Loss of fuel pressure

[Oregoncruiser]

Good evening, I’m trying to help my son get his pickup back on the road. Truck is a 2006 2500 quad cab automatic with 290k. It was starting hard and but ran fine once started, then the mods came.

Replaced lift pump with Airdog 100gph pump. Replaced injectors with thoroughbred 100hp injectors, along with 6.7 feed tubes. Truck would run great for about 20 min then seem to run out of fuel. Took it to a local shop who claimed Injection pump was losing pressure when the engine began faltering. So he brought it home and replaced injection pump. Same issues, runs fine for about 20 minutes then you lose fuel pressure, cel comes on and it’ll barely run.

Any ideas where to go next on this? Hate to see him continue to throw money at this blindly. I’d appreciate any suggestions you have.

 

[Topzide]

I think that the first thing would be to get a service manual for the truck. That way, you would be able to go through the steps to diagnose the problem, step by step.

Sounds to me that is losing power in the system. Good luck with the issue.

 

[Topzide]

This was in another thread; https://www.bluechipdiesel.com/troubleshooting-quick-reference

Might help in what you're dealing with, or give ideas on where to turn.

 

[sag2]

Before you replaced the HP pump it would have been wise to verify the lift pump pressure at the HP pump inlet. The CP3 hardly ever fails, especially intermittently.

 

[Crunch]

You don't mention it, but were any codes thrown? I'd check that before anything else.

 

[CharlesinGA]

Just my opinion here, but a 300K mile truck suddenly getting 100 hp mods (implying its being driven a LOT harder than ever before) is, in my eyes, a recipe for disaster.

Checking the lift pump for FLOW is essential. Pressure is only a couple of five psi, but if you have a flow issue..........

Charles

 

[AH64ID]

Good evening, I’m trying to help my son get his pickup back on the road. Truck is a 2006 2500 quad cab automatic with 290k. It was starting hard and but ran fine once started, then the mods came.

Replaced lift pump with Airdog 100gph pump. Replaced injectors with thoroughbred 100hp injectors, along with 6.7 feed tubes. Truck would run great for about 20 min then seem to run out of fuel. Took it to a local shop who claimed Injection pump was losing pressure when the engine began faltering. So he brought it home and replaced injection pump. Same issues, runs fine for about 20 minutes then you lose fuel pressure, cel comes on and it’ll barely run.

Any ideas where to go next on this? Hate to see him continue to throw money at this blindly. I’d appreciate any suggestions you have.

What codes is it throwing?

 

[Oregoncruiser]

You don't mention it, but were any codes thrown? I'd check that before anything else.

 

[Oregoncruiser]

Finally got my son motivated to get this thing going. Here’s some updates.

there were definitely codes, but they cleared them without noting them, so not helpful.

put a mechanical fuel pressure gauge on the lift pump and confirmed consistent pressure - set at 20psi.

Removed supply line from lift pump to Cp3 and watched fuel flow without any strange observations.

Here’s where I think the problem may be. Bullydog programmer/monitor was showing fuel pressure at 30, then suddenly dropped to 0 . I cannot confirm where this reading is from, but as far as I know there is no sensor on lift pump, so doesn’t this have to be fuel rail pressure? Maybe bad fuel rail pressure sensor or relief valve.

I appreciate all input, and I apologize that I don’t have better intel. Trying to help from a distance and eliminate throwing good money after bad.

 

[AH64ID]

Clearing the codes was definitely a mistake.

What is the AD doing for fuel pickup?

 

[Ozymandias]

20psi lift pump is to much for the CP3, 10 is normal.

30-something doesn't match any pressure the Rail has.
Idling you'd see 7000psi plus, maxing out at 23'000psi under some load conditions.

Try to start it with the fuel metering valve at the CP3 disconnected.

 

[Oregoncruiser]

Clearing the codes was definitely a mistake.

What is the AD doing for fuel pickup?

Not sure what you’re asking here. Supposedly they modified the factory sending unit with the AD kit. So I’m thinkinking the plastic fuel tube with the 45 is positioned in the bottom of the sending unit.

am I answering what you’re asking?

 

[Oregoncruiser]

20psi lift pump is to much for the CP3, 10 is normal.

30-something doesn't match any pressure the Rail has.
Idling you'd see 7000psi plus, maxing out at 23'000psi under some load conditions.

Try to start it with the fuel metering valve at the CP3 disconnected.

thanks for the tip on the cp3 inlet pressure. I’ll have him dial that back.

Regarding the monitor showing 30 on fuel pressure, I’m at a loss. I was originally thinking it was in 1000’s, rounded?? Whatever it’s reading goes to 0, and corresponds to the truck running rough. After it went to 0, he unplugged the fuel rail pressure sensor and it came back up to 2.

so I suspect a bad fuel rail pressure sensor thinking this…. When the gauge goes to 0 erroneously, the ecu throws more fuel at it to compensate. That’s when it loads up, and runs cruddy.

Would starting it with the fuel metering valve disconnected eliminate that compensation I’m referring to above?

 

[AH64ID]

Not sure what you’re asking here. Supposedly they modified the factory sending unit with the AD kit. So I’m thinkinking the plastic fuel tube with the 45 is positioned in the bottom of the sending unit.

am I answering what you’re asking?

Yes. Could the pickup be blocked and after a while the truck acts like it runs out of fuel?

Or sucking the pickup closed after 20 minutes.

thanks for the tip on the cp3 inlet pressure. I’ll have him dial that back.

Regarding the monitor showing 30 on fuel pressure, I’m at a loss. I was originally thinking it was in 1000’s, rounded?? Whatever it’s reading goes to 0, and corresponds to the truck running rough. After it went to 0, he unplugged the fuel rail pressure sensor and it came back up to 2.

so I suspect a bad fuel rail pressure sensor thinking this…. When the gauge goes to 0 erroneously, the ecu throws more fuel at it to compensate. That’s when it loads up, and runs cruddy.

Would starting it with the fuel metering valve disconnected eliminate that compensation I’m referring to above?

30K psi is high, but if it’s rounding then it could be that high especially if it’s not a stock tune. Stock runs 23,206 commanded peak.

The pressure dropping to 0 is likely the result of the issue, not the issue.

The ECM will try to command more fuel with the FCA on the CP3 but it won’t get any higher than the pressure relief valve allows which is 26K stock. It might make some timing rattle but that’s about it.

Disconnecting the FCA will let the CP3 run at max pressure, confining it can build max pressure. I wouldn’t drive it that way, but a good test when it dies to see if that’s the issue.