Hot Start Problem

[356-930]

This '79 930 engine refuses to start when the least bit warm/hot without falsely triggering the 7th injector. When it does catch and "light" without the false trigger, it shuts down as though it ran out of gas. Any idea what my problem may be?
TIA for your help.

[Porschephd]

Do you have an accumulator in place and a check valve? the head will evaporate the fuel out in a matter of minutes (About 5-10) and will partially vapor lock making it hard to start. BTW wonderful looking build!

[356-930]

Originally Posted by Porschephd

Do you have an accumulator in place and a check valve? the head will evaporate the fuel out in a matter of minutes (About 5-10) and will partially vapor lock making it hard to start. BTW wonderful looking build!

Dr.
Thanks for your kind comment and help.
Accumulator (plumbed right thanks to your advice) is in the the fuel system, (shows in photo below MSD). Front fuel pump (under fuel tank) has a check valve and is working. Don't know about the pump near the engine.
If engine is warm/hot and shut off for only 15/30 seconds, it won't start. Wait 15 minutes, starts. It's also a start made by opening throttle body just a bit. No throttle or too much throttle and it won't 'catch.'
I suspected vapor lock but engine compartment is force fed with ambient air when ignition is on. No mater how hot the engine gets, fuel head, intake plenum and intake manifold are cold to the touch. They do warm up on soak but the start problem occurs long before anything on top of the engine takes on heat.
Perhaps something in the WUR? Pressures are in spec. Pressure holds within spec for 20-minutes after power shut off. Unfortunately, I know nothing about how the WUR operates.
Chris

[Porschephd]

Well if pressure holds then we need to look else where, same with the WUR and pressures. If you have to feed it throttle that means the plate needs movement and is to lean to start and the aid in moving the plate a bit helps. Unless you tell me it bellows fuel when it does start then we are to rich, but flooring it during start up would also work and you make note it doesn't.

Things to check, CO when hot. Also check the height of the fuel plate. If the adjustment is off then the plate maybe be to high and not allowing enough movement.

Why will it start cold, well the CSI is doing its job. When hot it shuts down and lets the plate inject as it sees demand form the motor darning cranking.

[356-930]

Originally Posted by Porschephd

Well if pressure holds then we need to look else where, same with the WUR and pressures. If you have to feed it throttle that means the plate needs movement and is to lean to start and the aid in moving the plate a bit helps. Unless you tell me it bellows fuel when it does start then we are to rich, but flooring it during start up would also work and you make note it doesn't.

Things to check, CO when hot. Also check the height of the fuel plate. If the adjustment is off then the plate maybe be to high and not allowing enough movement.

Why will it start cold, well the CSI is doing its job. When hot it shuts down and lets the plate inject as it sees demand form the motor darning cranking.

Dr.
If I feed it a little throttle, it will start - but, if it does not start on the first crank, forget starting it within the next 15-minutes. No throttle, half throttle, full throttle does nothing - it's as though no fuel, period. I also sense on start the engine is lean for it does not come alive the same as when it's cold. Kinda get the feeling it's not going to keep running, then it does.
I believe you may have put your finger on the problem. I disassembled the air box to polish it, re-assembled as I believed it was. Did not know fuel plate was sensitive to height or for that matter adjustable. It does seem to sit slightly above level in its cavity. The cavity is closed but more than 1/2 the thickness of the plate is above what I perceive as 'neutral.' Is the adjustment straight forward? Easily accessible in an engine compartment without room to work in?
Many thanks for your help.
Chris