Lb7 no start??

Mxz8002003

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May 23, 2020
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2001 lb7
29,000 original miles
Completely stock
Last ran 6 weeks ago no problems except had to crank longer than normal before it started. Thought to be to week batteries. Went to start it last week and no go. Cranked over slow, found dead battery on passenger side and also primer would not pump fuel, rebuilt fuel filter head, new battery. Still no start.. IM getting no codes. So far i have tried to start it with the FPR unplugged (no go) Alot of pumping of filter primer while cranking, new fuel filter when rebuilt the head. Primer us working good and gets hard but goes soft after cranking.. (which i think is normal??). No visual leaks anywhere.. Also unplugged the Fuel rail pressure sensor. (No start, would it start with it being bad and if not would it start with it unplugged if it were bad???). I also did the diy return rate test of disconnected the Quick disconnect return fuel line on driver side back Of engine and rain a hose from that into a container. Also disconnected return line on cp3 pump. Plug the side of the line that goes to the distribution block and ran a hose from the cp3 pump Side to a container. Unplugged both bails on the fcim. Cranked until fuel came out of one hose first.. (which was cp3). Emptied the container Then cranked for 15 secs. I got just over or about 1oz out of the cp3 return and not even one drop out of the other main return line. Does this tell me no stuck injector?? Lastly pulled all eight glow plugs after all this cranking( ive had glow plug module Disconnect to help not were down battery's) all were very nice and dry. Didnt know if one might be wet with a stuck injector..?? Lastly all i have is in edge. I have the fuel rail pressure pid and it read 0.2kpsi with key on and does not move when cranking, although i dont know if the edge will read the rail pressure under cranking only. When i unplugged the Fuel rail pressure sensor, the edge read 23kpsi or something like that.. Anyone thinking the cp3 took a dump???? Or anything else, maybe fcim bad with no cel code?? Any other sensor keep it from starting.. And any way i can confirm it with what i have? Or do i need to get someone efi or tech11? Any suggestion would be Appreciated Sry about the long post.
 

Mxz8002003

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May 23, 2020
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I also removed the im calling it the brass pressure/bleeder port with the sHredder valve in it, located just to the left of the alternator. Hook a hose onto the and put it into a quart jar. I then pumped numerous jars of fuel and had/got no air while pumping To that point..
 

Mxz8002003

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May 23, 2020
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Tried my ficm on uncles duramax today, started right up couple times. So ruling that out..
 

gmduramax

Shits broke
Jun 12, 2008
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I’m going to guess injectors because of the hard starting prior. Pull your glow plugs and crank with the bale connectors unplugged. See if any fuel comes out of the glow plug holes.
 

Mxz8002003

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May 23, 2020
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Thank you I will try that, i believe the hard starting before was due to cranking slow Because of bad battery. I did pull all glows plugs after trying to start it numerous times Prior when trying other things and all were dry.. didnt think of cranking it over while they were out. My fuel pressure reg will buzz(Loud enough for no prob to here it) for 20 secs or so when key is first turn on then it stops, like it shut off??? Can someone tell me Does the regulator Actually due the regulating. Is it a mechanical part that could fail restricting the pressure and dont matter if you unplugged it or not it could be stuck???
 

gmduramax

Shits broke
Jun 12, 2008
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Nor cal
Thank you I will try that, i believe the hard starting before was due to cranking slow Because of bad battery. I did pull all glows plugs after trying to start it numerous times Prior when trying other things and all were dry.. didnt think of cranking it over while they were out. My fuel pressure reg will buzz(Loud enough for no prob to here it) for 20 secs or so when key is first turn on then it stops, like it shut off??? Can someone tell me Does the regulator Actually due the regulating. Is it a mechanical part that could fail restricting the pressure and dont matter if you unplugged it or not it could be stuck???
It could be stuck but it should be able to start.
 

Mxz8002003

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May 23, 2020
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Okay just pulled all 8 glow plugs, did one bank at a time, no fuel come out of any of them while cranking
 

Mxz8002003

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May 23, 2020
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Also did paper towel test and looks good, appears no fuel in oil. I certainly Dont think their would be high pressure leak under valve covers.
 

ippielb

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May 21, 2014
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Check for the ficm fuse in the fuse box under the hood. Should be a 25amp mini blade fuse, it is #1 on the diagram I believe between two relays.

If that has popped that means there is a short in the wiring between the ECM and the FICM, I had my wiring harness rub through right under the bale connectors above the driver valve cover. It rubbed on a fuel injection line.

Truck would crank and crank but no fire, it wasn’t triggering the injectors to fire.
 

fl0w3n

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Jan 8, 2015
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Thank you I will try that, i believe the hard starting before was due to cranking slow Because of bad battery. I did pull all glows plugs after trying to start it numerous times Prior when trying other things and all were dry.. didnt think of cranking it over while they were out. My fuel pressure reg will buzz(Loud enough for no prob to here it) for 20 secs or so when key is first turn on then it stops, like it shut off??? Can someone tell me Does the regulator Actually due the regulating. Is it a mechanical part that could fail restricting the pressure and dont matter if you unplugged it or not it could be stuck???
My brand new LBZ FPR in my brand new S&S CP3 made a loud buzzing, you could hear from the cab with door open and hood open if you listened hard enough. From some searching I saw that was maybe normal :confused: I eventually got my truck started so it didn’t seem to be an issue.
 

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The injectors need around 1300-1450 psi to fire. Looks like your not building enough rail pressure to fire the injectors. Did you notice any issues with the truck before this happening?

BTW that is a low mileage LB7 you got there! I got one with 22,000 original miles on it!
 

Mxz8002003

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May 23, 2020
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Thanks, im bumming its dead right now, unfortunately the low miles i am feeling may have lead to this problem. Alot of sitting...

No truck ran fine 6 weeks ago, cranked a little longer than normal but my battery's were low. When i say ran fine it idle for 2hrs. No codes, no smoke, smooth as can be for lb7, then did some short burst on the throttle up And down my 600’ drive way. Everything was good. 6 weeks later, no start, found fuel head primer would not prime up, thought that was the prob. Rebuilt it and still no start.

Fuses are good, did not loosen high pressure line yet, figure if the pump was pumping some but not enough to make pressure to fire, would i know difference if their was fuel there??

Just to confrim also from the research ive done, with either a bad fuel pressure reg and fuel pressure sensor, unplugging them, the truck should/would run??
 

Mxz8002003

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May 23, 2020
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Possiable have someone coming over with a computer tonight, i hope its one that can do everything i need it too. Which is my next question. What to test or see with the computer, actual and desire rail pressure.. anything else for now??
 

2004LB7

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Dec 15, 2010
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Desired vs actual fuel pressure is the most important right now. You need to get the pressure up while cranking. Like Brent said, 1300-1450 psi

The reason I asked about the high pressure lin s and if you are getting fuel, is if it is dry or very little comes out then you know you need to concentrate on the cp3 and not the injectors (at least for now). If you have plenty of fuel then it very well could be injectors returning too much dropping pressure. But as you mentioned above you didn't get any out of the return so it leads me to believe that the cp3 isn't building pressure.

Make sure the rubber supply hose to the cp3 has fuel, then make sure the cp3 pumps it
 

Mxz8002003

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2004lb7 okay makes since About the pressure line. I will have to check the rubber supply To the cp3. I know im getting fuel to at least the shredder valve test port because i pump fuel into a mason jar with the hose down into the fuel to see if i was pumping any air and i was not. With the return rate test i did. The cp3 return real close to 1.3oz. Does this mean the pump would be getting fuel? Thank you guys for your input
 

2004LB7

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Dec 15, 2010
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CP3 spec is 35ML (about 1.2 oz.) of fuel in 15 seconds of cranking. How long did you crank it for?

Getting fuel to the test port is good. Sometimes the hoses near the cp3 because they are exposed more to the engine heat start to degrade faster. Some crack and suck air, some kink and others sometimes collapse internally. When removing all that is needed to gain access, it may be easier to just replace the hoses. But if they look in good shape then verify good flow.

If you get good flow into the cp3 and none coming out then it's probably time to pull the cp3. If you get pressure on the output and return is in spec then you should probably start looking at the injectors or relief valve
 

Mxz8002003

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May 23, 2020
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CP3 spec is 35ML (about 1.2 oz.) of fuel in 15 seconds of cranking. How long did you crank it for?

Getting fuel to the test port is good. Sometimes the hoses near the cp3 because they are exposed more to the engine heat start to degrade faster. Some crack and suck air, some kink and others sometimes collapse internally. When removing all that is needed to gain access, it may be easier to just replace the hoses. But if they look in good shape then verify good flow.

If you get good flow into the cp3 and none coming out then it's probably time to pull the cp3. If you get pressure on the output and return is in spec then you should probably start looking at the injectors or relief valve
Okay just got home, all ive done so far is first look at supply rubber line to cp3. Look good. So then crack last injector line on passenger side rail and cranked, no fuel. Loosen some more cranked, no fuel. Removed flare nut slid up line, had open rail, cranked and no fuel what so ever. Will check rubber supply to make sure fuel is their
 

Mxz8002003

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May 23, 2020
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Question, is it work have the guy still stop over with computer?? I know what actual rail pressure will read now. But is demand important? Is their something electronically that can make the cp3 noT pump?
 

Bdsankey

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Okay just got home, all ive done so far is first look at supply rubber line to cp3. Look good. So then crack last injector line on passenger side rail and cranked, no fuel. Loosen some more cranked, no fuel. Removed flare nut slid up line, had open rail, cranked and no fuel what so ever. Will check rubber supply to make sure fuel is their
If the supply line is in good health (not sucking air) then your pump is DOA and needs replacement.
 

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