Can't get engine to run

[bwsimmons@shaw.]

Porsche 911S - 1977 Targa I removed engine and transmission replacing clutch, flywheel, and pressure plate. I also cleaned up the engine and replaced as many seals and gaskets as I could access without doing an engine tear down. I did not remove the distributor. I did remove the chain tensioners but I tied up the timing chains before removal. The engine has been reinstalled and will start but will only run for a few seconds. As soon as the key is released it quits. If I press the accelerator it runs at a higher rpm but still quits after a few seconds. If I continue to try and start it -- it will backfire after three or four attempts. I think I have the fuel lines connected correctly but something isn't right. Does anyone have any suggestions before I hire a professional to help?

[sww914]

Check to make sure that the spark plug wires are on in the right order. Check it twice without assuming anything.

[Henry Schmidt]

It sounds to me like a giant air leak.
Check to see if any of the hoses were knocked off during the r&r.
You can check if it's an air leak by removing the air filter and lifting the air metering plate with your hand while someone else cranks the engine over. By lifting the plate you simulate manifold vacuum.

[CliffBrown]

If the motor will only run with the key in the start position it sounds like the cold start valve is the only injector working.

Confirm the injectors are operating by turning the key to the run position, confirm the fuel pump is operating, lift the air metering plate and listen for a singing sound coming from the injectors.

[2.7RACER]

BW,
You mentioned the engine will run if you hold the ignition switch in the start position.
I suspect you are not getting 12 volts through the relay pin 87a. That's 87a, not 87.
When you are cranking the motor, the fuel pump gets it's power from the start contacts of the ignition switch to pin 87 through the relay to pin 30 and then to the fuel pump.
This happens as long as the air sensor plate is down, which keeps the air sensor plate switch closed. The air sensor plate switch is wired normally closed, so when you are cranking, BEFORE the air sensor plate lifts, the fuel pump relay is energized, from pin 87, sending power to the pump.
This only happens when the ignition switch is in the full cranking (start) position.
Once the air sensor plate is lifted by the motor vacuum, the air sensor plate switch opens, the fuel pump relay is de-energized, and now the power for the pump must come from pin 87a.
So, 87 when cranking, 87a when running.
87a gets it's power from the fuel pump fuse and the run contacts in the ignition switch.
Simple, put a volt meter across pin 87a and ground. Turn on the ignition briefly. You should see 12 volts at 87a.
You should also hear or feel the fuel pump relay energize.
When the fuel pump relay is energized it BLOCKS the power to the fuel pump. It doesn't run, until the air sensor plate is lifted.
If no voltage at 87a, double check the fuel pump fuse and wiring to it. Same story, 12 volts at the fuse with the ignition on. Might just be a loose or corroded connection at the fuse.
Could of course be a blown fuse.
If no power at the fuel pump fuse, it could be a loose or broken wire at the fuse or a problem at the ignition switch.
If you think the problem is at the ignition switch, you could run a 12 volt jumper to the fuel pump fuse while cranking the motor. Once it starts, remove the jumper, the motor will stop.
CAUTION: don't connect the jumper and wait to start the motor. This is a two person job.
Likely there is no power at 87a in the run position.
Good luck,

[Henry Schmidt]

If the engine ran fine before it was removed it is reasonable to assume that the problem should be installation related.
Loose hose, unplugged or faulty wire connection, you know, the simple things. There is no guarantee, but that's where I would start.

Think horses not zebras"