5.7 vortec long crank

[Schurkey]

When you say it should hold pressure for at least 30 seconds, do you mean it should STAY AT 60, or just retain SOME pressure?

It holds at 60 psi for the 2 seconds that the pump is running, then it drops slowly. After 30 seconds it still has 45 psi of pressure.

'97 C/K service manual, page 6E-856, paraphrased.

Cycle ignition to "on" allow fuel pump to prime for it's 2-seconds. Note pressure. Should be 60--66 psi for Vortec small-block. May have to cycle ignition switch more than once, with 10-seconds "off" then back on, to achieve max pressure.

Cycle ignition switch once more, allow pump to run for 2-second prime. "Monitor fuel pressure after the pump stops. The pressure may vary a few pounds, then the pressure should hold steady."

There is no time spec. given.

If you lost two or three pounds in thirty seconds, I'd say it's fine. Losing 15 psi in thirty seconds seems excessive.

 

[slow_c1500]

'97 C/K service manual, page 6E-856, paraphrased.

Cycle ignition to "on" allow fuel pump to prime for it's 2-seconds. Note pressure. Should be 60--66 psi for Vortec small-block. May have to cycle ignition switch more than once, with 10-seconds "off" then back on, to achieve max pressure.

Cycle ignition switch once more, allow pump to run for 2-second prime. "Monitor fuel pressure after the pump stops. The pressure may vary a few pounds, then the pressure should hold steady."

There is no time spec. given.

If you lost two or three pounds in thirty seconds, I'd say it's fine. Losing 15 psi in thirty seconds seems excessive.

Ok I will test that out tomorrow. When I did my test today I only turned the key on once.

So i turn key on for 2 sec, turn off for 10 sec, then turn back on and keep in that position, and record psi?

 

[1990Z71Swede]

1990Z71Swede already mentioned a potential leak at the check valve, and said it was unlikely because then it wouldn’t start better when the engine has been sitting overnight, which is what mine consistently does.

The reason you want pressure in the system after shutdown is to avoid issues with vapor lock. Some FI systems even have an accumulator for that.

If that would have been your problem obviously it probably WOULD start better when could, but then again your description of the problem was not consistent with that of a vapor lock related issue. And as it turns out, your main problem ended up being the leaking spider.

Now, liquids including fuel, can not be compressed. That means a tiny tiny leak will drop the pressure significantly, so you might be ok with what you have, but...

I'm not a Vortec or spider injection expert, infact the existance of the spider injection was unknown to me until about september last year .

I dont know how sensitive it is to vapor lock/heat soak, but normally on cars with external fuel rails 3bar of pressure seems to be plenty enough to prevent that, on the other hand, the correct function for those systems is for the system to drop 2-3 Psi when the pump shuts of and then hold at that pressure for atleast 10 minutes.

How much pressure do you have after 10-15 minutes? If it drops much further I'd say something is wrong.

 

[slow_c1500]

30 seconds after the pump shuts off, it drops to 53 psi. After 10 minutes it has 36 psi.

Not sure how important this is, but I noticed that my fuel pressure regulator has never had a vacuum line going from it to the intake, even on the original spider. Are these trucks supposed to have that? I remember this vacuum line being mentioned before.

 

[Schurkey]

30 seconds after the pump shuts off, it drops to 53 psi. After 10 minutes it has 36 psi.

Yeah, that's excessive pressure loss.

my fuel pressure regulator has never had a vacuum line going from it to the intake, even on the original spider. Are these trucks supposed to have that? I remember this vacuum line being mentioned before.

Is the hose missing, or is there no place to put a vacuum hose on the regulator? Is there an open nipple on the manifold causing a vacuum leak?

 

[slow_c1500]

There is a little pipe pointing downwards on the regulator, but there was no hose on it, and I can’t seem to find anywhere inside the intake manifold where such a hose would lead to.

I have seen videos of people doing this job before and none of their trucks have any hose on the regulator, but they still have that little downward facing pipe that has nothing on the end of it, just like mine. Again, I’m not sure if our trucks are supposed to have one.

Anyways, where else could I be losing fuel pressure from? Check valve?

 

[Schurkey]

If that nipple is enclosed within the plenum, there's no hose needed. It's exposed to manifold vacuum without a hose.

 

[slow_c1500]

Ok just wanted to make sure it’s not supposed to have a hose on it. I didn’t think so.

This might be a dumb idea, but maybe the reason I was losing fuel pressure too fast could be because the electrical connection for the spider wasn’t plugged in during my test? (Plenum off, no electrical connections plugged in, fuel lines temporarily connected) Could that have affected fuel pressure?

 

[Caman96]

Why not put upper intake back on at this point? You have a new spider and regulator, everything in there should be good to go.

 

[1990Z71Swede]

I wonder, since it's not been started yet, if there might be air in the system? It seems your pressure drop was less the second time you tested. If there is no visible leak anywhere. I'd button it up and put it back on the road with fingers crossed.