Need Help With Duramax 6.6L — Lack of Power Under Load

Joel Diagnostician Soquel, California Posted   Latest   Edited  
Question
Driveability
2002 Chevrolet Silverado 2500 HD 6.6L (1 LB7) 4-spd (4L80-E)
P0101 - Mass or Volume Air Flow Sensor "A" Circuit Range/Performance
Lack of Power
P1093 Fuel Pressure Low During Power Enrichment

02 Chevrolet Silverado 2500 HD 6.6l LB7 lack of power under load

1GCHK23122F186377 

DTC P1093 Fuel pressure low during power enrichment P0101 MAF sensor circuit out range .

diag​.​net/file/f4m56tl1y… ​ I was called for this diagnostic, customer concern lack of power under load, after scanning the vehicle I found the codes mentioned above, duplicated customer concern on road test, actual and desire fuel pressure did not match, I precede to visual inspection and I found some seepage around the fuel filter housing at this point I suggested to replace the fuel filter housing along with the fuel filter, start with the obvious and I though this one was easy. For the MAF sensor dtc I check the air filter it was dirty I recommended to be replaced with good quality parts.

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diag​.​net/file/f49zx1fqq… ​ Customer bought on eBay the fuel filter with housing a/c Delco parts and Wix engine filter. Replace them and both DTC returned and same customer concern lack of power (customer is replacing himself at his time this parts), I connected my scanner and also the fuel pressure/vacuum gauge to shredded valve port on scan data nothing change the fault occurred under the same conditions and scan data same than data before. My vacuum gauge under load was excessive at 25 inhg , spec are 8 to 12 inhg. Note: the vacuum gauge at 3000 rpm no load max vacuum reading 6 inhg , wot 8 ingh. Actual and desire fuel pressure only dropped during driving under heavy load only, 

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I keep looking for restriction recheck customer fuel filter installed , found 3 areas kinked lines by filter ,he said new fuel filter housing inlet and out let hoses were routed different he couldn't reused original fuel lines ( I called the dealer they said is updated part fuel lines have to be reroute ),

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nice I corrected that another road test , I still have the same scenario at the beginning same vacuum at wot 25 inhg. Scan data same I decide to scope test fuel rail pressure sensor capture is attached.

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I follow carefully the fuel lines starting from the gas tank looking for visible pinch/.restrictions , it has add on fuel filter/pump the fuel lines have been routed professional and good quality hoses , now I found something at some point the transmission was replaced and they did not attached the hard metal fuel lines on the brackets , they left the fuel lines hanging at a position I was compressing pinching the fuel lines rubber junction at LH driver side I reattached everything back together the fuel line kink seems to be recover , I go for my next road test guest what same 25ingh vacuum , lack of power present , I removed the fuel tank gas cap ,same result , I took out the picture by pass the add on fuel filter pump to eliminate plugged filter , same result than above no changes . Well I decide to remove a replace the fuel filter with wix just in case it had some manufacture issues now my conditions change with wix filter I get same conditions mentioned above but now I lose the fuel pressure to 0 mpa and vehicle stalled but restart with no issues , before replacing the wix filter minimum fuel pressure dropped to 16 mpa when lack of power was present . There is some smoke coming out the tail pipe assumed the fuel injector are already damages from lack of lubrication. I question the customer I wanted the complete history about engine performance repair ,customer stated about a year ago he bought the truck and was having a lot of smoke coming out the tail pipe he took it to a shop they diagnosis the fuel injector and high pressure pump to be defective , the 8 fuel injector were replace and the high pressure pump , he said after he pick up the truck at the shop after repair was completed and an his first road test going uphill and under load he experience lack of power he went back to the shop but no more smoke coming out tail pipe , they recommended to install an add on fuel pump to supply the low side of high pressure pump as they mentioned this vehicle has common issues feeding the hp. They installed and he had no more problems since them, until about 2 weeks ago check engine light came on accompanied of lack of power. Other testing I have done power balance test ,good /relative compression was good, the fuel injector balance rate on cyl 8 has negative -4 to -7 mm3 is removing fuel the PCM I am suspecting my smoke coming out is from this injector. I commanded the fuel pressure regulator to max fuel pressure both the actual and desire math each other with no issues. And I found the actual does not match the desire FRP only up hills and aggressive wot on flat surface on high way city is fine even at wot . 

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I am not diesel expert but I would like to fix this truck from the root of the cause as about a year ago they replaced the high pressure components. I know I will have to replace the 8 fuel injector with bosh units and the fuel junction box too. Many questions comes to my mine as what is the problem is because we are not feeding the high pressure pump with the right amount of fuel volume due to 25 ingh vacuum restriction?? Is the pump capable of producing the pressure? Or do we have any control of pressure release issues to maintain the adequate fuel pressure desire, I was reading the fuel pressure release valve is being issue on this truck but will this interfere with low side to create a suction issues also excessive fuel injector fuel return ?? How can this effect on low side to build up vacuum. Does this Duramax have fuel filter inside the gas tank as the power stroke on pick up?? Are there different fuel filter housing for this 6.7 engine why my fault changed with the wix filter ? I understand about smoke on tail pipe being fuel injector issues, any suggestion is appreciated and welcome here I am now last conditions .

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Bill Technician
Rosetown, Saskatchewan
Bill Default
   

You can get fairly high readings if you are dumping too much return, but I don't feel thats whats happening here. To me it seems that you have multiple issues. My recommendation would be to get a TP3018 fuel filter on there first off. Take some pictures of the fuel lines and send them from different distances in the fuel filter area. Looks to be a mess there? May want to go OEM. I think this…

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Joel Diagnostician
Soquel, California
Joel Default
   

thanks , how can I measure the return with pico what tool ??

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Bill Technician
Rosetown, Saskatchewan
Bill Default
   

You could infer relative flow/pressure with a pressure transducer on the return with a fuel loop or buy a flow meter. I have not done it at all really. On the bucket list.

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Michael Diagnostician
Elmwood Park, Illinois
Michael Default
 

Maybe temporarily bypass the filter housing to see if any improvements. I have never had to modify the lines on these for a OEM new housing to fit correctly but it is possible for it to be updated but verification should always be done that it is the correct part number. Also there should be a screen inside the fuel tank that you may want to check if after bypassing filter there is no change.

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Bill Technician
Rosetown, Saskatchewan
Bill Default
   

Michael, I would be worried about the risk of fuel contamination that could not be un done by bypassing the filter. Many of the failures on these trucks are caused by substandard fuel filters contaminating the system. I would feel personally that routing to a jerry can with a hard line temporarily, but still filtered, would eliminate a lot of restriction points. What if the tank is right full…

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Joel Diagnostician
Soquel, California
Joel Default
   

humm I have pressure transducer

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Michael Diagnostician
Elmwood Park, Illinois
Michael Default
 

Awesome you can Tee that in and watch the delivery pressure and ensure it doesnt fall on its face.

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Joel Diagnostician
Soquel, California
Joel Default
 

thank you,I Will keep it mind of the chek list

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Joel Diagnostician
Soquel, California
Joel Default
 

do you know if it is a screen on the ficm?? I am womdering because is cooldown by diesel

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Craig Mobile Technician
Watkinsville, Georgia
Craig Default
 

Hi Joel. I have seen at least 2 different trucks where the FICMs became clogged, causing a restriction in the fuel system. On both, I was able to used compressed air to remove the contaminates. I agree with others about using an temporary fuel supply, to bypass different sections of the fuel system, to determine the point of restriction. The LB7 Fuel Filter housings are different from the…

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Joel Diagnostician
Soquel, California
Joel Default
 

Thank you for your input , good info about ficm

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Dustin Owner/Technician
Cleveland, Oklahoma
Dustin Default
 

I was thinking the same thing.

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Joel Diagnostician
Soquel, California
Joel Default
 

me too ,😉

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

That engine is starving for fuel. At the fuel filter, you can unhook the hoses from the supply side of the filter and let the engine suck fuel from that point. That engine should idle around 4" HG. At that point there on the fuel filter, you could also flow test the electric pump. Divide the system in half, and conquer your problem.

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Joel Diagnostician
Soquel, California
Joel Default
 

thanks

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David Owner
Metter, Georgia
David Default
 

There is a fuel pickup screen on the sender unit inside the fuel tank. This is not an electric pump inside tank but rather simply a fuel pickup sender unit. Possibly this screen is clogged up from fuel contamination and causing the fuel restriction.

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Joel Diagnostician
Soquel, California
Joel Default
 

thank you sir , I will have to remove the gas tank and clean it no matter what since contamination is bad enemy of this system

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Joel Diagnostician
Soquel, California
Joel Update
 

Yesterday I split the system in 3 points of testing, conected external fuel source point 1- after the fuel filter , max vaccum 6 in hg at wot, no more lack of power, before filter same problem fix 8 in gh wot 3- by the fuel tank area where is the inlet for add on lift pump , still solved the problem . conclusion the problem is inside the fuel tank. I will be removing the fuel tank on saturday…

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

Yes it is cleanable. It is only a screen

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Joel Diagnostician
Soquel, California
Joel Default
 

thank very much.

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Bill Technician
Rosetown, Saskatchewan
Bill Default
 

Joel, Thats great. What did you find with the smoking with your substitute fuel system, or are you going to tackle that after the pick up is good? Are you making desired rail pressure now with the restriction corrected? Let us know the final conclusions. Glad you got the restriction nailed down. When I made the recommendation for the TP3018 filter it was because it does a very good job of…

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Joel Diagnostician
Soquel, California
Joel Default
 

Actual en desire match at all time under all driving conditions , plemty of power no smoke out tail pipe with out suction side restrictions.

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Bill Technician
Rosetown, Saskatchewan
Bill Default
 

Perfect. I would be leary not to oversell this as completely corrected. These systems can be a bit finicky and will both smoke and drop pressure intermittently depending on operating conditions. If I had just eliminated the restriction, like you have. I would feel 80% certain that I had corrected rail pressure issues at WOT if I monitored them on a half hour drive and I would feel 5% certain I…

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Albin Diagnostician
Leavenworth, Washington
Albin Default
 

Good thoughts. On this engine, any time there is a smoke issue, or power issue for that matter, I always pay close attention to the cylinder contribution data, and the injector command data.

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Joel Diagnostician
Soquel, California
Joel Default
 

Customer is aware of injectors he is ok to do them , we want to fix first fix the suction side isues and after that go to the next level.

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Joel Diagnostician
Soquel, California
Joel Update
   

I finished the diag and repair of the duramax , I remove the fuel tank and was not bad not plugged, I was hummm here is not my problem I remove every connection any where and blow with compress air, bingo the ficm area was plugged ,I tried many times to blow opositive way of the flow direction , I felt the restriction and no luck so I decide to blow the other end couple times and something…

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