Engine/Transmission (1998.5 - 2002) Idle lope after 275RV injector install

[C.Solomon]

I have searched almost all the threads about this issue but they all seem have this problem with a larger injector install then my 275's.



After I installed the 275's I noticed my idle lopes its not a miss. It almost sounds like a cammed gas motor. But it doesn't do it all the time it seems to do it after I have ran it for a period of time.

I have no leaks and it runs like a top off of idle.



Other then the idle lope I am very happy with these injectors.



Should I be concerned about this and pull my lines and sticks and reseat them or say F it and live with it?

 

[BillGotthelf]

It sounds as if one of the injectors is not opening with the lower fuel pressure at idle from the vp-44. When the rpm picks up so does the pressure from the injection pump. The easiest way to check this is to get an infrared thermometer. This is the kind that reads temps by a light beam (usually red) and looks like a plastic pistol. Run the truck up to normal operating temp. Then park it, let it idle and open hood. At 5 minute intrvals check the exhaust manifold temp at each cylinder as close to the cylinder head as possible. After 10 minutes all the temps should be within 10 degrees. If one is 25-30 degrees cooler you have found the bad injector.

 

[C.Solomon]

If that was the case wouldn't it sound like a miss?



If a injector is not popping off then it should create a dead cylinder.

 

[Vaughn MacKenzie]

C. Solomon did you use a torque wrench & claw's foot to torque down the fuel line nuts? Having them too loose or too tight will compromise the sealing between the tube and injector which can cause glitchy drivability issues.

 

[C.Solomon]

Sure did, I torqued everything to specs.

 

[obert]

..... lower fuel pressure at idle from the vp-44.

I really dont want to sound like a smart*****, apology in advance. But how does that work? I kinda thought the VP had delivery valves. A spring poppet valve thats set to open at xxxx psi should always open at said psi.



Honestly, I have had what sounds to be a similar situation, and I kinda thought maybey a bad nozzle, but thought it strange to happen only at idle (and in my case the A/C or steering pump over relief as a load is enough to make it go away). Is there more light on this?

 

[mgoncalves]

Honestly, I have had what sounds to be a similar situation, and I kinda thought maybey a bad nozzle, but thought it strange to happen only at idle (and in my case the A/C or steering pump over relief as a load is enough to make it go away). Is there more light on this?

Mine behaves exactly the same ever since I put the stock injectors back in. Turning the A/C on makes it go away instantly. I have also noticed that bio diesel makes it go away as well. I'm pretty sure one of my injectors is the cause, but I can never track down which one it is, either with an infra red gun or cracking the lines.



I'm hoping some new injectors should fix this, because it didn't do it with my old injectors.



Matt

 

[C.Solomon]

Speaking of trying to find what injector it is... .



I had a friend of mine who has a snap-on scan tool. He could go in do a cylinder test. The scan tool would shut off one cylinder at a time at idle.

That would be the easiest way to find out what injector(s) is causing the lope.



That's why I love posting here, someone will always shed light on something I didn't think about.

 

[gonehuntingagain]

When my VP-44 went, it was loping like you described. It was intermittent, and would occur at idle only, mostly when the engine was cold but slowly progressed to do it all the time. It stopped one day before I took it into the dealer and came back several months later - the dealer replaced the VP-44 after checking it with the Cummins tool that isolates it from the wiring harness.





Hopefully it is just an injector and not the pump.

 

[Oil Burner]

I tried cracking the lines to find my miss/stumble. When I opened a line it became a very pronounced miss. An isb on 5 cylinders sounds much different than my occasional miss/stumble. But that is how my sounds, yours might be different. jUst my experience.



I tried listening with a mechanics stethescope but couldn't pinpoint the miss. It seems to be really random and only when the truck is warmed up. When cold, it is smooth and steady.



Mine is completely gone under load. Just at idle or running in nuetral. I have heard automatics with the same problem behaving differently becuase of the load from the converter I guess.



I was thinking that my pump was getting weaker and the last 3 sets of sticks that i put in were set to pop at 305 bar. My stockers popped as low as 280 bar when I pulled them out and they ran very smoothly. Maybe they were working well with the weakening pump and I made the problem apparent with the higher popping injectors?????



I'm actually looking forward to replacing my vp to see if that makes a difference (not looking forward to spending the money!).



Have fun.

Jason

 

[C.Solomon]

I dont know what I was thinking, if you shut one cylinder off or crack a line you are going to create a miss. So the only way to know what injector is causing the lope would be a temp sensor.

 

[obert]

I dont know what I was thinking, if you shut one cylinder off or crack a line you are going to create a miss.

If an cyl. was already missing, there would be little change in RPM and sound when you open that cyl's line. You were on the right track... ...



I have only noticed this miss since the VP was replaced under warranty in '01. It has progressed to be more pronounced and more constant now than at first, but after nearly 100k miles of this I would've thought what ever was broke would be done by now.

Also, the rearward cyl's ( 5 and 6 mostly) have seen enough heat to melt pistons, at around 50k, and I am pretty sure the injectors were not changed



Weather this turns out to be injectors or the vp, I'll see it as an exuse for "better" parts... . Oo. Oo. Oo.

 

[BillGotthelf]

Guys I am not making this up. Once in a while an injector may have a seat spring pressure slightly higher than the other 5. It does not matter if its the delivery (lower idle vp44 pressure than new) and bad injector. It sounds like a lopy idle just as you described. The easiest way to check this is checking the exhaust temp at each cylinder at idle. The missing cylinder will only be pushing air. If you find one cylinder lower in temp than the rest switch that injector with one a couple of cylinders away and retest.