911SC no start

erkj79 · 07-04-2009, 05:13 AM

Basic question on CIS operation. I am not getting flow through my injectors during cold starts. I do, however, get flow when I lift the mixture control unit lever. Does anyone have some insight into this to help me troubleshoot?

erkj79 · 07-04-2009, 05:45 AM

clarification on question; As the mixture control unit lever does not move during cranking, how does fuel get into the cylinders during cranking, only by the cold start valve?

don gilbert · don gilbert's Garage

control press among other things could be to high. During cranking, the sensor plate will lift. There is a swith on the back of sensor houseingthat energizes the f/pump relay. might check that. need more info

erkj79 · 07-04-2009, 06:21 AM

ah, now i understand, so if the sensor plate is out of adjustment, that may explain why i do not have any flow to the injectors when i start?

erkj79 · 07-04-2009, 06:30 AM

ah, now i understand, so if the sensor plate is out of adjustment, that may explain why i do not have any flow to the injectors when i start?

ischmitz · ischmitz's Garage

Did you change something on your car so it doesn't start anymore? Maybe made an adjustment or change a part? If not I would look for likely culprits. Start with the simple things first:

Is the cold start injector getting power during cranking?
Do you get spark?

The sensor plate doens't just go out of adjustment by itself as far as I am concerned.

Ingo

erkj79 · 07-04-2009, 06:59 AM

I did a complete rebuild but i did not change the adjustment of the plate. I ruled out the fuel pump relay by jumpering it and then trying to start the engine which made no difference. It is odd though, because i put the injector line into a beaker while i tried to start the car and there was no flow into the container

ischmitz · ischmitz's Garage

OK, that obviously changes the ball game. Go back to the basics: The engine needs air/fuel and spark at the right time to run. Use starter fluid into the intake and try to start it. If it starts to cough and run you have rudimentary confirmed you have some spark. You still need to confirm that the wires are connected in the right order. If you get nothing that it's back to troubleshooting (see my previous post)

How sure are you that your cam timing is on and not 180 degrees out. Do you have compression? There is a host of possible screw-ups depending on what you did during your rebuilt.

Next, if the engine happens to run fine you might want to concentrate on the fuel and fuel for engine start. Maybe it is something simple like the cold-start valve isn't hooked up properly. As far as I remember on some CIS cars it was simply hooked to the yellow starter wire through a thermo-switch. Check with a voltmeter on the injector if it gets energized.

Ingo

erkj79 · 07-04-2009, 07:50 AM

Ingo
you did good man.....i took out the WUR to clean it up and get the plug in the right position so i can gradually knock it out while reading the control pressure. reinstalled it and then i took your suggestion on the plug wiring and guess what! you were right! the SCs turn ccw. i followed waynes book on engine rebuild and the picture of the wiring shows a cw rotation with a small note, which i missed, stating that the scs and turbos have to revise 4 plug wires.......****tt, bush league mistake! let me get the fuel pressures set, sway the plug wires, and i will let you know how i make out. looks like i owe some cervesas!

Silverbullet52 · 07-08-2009, 07:34 AM

I also have a no start problem when engine is cold. Engine cranks just fine. When I prime the air intake with starting fluid, starts right up and runs fine.

Next day same no start, I don't prime the intake but have a friend jump my battery and it starts right up.

Battery is brand new, alternatator is charging @13.7. 82 911 SC converted from a 2.7 to a 3.0 a year back, so I'm told?. Before my brother passed away he hooked up his laptop to the ECU and started fiddling with God knows what and the problem started.

Any ideas? Or should I call an exorcist

ischmitz · ischmitz's Garage

On a stock 2.7, 3.0 or even 3.2 there isn't really anything you could hook up a laptop to. The only thing that I can see is an aftermarket WUR or maybe an aftermarket frequency valve (not sure if that even exists) or even that your engine runs an engine management system. Maybe snap some pictures and post them. You never know....

The warm-up regulator (WUR) is a device that modifies the control pressure in the Bosch CIS fuel injection system. It is normally a little silver device that has an electrical connection and some lines going to it. The control pressure is what determines the fuel mixture.

There are aftermarket digital WUR devices that try to mimick electronic fuel mixture. They have a serial or USB connection so a laptop can modify their code. This is to adjust the mixture for various RPM and temperatures. Maybe your engine has one of these. Do you remember where exactly he hooked up to? In the engine bay or in the cabin.

Cheers,
Ingo