I'm new to this forum and tried to find something on this issue and couldn't. Need some advice please!!

I have a 96 s10 blazer 2 door 4x4. It has sat for awhile. Just put a new Delphi pump in. Tank was nasty, and cleaned it all out. Put a new fuel pump relay in and checked my fuses with a meter, not just a test light. Well, I've got 12v at relay and on fuse on both ends. Unfortunately I only have 8v at the pump. Pump is not building enough pressure at all and I'm assuming due to voltage. Has new fuel filter on the fuel rail and at the fuel line check valve I have 10-12lbs.

My question is:

1. Where would I be losing the voltage. (Bad ground location?)

TIA

 

Are you measuring 8v at the pump while it is running? A shorted pump can draw too high an amount of amps. If the amps are too high it can heat up the wire which then turns the wire into a resistor. I'm not sure on a 96', but if I remember correctly off the top of my head, on my 98' when you wire in the new plug for you fuel pump, there are two very similar wires that can easily be reversed because they are the same color. I'm not near my garage so I'm just trying to remember. It may be possible that those wires being reversed could cause too high of an amp draw (just speculating there since I don't have anything handy to reference). But yes, clean your grounds just to be sure you have good ground (wouldn't hurt). Also, voltage drop can also be caused by corrosion or a break inside your wire or bad connections. The drop won't show until the wire is actually under load.

 

8v running. All wires are exactly how they are supposed to be wired in based off schematic. I understand voltage drop and amp draw. Measured at the pump and measured mid frame. I also discovered that on a 96 the oil pressure sending unit ( next to the distributor) is in parallel with the fuel pump. Since it's cheap, I'm going to swap that out just to eliminate that. Then probably repin that wire and run a new one. Unfortunately I have to wait until I get home on Wednesday. Ugh the life of an IBEW electrician. Thank you very much for you're advice.

 

Being an electrician, you have a huge advantage over me when it comes to auto electronics. But, I kind of think of the oil pressure switch as running in series with the fuel pump being it supplies power to the pump in the event the relay fails. As long as their is 4psi at the oil pump switch, it will supply power to the pump via the "ECM B" fuse (on a 98). But I do see how it could be also considered in parallel if the relay is working properly. Can a circuit device be in series and parallel at the same time? I'm curious about that and would be an interesting new piece of info to learn. Or does one take precedence over there other? Thanks.

 

Lol.. that's getting into a whole different set of questions. If we are talking DC Theory. (Direct current). I've never seen a circuit in series and parallel personally. Depending on the circuit, in order to figure out voltage drop among other things at certain points in a circuit you have to simplify them. I.e. figuring out total resistance among the many other rules and formulas to figure it out mathematically. Ac theory is where it gets ridiculous.

As far as the blazer, I'm at a loss. Wire seems good upon visual inspection. But it could just be bad. I'm going to have to run through it all if oil pressure switch doesn't work.. Just didn't know if there was a common issue or somebody may of already ran into this....