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Terrible fuel pressure


Question

I have a 1997 Chevy C1500 with the 5.7L. Fuel pressure jumps to like 64 when pump primes then drops, no leaks are anywhere. Brand new pump (4th one in 3 months to test different pumps but same outcome everytime). When truck runs it holds at 55psi but when truck is off pressure drops down to 25-20 psi. I have no idea what it could be besides maybe faulty regulator that could be leaking? Should I pull the trigger and upgrade to the MFI injectors and a new regulator and see where that takes me?

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That spider assembly is a notorious leaker. One of the worst injection systems GM ever came up with. If you're not seeing  and smelling fuel externally,  it's either a bad regulator or an injector or more hosing down the bottom of the intake manifold. They always crack and spray fuel - sometimes causing a misfire, sometimes not.

 

I can't remember if that era had the capability to do an injector balance test with a good scan tool - that would be where I'd start. If not, time to start digging to get that intake manifold off.

 

If it's never been changed, it's the old style as pictured in the last 3 pics. The new style has actual injectors right at the ends of the spider legs, instead of the failure prone poppet valves. Probably wouldn't hurt to upgrade anyway if it hasn't been done already. If you see any clean spots in the lower intake manifold, that's a dead ringer for a leaker. This particular vehicle here got one just as preventative maintenance, since thousands had been spend in getting her running back in 2014. The first 2 pics are of the updated spider, last 3 of the OE spider on a '96 Tahoe 5.7:

 

29552-E93-59-D8-4-F6-A-98-F4-7269020-A61


78-C554-A8-5953-4-AD0-9-CC6-6903050-C898


B660-EAFA-3034-472-D-8771-F9-DF71-C15843


BB2085-D0-CD7-C-42-A6-9934-4-BA76-C39-B3


DB432455-AA29-4-D3-A-8815-B8074-D007-C57


 

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