Hot Start Problem After Injectors Serviced

[Gauche1968]

Interesting discussion, I can say this:

1.) New Bosch FPR as the old one was defective (no residual pressure). Pressure specs with this new FPR seem fine at idle with and without vacuum line attached, but the fuel pressure drops to something approaching 27/26 psi with the throttle open, which seems like the opposite of what it is supposed to do. I do not see any fuel in the vacuum line after shut off, and the injectors do not appear to be leaking down.

2.) The fuel pump is a newish Pierburg pump bought to replace a very noisy Bosch pump. Fuel filter is also new. Can someone explain the difference between a fuel pressure and a fuel delivery problem? Does adequate fuel pressure at the rail NOT rule out insufficient fuel volume?

3.) Still, its hard to see it as a fuel delivery/volume problem as it seems clear that somehow too much gas is finding its way into the engine between shut off and the next start. I haven't done Dave's injector firing test yet, but its on the list.
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1984 Vanagon GL
1984 Vanagon Westy

[Wildthings]

The fuel pump is pretty much a constant volume pump at its rated pressure. It will deadhead over 100 psi though. If you are seeing a drop in pressure as you put the engine under load then I suspect a blockage or a dying pump.

If you are seeing the pressure drop when you just rev the engine a bit, I am not sure what is happening.

You might want to do a fuel volume test and also test the deadhead pressure of the pump.

[djkeev]

Pressure, you can develop 100 psi of pressure in a 1/16" pipe,
But
If you release that pressure the volume will be an anemic piss.

You can have 100 psi in a 5/16" pipe,
But
Release that pressure and you've a volume of fuel that will quickly leave you wading in gasoline!

Unless
You've got a pump or a clog that cannot deliver volume, yet delivers constrained pressure.

A volume test is required if in doubt, if that passes, ignore the open throttle pressure reading you have, if it was important that it varies, Bosch woukd have printed specs for it.

There are volume soecs in the Bentley.

Dave
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[tjet]

Based on your input so far, here's my take on your current problem:

Your injectors were indeed bad. They were leaking into the cylinders after you shut off your engine. This is why you didn't have your current no start problem. Your freshly rebuilt injectors are not leaking. Your leaking injectors were masking another problem with fuel delivery (volume). You can rule out the FPR as static pressure is holding. Since your previos fuel pump was making noise, it probably injested something from the tank, as wildthings and dave suggested. The new pump is now sucking even more tank debris, causing a major flow restriction.

Good luck

[Gauche1968]

[tjet]

I would inspect the tank for debris first. There's also a screen in there that may be clogged.

You don't want to potentially damage your new pump, regulator, and injectors

[djkeev]

[Gauche1968]

Well, the issue persists. I am pretty sure the thermostat is stuck open. I cant see how this would cause the hot start issue, but I suppose you fix the problem you know you have and see what happens.
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1984 Vanagon GL
1984 Vanagon Westy

[xflyer]

gauche, did this ever get fixed?
As far as the fuel pressure dropping when the throttle is opened and the engine revs up, I have found this to be normal. Unless you rout the vac line from the pressure regulator to the throttle body. You need to use the fitting that goes to the vacuum retard on the distributor. Put in a T fitting. But as mentioned by others this is not terribly important as long as you have more than say 25-26 PSI. My theory is that where the FPR vac line attaches to the intake plenum gets a pressure drop (partial vacuum) as the engine revs up. Since the Digijet runs with a O2 sensor the fuel mix is set by that and the pressure can vary some without causing trouble.
I had a 1978 Bay window and discovered this fuel pressure drop back in the mid 1980s. Since that year does not have a O2 sensor fuel pressure will effect the fuel air mix. I did the above T mod and got more power.
When I later got the 1984 and sold the 1978 I tried the same mod which made no difference because of the O2 sensor.
The hard start you are having could be the control unit (computer).
Starting enrichment is handled by opening all 4 injectors for a short time dependent on temperature. Unless the Temp Sensor II or its wiring to the ECU is doing some weird failure this could be the ECU gone bad.
Test it this way: When you have the van in the condition that it gets a hard/no start and or floods, do not start it. First remove 2 or all 4 injectors. Leave them attached to the fuel lines and wire connectors.
Have someone turn the key ON, but DO NOT CRANK THE MOTOR.
Watch the injectors. You should see some fuel spray out for a SHORT time. If it looks like a fire hose for a second or more check the Temp Sensor II. If okay replace the control unit (ECU).
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