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I put a Jegs LS3 crate engine with the Jegs harness and ecu. in my 66 impala a few years ago now. Has roughly 5000 miles over the last 2 years on it. Was built over the last 10.
Recently its started stalling on me. Never really stutters, just stalls. Not popping any codes. I swear the pump kicks on every time i turn the key, but then acts like its been instantly starved of gas. The times it doesnt prime with ignition i believe is normal because there's already fuel pressure? At first it happened while driving, now i cant even make it out of the driveway or even keep it running today. It has gas. Does this sound like a gas or ignition issue? Something else?
May be related but for some very odd reason, for the last 12months or so the mellow slope in my driveway has often been enough to help it start first crank if facing down hill vs parked uphill which always takes 2 attempts...trying to attach videos but having a formatting issue so will post this anyway to hopefully get the convo going. RodRun is next weekend and this thing is buggin me!
Its a brand new(well, was two years ago)tank + pump, filter, lines, you name it. It all got swapped out for new stuff during the last phase of the build.
Its an intank pump with the filter/regulator nearby (pic below).
I have attached two shortened videos. First one is the first prime/crank with pressure gauge attached. Doesnt pressurize (68-70psi) until cranking but then does run fine from then on, despite that odd flicker on the gauge near the end.
2nd attempt fine.
3rd attempt pressure builds on ignition, drops like all the others but fails to build psi while cranking/running and I had to save it with the throttle. Idled fine after.
4th/5th both fine. Letting it sit for a bit before doing some more
Buy a GM brand/AC Delco from Summit or Jegs and not from AMAZON. Lots of fake overseas parts out there potentially. I would also check your inline filter for debris. Sounds like a fun car.
Also check the grounds on the back of the head for the harness to make sure they are tight and I assume you have a couple grounds from engine to chassis?
" The times it doesnt prime with ignition i believe is normal because there's already fuel pressure?"
Nope. If the key is turned all the way off, the pcm will trigger a pump prime cycle. Some systems have a short time delay built in, between attempts.
The pcm does not monitor fuel pressure to control pump starts.
If there are issues with "no prime", I'd be looking at the electrical system.
Awesome thank you guys. New regulator should be arriving at any moment this morning, so will know by tomorrow. Might just get finished in time for RodRun and Cars N coffee!
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6.2 LS3 1966 Impala running issue 
