Injector Knock

[yycguy]

OK, this started about a week ago. When I pull up to a stop light with the engine warm and stop, I get a slight miss or injector knock. This is only when the engine is fully warmed up and when the engine is under load and at idle. IE stop light and in "drive". I have had it to the dealer twice and they can also hear it. They did a Kill test on the injectors, and I think it was called a cylinder balance test ? all these where normal. But they can't do the kill test with the engine in "drive". This afternoon I had it down there again and they used a temperature probe and pinpointed that number 5 cylinder was hotter than the others by about 50 degrees. They feel it an injector running lean? They want to swap injectors around and confirm that it is the injector. I guess getting injectors from cummins is like asking for a new engine. any ideas?:-{}

 

[FPoitra]

I have had the same problem. When the engine is hot, I get a loud knock when I pull out from an idle. It is easy to hear when you press on the brakes and give it gas at the same time. You can hear it really well then. I know it is not right because it doesnt do it on short trips, only 50 miles or more. But I dont know if it is a bad or loose injector. Do they knock only when the engine is hot??

 

[yycguy]

Yes that is exactly what I get, it's only after driving at least 20 miles or so.

 

[DCTECH]

I have replaced several injectors for tris problem, STAR line had me switch injectors before would send me any. Noise moved with injector, caused by injector leaking fuel causing temperature to raise in cylinder and knock. Most noticeable when hot after driving a ways and at idle or just off idle at 1100 to 1400 rpm.

 

[FPoitra]

How long can a person drive it like this? I've been driving it like this for the past 3000 or so miles because I thought it was normal for it to make that sound.

 

[BHaner]

Is the only way to fix this loose injector problem to replace the injector? Is there a way to tighten it? Should I be checking the torque on something under the valve cover when I check my valves?

 

[BIGORANGEJEEP]

Mine had it also. Turned out to be a bad #1 injector. Had to fly one in from Minnesota or somewhere though. It took two trips to the dealer to figure it out but they fixed it. I would think about trying to get them to change the oil at ths same time as it might have been flooding the cylinder. 2003

 

[RankRam]

Could this be part of the problem with the lower than normal fuel mileage.

 

[Johnstra]

I haven't had any of the symptoms you guys are describing, but concerning fuel economy, I noticed around the base (where they attach to the rail) of 2 of my injectors a little grime - like they'd been leaking slightly - so I tightened them. Mileage on my overhead went from 17. 2 on the last tank to 19. 1 with 3/8 left on this one. Could be coincidence, but my last 8 or 9 tanks have all shown low to mid 17s on the overhead and my driving conditions from tank to tank are almost identical. It's hard to imagine that much of a leak, but...



-john

 

[rbattelle]

I have the exact knock described by DCTECH. However, I refuse to take it to the dealer, specifically because of the experiences of others' on this board. I will not take it to them and let them put their hands all over my fuel system, switch injectors around, run 3 weeks of diagnostics, inconvenience me by taking my only transportation for days on end, repeatedly tell me "it's normal, they all do it", etc. Instead, I will drive it until it experiences a specific problem that I can go in and any moron can say "yep, that's yer problem!". I have 4 more years and 75000 more miles on the engine warranty. This has been occuring since around 10000 miles (now have 25000 miles).



In the meantime, I have noticed no decrease in either fuel mileage nor power. And the engine does not make oil. Bear in mind, although DCTECH speaks the truth, a loose injector or even fuel line hold-down clamp can produce similar knocks (although engine temperature dependence would seem to indicate otherwise). My knock also tends to "come and go". It will be really really really bad for a few weeks, then disappear for several weeks, then return.

 

[Vaughn MacKenzie]

Originally posted by yycguy

. . . number 5 cylinder was hotter than the others by about 50 degrees. They feel it an injector running lean?

Just to clarify. . . an injector or cylinder running "lean" will cause it to run cooler, not hotter. It's the opposite of gas engines, and "lean" simply means leff fuel and less power.



I'd definitely suspect an injector if it's running 50F hotter, and knocking, meaning likely it's dribbling fuel or fueling too much or not shutting off properly.



Vaughn

 

[rbattelle]

Check out this thread also. Lots of good info there.

 

[CKruse]

I noticed mine was much louder at idle in high altitude situations. We just returned from a vacation in the Rockies, and I noticed the "clack" at hot idle while in the mountains. Once we got down out of there, it returned to it's normal quiet self. Just my observation. Put 2200 trouble free miles on it towing the Jayco on this trip. Temperature variations from 32 to 104 degrees. We were VERY happy with the truck's performance.

 

[yycguy]

Originally posted by Vaughn MacKenzie

Just to clarify. . . an injector or cylinder running "lean" will cause it to run cooler, not hotter. It's the opposite of gas engines, and "lean" simply means leff fuel and less power.



I'd definitely suspect an injector if it's running 50F hotter, and knocking, meaning likely it's dribbling fuel or fueling too much or not shutting off properly.



Vaughn

Thanks, I guess that makes sense.



Now since I have mods on my truck the dealership says DC is going to limit my warranty! too what extent they haven't heard back yet. Man they can be real ___ you now.

 

[rbattelle]

Originally posted by yycguy

Thanks, I guess that makes sense.



Now since I have mods on my truck the dealership says DC is going to limit my warranty! too what extent they haven't heard back yet. Man they can be real ___ you now.

What, exactly, in your list of mods has anything at all to do with the fuel system? Do you also have a box that you didn't list?

 

[rbattelle]

Just thought of something else. Are the injectors on these trucks held in the "off" position using spring pressure, fuel pressure, or some combination of the 2? If they're held off using fuel pressure, that might explain some of them "dribbling" when fuel pressure is low and load is high.

 

[yycguy]

Originally posted by rbattelle

What, exactly, in your list of mods has anything at all to do with the fuel system? Do you also have a box that you didn't list?

rbattelle,

None of my mods that where on the truck when it went to the dealership have anything to do with the fuel system! they are just being very difficult. The mechanic that was working on my truck seems like a real genuine man, he told me the shop Foreman was one of those individuals that likes to stir up trouble to make him self look good with DC. I am taking it back in there this week whether they warrant it or not it has to be fixed the knock is driving me nuts and I can't imagine it is doing the engine any good.

 

[rbattelle]

Best of luck... . please keep us updated!!