have a 1993 blazer with vortec 4.3 been having trouble with it loosing power took it to a shop and they told me it has low fuel pressure (i got new pump and new filter ) still low pressure what next does anyone know thanks mike

 

um... injectors clogged?

 

A clogged fuel injector would not cause low fuel pressure. The fuel pressure in the newer vortec SCFI motors (96+) should be maintained at 55-60psi. Anything less can cause problems. I am assuming that this is the same pressure that the earlier CPI-central port injection motors (what your '93 has unless its TBI-throttlebody injection) requires. The CPI motors are known for having the FPR-fuel pressure regulator blow out (literally) and dump fuel into the intake manifold. You may also have the internal fuel lines leaking inside the intake, but I wouldn't think this would cause low pressure.

Of the things that come to mind that could cause low pressure... Well, here's what I can think of:
[ul][*]weak fuel pump - already replaced[*]fuel filter clogged - should have been replaced when the pump was replaced[*]kinked supply line - check your lines for kinks in the hardlines. This would manifest itself more at higher fuel demands than at idle where the flow would be less.[*]bad fuel pressure regulator - typically fails and allows raw, unmetered fuel to run into the engine causing more than a simple power loss[*]internal fuel line leak on the supply line - would still think this would only be noticable at higher fuel demands (higher rpm)
[/ul]
I'm sure there are more areas, but I hit the high points. Did the shop run a leak down test? If the system pressure bleeds off, then there is a leak in the system somewhere. If nothing is visually leaking, then you've most likely got a leaking nut kit (internal fuel lines) or a leaking FPR.

If the fuel filter was not replaced yet, do that first.

 

How much did you pay for your new fuel pump and filter?

 

I have to ask some question that may seem silly, but I have to. Fuel filter is new, right???? While tank was off all the lines were checked for being unclogged, right?? I know, why ask those silly questions, right??? I do mean ALL THE LINES. VENTS??

Before taking everythig apart the whole vent system or "Evaporation control system" was checked completly right. BTW, just for info, this system will hold fuel back if the venting process to the tank does not work properly. It may even cause some weak tanks to collapse. NEVER seems to fail for anyone. Doesnt mean it couldnt, no-one ever services it either.

 

its funny you ask because one thing about this is that it was doing it before fuel pump change and thats why we did a change of fuel pump i got sick of messing with it so i sent it to a repair shop to have it scaned and they came up with low fuel pressure

 

A computer scan (especially on an OBD1 computer) will say nothing of low fuel pressure. You actually have to tap into the fuel supply line with a mechanical gauge to read the fuel pressure.

With what you just said about the problem being the same pre- and post- pump change, the pump definitely was not the issue. I suppose if the EVAP system were applying a vacuum to the tank without venting it or holding at a steady vacuum, it could restrict the flow out. This could be diagnosed by simply removing the gas cap (or loosening it a bit) and driving around. Now I would not do this on a full-full tank, but a half tank shouldn't cause anything to spill out. If the truck feels more lively, then you have a problem with the EVAP/PURGE system that needs further attention. If not, then it's mostlikely something in the fuel supply lines (ex. kink, blockage, clogged fuel filter).

 

Loss of power can be caused by a great number of things. Timing being retarded due to external problems causing the knock sensor to act up. All THAT takes is a bad load of gas. Low quality gas or an octane lower than the heat of the day requires may contribute. Is your engine running hotter than it ought? A higher than usual temp under the hood can cause timing retardation by the puter.

Is it possible that the whole problem is elsewhere? Anyone do a quick check of initial timing? Is the coil working ALL the time? Was the puter actually read out by a shop? Heck, a bad rotor button can make a good engine cry. Or is someone throwing good guesses out there. I have found that many good guesses can be very wrong. I made lots of them myself in the past. As a mater of fact, you could change a great number of things before actually finding the real problem.

Simply going on faith works sometimes, but the more modern computers are much more acurate at their self diagnoses than the older ones were. On an older model you could find three or four problems and still never cure the problem. This still happens but the occurrence of a number of things having to be cured is getting a great deal smaller.

Just throwing examples of some things out there. It may be just ONE thing, but in no way does it HAVE TO BE. A couple or three things on that list can add up to cause a real problem together.

 

i called the shop today to find out how they came to know that it was low fuel pressure and they told me that they put a gauge on it and it was lower than it sould be im going to try gas cap and go from there i do want to say thanks for all the input i have got and will post again to what i find .........mike

 

hi we too were told about a low psi
so we too put in a new fuel pump and filter $740.00 at chevy
but my friends did it for $400.00
no better
then new vacuum lines $95.00
no better
than i was told to check the
idle control valve $60.00 and with a "star wench" you can do it yourself
before you buy it do this
open your hood disconnect your idle control valve
and see how it runs
if it is an injector try this
get some techtron form 76 and run it 80-90 mph for 40 mi
that should clean your injectors
good luck
still waiting for my parts
suzanne