Fuel pressure drop

[AustinQuattro]

Older thread but should be relevant. I swapped an LS3 into my 57 Belair and I'm having issues. It's a crate LS3, Texas Speed & Performance put their PRC cnc'd heads on and stage 2 cam, and it's not running right. One of the biggest initial issues is it won't start without spraying starter fluid into the intake. Then it idles and revs and runs. Off Idle, if I stomp the pedal, it will stutter a bit, but if I ease in just a little, then I can stomp it and it revs quickly and smoothly. I had a shop tune it, and they've tuned this exact setup before (except it was a camaro with the same heads and cam, not a swap). I'm at a loss. It's obviously a fueling issue, I have fuel pressure even after it's been sitting off for quite a while. I'm wondering if it could be a bad fuel pressure regulator or maybe a sensor isn't grounding properly? Not sure where to look...

[chevynut]

Did it run right after if was tuned? Seems like they should have checked the fuel pressure. Is the fuel pressure correct now? If it is, it's probably some sensor like your MAF sensor or O2 sensor. Can you check your sensors with a scanner or DVM?

By the way, my 502 is running great now. I went ahead and hooked the vacuum port back up because I figured it was there for a reason. Yeah, I could let it learn without it, but my concern was that if I plug the regulator vacuum line off, and it blew again, it could spew fuel all over my engine and headers, and maybe start a fire. I'd rather have it dump into the engine.

[AustinQuattro]

Did it run right after if was tuned? Seems like they should have checked the fuel pressure. Is the fuel pressure correct now? If it is, it's probably some sensor like your MAF sensor or O2 sensor. Can you check your sensors with a scanner or DVM?

By the way, my 502 is running great now. I went ahead and hooked the vacuum port back up because I figured it was there for a reason. Yeah, I could let it learn without it, but my concern was that if I plug the regulator vacuum line off, and it blew again, it could spew fuel all over my engine and headers, and maybe start a fire. I'd rather have it dump into the engine.

Yeah, I'm going through all the sensors now. Seems the guy I had wire it may have not tightened a few things. Yesterday was a bad day. The guy who helped me get the engine & trans in apparently didn't put the fill plug on the trans...so when I made a small trip around the block checking things out, it got up to temp enough for it to come out and onto the headers and start a fire. All is ok, no damage, but lots of leaked fluid and scary!!!

It did not run right after the tune. Still wouldn't start without starter fluid, would rev only after coming off idle a bit, and in gear would not rev much at all.

It's obviously a fueling issue, just not sure what yet. Pressure is there from the fuel pump and the line is pressurized even after sitting, thinking it's something with the wiring, or a sensor not being grounded well, maybe even a bad crakshaft/camshaft position sensor or ground. I'm just going through everything now. Thanks for the response. BTW, I'm running C4 suspension front and rear like you, on a NerdRods chassis, with double adjustable coilovers all around. I really can't wait to drive this thing!