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05 LLY injector knock PLEASE HELP

I guess he knows wich bank is #1 ? I recently diagnosed a lly with a otc scanner. It was knocking on cyl number 8 also. Only scanner glitch I had was not being able to shut off cyl #1 injector.
 
Cylinders not shutting off, wrong cylinder shutting off, and balance rates not showing for the correct cylinder are all documented problems with 04-05 lly's. It gets even trickier as one person used a scope and found that the cylinder deactivation tool would switch which injector got turned off depending on rpm.
 
I have had the truck on a tech 2....balance rates are similar to the ones shown....he said the return rates looked fine..I am trying to post a video of the knock on YouTube right now
 
This is exactly what my truck sounds like....#8 and #5 were replaced like 6 months ago due to a no start issue....just replaced #7 because of this knock and had no change
 
Joshua05lly said:
I have had the truck on a tech 2....balance rates are similar to the ones shown....he said the return rates looked fine..I am trying to post a video of the knock on YouTube right now
Click to expand...
Return rates are not something you check on a scanner. You have to disconnect the return lines from the injectors, install test fittings in there place, crank the engine over for a specified time, and measure how much fuel is returned. There is also an enhanced balance rate test where you do the same test, but you do it with the engine idling warm for a specified amount of time. These 2 test's normally show which injector(s) are going/failed.
 
Ok...so just an update...I have now replaced 6 of the 8 injectors ( 2 about 6 months ago, and just did the other 4)...no change in the knock....(but they the knock noticeably went away when certain cylinder were shut down)......so after replacing the last 4 Injectors I start it up, went for a drive...still knocking....go home put it in park and it starts lopping!...balance rates wont show up.....I put it in reverse and it is smooth as glass and balance rates show back up....only does it when truck is at operating temp.....go back to the shop to have it looked over Again....actual vs desired are a little off...and kinda go wacky when romping on it....but no " shark fin" on the graph...no surging...so when it is loping in park we raise the fuel pressure up just a bit and it levels back out and rates show back up.......so...back to the knock....we shut each cylinder off one by one with the idle at about 1300 rpm and they don't make much change....the knock is much more prominent when driving (under a load)... I have it in tow haul and found the highest knocking point (32 mph) and drove like that while he shut each cylinder off...still knocking....he decided to lower the fuel pressure (dont quote me but I believe he said if it was at 50 he dropped it down to 40) and the truck was so quiet I couldn't believe it!!
Mechanic said he is leaning to the fpr...thinks that it was compensating for the old injectors for so long that when they got replaced they didn't need the compensation and the fpr is basically sticking to what it needed b4....makes perfect since really...but the graph didn't look crazy bad...truck has a ECM tune from PO.. I believe it to be efi tune but have no way to know for sure....but I'm wondering if the tune isn't at fault...
to be continued ............
 
And....the truck was knocking b4 I replaced the last 4 injectors.... so if the fpr is indeed going bad then it was going bad b4 the injectors...that's the reason I changed the damn things...
 
The regulator you're talking about is known as an fca. It controls how much fuel goes to the cp3. It doesn't compensate like you think. It has a preset table it works on to maintain actual rail pressure to the desired amount. If actual rail pressure is close to desired, its working correctly. It sounds like you need to pull all your injectors and send them out for testing on a bench.
 
The deal is...when driving or idling and shutting down each injector it doesn't stop the knock....only thing that made the motor quite was to drop total amount of fuel being delivered to all injectors
I am at a loss and the only think I can really suspect is maybe the tune....previous owner had one installed in the ecm....have no idea what it is or who it is from....but I'm wondering if maybe it is causing bad injector timing or something
 
I know it's a long shot...but any way I can possibly call and talk....so much easier to explain over the phone!!
Just dont understand y the rates look ok and shutting each cylinder down while revved in park and while driving under a load will not make a change but dropping overall pressure while driving will make it stop knocking
 
Lowering rail pressure will reduce the amount of fuel leaking if you have leaking injectors. Balance rates is only a small glimpse of what is going on. Even if you max out the rail pressure, it shouldnt knock. It will be loud, but shouldnt knock.
 
The return rate test requires special fittings to hook to the return ports on the injectors, you then run the hoses from those adapters into a graduated beeker set to measure how much fuel is being returned. Theres 2 return rate test's, the basic one where you check return flow during a 15 second cranking cycle, and enhanced where you check return flow during a 15 second run cycle. If you don't have the tool set or access to it, you're better off sending your injectors out to be tested. I would call Lincoln Diesel service and see if they do testing, or see who they reccomend.
 
You can't just look at individual balance rates to determine a bad injector. There is a base balance rate pid that is part of the equation too. The base balance rate is for all 8 injectors and then there is balance rates for each individual injector. If the base pid is out of spec then you can easily misdiagnose which injector is bad because it will adjust all 8. So you have to do math between the base rate and the balance rate for each injector to see which one is out of spec. 99% of people are not diagnosing duramax injectors correctly.

You have to raise rail pressure to a set spec at idle to check injector return rate property. But I've never seen that cause a knock.

I would take and oil sample and send it out and have is tested. It's a good way to see if it's a bearing failure.
 
Not 100% yet because I haven't replaced the part...but I may (hopefully!!)
Have found the problem...I have a huge amount of air going into my ficm....just at idle....I imagine a lot more when revving....it kinda explains the knock and loping...
 
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