Fuel pressure

[FABombjoy]

I connected the gauge directly to the pump at the tank and was only seeing 5 bars there, so I’m not starting from a good pressure.

Was the return loop still in place? Fuel pressure is created by restriction so if you have a leakdown between primary and return the whole primary side would read low.

You should definitely perform the rest pressure check as mentioned by 82DMC12 as this will let you know if the accumulator is suspect, or if there is some other path that bypasses the PPR. Your module has been used in other K-jet DMCs successfully and should be OK.

[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

[Bitsyncmaster]

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

That is normal for those crushed brass filters. I would check your control pressure without the filter installed. My guess is your WUR is bad if the control pressure is the same as your primary pressure.

[Ron]

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'd try powering the pump right off of a fully charged battery. And if the pressure, measured right at the pump, was still low, pull it. And if the pump intake was not restricted, I'd replace it.

[David T]

Typically the problem is not the fuel pressure, it is the injectors and vacuum leaks. Fuel pressure problems generally cause problems at high RPM's or under load. Have your injectors cleaned, very often injectors can be salvaged by a good cleaning using the injector tester/cleaner. If the injector seals are hard, replace them and use new copper washers.

[deloryan]

Thanks for the help everyone. I've got my fuel pressure dialed in and it is running great. Except with the A/C on. Then it really struggles to accelerate under load. Voltage at the jump start post is 13.6 with A/C off, 12.5 with A/C on. I'm thinking this must be voltage related. I've replaced the battery. Where should I be checking voltage? What should I investigate next?

Below are the other components I've replaced while getting the fuel issues sorted:

Fuel Pump - new style
Accumulator
Fuel Filter
Fuel Injectors
All new fuel hoses (replaced the 40 year old ones finally)
hot-start o-rings in PPR
Rebuilt CPR (rebuild wasn't nearly as difficult as I thought it would be)
Ran vacuum test and idle speed motor was leaking badly, so replaced that
New spark plugs
New battery

[MrChocky]

Thanks for the help everyone. I've got my fuel pressure dialed in and it is running great. Except with the A/C on. Then it really struggles to accelerate under load. Voltage at the jump start post is 13.6 with A/C off, 12.5 with A/C on. I'm thinking this must be voltage related. I've replaced the battery. Where should I be checking voltage? What should I investigate next?

Below are the other components I've replaced while getting the fuel issues sorted:

Fuel Pump - new style
Accumulator
Fuel Filter
Fuel Injectors
All new fuel hoses (replaced the 40 year old ones finally)
hot-start o-rings in PPR
Rebuilt CPR (rebuild wasn't nearly as difficult as I thought it would be)
Ran vacuum test and idle speed motor was leaking badly, so replaced that
New spark plugs
New battery

These voltages seem reasonable; but obvious things would be alternator and grounding. As an aside, DM's idle ECU does an "A/C bump" for idling with A/C, but that is not relevant to this.

[SupercoolBill]

I am curious, did you ever get this figured out?

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[deloryan]

I am curious, did you ever get this figured out?

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Yes, the final piece of the puzzle was the alternator. It was not making enough power at higher rpm. Once I replaced that it accelerates great again.