How to test lb7 injector return rates balance rates cp3 failure rail pressure relief valve regulator

This is a quick reference test to determine if there are possible issues w injectors OR cp3 pumps in the LB7 Duramax. It's always best to consult a manual for exact flow and return specs as this DOES NOT determine which injector, bank or if it's the cp3 that is producing the excessive fuel. This is only a starting point to determine if a condition exists. Other symptoms may exist such as; white smoke, fuel in oil, misfire, poor fuel economy just to name a few. Good luck and thanks for watching.

[@stevewaclo167]

I commented a year ago, and again want to congratulate you on emphasizing the importance of return rates, in addition to a simple balance rate check. Well done! I believe return rate problems (long crank) are due to ball/seat erosion and no amount of chemicals will fix that. My injector R&R project is at 50%.

[@stevewaclo167]

Richie, you are wise in the ways of Duramax! 👍👍👍 Some folks go to the trouble of checking return rates on each bank, but I believe if the engine has 60-70k on VCO injectors, the owner may not be well served by knowing which bank is particularly bad since “in for a penny, in for a pound” comes into play. If a mechanic needs to go in, the injectors are high mileage, and total return is out of spec (CP3 is OK) may as well do an entire set, preferably SACs, which are getting good reviews in the short term (I’ve not read of high mileage experience). And wow, does the engine you are diagnosing crank fast! New batteries, or low compression? That puppy is really spinning and the ball/seats in the in injector return system must be shot, if they can’t maintain minimum rail pressure for starting.

[@RayofallTrades]

Excellent video. Wish i found you sooner

[@richiestruckandauto7438]

Note: @ minute 1.20 it is stated the "bc balance rates show and acceptable quantity doesn't mean they are bad" I meant to state " just bc they are acceptable levels, doesn't mean the injectors are in good condition". Sorry guys. Camera shy.

[@a-1smallenginedieselrepair879]

Thanks for the procedure Frank

[@mattm5423]

Terrific Video, man. Good work, you know your stuff.

[@garrenacker]

great vid! keep em coming!

[@DirtyDanRacimg]

Ive found good way to rule out the cp3 when it wont start after a hot soak is to pour cold water on the cp3 and put a air line on it and cool it off. If it starts attempt to max the fuel pressure with a scan tool.

[@jeffscott3160]

How would I do this without a smartphone timer? All kidding aside, great video tutorial on this! Kudos to you for sharing this valuable information with the rest of us!

[@anthonyb8691]

Great video

[@kellynkarr]

Phenomenal video. Thank you so much

[@tunas66]

great video by the way

[@stevewaclo167]

Why do you think ULSD is responsible for injector failure? Lubricity? That's taken care of at the refinery when lubricity additives are put into the fuel. Would it have been easier to disconnect the return line near the firewall instead of under the truck? Finally, although internal condition of fuel lines is not necessarily related to the external condition, I believe it would be prudent to at least do an inspection. Rust particles can overwhelm the best filter and destroy new injectors in short order. Pretty good "one handed" camera work! 👍👍👍 How's that LB7 running?

[@DynoBros]

Man. I need to talk to this dude STAT

[@richardlittlepage9069]

Well explained 👍🏽👍🏽👍🏽

[@raygood7986]

so does this mean he needs a cp3 as well as the couple injectors ? or will the injectors be enough to fix this ?

[@ronallens6204]

Did i miss something ? So you are saying one injector is causing all of the excess fuel ? So the cp3 is good and one injector is bad and causing the hard start? Granted the one injector is out of spec on the scan, so why is it not the cp3 the culpret ?

[@mike4796]

Well done!

[@obet191]

nice vidoe i have a 04 and it won’t star after i put gas instead of deasel ranit about 20min and it died it havent start after that i took tank off and washed it rebuilt primer. and it still won’t start before this it ran good no smoke it ran fine took it to dealer they said 3 injectors 4,6,8 and 5 were stuck open and thats why it wouldn’t crank and needed all new injectors,but not shure any suggestions i’ll apréciate it

[@richiestruckandauto7438]

I apologize for this correction but the values recognized as Mpa is "Mega" pascal NOT mili pascal as that would be noted as a small "m" insead. The camera doesn't forgive mistakes! lol

[@evanch123456]

My LB7 has long cranks sometimes won't start. My balance rates are good and my return rates are less than 100 ml. Where would you go from here? Thanks

[@fowlercdff]

You mean mega pascals right?

[@glyshorts9107]

The desired frp said 55. Is that ×100? 5,500? At idle.

[@cody6.6max]

Yea

[@tristenfletcher577]

I have a lb7 and it has a code p0612 but it runs great would u know what makes the code pop up

[@ricardoayala5028]

Hello Mr. Richie in what estate are you located?

[@coltonsmith3397]

I've got a lb7 that doesnt hard start doesnt smoke white but has black smoke though out acceleration until it cruises and it has a p0087 code seems to be heat related help please

[@fanningconstruction2050]

What scan tool? Can u do this all with a tech two?

[@kev90sc]

Yes, the tech 2 is hands down the most accurate for balance rates

[@alspahi7760]

i hope u are to dmax's what powerstrokehelp is to fords diesels

[@richiestruckandauto7438]

Haha. I have a fairly decent understanding of these beasts. Been doing them since they arrived on the market and have 4 of them in the shop trucks 😉

[@tunas66]

I have an Autel just like yours on the injector readings i'm getting 0.24 what is a good reading for the injectors i have an 2002 durmax?

[@sterling29168]

Mine is also an 02, if that number is for one of your cylinder balance rates in mm3 then it is within spec assuming your rail pressure, fuel rate, temp and all other conditions for a balance rate test are met. Between +4 and-4 mm3 is within spec for an individual injector. All conditions for BR testing need to be met otherwise the BR numbers will not be accurate.

[@danielfarias2749]

On my I get a p0093 but it doesn’t smoke or anything doesn’t lag to start it says large fuel leak but can’t figure it out

[@cody6.6max]

Cp3

[@petergeralis3725]

I mean injectors OR cp3? Not just selling both

[@ryans7799]

I need my injectors replaced bad. To bad your in New York.

[@sirsweetness8332]

Is that an Autel DS708? I need to know to check balance rates

[@richiestruckandauto7438]

Sir Sweetness Idk what model it was? I no longer have that tool bc of the lack of updates. I now have the SnapOn VerusPro. Most decent scan tools will provide balance rates. Even some tuning devices offer that PID.

[@steveandant]

soo i have an 02 Lb7 i just bought. it will not build rail pressure, it will not build more then 10k when desired is anything higher then that. i do not have any hard starts. or rough idle, i have 2 injector balance rates at -3.0 , +3.2 at idle in park, every other is good. i put a lift pump on the truck and it didnt do a thing. im leaning towards a bad CP3. what do you think. thanks

[@richiestruckandauto7438]

For starters, what is the duty cycle of the FPR? Try ans unplug the FPR and see if it can build max rail pressure at idle. If not then move onto the test in this video. I have not seen many failed cp3s. Begin by testing the common items such as fuel pressure regulator, relief valve (test instructions in another video on this page) and delivery to the cp3.

[@MrAgatto2]

@@richiestruckandauto7438 Hey wont taking off the fpr cause the injectors stress and possible leaks ? I am also guessing we should see about 22000 pounds if the fpr is disconnected

[@richiestruckandauto7438]

@@MrAgatto2 No sir. A stock cp3 should not be able to build 22k+ of rail psi at idle. The pump isnt turning quickly enough to build the volume. You would most likely experience pressures in the mid teens like 13-15k at idle. Its only a test to be performed for a second and NOT to be driven in that condition.

[@brandycalvert3766]

I have a snap on verus pro scanner and the balance rate all show ethier 0 or 1 at idle

[@richiestruckandauto7438]

That is an acceptable reading. Keep in mind though, it's acceptable if all of the injectors are in good condition. If they are all damaged by age, wear, water, debris.....etc then the readings will be of permissible levels but flow in poor condition.

[@chrisao1987]

Couldn't you just pull the return line off under the hood and add a line and run it to a container from there?

[@cody6.6max]

U would think so right

[@evanch123456]

Which scanner is he using?

[@richiestruckandauto7438]

Autel

[@petergeralis3725]

How can you determine what is the culprit?

[@richiestruckandauto7438]

Peter Geralis the return circuit from the cp3 is through a single, small rubber hose. You could simply "pinch" off the flow at the hose to the return line to isolate the pump. 9 out of 10 Xs the cause for excessive return rates are due to injectors on LB7 engines but should NEVER automatically be assumed as such. Testing is paramount. Monitoring and receiving excesive duty cycle of the fprv (fca) and comparing to a known good value during operation "could" indicate an underlying issue w the cp3 or the FPRV and possibly not injectors. Do rember the regulator operates in reverse and not all scan tools will display the values that way. at 0% the regulator is wide open. At 100% it is completely closed. This is why known good values are always useful when trying to decipher a faulty component. Cp3 issues present variable symptoms related to performance (such as fuel rail pressure being less than desired or insufficient supply under power demand) rather than hard or no starts. FPRV can result in a no start when they fail as well so proceed w caution.

[@jeffrhodes3883]

2002 2500 hd 6.6 starts fine when it's cold but won't start when it's hot can anybody tell me what to do?

[@Dubsspeed]

Ever figure out your issue? Id guess it's possibly a fuel line heating up and collapsing/kinking when hot?

[@johnshoemake2939]

Have an 03 top kick we did injectors in. high balance rates, making oil. replaced all 8 injectors new bosch. lines and all the associated gaskets and seals. fired right up. no longer making oil but balance rates are still high as initial. frp good. Only odd thing i can find now is Fuel pressure regulated flo is all over the map at idle. Leaning towards a bad fpr. you can actually feel and hear it buzz key on engine off. just wondering if I'm head the right direction

[@richiestruckandauto7438]

John Shoemake sounds about right. I've experienced atleast 2 bad FPR valves right out of the box in the 14+ years I've been doing these motors. Before you go any further make certain you do not have contaminated fuel and the harness from the ficm isnt compromised in any way. Once this is confirmed, unplug the FPR harness and make sure u achieve max rail pressure at idle. Doing this, atleast you know it isn't sticking. DO NOT drive it in this condition.

[@johnshoemake2939]

Richie's Truck and Auto thanks for the insight. I will dig back into it tomorrow. Happy Thanksgiving

[@johnshoemake2939]

possible to call you or get a call from you. 301-268-4295. mashing my head off the wall here

[@richiestruckandauto7438]

John Shoemake the shop phones are on today until 630pm. We are performing shop maintenance throughout the weekend but I can try and help 516-680-7377

[@brandycalvert3766]

Is the return rate the same for the LBZ. I have a 2007 gmc 3500 I pull a 3 car trailer with. when I pull hard it throws p0087. never any hard starts, and just added a lift pump and still doing it

[@richiestruckandauto7438]

Yessir return rate is the basically the same. Inj flow rates and rail psi capabilities are a bit higher though. LBZs have known issues w the cp3 internal components. It's NOT highly common but I've seen a few in the past w pump issues. The 0087 is loss of rail pressure code. It could be from a tune commanding more fuel than the system can supply, leaking injector(s), cp3, rail pressure relief valve etc. Need to do a little more diagnosis before condemning the injectors as they are not nearly as common to fail as the lb7 is.

[@jldude555]

I Have one of Thies when I hook up my computer the fuel pressure is 20K+ At Idle and If I accelerate The Pressure will drop Low Enough to Kill the Truck Any Thots as to What Could Cause This

[@Franklinveterinarycenter1of4]

FPRV

[@SINISTER69er]

He’s listening to usher in 2017?