Fuel Prime Issue Causing Ridiculous Hard Starting

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east302

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So it runs up to 40-50 psi with the return open and hits 80-psi with it closed downstream of the regulator? If so, that sounds like it’s bleeding through the regulator back to the tank.

If the pressure continued to decrease, then that would point to an injector, external leak or pump check valve issue. Keeping the return closed, you’d then close the supply to see if it is an injector or pump.
 

ReallyRicky

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I've characterized it a little more. It takes 4 or 5 primes to build pressure. It'll start once it hits 10 psi if you don't build full pressure. But it takes a LONG time to build pressure. And it's not flooded when it does start. There must be a check valve in this pump/bucket assembly? Or maybe some real ignorance awaits me inside the tank?
Check your fuel cap
 

CrustyJunker

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Not sure if you had a chance to look at this or iron it out yet, but I had a weird similar experience...Only sharing because it took me a long time to find it.

Installed a new, cheap aftermarket fuel pump. -Ended up it split the plastic on the outlet side. It was hardly visible, a hairline crack going vertically and only must have opened up under pressure.

I either overtightened the hose clamp on it, it was too thin of a casting, or both. Being new, it tested good fuel pressure at idle/revving in neutral, but fell on it's face under load at various RPM's below redline. Almost acted like a misbehaving rev limiter.

Begrudgingly re-replaced the fuel pump/found the issue...And it all went away.

Made troubleshooting very difficult though. I figured the little rubber line with hose clamps may have gave me grief, but nothing seemed visibly wrong...It was the plastic of the pump itself the whole time!
 

Supercharged111

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I got the pump and bucket assembly a couple days ago, but the transmission is out of it too at the moment. I'm hoping to button it all up this weekend and report back on my findings.
 

Supercharged111

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So today I dropped the tank. I noticed the harness looked a bit not stock.

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Yep, that'll warrant further investigation.

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The plot thickens.

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There's that ignorance we were after! If you think this surprises me think again. Ground lug looks decent though, a wire brush on it and the frame and I'll send it.

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Bucket didn't look that old but was falling apart.

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Based on the rest of the crap I've pulled off I think it's safe to say this is among the most bottom feeder garbage Communist China has to offer. But then again that new "Genuine GM" bucket looks to be missing a post as well? It sure fought me tooth and nail going back in. I don't recall putting that much effort into pumps and senders in the past? Ended up using a screwdriver to pry against the tank to sort of roll the sender down into place. But I was ill equipped to deal with the connector so more on that tomorrow. We're it not for the connector tank would be back in along with rear driveshaft. I've never had the driveshaft out to drop the tank, man oh man is it easier this way!
 

454cid

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So today I dropped the tank. I noticed the harness looked a bit not stock.

Originally that would have had a sqaure-4 instead of a flat-4 connector.


...But then again that new "Genuine GM" bucket looks to be missing a post as well?

That was one of the reasons I didn't go with a Delphi when I did mine in 2018. I've got a Denso, which is made in China, but I suspect at there own factory.
 

Schurkey

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I remember that GM updated the wire harness connector on some of the fuel sending units/hangers. They'd sell you a replacement hanger assembly that included the updated wiring pigtail, the tech was supposed to splice the pigtail into place.

IF the guy doing the wiring work was doing a good job, it was decently reliable. If he was a hack, there were corrosion problems.
 

Supercharged111

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Remembered my convoluted tubing today and my 25ft jumper leads. Unplugged the connector, ohmed from there through the frame all the way to the battery and back and got all of 0.5 ohms resistance. I tried poking a shaved paperclip up the back side of the connector with the pump jumped at the relay but couldn't get a power reading. But with only .5 ohm resistance on the ground side I didn't see a problem and buttoned it up. The truck sat a while after jumping the pump. When I went for that initial start I was rewarded with exactly what I wanted, a near instantaneous start. I got a few more after that too, night and day difference. Onto the other 27 things I need to fix before the big trip.
 

Schurkey

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Glad it worked out...but voltage-drop testing would be better than ohmmeter testing.

Ohmmeters supply almost zero amperage. Testing under load shows more-accurate results for any circuit carrying enough current to be using multi-strand wiring.
 
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