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Discussion Starter #1 (Edited)
Just bought this truck in it's current state and am at a bit of a loss. I am a tech but on european cars so the specifics of the duramax is all new.

The truck is a 2004 lb7 with 200k. Currently will crank but not start. The back story as told to me is truck was running fine. Turned it off to go for lunch and would not restart afterward. Original owner sold it like that to the person I got it from. Seems like he was just knowledgeable to get into trouble OR he found out what it needed and realized he was in over his head. I hope not the second choice. Was told the initial breakdown was 5 months ago so god knows what all has been done and tinkered with in that time.

My quick assement of the truck.
  • oil smells heavy of diesel and is filled to the top of the hatch markon the dipstick
  • has 2 new batteries that are fully charged
  • cranking speed seems right (may even be a bit fast) I am a bit concerned about compression but after 5 months of the p/o trying to start it I would think is may be washed out.
  • primed the system with the hand pump (can feel pressure build in system when doing this)after cranking pressure is gone
  • only fault in ecu was for glowplug curcuit (failed to right down the p code but cleared it and it has not returned)
  • glowplug light comes on and seems to cycle as designed
  • immobilizer light comes on during initial key turn and then turns out as I suspect it should. (my only concern here is the key I have is just a metal key. I am not sure if there is supposed to be a chip in these keys or not.)
  • moved a/c comp. out of the way to access the cp3 pump to check for fuel flow. (with the feed line to the common rail T fitting removed and cranking the engine I get what I thinkis a VERY small about of fuel for such a "high pressure" system. The fuel exiting is clear and free of any air bubbles but only streams out in about a 1 1/2 inch geyser that I can easily but my finger over and restrict with very little resistance.) THIS SEEMS WRONG
  • If that is normal what is the next step for me to take???

Oh and I have not tried starter fluid while cranking. I would assume the p/o did that and got nowhere. I am feeling like either a pump issue or an open injector are the culprits but would like some more seasoned input. TIA

Ken
 

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Around that mileage and if diesels in oil i would say injectors but hard to say

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Lb7 injectors are know for problems fyi. See if u can get records that show if injectors have been replaced with updated versions

The warrenty on lb7 injectors is 7 year 200,000 so see when and with how many miles it was purchased at. Small chance warranty may stiil be there

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Discussion Starter #4
thanks for the reply. I have been reading about the injector issues but have not checked with the dealer to see if/when they were done. I guess that is a good start. Would it be normal for a vehicle with a failed injector to have what think sounds like low compression for a diesel? I honestly have never heard a lb7 start up before so mind you I have no standard for comparison
 

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i had thi sbroblem no diesel in oil but i went to my friends shut my truck off for 20 minutes came back out cranked but wouldnt start for 3 days finally took it in to the dealer the injector control module went bad
 

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1. Is there fuel in the tank?
2. Does it have a lift pump?
3. Do you have capability to monitor fuel rail pressure via OBD2 port?
4. If you are getting fuel, check compression.

LB7's are known for injector issues, but I find what most people say when selling a truck is usually not 100% accurate.

I would start by changing the fuel filter, sounds stupid, but who knows when it was changed last.
 

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Discussion Starter #7
i had thi sbroblem no diesel in oil but i went to my friends shut my truck off for 20 minutes came back out cranked but wouldnt start for 3 days finally took it in to the dealer the injector control module went bad
Interesting. thanks for the input

1. Is there fuel in the tank?
2. Does it have a lift pump?
3. Do you have capability to monitor fuel rail pressure via OBD2 port?
4. If you are getting fuel, check compression.

LB7's are known for injector issues, but I find what most people say when selling a truck is usually not 100% accurate.

I would start by changing the fuel filter, sounds stupid, but who knows when it was changed last.
1. yes there is fuel in the tank (about half full)
2. Umm? I dunno? Is there a way to determine?
3. I thought I did but I need to dig a bit more on my Launch scanner (going back to what I explained came out fo the pump during cranking I question the pump.
4. I know I get fuel to the cp3 but at what pressure I dunno and I know I need to prime it after each crank. as for a comp. test how involved on this engine??
 

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Interesting. thanks for the input


1. yes there is fuel in the tank (about half full)
2. Umm? I dunno? Is there a way to determine?
3. I thought I did but I need to dig a bit more on my Launch scanner (going back to what I explained came out fo the pump during cranking I question the pump.
4. I know I get fuel to the cp3 but at what pressure I dunno and I know I need to prime it after each crank. as for a comp. test how involved on this engine??
Typically you will see a lift pump installed on the frame rail fuel line if it has one. Duramax trucks don't have a lift pump from the factory (Except for vans). The CP3 sucks fuel from the tank and then pressurizes to variable pressure based on ECM tune.

I would start buy changing fuel filter and priming. You could have a leaking fuel housing or something along those lines which is likely in this situation. If there is a leak it may start and die right away after priming the fuel system.

I think you might be getting ahead of yourself by messing with the cp3, but just my thought. Maybe someone else will interject here shortly.
 

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Leaking fuel housing? How does the oil smell like diesel though?

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I have a compression tester i bought from napa. Had to get a special fitting from ebay though. Just threads into glowplug hole. Very easy to break old glowplugs so be careful or have a spare. They r 20$ at dealer for new glowplug

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Leaking fuel housing? How does the oil smell like diesel though?

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Do a drip test, this is likely due to an injector problem, but I'm guessing one issue may not be related to another.

Take oil and drip onto a paper towel, do you see a fuel ring around the outside?

The fact it ran and then wouldn't start leads me to believe it's not getting fuel. Since there is no lift pump, if you have a leak it will pull in air and not get fuel.

Fuel filter housing is prone to leaks, WIF sensor, etc..

Is your priming bulb on top of the filter hard or soft? Have you tried priming it?

Just start troubleshooting the basics before getting to far along, once you get it running then you can verify injector rates and return rates to see how the injectors look. If you have fuel in the oil then you probably are looking at injectors soon which are VERY common on LB7s. I recommend also changing the oil and filter if you have excessive fuel in the oil, as fuel is not a good lubricant.
 

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Yea that could be the no start reason. Wasnt thinking good call.

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Discussion Starter #13
Typically you will see a lift pump installed on the frame rail fuel line if it has one. Duramax trucks don't have a lift pump from the factory (Except for vans). The CP3 sucks fuel from the tank and then pressurizes to variable pressure based on ECM tune.
I did not think it did but was not going to assume anything.

I would start buy changing fuel filter and priming. You could have a leaking fuel housing or something along those lines which is likely in this situation. If there is a leak it may start and die right away after priming the fuel system.
I planned on changing the fuel filter anyway so I will try that first. the truck not even sputter much less start unfortunatley.
I think you might be getting ahead of yourself by messing with the cp3, but just my thought. Maybe someone else will interject here shortly.
Boy I hope so. A nice easy inexpensive fix would be great.

Leaking fuel housing? How does the oil smell like diesel though?

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fuel smell could be due to lack of oil change aslo. I am not sure when it was done last. oil and filter change are on the to-do list.

I have a compression tester i bought from napa. Had to get a special fitting from ebay though. Just threads into glowplug hole. Very easy to break old glowplugs so be careful or have a spare. They r 20$ at dealer for new glowplug

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sounds easy enough

Do a drip test, this is likely due to an injector problem, but I'm guessing one issue may not be related to another.

Take oil and drip onto a paper towel, do you see a fuel ring around the outside? Will try that

The fact it ran and then wouldn't start leads me to believe it's not getting fuel. Since there is no lift pump, if you have a leak it will pull in air and not get fuel. I understand but if that were the case would I be able to prime the system and get a firm bulb and shouw no air bubbles from teh bleeder once primed?
Fuel filter housing is prone to leaks, WIF sensor, etc..

Is your priming bulb on top of the filter hard or soft? Have you tried priming it? soft after cranking but will firm up after pumping 7 to 10 times.

Just start troubleshooting the basics before getting to far along, once you get it running then you can verify injector rates and return rates to see how the injectors look. If you have fuel in the oil then you probably are looking at injectors soon which are VERY common on LB7s. I recommend also changing the oil and filter if you have excessive fuel in the oil, as fuel is not a good lubricant.
ok so even if I have bad injector I should still be able to get it to run?? fuel smell in oil could just be from old oil and normal engine blowby so not reading to much into that just yet.
 

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Yea that could be the no start reason. Wasnt thinking good call.

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Just realized you weren't the OP, lol...

Yeah, I wasn't on my first post either, I read what he typed and then realized lets step back to basics...
 

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Get a V2 and see what the rail pressure is while cranking. What is it? Let me know.

Sounds like injectors are returning to much fuel and the rails cant make enough pressure to start. If you give it a tiny shot of starting fluid will it start and run and stay running? Its best to pull all the injectors and get them tested. Costs about $20 bucks each to have the injectors flowed and return checked. Fuel in the oil is usually a cracked injector body leaking and that could also be why your not able to build enough fuel rail pressure to get it to start.

If your on a budget get the one cracked injector replaced and go on your way. If you have the money, replace all 4 in that bank. If you want it done right, replace all 8 and be done. It will be fine to squirt it with a small shot of starting fluid. See if it starts and stays running.
 

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Get a V2 and see what the rail pressure is while cranking. What is it? Let me know.

Sounds like injectors are returning to much fuel and the rails cant make enough pressure to start. If you give it a tiny shot of starting fluid will it start and run and stay running? Its best to pull all the injectors and get them tested. Costs about $20 bucks each to have the injectors flowed and return checked. Fuel in the oil is usually a cracked injector body leaking and that could also be why your not able to build enough fuel rail pressure to get it to start.

If your on a budget get the one cracked injector replaced and go on your way. If you have the money, replace all 4 in that bank. If you want it done right, replace all 8 and be done. It will be fine to squirt it with a small shot of starting fluid. See if it starts and stays running.
Couldn't you just check the fuel return with a bottle to verify if it's returning enough it won't start?

I just think I would start with the basics before diving in or assuming it's this deep. I do agree the injectors are a likely issue, but I would try to get it running before pushing forward with injectors.
 

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Yes i agree, a bottle test will work good. Sometimes i think to fast and forget that not everyone can just rip their injectors out in a few hours, get them tested and throw them back in :)

I believe its the injectors giving fits. If he can test pressure while cranking that will tell alot. Do a bottle test too. I strongly believe one is either cracked or they are just old and returning alot. Balance rates wont tell you much because one injector could be fine but look bad because its making up for a couple bad injectors. If he just wants to replace 1 or 2 i strongly suggest pulling all 8 and having them tested to find all the bad ones.

If the truck started up after being primed i would say throw a lift pump on it and be done with it. We get trucks like that in all the time and it can be more costly to track down where the fuel system is bleeding off. Throw a $250 PPE lift pump on it and problem solved. Since it wont start after being primed then it takes me back to the injectors.
 

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Don't forget to check the wiring for the injector driver module, the harness is tied down to the aluminum bracket and grounds out. This creates all kinds of fun.
Just cut the zip tie, inspect for damage and if there is none wrap the harness with tape enough times to prevent it from rubbing again and do not tie it back down.
 

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Discussion Starter #19
great info guys many thanks. I now have a few things to do and check. curious if you have a pic or location description of this injector module harness I should examine.
 

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It is next to the altenator, the issuse is with the lly not the lb7. You are not keeping prime or an injector is leaking. Get a V2 or a tech2 to look at your actual fuel pressure to see if it is holding around 3,000 psi. If it won't the truck won't start, let us know what is going on and you can start to move forward from there.
 
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