Fingers crossed - started finally
 

My AEM AFR gauge came in today, so I thought I will give it a shot. Had bought a PLX one but the phone app just keep crashing. I re-connected the air-flow sensor switch, installed the AEM wide-band O2 sensor and gave it a shot. As a surprise the car started right away and wasn't smelling as rich as before, still rich though. I could slowly see the O2 climb to around 12 as the car warmed up. I waited for it to warm up and adjusted the mixture to about 14.5 O2. It would fluctuate between 14.5-14.7 at idle, over the next 15 mins even with several engine revs. I was surprised to learn how little (1/16th turn or less) you have to turn the mixture screw to make it rich or lean.

Here is my theory of what was wrong. I don't know if the Cold Start Valve is somehow logically connected to the air-flow sensor switch. With the AFS disconnected, the fuel pump would run without starting the car and along with this so would the Cold start valve (theorizing here). My car has numeric ignition lock and so it takes time between turning the ingition on and actually starting the car. With the weather being cold here most of the time, the CSV sprays because the thermo switch is closed, and floods the engine without cranking. Me blindly playing with the mixture wasn't helping either.

The high temperature is going to be -7C tomorrow so will have to wait for a couple of days for another cold start and hopefully a drive. If it starts first attempt on Wednesday I am buying this theory because the only that changed between yesterday and today is the AFS. Just a theory here, feel free to poo poo all over it.

There shouldn’t be any correlation between the AFS and the CSV.

I am spitballing here so bear with me. Is it possible the wires for the CSV and the AFS are switched?
I’m trying to think if that is even possible. And if so, what would be the effect? I’m just wondering since you found one wire disconnected... did someone play around with the wiring?

The CSV is controlled by the thermotime switch located on the left cam housing cover. The logic is basically, if the engine is cold, it fires. If not, it doesn’t.

I’d have to look at the wiring diagrams again but off hand I don’t think there should be any correlation between the two.

By the way... the idea of disconnecting the AFS seems to be a “trick” that some ill-informed mechanics seem to do on these cars. They somehow think it’s a shortcut to fixing CIS problems by having the FP run as soon as the key is turned and before cranking. When I bought my car I took it to a shop because of all the CIS issues I was having. That mechanic disconnected the AFS and told me he had done something else to fix it. That was the first and last time I used that shop. Been wrenching on my car ever since.

CIS Troubleshooting.........
 

Tim,

Some CIS mechanics or troubleshooters found out that disconnecting the AFS plug helps start a stubborn engine. And became a common procedure without really understanding the real culprit/s. What a disconnected AFS plug does is make the FP run before turning the ignition to START position.

Inspect the electrical plugs for the CSV & AFS by checking the wire color for the AFS. The AFS plug has two (2) brown wires (one with a red stripe). Confirming the right plug at the AFS, will also do the same for the CSV.

Tony

Providing starter is being cranked.

From the wiring diagram looks like the CSV is only energized when the starter is engaged.
http://forums.pelicanparts.com/porsche-911-technical-forum/205716-911sc-wiring-diagrams.html

I am not sure what fixed the cold start. I am not even sure if it is fixed because I started it only one. Maybe adjusting the cold control pressure along with the mixture setting did it. Will try to start again in a couple of days, when I can open the garage comfortably.

Tony, I will also check the wires going to the air-flow switch. But my guess it is hooked correctly and cross connected with the cold start valve.

Test and confirm........
 

Blue,

Test and confirm. You are doing too many guess-work troubleshooting. Stop guessing and inspect the CSV, AFS, and TTS. For starter, test terminal #85 (FP relay socket) for ground. Use a test light or continuity tester to confirm that the switch is working when you lift up the air sensor plate.

The electrical plugs for the CSV and AFS could be installed incorrectly (interchanged). Keep us posted. Thanks.

Tony

Yep. Just a point of clarity. Nothing more.

FWIW I know that on the mid 70's D-Jet based Jag XJ's the cold start injectors would ramp down the spray duration based on the valve's internal heat build up - just from cranking a stone cold engine. First start attempt, say seven seconds. Second attempt, five seconds. Etc

I don't think ours do that. They just spray when the starter is engaged until the cut off temp is reached from a warm engine.

Recently my friend called me to talk about a problem with he was having with his '94 Mustang. He rebuilt the engine and it was dumping tons of fuel into the cylinders. He was racking his brain and needed to talk it through with someone. We checked the fuel pressure regulator. We tried to see if something was causing the computer to think it was lean and over-compensating on fuel delivery. After 2 days of fighting, he finally tried something remarkably simple. Turned out he had bought new fuel injectors for the rebuilt motor and every one of them was bad. He put the originals back in and it fired right up and ran like a champ.

The lesson here is sometimes it's best to not overthink a problem. It's easy to overlook the obvious. Verify the basics. You verified the injectors. Good. Now double check that the AFS and CSV aren't incorrectly wired.

End of story........
 

Blue,

What is the conclusion at the end. Did you finally able to find the culprit/s and solved the problem/s? Keep us posted. Thanks.

Tony

Tony
From what I can tell the car running too rich was the problem. Adjusting the CO seems to have fixed the problem. Started without any problems from dead cold 3 to 5 times after the adjustment. But do not know have a long term test. Essentially after all this work I had to store the car for winter. Hoping it will start right back up.

My cold start issue was relatively easy. Check valve in the neck of the fuel pump failed.

Good luck.

Mine was pretty easy too. I mistakenly disconnected my cold start valve by accident when I installed my engine doh! (happened when I pulled my air hose, on the air boot, out of a pinch with the front of the engine bay (another doh!)). After a few tries to install the connector in situ I finally got it. Thank goodness for my necked inspection camera on wifi.