Warning, This is a long post.
Interesting results from the pop test. I went to Diesel Fuel Injection Service locally to get all my injectors pop tested. They were nice and took care of it while I waited and didn't charge me anything. While I was waiting I asked them a few questions and it quickly became apparent that this was not a performance oriented shop. Great guys and willing to do whatever I wanted but they steered away from suggesting any directions related to performance. I would need to know exactly what I wanted before hand but they did offer extrude honing (that they outsourced) in three levels: Phase 1 ~ 40hp, phase II ~ 60 hp, phase III ~ 90hp. So here are my pop results.
Stock set (should be 245 Bar)
1 - 225 Bar
2 - 234 Bar
3 - 240 Bar
4 - 236 Bar
Modified set (tech estimated they were probably set to 260 Bar)
1 - 255 Bar
2 - 248 Bar
3 - 242 Bar
4 - 237 Bar
The tech noted that all the injectors were still giving a good spray pattern and are usable. This somewhat surprised me as I thought my stockers were on their way out. I asked about spray angle and they said they'd need to take the injector apart to get to the numbers listed on the nozzle to find out. The wide variation in pop pressures has me concerned but it wasn't enough information to make a decision so I told him I'd like to do more research (since they didn't really offer any new ideas) and think it over before doing anything.
The theory I was trying to support was that the pop pressures being too low/too different from each other is causing hazing/smoke. I found a suggestion that a ~20 Bar difference equates to 1 degree retarded timing. What I'm not sure about is if one degree difference between injectors would cause that kind of haze.
I decided to try out the stock injectors. Pop pressure is tuned by shimming the internal injector spring, more preload/shims = higher pop pressure. I didn't want to pay ($28 per injector) to get the stock set reset but I did want to bring Stock-1 up closer to the others. I took apart Stock-1 and Modified-1 to see what my shim options were. I ended up adding .015" in shim thickness to Stock-1 as a guess to bring up the pop pressure on Stock-1. While I had Stock-1 and Modified-1 apart I took a look at the nozzles for numbers. Modified-1 did not have any numbering so I figure it was a blank nozzle that was modified to what it is now. Stock-1 did have writing on it.
DSLA 155 P278 66521 is what I found and the only information I found through searching is that this is a 5 x .012", 155 degree spray angle VCO or Sac-less injector that looks like maybe a marine 370. What's very interesting is that it is a 155 degree pattern. That makes me wonder what the pistons were in my engine before I rebuilt it. Conveniently they match the pistons I have in the engine now and with the tech stating the pattern is still good I just had to try them out.
I used some middle sized seal washers (~.062" thick) and installed my stock set of injectors. Tuning was off of course but after a few adjustment these injector appear to be working. Crazy, I had a decent set of injectors to power my twins all this time and didn't know it.
With the engine cold they haze at idle like any other injector; however, once everything was warmed up they are clean at idle no load. I shifted to drive and put on the line lock to simulate a load (as if I was at a stop sign in drive with the brakes on) and with it idling there was no haze. I had a chance to follow my wife with her driving the truck and cold it hazes as expected but once warmed up it is much cleaner than before. I drove it to work today and could not see a trail in the headlights behind me like with the Modified injectors. I'm currently seeing 40psi max for total boost. I did turn in the power screw 1/4 turn in more than I've ever had it with the fuel pin at only 50%. I'm at 18 degrees timing and may bump that down one degree to see what it does. Comparing the two injector sets (I know it's not really apples to apples) the stock set seems to run a little smoother and the power delivery is smoother. The Modified's felt more powerful at the same pump settings but tuning will probably make up for that. It's still possible that I needed to run more timing for the Modified set to help clean them up but I'm afraid drivability might start to suffer with the timing they might have needed.
At this point I will continue tuning the stock/original set and probably look into a fuel pin. If that gets me where I want I'll have this set reset for pop pressure and enjoy.
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