Rebuilt Engine Won Idle

[Swazzy]

Hi all,

First timer. Restoring a 1979 SC 3.0 CIS top to bottom.
Diligently followed Wayne's book on the engine rebuild. After the initial 20 minute engine break in (still can't believe it started!), I tried to get the engine to hold idle and I can't. With a helper's foot on the gas I was able to get the timing correct at 950, and the mixture seems good. But even after turning the large idle all the way in, it just dies out.
All new vac lines, rebuild WUR, rebuilt Fuel Distrib, new injectors etc, new MSD ignition and coil.
On rebuild I deleted cruise control and EGR Valve, and added SSI's, everything else basically stock.
It's a home garage with limited (as in none) testing equipment, but I was hoping you guys can give me some pointers on common causes I can check out.
Thank you!
Marc

1979 911SC CIS Petrol Blue Metallic

[Flat6pac]

Wrong coil for the Bosch CD. Requires a Bosch 001
Too many rehabbed parts.
Vacuum leak on oil tank hoses?
Are you vacuumed the distributor at idle, requires high RPM advance
Bruce

[proporsche]

As Bruce said..check for a vacuum leak ..did you closed the distributor vac.adv. hose?
also do you have pop off valve behind the air filter ?
The times has to be set on a warm engine otherwise it will be off.
Also your sensor plate is it positioned correctly?That has to be checked on a cold engine or no fuel press, in the system at all.
check and report back...

Ivan
sensor plate

[Swazzy]

Thanks guys, I plugged the advance vac on the distributer. I thought that no vac was correct at idle. Is that wrong? How do you get high advance then to the distrib?
It's not a Bosch CD. It's an MSD and that is the correct coil pretty sure. It's a MSD Blaster II
By "pop off valve" do you mean the backfire relief valve on the spring hinge right behind the air filter? ? Yes I have that.
I'll check the sensor plate position when cold and report back. Ivan, what is that measurement supposed to be on the plate by the arrow?
Thank you!

[proporsche]

the vacc.hose plugs behind the throttle body search for a diagram..
The sensor adjustment is what you see on the picture..left side aligned to the edge...if it off that would also change your fuel mix if you have to correct it...
The valve yes, have you looked if by any chance got stuck open?

Ivan

[Swazzy]

OK thanks for clarification on the plate. Will check.
Yes, the vac hose from the throttle body to the advance unit on the distrib is connected correctly. But i had it disconnected to do the timing as I thought that was the right thing to do at idle. Will reconnect.
Sorry not sure what valve you are talking about may be stuck open?

[proporsche]

look here one of the vac.hose on the left of the thr.body--never mind the arrow



here black and white diagram
https://jimsbasementworkshop.com/CIS/pages/air_vaclines.html

[manbridge 74]

You turned the idle screw all the way in? That LOWERS idle because it cuts off air. Screw it out to increase idle speed.

[proporsche]

Originally Posted by manbridge 74

You turned the idle screw all the way in? That LOWERS idle because it cuts off air. Screw it out to increase idle speed.

i was hoping he already did;-))))))))))

Ivan

[Swazzy]

Ivan, yes I have it connected correctly however on my throttle body there is also a port on the other side that does the same thing as it's above the valve. However to make sure I will switch to your suggested port.
Jeff - Yes I was totally doing that back asswards and will try the other way!
One more question - when I removed the EGR valve, I totally removed it and plugged the hole at the very bottom of the air box where the EGR pipe entered the air box. Does that effect vacuum source? I thought that because it is at the lower end of the air box it does not. Can you clairify?

[Swazzy]

"i was hoping he already did;-))))))))))"

Ivan you are giving me too much credit !

[Funracer]

Off topic but that PBM is an awesome color. Have faith you will get her going soon.

[Quinlan]

Doyle check that the distributor isn’t one tooth off. Ask me how I know...

[targa80]

Did you perform a vacuum leak test using a cheap homemade smoke machine? Any false air getting into the vacuum side of the fuel injection system will cause idle and running issues.







Did you test the fuel injection system using a fuel pressure gauge to verify fuel pressure and control fuel pressure? A CIS fuel pressure gauge set will cost around $100 and is essential if you do all your own work. Do search for a thread on CIS fuel injection for dummies. It will provide all the info you will need to help test and isolate your issue.

[Paulporsche]

I have an MSD/Blaster 2 setup for my 80SC engine. The coil is red and has to face upright. Looks like yours is black and facing with the terminals facing down. Are you sure you have the right part?

[Swazzy]

Thanks Paul and Pat,
It's an MSD High Vibration Coil PN 8222 and according to instructions should work with the MSD 6AL-2 Ignition box I have, and can mounted "in any position due to its epoxy potting compound." according to instructions.
I found the link to the thread CIS for Dummies and I'll start testing...

[proporsche]

Marc..did you by now unscrew the idle adjustment screw or not yet??

Ivan

[Swazzy]

Yes, I did back it off the adjustment screw a bit and it idled better for about a minute before it quit. I ran out of time to play around and will get back at it over the weekend for sure.

[Paulporsche]

Have you checked your fuel and control pressures yet?

As Pat mentioned, you need a gauge to check your cold and warm control pressures, your fuel pressure and your residual fuel pressure.

You also want to make sure all ignition components are up to spec.

Let us know the number of the WUR you have and the pressures you get at the ambient temperature you tested. We can then compare them with a chart for a 79.

Until you get a test gauge, you can try loosening the big air bypass screw and see what happens. Loosening it should raise your revs.

I don't know where you are located but here in Toronto around this time of year, your cold start should raise the revs to about 2500 or so at first and then gradually lower them to about 900 after about 4 minutes or so. This will give you an indication for now, without gauges, if your WUR is operating about as it should.

You should also verify your fuel mixture is within range, as this also affects idle speed.

[Paulporsche]

Chart for several WURs. Verify your number with this.