LB7 Throwing P1093 Fuel Rail Pressure Low during power enrichment - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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Duramax First Generation: 2001-2004 (LB7) Discuss the first generation (2001-2004 LB7) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 08-22-2019, 02:02 PM   #1 (permalink)
rickbat
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LB7 Throwing P1093 Fuel Rail Pressure Low during power enrichment

Recently purchased a 2002 Duramax with tons of issues so far. I have most squared away but im getting a P1093. I'm running autoenginuity Scanner to monitor Desired vs actual fuel rail pressure. I can see the truck is asking for 21000 at WOT and only betting about 8000.

Mods:
Stock truck to the best of my knowledge.

Things i have already done:
1. Replaced the MAF
2. Replaced FPR
3. Replaced PRV with race plug
4. Replaced rubber lines on the 1/2 fuel feed line.
5. Checked lines coming to and from fuel filter.
6. Replaced fuel filter

I'm thinking i'm running out of cheap items and iin denial of it maybe an Injector pump issue...? In my past life owning a 60. Powerstroke a dead Injector pump meant no start condition is the Duramax pump that different?

Need some Duramax expertise...

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Old 08-23-2019, 07:52 AM   #2 (permalink)
Rvn4me
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P1093 Large Leak; difference between commanded fuel pressure and actual pressure is greater than 20 Mpa. Large leak means there is a leak in the high pressure system. Large leaks go into the return system and flow back to the tank, these are not external leaks.
1) If P0087 is set, solve P0087 first.
2) Similar Diagnostics to P0087

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. Buy Racor Fuel Filter Head Assembly
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.
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.

Also note that 1 MPa (megapascal) is equal to approximately 145 PSI, 100 kpa is roughly 14.5 PSI.


Last edited by Rvn4me; 08-23-2019 at 07:58 AM.
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Old 08-23-2019, 09:00 AM   #3 (permalink)
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Thank you for the reply!

I'm going to pickup some 1/2 clear tubing and look into setting the rail pressure at idle to 21000 psi. Need to figure out where to command that in autoenginuty cant be to hard to do im sure.

The truck throws the code every time you put the pedal to the floor and make it try to take off. If you try this from a dead stop on a steep grade the truck just sits in place wont move or build rail pressure.

I ran the injector balance test on all 8. They all showed between + or - 2. It sits and idles perfectly not much smoke from tailpipe ever. A friend also told me try to run the contribution test on the injectors.

Will keep you posted...
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Old 08-23-2019, 09:14 AM   #4 (permalink)
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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. Follow the GM fuel system diagnosis in the service manual.

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 Ė 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 donít 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.
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Old 08-30-2019, 05:11 PM   #5 (permalink)
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I have done some more work and some additional testing. I have replaced all the line from the fuel tank to the front and added lift pump inline to help with fuel delivery. What i see now when scanning is a bit different but still under load the truck will not achieve desired rail pressure. If its in park and you rev it it can hit as high as 17k actual rail pressure. When under load will not go above 8k.

Also seems odd to me if i command 21k rail pressure the truck only hits about 8k. But if i rev it in park it has hit 17k seems odd to me.
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Old 09-03-2019, 08:54 AM   #6 (permalink)
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Did a return test 15 second crank 91ML so guessing injectors are not leaking etc. Time to purchase a new CP3 i'm thinking. Anyone have recommendations? Not looking to build the truck just want reliability thinking remaned Bosch or new. Im sure new is the safest and more money any reputable remans or just go new?
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2002 Duramax LB7 220K

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Bosh injectors at 153K
CP3 New Bosh at 220K
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Old 09-03-2019, 09:11 AM   #7 (permalink)
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We have great prices on our Brand New Bosch CP3 pumps! In stock and ready to ship! Let me know if I can help.
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Old 09-11-2019, 08:26 AM   #9 (permalink)
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I finally installed the new CP3 and the truck now hits desired rail pressure immediately. The pump was leak and on its way out!.

So now what I'm noticing is when you hold the brake and push the throttle to the floor the desired is only 6k and the truck does nothing. Also if you put the truck on a steep grade it will sit at 6k desired and not move or it will build desired pressure slowly and start to take off. This seems like if I would put a heavy trailer on it would do the same and would be dangerous. I'm not real familiar with Duramax but th
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Old 09-11-2019, 08:28 AM   #10 (permalink)
rickbat
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I finally installed the new CP3 and the truck now hits desired rail pressure immediately. The pump was leak and on its way out!.

So now what I'm noticing is when you hold the brake and push the throttle to the floor the desired is only 6k and the truck does nothing. Also if you put the truck on a steep grade it will sit at 6k desired and not move or it will build desired pressure slowly and start to take off. This seems like if I would put a heavy trailer on it would do the same and would be dangerous. I'm not real familiar with Duramax but this seems wrong.

The throttle position sensor is reading and boost had gone as high as 32psi on scanner starting at 14 from idle. No codes after cp3 install.

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2002 Duramax LB7 220K

CAI
Bosh injectors at 153K
CP3 New Bosh at 220K

Last edited by OkDually; 09-11-2019 at 08:46 AM. Reason: sig
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