bad or going bad injectors?? im a noob.

[David_1025]

Hello, i have 2003 2500hd lb7 with efi live ,stock injectors and internals fuel rate of 5mm cubed "supposed to be around 8mm cubed" with the rates per cylinder as follows: test was taken by use of snap on Apollo D8 scanner at operating temps no codes no other errors besides i an disconnected air bag and a bad glow plug rail .

break down with minus 3mm that missing from fuel rate below on the right

1: 2.1 1: 0.9
2: 1.4 2: -1.6
3: 1.6 3: -1.4
4: 0.2 4: -2.8
5: 0.7 5: -2.3
6: 1.0 6: -2.0
7: 1.3 7: -1.7
8: 1.0 8: -2.0

First off , Im a noobie to diesel engines, my concern is at idle sounds great runs smooth, during any acceleration there is a profound knocking or should i say clacking sound until rpms drop i.e. like going into overdrive , then it goes away.
am i possibly hearing to whats been referred to "fuel knock " ? any help, advice on how to move forward would be much appreciated. p.s if i posted in wrong section... im also a noob to the forum enviroment too, my apologies

 

[2004LB7]

You might want to return the tune to stock and test again. The knock could be injectors or could be a bad tune with too much timing or both.

 

[David_1025]

You might want to return the tune to stock and test again. The knock could be injectors or could be a bad tune with too much timing or both.

first off thanks for taking the time to reply. its greatly appreciated!! definetly worth a shot to try, does anything look out of place with the numbers i posted? further more was my math correct with deduction 0f 3mm due to my fuel rate

 

[David_1025]

i should also point out i bought this truck as a basket case.. slowly building it. ecm already had efi live installed by previous owner, and i do not currently have the ability to revert to stock myself.. so i do not have the factory flash.

 

[2004LB7]

first off thanks for taking the time to reply. its greatly appreciated!! definetly worth a shot to try, does anything look out of place with the numbers i posted? further more was my math correct with deduction 0f 3mm due to my fuel rate

I think you need to add back in the missing mm3 to the balance rates. Not subtract it. The ECM already subtracted it from the main rate because it's artificially added in through injector leakage. Add the "missing" amount to the balance numbers

 

[DAVe3283]

Since you have a scanner but no EFILive, you could just log it during the knock and see what is going on. I'd log

- RPM
- fuel pressure (desired)
- fuel pressure (actual)
- main timing
- main pulse width
- pilot timing
- pilot quantity (mm³)

We could look at those values and see if things look reasonable for whatever tune is loaded.

Main rate being 5 mm³ could be from a weird tune, but is more likely to be failing injectors, especially if they are stock size. Most tuners don't touch the idle area on stock injectors because there's no real reason to.

Sent from my FlashScan V2 using Tapatalk

 

[David_1025]

thanks for the advice , i will try to get any / all of them i have access to with the apollo d8 . will post immediately after. thank you for your time. greatly appreciated!!

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[JoshH]

Just post the balance rates as they are displayed on the scan tool. There is no need to attempt to correct them for bad injectors.

 

[David_1025]

here is what i could grab this evening, if i missed anything that you need or want to see please let me know and i will try to provide it. thanks everyone.

 

[2004LB7]

Your MAF at only 2.24 grams/sec is way off. I'd correct that before looking at the injectors

 

[David_1025]

thank you for pointing that out!! thank you for taking the time to respond. like i said in my original post, im a noob to duramax.. how far off am i from what it should be reading, and would you recommend attempting to clean, or just flat out replace per what you seen from my scan log?

 

[2004LB7]

They run around 40 gm/sec or so. Try cleaning it. Nothing to loose

 

[David_1025]

i will do this first thing in the morning when parts store opens... i will post updated results from scan tool after . thank you. is there any other snapshots that the scan tool can provide that you would like to see?

 

[gmduramax]

here is what i could grab this evening, if i missed anything that you need or want to see please let me know and i will try to provide it. thanks everyone.

Are those balance rates in park or in drive on the brakes?

 

[David_1025]

gmduramax , those reading are in park, 0% throttle , no brakes applied. "2004lb7" mentioned checking the MAF, which I did last night and its covered, I'm about to leave to go get MAF cleaner , and rerun data log . I've never had a CEL or p0 code for the MAF, thus the reason i completely overlooked it.to give you some back story on the truck itself, I purchased it as a basket case...blown drivetrain, to include OG engine,trans, t case. I purchased complete drivetrain : "engine, trans, t case" from a wrecked truck. pervious owner had put in efi live with 5way switch.. i speculate thats how all thats was blown. I do not have flash scan as of yet to pull it out of the truck and revert to stock for diag purposes, but really want to so someone can look at the mapping on it to see if that may be where the problem lies. I'm using a snap on Apollo D8 scantool to do my data logging, if there is something specific " PID " that you would like to look at pleas let me know and i will post it as soon as possible. Im learning as I go, and appreciate everyone that has responded to this thread. If this was a LS motor i would have already had this figuerd out..lol diesel engine is a whole other animal .​

 

[DAVe3283]

Was the previous engine built? If the previous tunes were for a larger set of injectors or different cam, that could easily cause a stock engine to rattle while accelerating.

Some LB7s read as low as 20-25 g/sec at idle, but for sure it should not read 2. If you clean it and it reads somewhere between 20 and 40 at idle, you're probably fine. Also double-check it is installed the correct direction, not backwards.

But really, you should find a way to put a stock tune back in the ECU, otherwise trying to diagnose a stock engine with a modified tune is just chasing your tail. Depending on what is in the tune, it could be responsible for the inaccurate MAF.

 

[David_1025]

ok so replaced MAF , cleaning it made no difference. tried to go ac delco on replacement however all three parts carriers in my town was out of stock so i went with what they had Blue Streak Part # MF12543N . i do have an ac delco on order. i have to use this truck as its my primary. below are the snap shots from the scan tool.. balance rates zeroed out across the board, i.e " 0.0 " main fuel dropped from 5mm cubed to 2or 3 mm cubed and idle mildly rougher like is has a small cam in it.. after 10 min or so of driving to let system acclimate to the new MAF , it has smoothed out some, but its still noticeable.

 

[David_1025]

Was the previous engine built? If the previous tunes were for a larger set of injectors or different cam, that could easily cause a stock engine to rattle while accelerating.

Some LB7s read as low as 20-25 g/sec at idle, but for sure it should not read 2. If you clean it and it reads somewhere between 20 and 40 at idle, you're probably fine. Also double-check it is installed the correct direction, not backwards.

But really, you should find a way to put a stock tune back in the ECU, otherwise trying to diagnose a stock engine with a modified tune is just chasing your tail. Depending on what is in the tune, it could be responsible for the inaccurate MAF.

from what i could tell with the OG engine it was stock. previous owner snapped the crank between the #1 & #2 journal . what part numbers i could find on some of the components during the mild tear down to see if block was hurt , all checked out to be OEM from GM assembly line build . as far as replacement engine i bought , it is in fact stock , with that previous owner having the valve cover gaskets redone for a small leak before 5k miles before he wrecked his truck. mileage on this engine was roughly 80k and i have probably put on maybe 35-40k since i have owned it.

 

[DAVe3283]

from what i could tell with the OG engine it was stock. previous owner snapped the crank between the #1 & #2 journal . what part numbers i could find on some of the components during the mild tear down to see if block was hurt , all checked out to be OEM from GM assembly line build . as far as replacement engine i bought , it is in fact stock , with that previous owner having the valve cover gaskets redone for a small leak before 5k miles before he wrecked his truck. mileage on this engine was roughly 80k and i have probably put on maybe 35-40k since i have owned it.

So if I understand the timeline, you bought the truck with a bad motor (snapped crank), and dropped in a used stock 80k mile engine, and have since put 35-40k miles on it?

If so, when did the knocking on acceleration start? Has it done it the whole time, and you are trying to get to the bottom of it? Or is this a new behavior?

 

[David_1025]

So if I understand the timeline, you bought the truck with a bad motor (snapped crank), and dropped in a used stock 80k mile engine, and have since put 35-40k miles on it?

If so, when did the knocking on acceleration start? Has it done it the whole time, and you are trying to get to the bottom of it? Or is this a new behavior?

correct on the timeline... it has been doing this the entire time, however my lack of experience with these..I didn't notice this until my stepfather had recently bought one as well ( 03 LB7) and they don't exactly sound the same when running next to each other. that's when I got on here started doing some research...which led me to checking rates, learning about " fuel knock " and so on. running wise its has been very reliable its been to FL, NC, and CO. i dont want to hurt the engine if i havent done so already without knowing.