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Old 09-17-2019, 11:28 AM   #1
Tar Heel
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Default LML CP3 conversion

We have a '15 LML with 98K so the warranty is about to expire. I plan to keep this truck for a long time so the CP4 issue concerns me. I contacted a local, reputable diesel performance shop and they want $4K out the door to do the CP3 conversion. I know the parts alone are almost $2K. Is this a good deal? Although I've been building and racing drag cars for 30+ years I know very little about diesels and specifically working on them other than routine maintenance.

Also, while they had it I was going to do a lift pump for the extra filtration and water separator. They want $1500 to do that and they provide everything. I know the lift pump itself is almost $800.

So, for $5500 I could get the conversion and lift pump done and hopefully get another 400,000 (?) trouble free miles?

Now that the warranty is about up I'm also going to talk to them about doing a delete and a tune as well.
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Old 09-17-2019, 07:11 PM   #2
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Default Re: LML CP3 conversion

I don't think should worry about your CP4 failing.
I'm going to say that most CP4 pump failures are misdiagnosed, The real problem is an injector failure. I do diesel repair literally everyday and I haven't seen one legit pump failure yet, I've seen plenty of failed injectors tho.

What really happens on a common rail is an injector won't hold the pressure and fuel pressure leaks into the cylinder. I've even seen the exhaust systems dripping fuel out. So, when somebody scans it they see low rail pressure and they sell a whole fuel system because they figure pump doesn't make enough pressure, but the real problem is an injector, it can't hold the pressure. I've had a couple of trucks towed in this year from the dealer that were misdiagnosed and they tried to sell a whole fuel system. I fixed with a full set of injectors for much less.

I have a no-start LB7 here right that makes 275 PSI of rail pressure, I'm pretty sure it's an injector. The way to figure out which injector it is you have to take off the injector lines one at a time and cap the rail side and see when it builds rail pressure, then you can tell which injector it is and verify the pump is good.

If your still worried about it I've heard somebody makes a CP4 disaster kit, it catches any debris before it gets to the rails and injectors.
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Old 09-18-2019, 09:49 AM   #3
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Default Re: LML CP3 conversion

Quote:
Originally Posted by Gdogg View Post
I don't think should worry about your CP4 failing.
I'm going to say that most CP4 pump failures are misdiagnosed, The real problem is an injector failure. I do diesel repair literally everyday and I haven't seen one legit pump failure yet, I've seen plenty of failed injectors tho.

What really happens on a common rail is an injector won't hold the pressure and fuel pressure leaks into the cylinder. I've even seen the exhaust systems dripping fuel out. So, when somebody scans it they see low rail pressure and they sell a whole fuel system because they figure pump doesn't make enough pressure, but the real problem is an injector, it can't hold the pressure. I've had a couple of trucks towed in this year from the dealer that were misdiagnosed and they tried to sell a whole fuel system. I fixed with a full set of injectors for much less.

I have a no-start LB7 here right that makes 275 PSI of rail pressure, I'm pretty sure it's an injector. The way to figure out which injector it is you have to take off the injector lines one at a time and cap the rail side and see when it builds rail pressure, then you can tell which injector it is and verify the pump is good.

If your still worried about it I've heard somebody makes a CP4 disaster kit, it catches any debris before it gets to the rails and injectors.
Thank you! Is this the kit you're talking about:

https://www.alligatorperformance.com...6l-duramax-lml

What about a lift pump? Are there benefits to adding one of those? I'm thinking better filtration, help with fuel delivery and water separation.
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Old 09-18-2019, 07:58 PM   #4
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Default Re: LML CP3 conversion

IDK if that's the kit, I've never used one or even seen one, I've only heard of them.

As far as a lift pump, a stock or slightly modified truck probably doesn't need it.
My wifes diesel Jeep is tuned and deleted and has a eco tune. Its got 200k on it without a lift pump. Now if you go on some of Jeep sites everybody says you need to add a lift pump. So, I'd say they're full of shit.

Now something that makes a lot HP than stock will need a lift pump.
I was at PRI and FASS had a spot there, I talked to the owner about why would some body need to upgrade their fuel system to his. They had a working fuel system on display, he showed me how under a heavy fuel load the suction side can go negative pressure, that causes air bubbles in the fuel, those air bubbles are the kiss of death to a fuel system/hydraulic system, it's like running an engine out of oil.

If you can hear a hydraulic system buzzing (example zero turn mower) when it's under a load it's because the suction side went negative because the filter is restricted and oil bubbles formed, it won't take long to blow up the pump when this happens.

So, I'm thinking some of those legit CP4 failures are probably caused by this and I'll bet the trucks are deleted and modded and probably making 200hp over stock. So I'd definitely put a lift pump on something thats making some HP.
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