Good evening all,

 

Huge fan of this forum, it's taught me a lot about working on my truck and I'm hoping I can get some help pinpointing a problem.

 

I've got a 99 24V 4WD with an NV4500 5 spd manual transmission, about 325K miles, bought it about 4 years ago with 272K miles. Over the last weekend I replaced the injectors with some Bosch 75hp, I replaced the crossover tubes with new ones while I was in there, all with new o-rings and new copper washers, and I also adjusted the valves. Followed torque procedure when putting everything back together. Before this was done the truck was pretty sluggish with acceleration and building turbo pressure. Now she accelerates great and builds pressure no issues, but I'm experiencing what feels like a stalling or lope issue when I come to a stop and push the clutch in. Engine sounds like it revs down and then up and then down and then up again before returning to a normal idle. It didn't do this before replacing the injectors and tubes. VP44 is fairly new, maybe 20K miles on it, lift pump is a Fass.

 

The previous owner kept a log of everything done to the truck since mid 2014, I've kept up that tradition.

 

Is this normal after upgrading injectors, or is it something I need to diagnose and repair? Thanks!

 

 

8 hours ago, Thr333_Arr0ws said:

Engine sounds like it revs down and then up and then down and then up again before returning to a normal idle

 

I am not going to be of much help here, but can you describe the above in more detail?  Is this a rapid change in rpm - such as, 2 or 3 times per second?  Or, is this a much slower change? 

 

Also, what were the previous injectors - stock, OEM, etc.?.  Are the replaced Bosch injectors new, or re-manufactured?  Do you know where the VP44 came  from and did it come with a new PSG or a used / reconditioned one?

 

I asked these questions because others more knowledgeable than me, will come to your aid shortly and they will probably want to know some of these answers.

 

It sounds like the truck has been well maintained by the previous owner and currently by you. 

 

- John

 

Hi Tractorman, great questions and I appreciate you asking them, hopefully the answers will help others to diagnose my problem

 

The rev up and down twice is in quick succession, takes about two to three seconds to complete the rev up and rev down cycle before returning to normal idle, this happens every time I come to a stop and push in the clutch, it doesn't matter whether I keep it in gear or take it out of gear, the rev cycle persists. At idle, truck sits just a hair above 800rpm. 

 

I'm not sure about the previous injectors, they weren't Bosch, and the log has no mention of the injectors being done, but there's a 15 year gap from when truck was purchased to when the log was started so they may or may not have been done. The new injectors I believe are new regular injectors from Bosch that they "rebuild" to be the +75HP. The VP44 was new and came with a new PSG.

 

Also, I replaced the lines from the fuel filter to the VP44 with some bigger half inch lines a while back when I upgraded to the Fass, fuel pressure sits at 17PSI when idling.

 

I was very fortunate that the previous owner started the log book, thank you!

 

 

Yeah injectors only last up to 100k miles. Typically pop pressures tend to fall off and spray isn't as good.

 

The only injectors I will buy is non-Bosch injectors which custom built and been flow matched.

@Thr333_Arr0ws, it may be that nothing is wrong.  The following is only my thoughts, but it would seem to me that the ECM easily has the capabilities of operating stock injectors smoothly through all engine rpm's and engine loads, including engine idle.  But, when you replace stock injectors with significantly higher horsepower injectors, then I could see that the ECM may struggle to arrive at and maintain a smooth idle. 

 

Look at it this way - the engine is going to use the same amount of fuel to idle whether it has stock injectors or high horsepower injectors.  The difference would be that with the high horsepower injectors, the ECM would have to cut fuel duration time way back for the engine to idle at the same rpm.  To me this could make it difficult for the ECM to precisely meter the exact amount of fuel required to make a smooth transition to idle with high horsepower injectors.

 

I currently run RV275 hp injectors in my truck - that is only a 30 hp bump.  While I have no change in the way the engine arrives at idle, I do now have a slight hunting in rpm's at times during clutch engagement.  I attribute this to what I just mentioned above and consider it normal.

 

Again, these are only my thoughts - no verification that this is even happening.  There could easily be something else going on.

 

- John

I was kind of going down that same path, it makes a lot of sense. I'm about a week in with the new injectors now and she is running better than ever, it never actually stalls so no real driveability issues. I'll just keep monitoring for any changes and go from there. I appreciate all your input!

 

-Sean

23 hours ago, Tractorman said:

then I could see that the ECM may struggle to arrive at and maintain a smooth idle. 

Not true. Being that Quadzilla drops out and the ECM controls the idle. At an idle the ECM controls the timing and fuel directly. Once RPMs rise above about 1,200 RPMs then Quadilla takes over and uses it timing anf fueling maps. 

 

23 hours ago, Tractorman said:

Look at it this way - the engine is going to use the same amount of fuel to idle whether it has stock injectors or high horsepower injectors.  The difference would be that with the high horsepower injectors, the ECM would have to cut fuel duration time way back for the engine to idle at the same rpm.  To me this could make it difficult for the ECM to precisely meter the exact amount of fuel required to make a smooth transition to idle with high horsepower injectors.

Like my 7 x 0.010 injectors popped at 320 bar (+10 bar over stock) it idles today at about 7% to 9% when they were new injectors the engine load was closer to 13% to 14%. Still in all at an idle, the timing is controlled by the ECM but the fuel is controlled by the IVS switch in the APPS which flips the ground for the IDLE and then the ECM ignores the APPS values and uses ECM software to hit 800 RPM idle. 

 

23 hours ago, Tractorman said:

I currently run RV275 hp injectors in my truck - that is only a 30 hp bump.  While I have no change in the way the engine arrives at idle, I do now have a slight hunting in rpm's at times during clutch engagement.  I attribute this to what I just mentioned above and consider it normal.

This is due to the stock fuel map not being designed for oversized injectors. Beast is a little picky launching and may stall if you just ease out on the clutch. This is due to the fuel map being wrong on the ECM and the timing map was designed for stock injectors since the Quadzilla is not active at RPMs below 1,200 RPM it's very possible to have this issue. With larger injectors, you need more timing hence why I'm running 24.5 degrees at 2,000 RPMs. You're correct the duration is much shorter but that same amount of fuel was blasted in quicker and needs more time to heat the mist, to vapor, bit more to go BANG!