Lb7 quick start?

[2012 LML Duramax Diesel]

I've set out on a mission to understand how and why and if there is anything to do about how long an lb7 takes to crank up. Naturally an lb7 takes longer to crank up, but why? My 06 lbz cranks up in 1 second, flick of a key, and my dad's lly take a second longer than the lbz, but one thing I noticed between the lb7 and the lly-lbz, when you turn the key to the run position without cranking, you hear a thud as if the fuel system gets a quick prime for quicker required cranking pressure to start faster. On my lb7 I have airdogg II 4G 165, and it seems to start a tad faster since I installed that, supplying slightly more pressure to achieve desired cranking pressure sooner. I dont know if the lb7 cp3 has the small pump on the back like the lly and lbz do. If not cant I just install an lbz cp3 on my lb7 like many others have and get this quicker crank up. I already know using an lbz regulator you have to have efi live tune to make it work seamlessly.

So please if you have any insight into this, I would much appreciate being educated.

Not that a longer crank detracts me from my lb7, I just wish to continue bringing it into the modern age more than it already has been.

 

[DAVe3283]

Your CP3 is probably getting weak on the LB7, or the injectors. My LB7 cranks up as quick as any new truck, but it has fairly new injectors and CP3. As the injectors age, they start returning more fuel, which makes it harder for the CP3 to build the minimum pressure required. A weak CP3 can just be slower too.

If you are referring to the glow plugs, I am not sure you can put the LLY system on, I think you just have to deal with the longer wait to start condition. Though now I wonder.... hmmm, might have to do some tinkering.

The only difference between any year CP3 pump is the regulator that is used. You can use the LBZ/LMM regulator on the LB7 with a tune adjustment, and many people do this, including me. I don't think that affects the cranking time though.

 

[2004LB7]

Not really sure what "clunk" you are referring to. The Duramax, wether that be an LB7, LLY, LBZ, etc doesn't have any factory installed lift pump or any other means to prime the fuel system as you turn the key. The gear pump on the back of the pump is what draws the fuel from the tank and pressurizes the high pressure pump.

Like dave said, if your LB7 take noticably longer to start then another then you likely have a weak pump or injectors returning a little more than they should. One thing you may also want to look into is your batteries. If they are getting week and it is turning over slightly slower that can lengthen the time it takes to start. Small air leaks on the fuel line can do this too as it will need to purge the air before any real pressure can be delivered

On a fresh set of injectors, my LB7 started up quicker then my current LMM

 

[TheBac]

Never, ever have had a hard-start issue with my LB7.
I can go weeks without driving the truck and it'll still start quickly when I do hit the key.
The only time Ive ever had a lengthened start time was when the batteries were worn out.
Id be looking at injectors and/or CP3 like Dave said.

 

[apwcu]

I know what he is describing as I have noticed the exact same thing with the lb7 vs lbz. The lb7 take a few revolutions to start and the lbz starts almost instantly.

My lb7 has brand new batteries also.

Sent from my SM-N950U using Tapatalk

 

[2012 LML Duramax Diesel]

My truck has had the cp3 replaced 50k ago, injectors are having but balance rates are within spec. By no means is it hard to start or cranking for an insane amount of time, just noticed how the lbz starts faster than you can let go of the key, and my lb7 takes a second or two longer than an lly or lbz. I encourage you of you have lly+, go out to your truck, with your door open, turn the ignition on, you will hear a thud, they all have it. Let me know what you think. My other question, lb7 lly and lbz all have the same starter, but why does the lb7 crank at a slower rate than the newer ones, no my starter isn't going bad. It's just another lb7 quirk, but why does it do these things, duramax is a duramax hard parts wise, heads, block, valve springs, crank and cam shaft, what makes the lb7 crank at a slower rate than the lly and lbz+. I think that's the key question, cause I think, you get the lb7 to crank at the same speed as the lly and lbz, you would get it to crank up alot quicker thus satisfying my questions. Help me out with some wisdom. Money doesnt entirely matter, but I want to tackle it myself rather than having a duramax specialist do it. :woott:

 

[2004LB7]

Do you have any way of monitoring fuel pressure and rpm while cranking?

And the "clunk" you describe may be the air intake valve opening up all the way

 

[OregonDMAX]

my lb7 starts just as quick as my brothers lml and any other duramax iv'e heard start even after sitting for months. the only time it has ever taken longer is when its in single digit temperatures, you probably have a weak cp3 or you are getting air in the system and losing prime

 

[DAVe3283]

Your starter might well be going out, for one. I rebuilt the starter on my Suburban, and it now cranks over faster than it did before. They start getting weak so slowly you don't notice. My Suburban (17.5:1 compression) cranks WAY faster than my built motor (16.5:1) due to the healthier starter.

The 2006+ motors are all 16.8:1 compression or lower, which helps them spin easier too.

The clunk could be the EGR shutting, or even the FPR activating with the ECU. Lots of solenoids that could be activating when the key turns on, and the newer the motor, the more there are to hear.

 

[gmduramax]

The LB7 we have cranks faster and starts sooner than the LLY, LBZ, LMM, and LML. The L5P cranks the fastest but it takes time to start.

 

[zakkb787]

My old truck started just as fast as my lbz or lly

 

[THEFERMANATOR]

In all honesty it's a crap shoot. I just helped somebody with an 03 last week. He put injectors(torque masters from s&s if it makes a difference) in it but had it was running max rail pressure. It started fairly normally, but rail was 175mpa at idle. Ended up being the ecm was shot, so had to put an ecm in it. Afterwards it has a longer crank time, even after I flashed it back to stock.

Mine I know for a fact builds rail pressure instantly, but through 3 sets of injectors, the only time it cranked quickly was with the JUNK pensacola remans that rolled out blue smoke everywhere. When I put remans in it from GM in August of 09, it had the extended crank to it. It took twice as long to start as it did with junk injectors. I did the 45 over sacs and now my crank time is better, but still not as fast as some.

And when my cp3 died on mea few years ago, I replaced it hoping that would also help my starting time(I had the GM remans then), but it made no difference. Some just start quicker than others while others take longer. But I think cranking rpm's plays a bigger role in it than anything else. I know mine has an Isuzu starter on it, not the GM one, and it cranks over a bit slower than the origanal starter did.

 

[snowman22]

My LB7 was a slow cranker until the starter finally died. I also just thought it was an LB7 thing. With a new starter it turned over faster than my current LML.

 

[2012 LML Duramax Diesel]

Well I guess I'll have to look into it. I'm battling with cheap batteries constantly affecting my crank times. I recently replaced my injectors with new OEM Bosch. That hasn't yielded much result in cranking. Old ones fired right up compared to the new ones. Thought maybe I should try out a lbz cp3, more pressure faster. I want more power so more fuel is required anyway. Win win, maybe an extra win if it builds pressure tad quicker. Will keep ya'll posted as things develop. Thanks for the advice.

 

[zakkb787]

Only difference in an lbz and lb7 pump are the Fuel Pressure Regulator. If your pump is healthy then swap a lbz fpr onto it and have it tuned for it.

 

[THEFERMANATOR]

Only difference in an lbz and lb7 pump are the Fuel Pressure Regulator. If your pump is healthy then swap a lbz fpr onto it and have it tuned for it.

The lbz cp3 is designed to run higher pressures, and does so better than a lb7 cp3. It doesn't push more fuel, just the same amount at higher pressures. And unless his cp3 is DEAD! It's not gonna make a difference. Even a dieing cp3 has little to no trouble building the required 1800 psi to make the injector pop.

 

[zakkb787]

The lbz cp3 is designed to run higher pressures, and does so better than a lb7 cp3. It doesn't push more fuel, just the same amount at higher pressures. And unless his cp3 is DEAD! It's not gonna make a difference. Even a dieing cp3 has little to no trouble building the required 1800 psi to make the injector pop.

Wasn’t aware of this. Always thought they were the same. Thanks for the knowledge FERM

 

[TheBac]

Moved over to the LB7 section.


Some LB7s are fast turners, some are slow, the same as some are quiet, some are loud.

 

[THEFERMANATOR]

Moved over to the LB7 section.


Some LB7s are fast turners, some are slow, the same as some are quiet, some are loud.

Mine kicks over plenty quick, it's just never popped off quickly. I've run multiple operating systems, bad cp3, new cp3, and several sets of injectors. So far the only time it popped off semi-quickly was with the junk pensacola injectors, in which case it chugged to life with the bump of the key, with blue smoke galore everywhere, and it ran the quietest with those injectors too. But I know it wasn't right when it was that way. Whats weird is I know it builds rail instantly because it will normally show 3k+ when it starts up, and the injectors are triggered as soon as the ecm reads cam and crank to know where its at. Yet it still takes its time to pop off. So it's just a roll of the dice.

 

[Dkatubi06]

That “thud” your hearing may be the ABS pump cycling. When I swapped my 02 over too everything 2005 for my lly conversion, I heard a thud and found it’s my abs pump cycling