LBZ injector issue [Archive] - Duramax Diesels Forum

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juddski88
11-18-2012, 10:34 AM
So a few weeks ago, I was helping a friend out by do an EGR delete and new MFE 40% tips, as well as replacing 2 injectors that had balance rates that were out of spec (3 & 5). I got it back together, started it up on the new modified tune and went to back it out of the shop and it started stumbling and billowing white smoke and knocking. Idles and starts like stock, rail pressure holds constant whether it is idling smooth or not. During logging, I noticed that it would only stumble and start knocking above 60MPA. Sometimes it will recover when brought back to idle, sometimes it won't. I tried to use DVT functions to shut off each injector while it is knocking, but I have not gotten it to work properly. Only once out of a dozen or more tries have I gotten it to even respond when I shut an injector off. I've tried restarting the ScanTool each and every time I try using DVT, still no difference. I checked my injector connections, I checked the tightness of all fuel lines, I bled the system of all air via the test valve, and I checked the tightness of each hold down bolt just in case the injectors weren't sealing completely. New balance rates, even with stock tune in and warmed up, are fluctuating all over, but the worst ones are 5 ( -2.xx) and 8 ( +2.xx) in park. I am about to tear into it again, as I have been away for a couple weeks, and I am going straight for #5 injector first and replacing it with the injector I took out of #5 originally. Any other Ideas?

RPM Motorsports
11-18-2012, 10:51 AM
Sounds like what happened to me when I got 30% over LBZ tips instead of LLY tips. Bellowed white smoke.

juddski88
11-18-2012, 01:49 PM
Replaced #5 with old one, balance rates got worse all around and still knocked, unplugged #8 and knock stopped, plugged back in, #3 and #8 balance rates became -12 and +12 respectively? Has anyone figured out which injectors correspond directly to each other and affect each others flow?

juddski88
11-18-2012, 02:22 PM
just replaced #8, balance rates are much more consistent, #3 is highest now though with a +3.xx...still knocks, now not til 75MPA, and clears up when brought back down to 40. still smokes white when knocking and running rough, but not as bad. I guess I'll change out #3 and see what happens

slipclutchms
11-20-2012, 02:50 PM
Subscribed :)

juddski88
11-20-2012, 10:03 PM
swapped #3 with #5, after determining that it wasn't a bad injector or tip, bad balance rate stayed in cylinder 3, +12 when cold, +4 when warm. Injector tip comes out soaked in fuel every time, some fuel in the oil, but no noticeable change in oil pressure or crankcase pressure. Radiator hose is not hard, no coolant use. I am leaning towards hairline crack in #3 piston. Compression test tomorrow should verify that. Makes sense though. When it came in, #3 had the worst rate at +5 and #5 had a -2. truck has 52k on it, mild tune for only a thousand miles or so, and before that had an Edge on it for an unknown amount of time. Figured it needed 2 injectors, not a big deal. well he wanted bigger tips because he had some play money, so I did them. The bigger tips multiply the problem balance rate. I didn't look at it that way until I exhausted all other options.

All in All, a good learning experience I guess.

Hot COCOAL
11-20-2012, 10:24 PM
Cracked piston?:eek:
Can a person see with bare eye a cracked injector? Or body?
How would you determne the difference?
Sorry if this is a stupid queston?

juddski88
11-20-2012, 11:34 PM
not usually, but I know it's not, because I swapped 4 different bodies around with that tip, and tried different caps, just in case. Then the final test of the balance rate staying the same in #3 when I swapped the injectors tells me it is not the injector, but the cylinder instead

Hot COCOAL
11-21-2012, 02:11 AM
That make sense, thanks for answering my question.
Next ignorant question, can you replace only one piston?

juddski88
11-21-2012, 06:55 AM
Yep

juddski88
11-21-2012, 04:20 PM
Pumped a whopping 320psi cold....motor is coming out as I type

juddski88
11-29-2012, 04:37 PM
Ended up being a bent rod due to hydrolocking. presumably because an injector leaked down or hung. piston was -.020" from deck height.

Evan@LimitlessDiesel
11-29-2012, 05:03 PM
Ended up being a bent piston due to hydrolocking. presumably because an injector leaked down or hung. piston was -.020" from deck height.

Are the LBZ's prone to bent pistons? Have you seen alot of bent pistons from this type of event? Sorry for all the questions im trying to learn and thanks for the reply in advance.

juddski88
11-29-2012, 05:12 PM
Hahaha, nice catch. F*** me

TeaBagger2006
11-29-2012, 06:02 PM
Lol.... I was also wondering how a cast piston bends but I know you ment rid lol

Sledheadxp800r
11-29-2012, 06:06 PM
:spit: :thumb:

dmax711
11-29-2012, 06:08 PM
Are the LBZ's prone to bent pistons? Have you seen alot of bent pistons from this type of event? Sorry for all the questions im trying to learn and thanks for the reply in advance.
:spit: