5.7 Vortec intermittent long crank --> crank no start, backfires, clunking

[slow_c1500]

Fuel pump is original. Do you mean a leak at one of the o rings connecting to the fuel pump? And could it also be the o rings at the fuel filter since I haven’t changed those?
Injectors and regulator are new so I would expect them not to leak but I will still take a look.

 

[docstoy]

So if you are completely crimping hoses it looks like you have 2 leaks one at fuel injectors/pressure regulator and at fuel pump . Is fuel pump O.E.M. or has it been replaced ? Really thinking it's your fuel pump but hate swagging and throwing parts but also hate walking without my walking shoes . And it's not easy to inspect either .

 

[slow_c1500]

One gentleman on the last thread suggested starting it with the injectors disabled, and if it starts then it means fuel is leaking into the cylinders, probably via injectors. I will definitely try this, do I just unplug the fuel pump and try starting it?

 

[docstoy]

I have another thought , it seems your fuel pressure is adequate, but your complaint is long crank time. , so going by your description when you started thread I, over 15 minutes and crank time is long , indicates either fuel pressure regulator or voltage drop or low voltage . You've already replaced regulator , so we can pursue the fuel pressure bleed off or focus on original complaint, I'm going to look at your complaint . First things to do , remove battery cables, negative first , inspect for corrosion, especially positive cable spacer , if needed clean. small positive cable that runs across radiator support first then spacer and cable to starter and then negative. Next underhood fuse /relay panel , remove inspect for corrosion, clean if needed all fuses and relays. Start and either drive or warm to operating temp. Shut off and allow to set . Do this a few times to see if it improves.

 

[docstoy]

So by cking cleaning corrosion could help voltage drop but if relay contacts don't make well then voltage could be low and cause extended crank time, hope you see where I'm going with this

 

[slow_c1500]

But if the battery terminals were not making good contact, wouldnt that mean a long crank every time?

 

[docstoy]

Just trying to eliminate any possible causes of your complaint.

 

[slow_c1500]

Ok Ill start by checking terminals and double checking injectors and regulator. Then ill do the o rings at the fuel filter.

 

[docstoy]

Your fuel is fine all you have going on there is slight pressure drop . Your most likely cause for intermittent long crank is voltage drop most likely across relay contacts . Slight pressure drop over long period of time, but fuel pressure at time of cranking in spec.

 

[Schurkey]

Long cranking time has NOTHING to do with the starter, or battery terminals--although cleaning the battery terminals is good practice and can't hurt.

Does the vehicle have spark when experiencing "long crank"?

Your fuel pressure doesn't drop slower when the regulator hose is clamped-off than when it's not clamped-off. The regulator isn't leaking.

Fuel pressure does drop 12psi when the supply hose is unclamped. Indicates a leaking check-valve in the fuel pump, or (unlikely) a leak in the supply plumbing rearward of the clamping point, which should result in a gasoline trail at the leak point. Whether this is significant in terms of the long crank time is debatable, since the vehicle has adequate fuel pressure at prime.

Verify all "tune-up" items and procedures

Connect a scan tool, verify EVERY sensor and EVERY computer output paying particular attention to the coolant temp sensor, TPS, IAC, and a sticking EGR valve.