83'SC starts but won't run for more than 5-8 seconds

[fast911ray]

Ok boys and girls, here's the scenario. I removed the motor about a year ago to replace a leaking head gasket #5 cylinder. Reassembly went with no glitches, and after rotating crank for valve timing verification, the cover was installed. Incidentally, prior to removal the engine fired without hesitation every time...which is no longer the case.

Motor now fires and runs for about 5-8 seconds, then dies. My first thought was fuel pump relay which I tried to prove by doing the old #30 to 87a bypass. No change..fires then dies, however if I hold the fuel distributor plate down slightly (with a wee bit of throttle) it continues to run...albeit a bit ragged, but runs. So I'm now at wits end, and humbly turn to the forum with high hopes that some of our resident 911SC/K Jetronic genius's have some suggestions..

RB

[Carlito]

Originally Posted by fast911ray

Ok boys and girls, here's the scenario. I removed the motor about a year ago to replace a leaking head gasket #5 cylinder. Reassembly went with no glitches, and after rotating crank for valve timing verification, the cover was installed. Incidentally, prior to removal the engine fired without hesitation every time...which is no longer the case.

Motor now fires and runs for about 5-8 seconds, then dies. My first thought was fuel pump relay which I tried to prove by doing the old #30 to 87a bypass. No change..fires then dies, however if I hold the fuel distributor plate down slightly (with a wee bit of throttle) it continues to run...albeit a bit ragged, but runs. So I'm now at wits end, and humbly turn to the forum with high hopes that some of our resident 911SC/K Jetronic genius's have some suggestions..

RB

I'm having a similar issue with my '78 sc...going to do some fuel pressure testing today. Let me know if you figure it out.

[Bob Kontak]

Originally Posted by fast911ray

however if I hold the fuel distributor plate down slightly (with a wee bit of throttle) it continues to run...albeit a bit ragged, but runs. So I'm now at wits end.....

Plate down provides less fuel. Throttle open allows more air to enter.

How does it run the first 5 seconds? Does it eventually catch?

If you lift the sensor plate with key "on" do the injectors make a squealing noise?

[boyt911sc]

Originally Posted by fast911ray

Ok boys and girls, here's the scenario. I removed the motor about a year ago to replace a leaking head gasket #5 cylinder. Reassembly went with no glitches, and after rotating crank for valve timing verification, the cover was installed. Incidentally, prior to removal the engine fired without hesitation every time...which is no longer the case.

Motor now fires and runs for about 5-8 seconds, then dies. My first thought was fuel pump relay which I tried to prove by doing the old #30 to 87a bypass. No change..fires then dies, however if I hold the fuel distributor plate down slightly (with a wee bit of throttle) it continues to run...albeit a bit ragged, but runs. So I'm now at wits end, and humbly turn to the forum with high hopes that some of our resident 911SC/K Jetronic genius's have some suggestions.

RB

RB,

Since you are familiar with the FP test, check your fuel pressures (system, control, and residual) for starter. You need a fuel pressure gauge to do a meaningful diagnostic test for any fuel injection engine regardless what type of system. Without one, you are working blind and hope to be lucky.

No need to run the engine. Have a fully charged battery and measure the fuel pressures by running the FP only. Record the first 5 mins. only from a stone cold engine. Unplug the WUR electrical connector and run the FP. The first reading is your cold control pressure at start (zero sec.). Plug back the electrical connector to the WUR and start the measurements (1, 2, 3, 4, & 5 mins.). Please post these data you collected.

Double check the vacuum hose clamps and other fasteners for the vacuum system. You could have some unmetered air (?). Keep us posted.

Tony

[T77911S]

pulling down caught my eye too. push it up to add fuel

check for big air leaks.

the other thing is fuse 18. make sure you have the corrct connector going to the frequency valve. mkae sure it is vibrating. check the relay for the FV.