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LS swap won't start

K30Blazer

K30Blazer

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Swapped an LQ9 into my K5 and have put about 500 miles on it with just the normal break in issues. In the last week it started acting funny during startup and would crank but not fire. Did it once and started the next try. Two days later wouldn't start and I check the wiring at the pump and grounds etc and it started

Then it wouldn't start at all and with relays firing for pump, I couldn't hear the pump priming on startup.

Thought I had a bad pump. I had ran out of gas and thought that I might have fried it. It was a Walbro high pressure pump for the LS motors.

Swapped out the pump for a AC Delco 62 PSI pump and still no go. The pump is priming but I have no pressure at the rail. The inline filter / regulator is clear but nothing.

Every tenth try it tries to fire, but doesn't. The PCM is seeing RPM so I don't think it is cam or crank sensor.

I am completely out of ideas and ready to burn the f$*#(# down.
 
Double check your knock sensors if you didn't replace them when you did the swap

Plus you can always do the whole starting fluid down the intake to pin point the issue, whether it be fuel or spark
 
I've started a few on starting fluid on the ground in the shop, just like a 2 or 3 second spray in the intake to see if it'll even fire on starting fluid
 
How is your fuel system ran? Did you do a vette regulator? Or is your regulator on the fuel rail?
How is your pump attached to the sending unit?
 
Might sound dumb but the small rubber hose in the tank that connects the pump to the sending unit needs to be upgraded to EFI rated rubber hose, otherwise it splits pretty quick
 
it is a returnless system that has the vette regulator / filter down on the frame rail. The filter is on in the correct orientation and is clear. I cracked the lines and gas is pouring through just fine. When I pulled the old pump the connection hose was fine. I replaced it anyway when I put the new pump in.

I am really thinking it has to be something electrical, I am just not throwing any codes. It just cranks and cranks and won't make pressure.
 
pump cycles, doesn't seem to be making pressure. I check the bleeder on the rail and there is nothing there. But I can hear the pump priming. It is pretty loud
 
heck if all else fails just make a jumper lead from the battery to the fuel pump at the tank and then crank on it and see what it does
 
Crazy idea but who knows, depending on how your harness is wired you maybe running into a bad oil pressure switch.

I know GM did it for awhile if the computer didn't see oil pressure while cranking it wouldn't turn on the fuel pump.

Plus the factory oil pressure switch on these are in a prime location for damage during install or snug fire wall clearance.

Other than that, I'd go over the ground for the injectors and just do a once over of my fuel lines and make sure nothing got pinched or smashed
 
take the line lose at the filter and see if your getting fuel there when you hit the key, it will give you an idea if its at the motor or the tank.
 
so i dove back under there today and hooked up 12 v to the pump and opened the fuel filter lines. No gas coming through when pump is energized. My last thought, and it just came to me was I must have the pump + and - hooked up backwards turning my pump into a blow. When I got the pump, the fittings wouldn't work with the sender so I had to cut the wires and solder them on. There was no definitive + and - so I took a reasonable wild ass guess. I was wrong. Reversed them and pump is pumping. Engine is running.
 
Hope you called yourself a swear word and laughed it off :D

We've all been there once or twice, once that we might admit.
 
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