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Discussion Starter #1 (Edited by Moderator)
Been troubleshooting a P0087 code. Changed the 2 kinked fuel lines up towards the motor. No change. Just tried the vacuum gauge on the test port. Start the truck and it starts at 5inHG and steadily climbs to about 10 or 15. Once put under load it climbs all the way to 25 and stays there, even when back at idle. I reckon the fuel lines by the cooler and tank are next, although under physical inspection, there doesnt appear to be kinks. Does the tank pickup have a screen?
 

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Have you tried removing the fuel tank cap to see if that has an effect? I believe the fuel tank does have some kind of mesh at the pickup.
 

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P0087; fuel rail pressure is less than 22.5 MPa at more than 600 RPM, fuel rail pressure too low.

1) Excessive restriction, fuel supply, plugged filter or sucking air. Install special tool J44638 to check vacuum restriction on fuel supply to the high pressure pump. Maximum restriction at WOT (wide open throttle) is 5 inches HG in park. When driving under hard acceleration maximum would be 7-8 inches Hg. If too high replace the fuel filter and retest.
2) If restriction is only a couple of inches vacuum, that could indicate that the fuel supply system is sucking air, use clear fuel lines at the filter head to check for air.
3) Excessive restriction could also cause a DTC P1093 to set at the same time.
4) Rail pressure should read 1-1.8 MPa with key on and engine off. If out of range replace the rail pressure sensor. (0 PSI LBZ)
5) Check fuel return from the high pressure limit valve or fuel pressure relief valve. If it is leaking then it will need to be replaced. We have also heard of race plugs leaking, even if you have a race plug, you may want to check for leakage at max rail pressure.
6) With the engine up to operating temperature, use the scan tool to command rail pressure to 21,000 PSI, if the rail pressure will not achieve 21,000 PSI at idle you most likely have a problem with the injectors, especially if you are having a hard start, miss, rough run or smoke and balance rates are excessive. Perform the enhanced injector return test.
7) Disconnect the fuel rail pressure sensor the fuel pressure should be greater than 175 MPa as displayed on the scan tool.
8) If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.

Fuel Supply and Fuel Filter Housing

The fuel filter housing is on the suction side (there is not a supply pump from the factory) and are prone to suck air.

1) Install fuel vacuum test tool.
2) Prime the fuel system with the hand primer until 10 PSI is indicated on the gauge, check for external leaks and repair. If the pressure drops from 10 PSI to 2 PSI in less than 1 minute, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for 2 – 15 second intervals, the high pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system it will cause a false/low reading.
3) Install clear hoses at the inlet and outlet of the fuel filter housing. Re-prime the system and then start the engine, there should be very little air going into or coming out of the fuel filter housing.
4) Common air ingestion places are the filter housing, plugged filter, drain valve, rubber hoses and connections. You need to use clear lines to isolate where the air is coming from and work your way back toward the tank until you don’t have any more air coming through the clear line. Unless you know where to get the tool that sees through black rubber lines to find air, your only other option is to bounce around and replace parts.

No Start or Hard Start

1) Excessive fuel restriction, check or change fuel filter
2) Use vacuum gauge, check the suction, you should have no more than 5 inches Hg at WOT (wide open throttle) or 7-8 inches Hg under load. If you have too much suction, after changing the fuel filter, the restriction could also be the sock in the tank. Too little vacuum (less than 2 inches Hg) means that it could be sucking air.
3) Check for air in fuel system, install clears lines before and after the filter housing to check for air in the lines.
4) Confirm actual versus desired rail pressure, even under crank no start conditions
5) If the above check good, then it comes down the following.
a. fuel injectors (see injectors for more diagnostic information)
b. high pressure injection pump – CP3
c. Fuel pressure regulator, check to make sure it is not stuck.
d. fuel pressure relief valve (high pressure limit valve), check to make sure it is not leaking into the return system when rail pressure is 160 MPa.
6) Before condemning the high pressure pump you need to make sure there are no high pressure fuel leaks. Use the EN-47589 (same block-off caps as #9011 SPX Miller tools) cap set to cap off the injector rail to isolate the injectors from the injector return system.
 

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Discussion Starter #4
Have you tried removing the fuel tank cap to see if that has an effect? I believe the fuel tank does have some kind of mesh at the pickup.
Ill have to try that next. Does the cap act as sort of a breather or pressure re regulator?
P0087; fuel rail pressure is less than 22.5 MPa at more than 600 RPM, fuel rail pressure too low.

1) Excessive restriction, fuel supply, plugged filter or sucking air. Install special tool J44638 to check vacuum restriction on fuel supply to the high pressure pump. Maximum restriction at WOT (wide open throttle) is 5 inches HG in park. When driving under hard acceleration maximum would be 7-8 inches Hg. If too high replace the fuel filter and retest.
2) If restriction is only a couple of inches vacuum, that could indicate that the fuel supply system is sucking air, use clear fuel lines at the filter head to check for air.
3) Excessive restriction could also cause a DTC P1093 to set at the same time.
4) Rail pressure should read 1-1.8 MPa with key on and engine off. If out of range replace the rail pressure sensor. (0 PSI LBZ)
5) Check fuel return from the high pressure limit valve or fuel pressure relief valve. If it is leaking then it will need to be replaced. We have also heard of race plugs leaking, even if you have a race plug, you may want to check for leakage at max rail pressure.
6) With the engine up to operating temperature, use the scan tool to command rail pressure to 21,000 PSI, if the rail pressure will not achieve 21,000 PSI at idle you most likely have a problem with the injectors, especially if you are having a hard start, miss, rough run or smoke and balance rates are excessive. Perform the enhanced injector return test.
7) Disconnect the fuel rail pressure sensor the fuel pressure should be greater than 175 MPa as displayed on the scan tool.
8) If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.

Fuel Supply and Fuel Filter Housing

The fuel filter housing is on the suction side (there is not a supply pump from the factory) and are prone to suck air.

1) Install fuel vacuum test tool.
2) Prime the fuel system with the hand primer until 10 PSI is indicated on the gauge, check for external leaks and repair. If the pressure drops from 10 PSI to 2 PSI in less than 1 minute, remove the fuel outlet line from the filter and cap it. Remove the ignition 1 relay and crank the engine for 2 – 15 second intervals, the high pressure pump should pull at least 12 inches of Hg vacuum. If air gets into the system it will cause a false/low reading.
3) Install clear hoses at the inlet and outlet of the fuel filter housing. Re-prime the system and then start the engine, there should be very little air going into or coming out of the fuel filter housing.
4) Common air ingestion places are the filter housing, plugged filter, drain valve, rubber hoses and connections. You need to use clear lines to isolate where the air is coming from and work your way back toward the tank until you don’t have any more air coming through the clear line. Unless you know where to get the tool that sees through black rubber lines to find air, your only other option is to bounce around and replace parts.

No Start or Hard Start

1) Excessive fuel restriction, check or change fuel filter
2) Use vacuum gauge, check the suction, you should have no more than 5 inches Hg at WOT (wide open throttle) or 7-8 inches Hg under load. If you have too much suction, after changing the fuel filter, the restriction could also be the sock in the tank. Too little vacuum (less than 2 inches Hg) means that it could be sucking air.
3) Check for air in fuel system, install clears lines before and after the filter housing to check for air in the lines.
4) Confirm actual versus desired rail pressure, even under crank no start conditions
5) If the above check good, then it comes down the following.
a. fuel injectors (see injectors for more diagnostic information)
b. high pressure injection pump – CP3
c. Fuel pressure regulator, check to make sure it is not stuck.
d. fuel pressure relief valve (high pressure limit valve), check to make sure it is not leaking into the return system when rail pressure is 160 MPa.
6) Before condemning the high pressure pump you need to make sure there are no high pressure fuel leaks. Use the EN-47589 (same block-off caps as #9011 SPX Miller tools) cap set to cap off the injector rail to isolate the injectors from the injector return system.

Thanks for the info. Ill try what i can but i have no scan tool to manipulate pressures. Do you have a model of scan tool to recomend? I know the techII is what is recommended but i cant seem to find a trustworthy source to purchase one that has programming.
 

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As fuel is removed from the tank, it must be replaced by air that is admitted by the cap, but the cap must seal if there is pressure in the tank. If you find that removing the tank cap makes a difference, you could try to wash the cap with hot, soapy water and see if cleaning makes a difference.
 

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Discussion Starter #6
The cap trick didnt seem to have an effect. And hooking up the gauge, pumping the primer to 10psi, it drops from 10 to just a hair above 7 in 1min. I see no sign of fuel leaking.
 

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Been troubleshooting a P0087 code. Changed the 2 kinked fuel lines up towards the motor. No change. Just tried the vacuum gauge on the test port. Start the truck and it starts at 5inHG and steadily climbs to about 10 or 15. Once put under load it climbs all the way to 25 and stays there, even when back at idle. I reckon the fuel lines by the cooler and tank are next, although under physical inspection, there doesnt appear to be kinks. Does the tank pickup have a screen?
I have a kinked line I need to replace. The GM tech bulletin says to use 100R3 hose. Well that is not available in canada - could I use fuel injection hose?? My truck is stock with no lift pump yet (will happen) and just want to know what hose you used to replace your kinked lines. Thank you
 

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There are LOTS of diesel trucks in Canada that need replacement fuel lines. Look for a diesel repair shop or a parts house that specializes in diesel parts or makes hydraulic lines for construction equipment. They are very likely to have what you need.
 
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