93 blazer won't start

[vettracer91173]

I've got a 93 blazer with a 4.3 votec. I've replaced the fuel filter, gave it a tune up and replaced the cpi spider unit. I've also tried a new computer and it still only starts when it wants to. The only thing I've noticed is that with a fuel pressure guage hooked up, when you turn the key on sometimes it reads 50 psi and other times 60 psi. It will start when it reads 60, but not when it reads 50. What would make it fluctuate so much? I've also tried a different fuel pump relay. it changes nothing. Please help.

[busa_4]

a failing fuel pump can fluctuate fuel pressure. i think its time to retire your fuel pump.

[busa_4]

i was also thinking you might have a fuel pressure regulator problem as well but as you stated you already replaced the cpi unit.

[vettracer91173]

I finally got time to replace the fuel pump, and it runs just fine now. I guess just because the pump runs and puts out a fair amount of pressure, not to assume it's good. Thanks!!

[busa_4]

glad you fixed it! the cpi system requires high pressure to open the mechanical poppets, if you fall below that threshold it wont run. i think its around 55psi to open the poppets which is very high. good job on your recent fix.