1981 new build - START ISSUES

[drewwidman]

I am having start issues with a new build that I’m hoping I can get resolved with the support of this group.

1981 911sc (ROW) with ROW engine
Everything on engine/car either new or rebuilt on engine (it has not been driven yet since full restore)
MSD ignition
No lamda

Here’s what’s happening: when cranking, I can get the engine to fire, but only for 1 second and then it dies. If I open the air box, I can have a helper lift the air sensor with a 2x4 to activate the fuel pump and keep it running HOWEVER it will soon suck right up on its own and send RPMs to the moon — I then kill the ignition.

What I’ve tried:
-removed the brake booster and used a smoke machine to see if there are any vacuum leaks. Nothing significant.
-adjusted idle position in several positions

What could it be? Cold start valve? Warm-up regulator? Improper vacuum line set-up (this has been a challenge as there are so many different ports on throttle, etc.)

I’m a newbie, but I assumed I need enough fuel to start the engine, then the engine would naturally “suck” the air to move the sensor plate, which then pushes fuel through the fuel distributor and self regulate from there.

Thanks! Drew

[yelcab1]

Typically, there is a cold start injector valve to squirt some gas into the engine to get it started. Then suction will pull down the meter plate and a certain amount of gas will be delivered continuously to each injector.

[Schulisco]

Always the same....tons of money thrown into the engine and then failing on the home straight with the CIS ... I bet the bad CIS caused the overhaul.... Wouldn't be the first and last unnececssary overhaul ...I deeply hope for you that there were a lot other and.more reasonable issues for the overhaul...Anyway.

1. Make sure the sensor Plate height is adjusted correctly
https://forums.pelicanparts.com/porsche-911-technical-forum/1108835-cis-sensor-plate-height.html#post11549412

2. Make sure that WUR control pressure is in spec

3. Make sure that the system pressure is in spec

4. And most important: Make sure that the basic adjustment of CIS is correct:
https://forums.pelicanparts.com/porsche-911-technical-forum/1161760-wur-adjustment-warm-control-pressure-2.html#post12255117

That all the rest of CIS is tight, no vacuum leaks and all CIS parts are working is mandatory.

Thomas

[proporsche]

Try to disconnect the safety plug at the sensor plate...after with the key on the pump should run..
report on progress

Ivan

[wazzz]

Ivan is on a good track here. Check this switch and make sure it opens when sensor plate is pulled. When sensor plate is pulled and ignition is on, if switch is correctly opening, you should hear the pump running.
If not check the fuel pump relay, it may be bad and in this case the fuel pump is powered only while cranking. That would explain why the engine starts then immediately dies.

[timmy2]

Which MSD? And did you cut one of the small blue or red wires?

[pmax]

Is the cruise control , in front of engine compartment on top, pulling the throttle cable ?

[drewwidman]

Appreciate the insight so far!

I can hear the fuel flowing when manually lifting the sensor plate so I’m assuming the fuel relay and sensor plate switch are working correctly. What I can’t quite hear is if the fuel system is flowing when the engine is running (though can assume it is to keep running…)

The MSD is a 6AL and I did cut the wire to run as 6 cylinders.

I have not yet tested the fuel pressures but I will need to do this in the coming weekends.

Also, I bought the car in this “project” state with the trans and engine overhauled (powder coat, zinc plated, etc) — I am not exactly sure what prompted the reno several years ago by the previous owner but no expense was spared. That being said, I have to make a lot of assumptions about whether the fuel distributor was dialed in, idle position correct, sensor plate adjusted, etc.

[drewwidman]

I removed the boot over throttle and it is closed and not impeded. I also don’t have cruise control.

[Schulisco]

Drew,

This is a video showing how the injectors will whine (and spraying fuel) by lifting the sensor plate:
https://youtu.be/4iWZdvOow0g

I also recommend you urgently to get familiar with the function of the CIS and it's components by literature. Without a deep understanding the principles you'll get annoyed pretty quick.

I also recommend urgently to watch the fabulous video series of Curt from KlassikATS about the 2,7 CIS 911, which is pretty identical to the CIS of later models, even those like yours without lambda control.
https://youtube.com/playlist?list=PLkWFofpgz2OgF9FdliKnlzuY0pygqRkMj

My advises before are just the essentials steps of testing and their sequence...CO and idle adjustments make no sense if the steps before haven't been worked. All of the components have their own purpose and making sense.

Thomas