1980 engine rebuilt and in but won’t run

[worn]

Finally I got the motor in my 1980 rebuilt and attached to the car. Want to run in everything but the motor starts and then dies after about 4-5 seconds. When it first starts it sounds pretty good, running up to 2-3 k RPM. I checked the timing, and it seems pretty close, with the timing light blinking away to indicate that #1 is firing for as long as the motor spins.

The motor:
911 SC with stock fuel injection
Dougherty DC15 cam shafts
Backdated SSI heat exchangers
While I was at it, 98 mm Mahle cylinders with CP pistons
MSD ignition with epoxy potted blaster coil.

The only thing new since it last ran are the pistons and cylinders.

Any suggestions? The thing will run, but only for short bursts. I cannot quite get from the key switch back to the throttle butterfly before it dies.

Left the whole mess lie on the lift and drove my TR6 home. Which was pretty good.
Thanks

[Flat6pac]

Sounds like fuel delivery
Can you lift the air flow sensor while trying to run
You need help on the key...
Bruce

[Walt Fricke]

My thought too - maybe it is starting on the cold start valve's contribution, which is designed to be short lived.

You could disconnect the red/black wire on the thermo time switch to disable the CSV, and see if it even coughs when you try to start.

Time to acquire the system/control pressure checking gauge stuff and see what you have for cold control pressures, and for system pressure.

Another check: disable the fuel pump safety feature by pulling the plug off from behind the right side of the intake. This will allow the fuel pump to run as soon as the ignition is turned to the on position. Pull an injector and stick it into a bottle. Key on, lift the sensor and watch what comes out of the injector. It should flow.

If it does, and the pressures are reasonable, maybe the mixture screw is way out of whack? Hunting around on posts on CIS should lead you to some ways of setting the mixture screw to ballpark before you even try to start, I think I recall.

You can get a remote starter from a FLAPS for peanuts so you can be back there, but why? The pedal will blip the throttle just fine. Granted, adjusting the idle screw is better with a running engine.

I take it that you can't keep it going with the throttle? If you can, then it's not a CSV only fuel issue, but more likely a fuel quantity adjustment issue.

Your larger displacement means more fuel needed, but I'd not think that at idle that would be enough that with the throttle cracked it wouldn't keep running. And your cam you say worked with the stock ps and cs, so it ought not to be an issue.

[ed mayo]

It's possible you just have an air leak from something you missed in reassembly.

[Bigtoe32067]

Carb clean it and see if it stays running. That’ll tell you if it’s fuel delivery pretty simply.
Good luck

[worn]

I have the fuel pressure hardware, so it is off to test pressures today. Thanks so much for all of the help.
I er, ahem seem to have found a plug end. Here is a photo. I cannot identify it, but it might be important. It is on the engine wiring harness.

I know that I have plugged in: WUR, TPS, lambda valve, cold start valve, aux air, air plate switch. There are several red/white and ground wire possibilities on the wiring diagram...
THanks.

[911 SLANT]

This is exactly why I went with carbs on my 1976 911S CIS car. Much more easier to diagnose.

[Lyle O]

That connector looks like the one for the heater blower motor. Hard to tell from the photo, though.

[worn]

Here is another angle. Heater blower wires are accounted for.

Any more thoughts?
Thanks

[gsxrken]

On the turbos there are two plugs like that go on solenoids for distributor related vacuum advance and retard for warm up and pollution control. Not saying that’s what they are on your ca but they look similar

[worn]

Disconnected wires from thermo-time switch. No change in behavior. Motor spins up to about 2k rpm, sounds great for a few seconds - then dies with some backfires through the intake.

"Time to acquire the system/control pressure checking gauge stuff and see what you have for cold control pressures, and for system pressure."

Yeah. Need to hook it up.

Key on, lifted air plate. Fuel pump ran and injector #4 at least sprayed fuel.

"If it does, and the pressures are reasonable, maybe the mixture screw is way out of whack? Hunting around on posts on CIS should lead you to some ways of setting the mixture screw to ballpark before you even try to start, I think I recall."

I will check that out.

"I take it that you can't keep it going with the throttle? If you can, then it's not a CSV only fuel issue, but more likely a fuel quantity adjustment issue."

I can keep it going with the throttle. But iyt isn't very stable, so the rpms zoom up and then down with backfires in intake.

[boyt911sc]

worn,

If I were in your shoes, I would check the following:

• Inspect if the CSV is working.
• Use a smoke generator to locate hard to find leak sources if any.
• What are your fuel pressures (CCP & SP). You can not check the WCP at this point.
• Refrain from tinkering the fuel mixture. Wait until you get the motor to start and idle.

Keep us posted.

Tony

[Walt Fricke]

Red/Wt//brown connector. Maybe for the rear window defogger?

So, sounds like you are getting fuel (which is better than not). And enough that you don't need the CSV to start promptly?

Which suggests maybe mixture is way rich?

Have you pulled a spark plug? It might be wet with fuel?

[Flat6pac]

That plug For thermal switch isn’t used on an 80 and later
Bruce

[Jeff Alton]

Start with the basics. Verify compression and leakdown in each cylinder (should be done on every build). Verify cam timing and ignition timing. Smoke test for vacuum leaks. If all good, then start diagnosing the CIS system

[mikedsilva]

Don't laugh at me, but does the oil cap need to be on? Like on a 3.2 ?
Could the vent hoses be incorrectly connected?

[jcvass]

pull 1 injector out of its fitting in the intake runner and have someone hit the ignition or use a remote switch of the starter . See if you are getting fuel delivery to the injector and or push the plunger up under the fuel head and see what kind of spray pattern you have . Sounds like a fuel problem . Verify that the pump is running as well

[al lkosmal]

The connectors for the cold start valve and the fuel pump shut-off (air-flow switch) are the same color.....if the mating connectors are connected to the incorrect place...I.E. if the cold start connector is connected to the fuel pump shut-off and vice-versa.....it results in a no-start condition like you are describing.

Easy test....swap the cold start connection with the fuel pump connection and try to start/run.



regards,
al

[Walt Fricke]

Good point, Al. Easy to make this mistake after the engine was out. Would the CSV plug attached to the safety switch cause the fuel pump to run as soon as the key is turned to on? Or would it provide a ground for the FP relay?

Looks like it would provide a ground for the CSV, and maybe some current via the FP relay coil as well? But enough? But either a ground or no ground to the FP relay? Which would have no effect either way? Or a dead short?

Won't start turns out not to describe the problem. It does start, even without the CSV being hooked up (unless connecting the safety plug to the CSV causes the CSV to run continually). It just won't stay running without some fair amount of throttle, and then poorly it seems.

A CSV which kept spraying would certainly make things way over rich.

One test of all this would be (perhaps as part of checking connections) to disconnect both and try to start it.

[al lkosmal]

easy thing to check.......