off idle stumble/hesitation (BOMBED or stock)

[RankRam]

These are some great posts Julius!



They are very informative, thanks...

 

[JStieger]

Problem Solved!!!

My truck is like new again! Woo hoo!



Well I went back to Industrial Injection yesterday for the rest of the troubleshooting. This is what we found after pulling the injectors. First, an analogy-



Picture a brand new Shower Massage head - see how nice it sprays! Now, picture a scaled up Shower Massage head - see how it dribbles and sprays at the same time?



That is what my DD3 injectors looked like! Un-frickin believable! They were all carboned up - as in all 6 of them. Cody put the DD3 injectors on a test stand that can pump up to ~5,000 psi or so diesel through them with an electrical current to activate the injector solenoid. Below 4,000 psi it was all dribbling - no spray at all. At a little under 5,000 psi (i. e. just off idle rail pressure levels) only 1/2 of the holes in the injector nozzle were spraying, whereas the other half were spraying somewhat OK. Then at 5,000 psi (i. e. , about a gentle start 1200 rpm +/-) the injectors started spraying fully.



So in short poor atomization followed by the transition to a full spray wreaked havoc with my injection timing. The poor atomization off-idle caused the injector knocking (loss of pilot injection essentially). The dribbling transitioning to 1/2 to full spray coupled with the high compression of the Cummins caused the fuel to ignite late or not at all. All this caused the rough idle, sputtering, poofing white smoke, hesitation, and injector "misfiring". And this was all with no codes because the injector was actually still firing (injecting fuel!).



What really showed this phenomena was watching my fuel pressure gauge at the CP3 feed. Normally on acceleration the gauge movement was very smooth and steady up or down. Whenever, the stumbling occurred on slow acceleration the fuel pressure gauge would sharply and quickly drop by 1 psi or so and then come back up just as fast. Tracy, the II mechanic, said that as soon as I told him this he thought "injectors" based on seeing this observation on other diesels.



As you can see from the pictures that follow, these injectors were beyond hope to clean up then and there. Cody pulled one apart and found carbon inside of it too. It was probably extremely lucky that an injector didn't stick open from this carbon.



With the 3rd gens and injector upgrades, most get (maybe new) nozzles and then the originals go back as cores. From what I understand there are basically 2 manufacturers for nozzles - an Italian company called "Sprint" and Bosch. Bosch are the preferred nozzles, but Bosch doesn't sell nozzles separately yet (hopefully soon!) so you can see there is a lot of risk involved in getting high mileage nozzles. I ended up replacing my DD3 injectors/Sprint nozzles with II 3-Flow injectors with Bosch nozzles and the difference was night-and-day with the DD3/Sprint nozzle in the area of less smoke for the same SOP feel as well as less "fuel smell" out the pipe. With the DD3 I believe I may have gotten some high mileage Sprint nozzles by the luck of the draw, but I guess that is the risk I took with the BOMBs so I have no one to blame but myself. So buyer beware - when upgrading injectors insist on finding out the mileage on the nozzles as well as sticking to Bosch. I have a strong feeling that if my DD3 had low-mileage Bosch nozzles, they would have been a heck of a lot better so I hope people do not take this as a slam against DD products.



I really have to give kudos to Tracy, their mechanic and technician. He is a master at deciphering the DRB data as well as going back to the basics in terms of diesel operation theory to solve a problem methodically and without throwing parts at stuff. If any one needs a shop to go to to diagnose and repair a problem, I strongly recommend Tracy at II! Very straight-up too and let me watch while explaining how everything fits together and how cleanliness and proper torque sequence is crucial to our fuel injection systems. The rest of the guys there were pretty straight-up too and just a bunch of diesel BOMBaholics.



Also, I have to be honest - I did end up trading my HTB2 62/14 for their SPS 66 turbo because of a deal I couldn't refuse, but that's a topic for another thread!



Well I only have pictures of my injectors before my battery died so enjoy:

 

[rbattelle]

Very straight-up too and let me watch while explaining how everything fits together and how cleanliness and proper torque sequence is crucial to our fuel injection systems.

Wow! I'm very glad to hear things have worked out. Can you comment in a little more detail about how they made sure they were clean about things. I'm curious because I want to know if there's anything particularly special I need to do when working on the "clean side" of my fuel system...



-Ryan

 

[JStieger]

Wow! I'm very glad to hear things have worked out. Can you comment in a little more detail about how they made sure they were clean about things. I'm curious because I want to know if there's anything particularly special I need to do when working on the "clean side" of my fuel system...



-Ryan

Lots of it was just basic stuff people take for granted, but when you start analyzing what's going on it is pretty interesting, such as:



1) Everything was done in a nicely enclosed shop. Personally, I would not do this outside where I live because of the wind blowing dust around a lot.



2) The tech must have washed his hands a million times! He had a box of lint-free paper towels off to the side and anytime his hands got dirty from touching anything but the fuel system he wiped his hands down as a minimum.



3) In theory one could have started working on the turbo swap too, but this would have easily introduced dirt around the fuel system while things were apart.



4) Tools nicely laid out and wiped down before using. All "dirty" parts such as nuts and bolts with oil went in one stainless steel like medical tray. All the fuel contacting parts went into another stainless steel like medical tray.



5) Fuel contacting parts then cleaned up and inspected for burrs, nicks etc on sealing surfaces. The end of the injector lines have a multi stepped surface if you look at it closely. The first step nearest the end of the line is the sealing surface so it is important that this step doesn't have any nicks and burrs.



6) New injectors were kept wrapped up until just ready for installation.



As far as "special" tools:



-Very small slide hammer to pull injectors using gentle taps

-90* needle nose pliers to pull connector tubes

-in-lb torque wrench

-ft-lb torque wrench



Also, nothing was forced or reefed on. Tech advised that if you feel that you have to force something, don't! unless you want to buy new tubes, etc. Reefing on the line nuts can twist or deform the injector line or ruin its sealing end.



Also explained to me was that the most important torque requirement was setting the injector into the head in order to "crush" the copper washer evenly and seal off the compression from the cylinder. The next important was setting the connector tube. If the injector is sitting evenly, then the tube has a straight shot to the injector thereby getting the best seal.



I know that if I would have attempted this myself previously, I would have FUBARed something for sure! After watching this done, I feel pretty confident that I can tackle it myself.

 

[Mad Bomber]

got going

WOW JS, what a write up glad your back to running.

 

[JStieger]

Here's some more FYI for the folks interested in these fuel systems. When the II tech was replacing the injectors we noticed the sealing surface on the #1 injector fuel supply tube was nicked (tube from rail to rocker housing under valve cover). This tube was actually a real biatch to loosen as it wanted to turn with the nut and start bending - the nick was why. The nick is only enough to barely grab your fingernail. So we looked over the sealing surface, which is "three-stepped", and found that the nick was on the first step nearest the end. According to Cummins, the sealing is done via the remaining steps along with proper 22 ft-lbs torque so we decided to reuse the tube. Everything was buttoned up, test drove, and further 300 miles back home with no leaks.



So yesterday I start smelling diesel in my truck and just chalked it up maybe leaving a dirty rag in my truck. Today I smell the diesel again, but stronger, so I crawled under the truck and see fuel dripping off my bell housing. WTF??? I pop the hood and see a puddle of diesel on my intake manifold so I got brake cleaner and cleaned everything really well and then used a piece of cardboard to check for high pressure leaks - nothing! Then I see the drip, drip, drip - note no spray at all - from #1 injector tube as it enters the rocker housing. I call it the early day on my jeep project, drive 65 miles back into town, and go to Cummins Rocky Mountain and pick up the connector tube on a hunch.



A hour later I had replaced the tube, torqued all the fittings, fired up, and no leaks! The nick on the old tube had migrated barely to the second step causing the fuel leak. Here are some pictures of the old tube. They were hard to take due to the reflection and lighting, but if you look closely you can see the nick.

 

[rbattelle]

JSteiger, awesome work. Truly you have become an expert on the high pressure system. What are you going to do with the old tube? Is it possible to "polish" off that nick and keep the tube as a spare?



BTW, can you give me the P/Ns on the Cummins fuel system manuals you've been using?



-Ryan

 

[JStieger]

Haha! Expert? Far from it - I just like to buy peformance stuff just to see what goes wrong so I can spend endless amounts of my time fixing it. Now I know what "You pay to play" means... :-laf



I got the manual off the DC Tech Authority website. The HPCR "manual" is actually a classroom book written with lots of pictures and pretty "meat-and-potatoes" / laymans explanations. Half the manual is the instructor version with all the answers to the tests, while the other half is just the student version. The manual also comes with a CD ROM with the written manual all in Powerpoint version.



The diagnosing explanations also detail DRB3 use and interpretation of it, use of a scope, as well as some other things not mentioned in the service manual. At $3XX it was kind of pricy, but it paid me back that already. The Industrial Injection tech said that I saved him about 1/2 - 2/3 of a day in work just because of what I followed in the manual as well as enabling me to speak in his "language". Incidentally, the DRB3 software for the 305/555 really sucks and is not as robust and complete as the later years for whatever DC reasons.



The other manual I picked up from the Tech Authority site is the official code and subsequent diagnosing book. It lists every OBD code in there as well as the appropriate IF-THEN diagnosing steps.



As far as the injector tube, I don't think that I will even attempt to polish it, although I will still use it as a spare in a pinch. Since the sealing surfaces are fairly well machined to sustain high pressures I think by polishing it that I will make the seal even less.

 

[radar doctor]

this looks good thanks doc

 

[radar doctor]

thanks guys good info DOC

 

[radar doctor]

this is good stuff thanks DOC

 

[DF5152]

any idea why the injectors got all carboned up?

 

[JStieger]

any idea why the injectors got all carboned up?

Probably from not driving it like I stole it!



I also have a theory that higher fuel rail pressure helps keep the injectors cleaner due to better atomization, especially when running a bigger injector. My problems didn't start happening until I switched from a 100% pressure box (VA C3. 1 or DD TTPM) to a timing/duration/mild pressure box (Edge Juice).



With the replacement injectors I've had no problems yet. However, I've been towing with the truck a lot more and running a bigger turbo, which means less boost and subsequently hotter EGT during cruise to possibly "burn off" the carbon.



However... the other interesting thing I've noticed is with the TST box on, my rail pressures at cruise have been similar to when I ran a pressure box - about 1,000 psi higher than when I ran the Juice, which should translate to better atomization.



The way these boxes interact with the ECM is sure interesting...