this to happen, so there might be an error in the hose routing. Unfortunately I couldn't find any diagrams of the "pre 1985/2" routing.
Does anybody have a diagram (OEM or home made), or does anybody can tell me how the AC air solenoid should be hooked up correctly?
2) altidude switch
From the wiring diagram I read that an altitude switch is connected to the ECU. The reason for this puzzles me as well, because the MAF used in this application actually is a mass air flow sensor, so a low density operation (mountains) would not lead to incorrect A/F-ratio (in theory). I also do not see any reason for changes in ignition mapping at altitude, but I was not involved in the system design, so I don't know the reason behind it.
Main question: should the sensor be "closed" (zero Ohm) at sea level?? (and open at 3000 ft??) This because the wiring diagram suggests that the contacts would be "normally open" and at the car I'm working on the contacts are closed (I live at, or even slightly under sea level;-)
Second question: where is this sensor/switch located?? I can't find it!!
Thanks for all valuable tips!!
Toni
PS all suggestions for bad cold starting are very welcome, apart from my two main questions.
PPS I have access to (and read) the 944 WSM.
I'm working on a bad (cold) starter, and carrying out the required checks.
When measuring CO% during (cold 20°C) starting I see that there is very little enrichment at cold running. The A/F-ratio during cranking not measured yet, but expected to bee not rich enough, causing the bad starting. The engine runs fine when warm, with correct CO% etc. For this reason fuel pressure is not measured yet.
First suspect: coolant sensor, but it reads approx. 2.5kOhm at the ECU connector at approx. 20°C; no mass connection, no wire problem. Does anybody has a specification (resistance vs. temp) of this sensor?
All other ECU inputs outputs seem to be OK as well (after I corrected the throttle stop, so now the idle contact of the TPS works as well, unfortunately no influence on cold start)
CO% was generally a bit low, but re-adjustment did not have any influence on the bad starting next morning.
I have two issues that are not clear for me: 1) "vacuum" hose routing and 2) altitude switch.
1) "vacuum" hose routing (944NA, 1983, without canister purge system)
What puzzles me is the way the extra air for the AC is controlled. One side of the extra air solenoid valve is connected to the manifold, but the other side is not connected to anything! So when the AC is operated, extra air is dragged into the engine NOT PASSING THE MAF!! I doubt that the Porsche engineers wanted this to happen, so there might be an error in the hose routing. Unfortunately I couldn't find any diagrams of the "pre 1985/2" routing.
Does anybody have a diagram (OEM or home made), or does anybody can tell me how the AC air solenoid should be hooked up correctly?
2) altidude switch
From the wiring diagram I read that an altitude switch is connected to the ECU. The reason for this puzzles me as well, because the MAF used in this application actually is a mass air flow sensor, so a low density operation (mountains) would not lead to incorrect A/F-ratio (in theory). I also do not see any reason for changes in ignition mapping at altitude, but I was not involved in the system design, so I don't know the reason behind it.
Main question: should the sensor be "closed" (zero Ohm) at sea level?? (and open at 3000 ft??) This because the wiring diagram suggests that the contacts would be "normally open" and at the car I'm working on the contacts are closed (I live at, or even slightly under sea level;-)
Second question: where is this sensor/switch located?? I can't find it!!
Thanks for all valuable tips!!
Toni
PS all suggestions for bad cold starting are very welcome, apart from my two main questions.
PPS I have access to (and read) the 944 WSM.
