89 TBI 5.9l?

[whistlin']

Working on a friend's 89 conversion van w/5.9L TBI. First I'll give the symptoms. The van runs great and starts good when cold. After driving around for awhile then park it and shut off, it has trouble starting. If starting it immediately after shutting off, it starts fine. 20 minutes after shutting off, it takes a lot of cranking to start. 1 hour after shutting off, it starts fine. If it was carburetted I would say the symptoms are like boiling over. He took it to a shop and they told him it was the fuel pump. I changed the pump for him even though I didn't think it was bad. My first thought was a leaky injector. I shut it off and looked down the throttle body and didn't see any fuel leaking.
I then checked fuel pressure. 15-17psi. Funny thing is, as soon as I shut it off the pressure dropped to 0. I pinched off the return line and tried again, 17 psi until shutting off then 0. I took the van for a drive with the dog house off and watched the pressure, stayed right at 17 regardless of driving technique. I disconnected the vacuum line to the regulator, no change. I would assume the regulator was bad but I couldn't feel any vacuum from the line going to the regulator.
When I returned home I connected a vacuum line to the regulator and applied vacuum(sucked) The pressure then dropped to about 5 psi, I could just about shut the motor off by doing this.
So.... is the vacuum line going to the regulator supposed to provide manifold vacuum? If so, any reasons why this one isn't?
And does the fuel pump have a bypass built into it? Wondering why I didn't get a pressure spike when pinching return line. Any help would be appreciated.

[flatlander757]

I've seen a crank sensor starting to go bad do similar things.


To diagnose if it is something fuel pressure related, try this:

Let it sit for a while like when the symptoms occur...
The cycle the key to the on position then off, on, off, on, off... letting the fuel pump cycle. Then try starting.

I just noticed you have a fuel PSI gauge as well... get the pressure to 0, attach the gauge, then cycle the key to the on position ONE time. Does it immediately go up to the normal 15-17psi? Or can you cycle it again to make it go higher?

[whistlin']

Quote:

Originally Posted by flatlander757 I've seen a crank sensor starting to go bad do similar things.

I don't think the 89 has one

Quote:

Originally Posted by flatlander757 I just noticed you have a fuel PSI gauge as well... get the pressure to 0, attach the gauge, then cycle the key to the on position ONE time. Does it immediately go up to the normal 15-17psi? Or can you cycle it again to make it go higher?

It drops back to 0 when the pump shuts off. Cycling the key doesn't make a difference.
One of my biggest questions is the vacuum line to the regulator. It comes off a port on the throttle body which I assume would provide manifold vacuum. Only thing is I can't feel any vacuum and the fuel pressure doesn't change over different throttle positions. I probably won't mess with it again until Saturday. I was thinking of running a direct manifold vacuum to the regulator and seeing what happens. If the motor is shutting off with too high of fuel pressure it could be flooding itself, just a thought. Thanks!