CIS Rebuild-Won't stay running

[Topgun63]

After a complete fuel system overhaul, my 1977 2.7S stock motor, previously running, will only start after I have raised arm on FD for a couple seconds then it dies instantly. All pressures are within spec as verified by appropriate pressure gauge, FD, WUR and injectors recently serviced by CIS Tech Larry Fletcher. Entire fuel system is NEW, form the clean tank to the new pump to new lines by Len Cummings, new filter and accumulator also. WUR takes 2 minutes to raise pressure from 22 lbs to 42 lbs. I haven't done any adjustments to the mixture. System pressure is 72 lbs and cols pressure is 22 lbs. Any suggestions??

[Walt Fricke]

One thing I think I have learned is that for cold start issues, who cares if the WUR raises pressure like it should as the engine (in theory) warms up. You want a richer mixture to help start. Seems like you have it.

Is this the sequence: raising the arm, engine starting, and instant dying when you drop the arm?

Is the sensor plate where it should be?

What about cranking the adjuster screw, say a whole turn clockwise (way more than the usual nudge turn at less than 1/16 when setting the emissions)?

If you disconnect the fuel pump interlock on the back of the FD, do you get the same instant stopping of the engine? (disconnecting is much easier than fussing around with shorting things at the fuel pump relay up front).

[Topgun63]

Sensor plate is in correct position. I am raising the arm for a few seconds,releasing it, then cranking with starter. I'm not sure I follow you on the fuel pump interlock, I don't have any wiring to the FD. I jumped the fuel pump relay to check pressures, then reinstalled the relay.

[47silver]

sounds like you have spark and fuel so it should be an adjustment to get you going.
i know of 2 times that can be adjusted.
the idle mixture screw (3mm socket headed bolt in the middle of the fuel distributor and the idle adjustment screw (a large slotted screw on the left side of the throttle plate.
i used this thread to get mine running after i had it apart.

Base setting of mixture for CIS 1980SC?

[Walt Fricke]

Top

There are two of those gray Bosch wire connectors on the front (hard to reach) side of the fuel delivery stuff. One (the leftmost) plugs into the cold start valve, while the other plugs into the FD assembly (actually, into the silvery metal casting under the steel FD).

Since you had everything apart, you pulled these plugs, and then reinstalled them. Reversing them means the CSV won't work. Don't know if the CSV could confuse the other one if it was plugged in there. However, for diagnostic purposes, it is much easier to pull the (properly connected) interlock plug. Then the fuel pump will run every time the key is in the run position, just like it will with what you did up front with the relay.

It would help if you purchased or fabricated a remote starter switch. You connect it to the starter so you can push a button and direct current from the big cable from the battery to the small tab connection which actuates the starter relay. That way you can crank the engine while you have, for instance, your finger on the lever to see if having that up a little bit will help keep things running. Sort of like pumping the gas pedal on a carbureted car.

What you are doing with the lever pumps you describe is what the cold start valve is supposed to do - add a little more fuel to help with starting. But why doesn't it keep going once that little bit is used up?

One thought might be a giant air leak. Not just a little one which messes with idle or CO or the like. A big one, like not having the rubber boot which connects the two sides of the system together attached on one side. Or having a crack in it which admits a lot of air. Or not having one of the fittings which go into it (if that's how yours works) well seated, or one of the hoses connected to it displaced.

In short, while the cylinders will create a vacuum while cranking, and thus respond to the fuel you squirted directly in to the intake manifolds, if that vacuum gets lost on its way over to the sensor plate, no air will flow through the plate, the metering cylinder inside the FD won't rise, and you won't get any fuel injection as a result.

Have you tried ether starter fluid? While cranking, spray some into the area just below the lever - where air gets sucked (well, pushed by the atmosphere) up into the system. Does that cause the engine to try to run? Will more keep it running? If so, maybe no big air leak.

Otherwise, you can use it to check for air leaks - spray some around the rubber boot to see if the engine reacts. Spray some around each of the rubber boots which connect the air box to the manifolds. This testing works best, though, on an engine which runs, albeit poorly and you want to sort that out.

You'll get there.

[Topgun63]

Walt,
I did take the entire CIS system off while I had the engine out, replace the boots and reinstall. I will check the harness, I just don't remember at this point, but I'm fairly certain I reconnected them correctly. Thanks.

[T77911S]

if you are raising the sensor plate, then it starts but dies, you are basically performing the function of the CSV. if it starts but then dies, the CSV has nothing to do with keeping it running and i would not worry about that now. it sounds like you have a mixture problem

just remove the plug from the top of the AFM for now. with the key on, th eFP should run.

the other thing i would check is the vacuum line from the WUR to the throttle body, actually to the thermo time valve (TTV) (which you dont really need) then to the top of the decel valve(DV) then to the throttle body. it would be great if you have a hand pump to pull a vacuum on the WUR to see if the pressure goes up to around 3.6bar. if not, you can skip this for now. it can be checked once the engine is runnig.
2.8bar is correct if the engine is not running.

first i would turn the idle screw, the large one onthe TB, CCW a few turns.
i would have someone start the car while you move the sensor plate up or down. this will correct an incorrect mixture setting. if you push it up to keeo the engine running, the mixture needs to be richer, pulling down means leaner.

[eastbay]

This should help you out if you have not initially set the mixture. Posted by others before, very useful information.

[Topgun63]

After turning the mixture adjustment screw a couple turns clock-wise, the engine will fire with starter, but dies instantly. I went too far and got gas from exhaust, so I backed screw slowly counter-clock wise, but still won't stay running.

[Paulporsche]

Have you checked for vacuum leaks?

[T77911S]

pull the connector off the back of the AFM and turn the key to on, make sure the fuel pump is running.
i hate to send you off on a tengent, but put a timing light on it and check the timing while cranking. set it for TDC.
check the firing order. make sure the plug wires are correct.

leave the connector off of the WUR until you get ti started. that will keep it from heating up while working on it.

[kodioneill]

Did the engine have a EGR valve on the right side of the engine? Did you remove it and forget to plug the hole in the bottom of the air box? Did you bleed the injector lines? It does sound like an air leak issue though.

[boyt911sc]

Originally Posted by Paulporsche

Have you checked for vacuum leaks?

Do a pressure test of the system. Not being able to locate an air/vacuum leak does not mean you don't have any. Test and confirm. I bet you have one. And a big one to affect your combustion during start up. Keep us posted.

Tony

[Flat6pac]

Is the fuel distributor center pin free to move inside the distributor?
Bruce

[Paulporsche]

911sc engine wont stay on.... Have a look at the "911SC engine won't stay on" thread currently on this BB.

[Topgun63]

Update to this thread......Yes, I found the massive vacuum leak that was proposed. Apparently, when I removed the rubber boot from the throttle body to remove the fuel distributor, the metal line on the backside wasn't tight and slipped out. After re adjusting and clamping tube and resetting the fuel flow as per factory directions, it started instantly. Thanks to all.

[Walt Fricke]

Paul - your resolution of your problem is a good reward for those of us who guessed correctly.

And adds this, if it wasn't there, to the troubleshooting vocabulary of others who pointed to other things we can do (and often have done) wrong when working on our engines.