S10 Fuel pressure problem

tdark

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Make
Chevy
Model
S-10
Year
1993
Miles
?
Engine
4.3 Vortec w/ CMFI (Eng Code W)
I am helping a friend with his 1993 S10 Blazer 4.3 Vortec w/ CMFI (Eng Code W)
Fuel pump has been replaced along with new filter. Pressure gauge connected and tied up where he can see the reading . He drives it and said at first gauge reads a steady 60 psi but as I soon as you accelerate hard it runs terrible and fuel pressure drops to around 30 and the needle on gauge jumps back and forth like crazy but it still wont' go higher than around 30. I guess you would say it flutters pretty bad.
He lives too far for me to go see if can gets hands on and help so maybe someone here could shed some light on this problem. Does this sound like a fuel pressure regulator issue ? Thanks
 

paulo57509

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My '03 Safari has a similar system (CSFI) that's sequential instead of "fire all at once" like the one you have. The CxFI systems are known for leaking.

I would see if a leak-down test shows anything. Connect the fuel pressure gauge. Do a few key-on-engine-off cycles to get max pressure and note the pressure reading with the key off. It should hold pressure for at least 30 minutes. You'll know right away if there's a leak.

To get to the "spider", the upper intake manifold needs to be removed.

This article gives a brief theory of operation and mentions a way to peek into the intake manifold to see if raw fuel is present:

 

billr

wrench
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Or, the fuel pump could be getting tired. So, how do you tell if the problem is the pump, FPR, filter, or load (spider/injectors)? Not so easy to do; I would start at the pump, see if it can maintain pressure (100 psi or so) while flowing 1/3 gal/min. That isn't an exact spec, but should be good to regulate down to 60 psi and enough flow for up to 240 hp.

Such testing will be hard to do "long distance", he/you may have to resort to parts-swapping.

Maybe you can direct him to tapping the gauge into different places than just the standard rail test port. Checking just after pump and just after filter may give some clues. Checking for return flow from the FPR when pressure drops (should be no flow then) could also give a clue. Has the FPR vac line been checked for fuel in there?
 

grcauto

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Or, the fuel pump could be getting tired. So, how do you tell if the problem is the pump, FPR, filter, or load (spider/injectors)? Not so easy to do; I would start at the pump, see if it can maintain pressure (100 psi or so) while flowing 1/3 gal/min. That isn't an exact spec, but should be good to regulate down to 60 psi and enough flow for up to 240 hp.

Such testing will be hard to do "long distance", he/you may have to resort to parts-swapping.

Maybe you can direct him to tapping the gauge into different places than just the standard rail test port. Checking just after pump and just after filter may give some clues. Checking for return flow from the FPR when pressure drops (should be no flow then) could also give a clue. Has the FPR vac line been checked for fuel in there?
They put in a new pump and filter. There's likely several if not all the poppets having problems.
 

grcauto

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You can try doing a professional cleaning using the proper equipment to run it straight off the cleaner with fuel pump disabled. It works well with typical injection systems but I'm not positive how it does with the poppets.
 

billr

wrench
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OK, I didn't read (or remember) well enough to note the pump/filter change; but we still can't ignore the pump. The pump may not be getting proper power, or the replacement may have been bad. In this age of "unlimited returns", parts from a store are always a crap-shoot.

Is there any hint of the injectors leaking or holding open, like rich smell or black smoke? That would be the only way the injectors/spider could drop fuel pressure, by dumping gobs of fuel into the engine.
 

grcauto

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OK, I didn't read (or remember) well enough to note the pump/filter change; but we still can't ignore the pump. The pump may not be getting proper power, or the replacement may have been bad. In this age of "unlimited returns", parts from a store are always a crap-shoot.

Is there any hint of the injectors leaking or holding open, like rich smell or black smoke? That would be the only way the injectors/spider could drop fuel pressure, by dumping gobs of fuel into the engine.
These are not injectors they do not work the same way. The regulator is integral with the poppet nozzle unit. It may be the regulator is bad. Instead of leaky injectors this thing will leak bad at the regulator. You can look into the intake with a flashlight and see if it's leaking.
 

billr

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What is your point? I already suggested (in reply #4) that the FPR return line be checked for excessive flow. It doesn't matter what the exact "FPR" config is. There is a line to return fuel to the tank with this system, correct?

Dumping fuel into the manifold will cause the extreme rich running I am asking about. Isn't it easier to sniff for rich, and look for a black cloud, than remove a TB (or whatever) to look for fuel puddling in the manifold?
 

tdark

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Sorry I have not posted back but my friend has had some problems and has not had time to work on this S10. I will report back when he has time. Thanks for the tips
 

tdark

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He said he found a bad wiring connection going to spider. Repaired and he is happy. Thanks for all the tips. Tom
 
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