Fuel related issues

[Oldsman207]

After 2 years of neglect, I finally had an opportunity to get the W cars out.  I started with the '94 Cutlass Supreme and found a no start issue.  Cranks but doesn't start.  Put the fuel pressure guage on the rail and no pressure.  I don't hear the pump when turning on the key.  I moved onto the '95 and it cranked for a while and then finally started but ran rough with a miss.  Checked all the plugs and they looked good.  Verified spark from the all the coils.  I hooked up the fuel pressure guage and it only pumps up to 22#.  Started the car and it came up to 32#.  I shut the car off and the pressure slowly bled off over the next 30 minutes to 22# and held there.  I decided to walk away and start a '92 Custom Cruiser and guess what - cranks but won't fire.  The fuel pump is not working there, either.

Questions are these:

1) Is it typical for these pumps to not want to work after setting for a couple of years?  If so, is there a way to resurrect or are they toast?

2) 22# of fuel pressure appears to be about half of what it should be.  I can see that it might cause a hard to start situation.  Running at 32#, is that low enough to cause a rough running situation?

3) If I bypass the pump relay, how high should I expect the pressure to go?

I don't relish dropping a bunch of fuel tanks if I don't have to.

[rich_e777]

1. Any fuel system with ethanol in it will be suspect after awhile of no use. In my experience(which isnt a yuge amount but still...) a fuel pump either works or it doesnt. If your getting only part of the PSI you need then I`d look at the filter or some other spot a blockage might occur first.

2. Yes, the injectors wont function right without good fuel PSI

3. If your getting 12V to the fuel pump with the key ON then the relay is working.

Edited April 26 by rich_e777

[Schurkey]

In-tank fuel pumps have two sections.  There's the electric motor, and there's the pump.

Low fuel pressure can be a worn/damaged pump section, or it can be poor voltage to the motor that spins the pump.  It can also be a plugging fuel filter as said already.

 

In a perfect world, nobody would drop the tank until they've verified that the pump is getting voltage and amperage sufficient for proper operation.  Making this worse is that GM is known to use undersize wiring in the fuel pump circuit.  My '92 and '93 Luminas each have about two volts of voltage drop (VD) on the supply side, and about one volt on the ground side.  With 3 volts of VD, and battery voltage of 12.x; the pump is running off of only 9.x volts.  Engine starts, alternator jumps the voltage to 14.x; pump is still only getting 11.x volts.

[Oldsman207]

I’m a little confused about the voltage drop mentioned on the ground side.  I understand the voltage drop from + battery terminal to plug at the pump but isn’t it all referenced from chassis ground?  How are you measuring that drop?  I did finally locate the pump prime connector and did notice that it’s a small gauge wire so it’s not going to handle extra loads very well.  
As far as fuel restrictions, I would think that even a restriction in the sock or filter would still allow pressure to build without the motor running.  It just might take longer to build using the prime.  In this case, the prime never gets above 22lbs at the rail and the pump sounds like it’s laboring.  I’m guessing, at this point, it’s a low voltage issue or a pump going out.  I hope to get it on a lift this week to take some voltage measurements. Thanks for all the info.

[Schurkey]

Voltage drop on the ground side is exactly like voltage drop on the positive side.

The pump grounds through a wire, the wire has multiple connections which end up screwed to a body panel--perhaps under the seats.  Then the body is the ground, which may be connected to the battery via the negative cable.  At each junction, there's some resistance.  Defective or undersized cables add to the resistance.  So the ground side has it's own resistance in addition to whatever resistance is on the positive side.