Low fuel pressure.

[axlealex]

So I finally got back to working on this fuel pressure problem (dang life getting in the way). New unit from DmcCal. Checked to make sure it was getting the right voltage, which it is 12.4V. I also hooked it directly to battery to make sure pump was getting the right voltage. Good to go on that. Now I am up to about 45psi the rpm relay is jumped. At a loss here. The sensor plate has to much resistance on it, not free floating. It's like there's pressure pushing plunger down. Not sure that has to do with the lack of pressure, and no injectors opening. image.jpgimage.jpg

[Bitsyncmaster]

So I finally got back to working on this fuel pressure problem (dang life getting in the way). New unit from DmcCal. Checked to make sure it was getting the right voltage, which it is 12.4V. I also hooked it directly to battery to make sure pump was getting the right voltage. Good to go on that. Now I am up to about 45psi the rpm relay is jumped. At a loss here. The sensor plate has to much resistance on it, not free floating. It's like there's pressure pushing plunger down. Not sure that has to do with the lack of pressure, and no injectors opening. image.jpgimage.jpg

To check primary pressure, you need to close off the hose going to the warmup regulator.

With that rest pressure of 45 psi, the air plate will have pressure and not float.

Injectors will only spray when you press that air plate down with fuel pressure.

[axlealex]

Thanks Dave T. I closed off the line going to warmup regulator. No difference, actually now getting 38-40 psi. It has to be the pump, right? I've exhausted all other measures. Or am I missing one? Followed all diagnostics in Manuel. Guess I'll hand it off to the guys at DmcCal, let the experts handle it. Also when the temp outside is 111, makes working on the D that much more painful.

[DMCMW Dave]

Thanks Dave T. I closed off the line going to warmup regulator. No difference, actually now getting 38-40 psi. It has to be the pump, right? I've exhausted all other measures. Or am I missing one? Followed all diagnostics in Manuel. Guess I'll hand it off to the guys at DmcCal, let the experts handle it. Also when the temp outside is 111, makes working on the D that much more painful.

Or a plugged pickup filter or the filter under the car. Or as mentioned the hoses are backwards, or kinked. A kinked return hose will cause some pretty strange readings too. Check that the inline check valve is facing the right way, although if it's backwards the pressure should be closer to zero.

[Ron]

$.02

Sounds like the pump or pump filter to me -- you should have got >90psi when you checked it at the pump (assuming all else was disconnected)...

[Bitsyncmaster]

I have seen a plugged fuel filter cause zero pressure at the normal pressure test position. I was amazed that could happen and though maybe the filter had a defect somehow.

40 PSI is pretty normal for rest pressure which is why I thought you may have been testing without the WUR hose blocked off (the tester valve closed).

[Rich]

So it's a little confusing, this data.

Is this reported fuel pressure reading (~45PSI) obtained when the pump is running with RPM relay jumped or is it the rest pressure (seen at some time after pump has been off)?

It's OK as rest pressure, not OK as system pressure.

So I finally got back to working on this fuel pressure problem (dang life getting in the way). New unit from DmcCal. Checked to make sure it was getting the right voltage, which it is 12.4V. I also hooked it directly to battery to make sure pump was getting the right voltage. Good to go on that. Now I am up to about 45psi the rpm relay is jumped. At a loss here. The sensor plate has to much resistance on it, not free floating. It's like there's pressure pushing plunger down. Not sure that has to do with the lack of pressure, and no injectors opening.

[Bitsyncmaster]

You should be getting 75 psi with the pump running. Then when the pump is turned off the pressure will drop very quickly to 40 to 43 PSI rest pressure.

[axlealex]

That's why I'm so confused. I'm getting 38-40 psi with pump running and rpm relay jumped. I tested the pressure where the fuel enters the distributer to see if fuel filter was plugged, and then tested right at the pump. Had the same readings of 40psi, both with fuel pressure gauge forward and aft of fuel filter. Filter would be bad if I got two different readings, right? Not seeing any kinks or bends in pressure or return lines. No leaks.

The check valve is facing the right way, because I do get pressure. I put test gauge forward and aft of check valve to see if I got different readings. No effect. Double checked that hoses weren't backward. The pump is receiving the right voltage. Rest pressure holds steady at 40psi when pump is off.
Appreciate all the responses.

[Bitsyncmaster]

What sets the 75 PSI is the primary pressure regulator inside the fuel distributor. So checking the pressure at the pump you should be reading higher than 75 PSI, I would expect 100 PSI or more.

It sure sounds like your pump is faulty since you have verified you are getting 12 volts over the two pump terminals.