Fuel pressure before startup...

[Brian Smith]

In my Volvo 145 with D-Jetronic fuel injection, when the key first reaches the on position during startup, the fuel pump is aumatically switched on for about 1 sec. to build fuel pressure. The result is starts as quick as you could expect. In my e12, I sometimes have to turn the key to start for a sec. or two, in order to build fuel pressure, and then switch the key away from start for an instant and then restart the car.
I haven't used a fuel pressure gauge to monitor how long it takes to lose the pressure. I may possibly have some leaky injectors. I have verified that my cold start vale is good, and that my pressure is within normal limits when the pump is running. Even with leaky injectors, the D-Jet system would work perfectly for starts. I wonder why the move went away from that design. It was always actually reassuring to hear the fuel pump noise for an instant on your way to starting the car. One can't help but notice a change in noise of the fuel pump when the engine is not running, however while the engine is running, the noise change of a pump operating strangely is just lost to all but the most perceptive ear.

So, here is the question:
Does anyone else experience this fuel pressure building problem while cranking?
Is there anything else that is switched on momentarily when the key first gets to the on position, that I could also tether to a relay to switch on the fuel pump for a sec.?

-Brian

[BradInTexas]

My 914 with D-Jet works the same way. I don't think you'll be able to accurately diagnose this without setting up an in-line pressure tester but you might try this (which really only helps confirm what you already know). You can jumper the fuel pump at the combo relay to make it run all the time. Do that and try to immediately start the car. If you get the same symptoms (won't immediately start), it could be a pump problem. If it starts right up, I am not sure you have learned anything (since the pump is already continually running) other than it might be a relay. I doubt a leaky injector would bleed down the pressure as quickly as you described, but as I am learning with my own e12 travails, anything is possible.

The only other thing I can think of is a faulty in-tank pump. Maybe the primary fuel pump is not getting fed enough. That seems a stretch tho...

[Mike W.]

The system should hold fuel pressure. I've cut into fuel lines in junkyard cars that have not run in months and been greeted with a spray. So it should hold. Leaky injectors can cause it to be hard to start due to it essentially being flooded, not due to a lack of fuel. It's possible the check valve in the fuel pump isn't holding, IIRC some were installed on some E23s due to that problem, or your FPR might not hold. E21's did the fuel system prime for a second or 3 also, but they were different as they were mechanical and needed pressure to open the injectors.

[Lenny D.]

...and I might add that I have experienced the same condition in a properly operating fuel system. It is also my understanding that the FPR does fail but they were designed to fail rich, not lean, and you would experience drivability problems associated with that failure.

[Brian Smith]

Thanks all for the replies.
I'll have to leave the fuel pressure gauge attached and see how long it takes to bleed pressure on the system.

Maybe the engineers at Bosch figured that owners needed a way to diagnose leaky injectors without a gauge, so they deleted the pre-start fuel line repressurization cycle.

I'll try the relay jumper to be sure that fuel pressure is causing the symptom, too. It always restarts as I want it to as long as I've shut it off in the last 10 minutes or so. The car is by no means difficult to start, even after sitting for a week. A short stab of the throttle while cranking also does the trick, but I know that it should start without any shenanigans like that.