LS swap starting issue

[Cudajeff]

Hey guys, I’ve just finished up the 5.3 swap in my ‘97 c1500. (The LS harness is integrated into the factory one. 0411 pcm) After the usual amount of complications and challenges the build finished up well. Everything is new, from the radiator to the differential cover. Nothing came off a donor vehicle. The only small issue I’m having is that 6 out of 10 times when I go to start it, it doesn’t immediately fire on the FIRST key turn. It will crank as long as I hold the key engaged but not fire. (Not a fuel pressure issue) If it doesn’t fire in the first 2 seconds or so I can turn the key back one position then immediately re-engage the starter and it pops right off. It’s very strange. The other 4 out of 10 times, it busts right off. Anyone ever run across this? It’s not a huge problem, it’s just not right. Any thoughts?

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[0xDEADBEEF]

Is the engine stock? If not, it could be a tuning issue.

 

[Cadillacmak]

Hey guys, I’ve just finished up the 5.3 swap in my ‘97 c1500. (The LS harness is integrated into the factory one. 0411 pcm) After the usual amount of complications and challenges the build finished up well. Everything is new, from the radiator to the differential cover. Nothing came off a donor vehicle. The only small issue I’m having is that 6 out of 10 times when I go to start it, it doesn’t immediately fire on the FIRST key turn. It will crank as long as I hold the key engaged but not fire. (Not a fuel pressure issue) If it doesn’t fire in the first 2 seconds or so I can turn the key back one position then immediately re-engage the starter and it pops right off. It’s very strange. The other 4 out of 10 times, it busts right off. Anyone ever run across this? It’s not a huge problem, it’s just not right. Any thoughts

Nice truck!!! Don't rule out the ignition, is it actually sending power every time?

 

[Cudajeff]

Thanks for the replies. No, it’s not stock. I started with a 450hp crate long block from Summit then added the intake, ignition, Painless 0411, exhaust, Holley accessory drive, Circle D 3000 stall TC, built 4l60e, Eaton lsd, Richmond 3.73’s and on and on. It’s been quite the journey but it’s a labor of love. You guys know how it is. Thanks for the compliment, my son and I worked hard on it.
I had it tuned by a professional on a chassis dyno and he couldn’t explain the ignition issue either. If it doesn’t fire on the first turn of the key it ALWAYS fires on the second. If sometimes it took 3,4,6 try’s I’d think there might be some voltage or ground issues but that’s not the case. It’s almost like I have to “wake” the pcm up but that makes no sense. Like I said, it’s not really a problem… it’s just not right and I can’t figure it out.

 

[Drunkcanuk]

I know you said you're running a 411, so you have any other electrical boxes in play here?
Reason being, I've read that other EFI systems, like Holley, take a few seconds to "boot up" before firing up, unlike a factory ECM.
Just tossing it out there.

 

[Cudajeff]

No sir, just the 411.

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[KansasOBS]

Not of any help for your issue, but whats the cruise control off of? You said no donors, but that cable sure looks long.

 

[Cudajeff]

The cruise control is original to the truck. I used the stock CC and throttle cable’s. I modified the original cable bracket so it would attach to the FiTech throttle body. I know they’re long but they are functional, free and I didn’t have to mess with installing new ones.

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[0xDEADBEEF]

Can you hook up an OBDII scanner? Curious if it shows any RPM while cranking. I know you said fuel pressure is ok, but do you hear the pump turn on if you turn the key to on (but not to start)?

It should prime and then turn off until it sees RPM via the crank position sensor and then turn on again.

 

[Cudajeff]

I ran the stock fuel pump for the first month after I finished it then it took a dive. I put a Holley in the tank three weeks ago (nice pump, extremely quiet) and no change. Pressure gauge pops to 60 instantly when I turn the key.