Fuel pressure

[deloryan]

I’m trying to diagnose an issue where engine really stutters on acceleration. It is idling okay but doesn’t want to rev. My fuel pressure on both control and primary is low but adding shims is not helping. I replaced my fuel pump with the new style thinking maybe the old pump just wasn’t putting out enough pressure.

I’m checking a few other things and am wondering if my WUR has a dirty screen or is this the screen itself. It doesn’t look like other pictures I’ve seen.

5740044F-4A69-41E6-A413-948AAE896BC5.jpg

[Helirich]

Have you checked/replaced the fuel filter. I haven't had much luck with the shims either.

Is this a problem that just started? Or are you working on a car that's been sitting?

There are several screens stacked up in there. You might want to remove them with a pick. If the screens are clogged, you will have high control pressure.

[deloryan]

I replaced the fuel filter today. I’m only getting 5 bar directly at the fuel pump. And about 4.5 bar where the line enters the fuel distributor. So I think that tells me the fuel pump is not strong enough, even though it is new. It’s the AC Delco MU1777. And the accumulator, filter, and lines are restricting a bit of pressure. So it isn’t going to matter how many shims go in if the base pressure isn’t even high enough.

Car sat the last two summers. I drained and cleaned the fuel tank, too.

[Ron]

Something seems wrong here -- The pressure at the FD should match the pump pressure. (The accumulator, filter, and lines might restrict flow, but not pressure to the FD).

Also, with 4.5 Bar at the FD, the control pressure being low wouldn't have anything to do with the pump...
So I would suggest checking for leaks, the fuel line routing, and double checking the pressure at the pump (and replace it if not >6 Bar before going further).

FuelHose2.jpg

[FABombjoy]

You can also leak past fuel the accumulator seal to the return line which would present similarly. That is, higher pressure at pump than at fuel distributor. This is a failure mode not discussed much but happens with time.

[deloryan]

You can also leak past fuel the accumulator seal to the return line which would present similarly. That is, higher pressure at pump than at fuel distributor. This is a failure mode not discussed much but happens with time.

I’ve ordered an accumulator as this one is about 15 years old, so could be an issue. I also think something must be wrong with the new fuel pump itself since I’m not seeing great pressure there. Battery is new and voltage is good at the fuel pump.

[Ron]

^^^

You can also leak past fuel the accumulator seal to the return line which would present similarly. That is, higher pressure at pump than at fuel distributor. This is a failure mode not discussed much but happens with time.

+1!

[deloryan]

Making some progress on the fuel issues. My primary pressure is still low, but about the same as at the pump, 4.5 bar. I replaced the accumulator, previously replaced the PPR o-rings, new fuel filter, and new-style fuel pump.

I pulled the injectors, one was barely a dribble, one sprayed a stream, and the rest were only misting out of half the cone. I'm getting new ones. Car starts fine, but won't accelerate. Idle is pretty shaky, too. Hoping most of my issues are now injector related. I still have the original fuel lines so will be replacing those at the same time.

I'm also cleaning up the CPR. My original post had a picture of the screen, and I pulled it out today, but had to drill a screw into it to remove it. What kind of material is this? It's like a copper cotton ball, but it's so crushed together that nothing was flowing through. I've ordered a rebuild kit, but now that there's no filter, can I put one of these filter baskets back in the hole or do I need to come up with something else? https://www.deloreango.com/us/fuel-d...ne-filter.html

CPR filter.jpg

[deloryan]

Something seems wrong here -- The pressure at the FD should match the pump pressure. (The accumulator, filter, and lines might restrict flow, but not pressure to the FD).

Also, with 4.5 Bar at the FD, the control pressure being low wouldn't have anything to do with the pump...
So I would suggest checking for leaks, the fuel line routing, and double checking the pressure at the pump (and replace it if not >6 Bar before going further).

FuelHose2.jpg

Not seeing any leaks and nothing on the ground. I haven’t messed with fuel lines(except the one for pressure testing) so they are all routed correctly. I agree, it seems the fuel pump might be the issue even though it’s new. Any recommendations on a better replacement? I don’t want to go back to the old style.

[Jonathan]

Double check the two hose connections on the fuel pump, maybe they got switched around?