Low fuel pressure.

[axlealex]

So I'm getting 28 psi from the fuel pump. That's bad right? New fuel pump/sending unit. May be clogged. Shop that put in new one, may not have throughly cleaned tank. Are the new pumps able to be disassembled?

[sdg3205]

Where are you measuring this from? Is this while the pump is jumped? Does it hold rest pressure?

I've had shops claim they cleaned tanks and it was pure lies. Other than Dmc vendors, take what a lot of shops out there claim they do with a grain of salt. They don't care about your car, and they will cut corners if they think they can.

[Bitsyncmaster]

My guess would be they swapped the hoses at the fuel pump. Other possibility is the PPR O-ring has failed but I've not seen a PPR fail that badly.

[DMCMW Dave]

My guess would be they swapped the hoses at the fuel pump. Other possibility is the PPR O-ring has failed but I've not seen a PPR fail that badly.

I've seen fuel distributors with no o-rings and the pressure will be higher than that.

[David T]

I've seen fuel distributors with no o-rings and the pressure will be higher than that.

The pump can't be taken apart. Actually it can but you can't put it back together so don't take it apart. Low pressure can be because of a plugged input screen or a collapsed pick-up hose. The thing to do is to empty the tank, take all of the parts out, clean everything thoroughly, and reassemble properly replacing any bad parts. If the pick-up hose is soft and kinks easily put a spring in it and/or replace it. I would not jump to conclusions about the PPR just because of low pressure.

[DMCMW Dave]

So I'm getting 28 psi from the fuel pump. That's bad right? New fuel pump/sending unit. May be clogged. Shop that put in new one, may not have throughly cleaned tank. Are the new pumps able to be disassembled?

Yes, the lower baffle can be removed, pump motor pulled out and the inlet filter replaced. Look down into the baffle, if it's full of crud you need to clean it up. And you'll probably need to change the main filter again if they didn't really clean out the tank.

I agree with the above comment - we've done a few cars where the tank was so-called cleaned by someone else. To the average shop cleaning the tank means emptying it out and filling it again. To me it means emptying it, cleanout out everything so that it's perfectly clean and dry, then vacuuming the remaining dust/dirt out. Takes 1-3 hours depending on what you are starting with, and it's done without taking the tank out of the car.

[Rich]

So I'm getting 28 psi from the fuel pump. That's bad right? New fuel pump/sending unit.

New pump? Good connections to it?

Low voltage (measured while it runs) or bad ground to pump can cause low fuel pressure.

[axlealex]

Thanks for the replys. I tested the pressure at the distributor. Read 28 psi, so then i tested at the pump thinking it might be the filter is plugged. Got the same reading, 28 psi. Fuel pump was converted to new unit, no baffle. So the pickup screen at the pump motor must be clogged? I removed the unit and there was brown gunk underneath it. If I can't take the new unit apart, then I guess a new one is in order? Or can I send it in to be fixed?

[axlealex]

Oh forgot. It holds rest pressure.

[DMCMW Dave]

Thanks for the replys. I tested the pressure at the distributor. Read 28 psi, so then i tested at the pump thinking it might be the filter is plugged. Got the same reading, 28 psi. Fuel pump was converted to new unit, no baffle. So the pickup screen at the pump motor must be clogged? I removed the unit and there was brown gunk underneath it. If I can't take the new unit apart, then I guess a new one is in order? Or can I send it in to be fixed?

Which "new" pump(?), you don't mention where it came from. Got pictures of the screen?

I've never seen any pump do low pressure like that. Are you sure the gauge is working?

[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. 3522235223

[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. 3522235223

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.