The OP's situation is precisely why I'm not a huge advocate of the mantra of TIMING TIMING TIMING.
From
a previous post:
I've seen this discussion several times on this forum, and I respectfully disagree about the statement that the timing gun is the best way to properly time an IDI. That said, I not supporting the inverse: timing by ear. Instead, I'd argue that the timing gun is only a minor tool in the process of what I call "timing by performance."
I've owned a timing gun and ferret meter for years now. All a timing gun is good for it telling you a number. That number may have very little impact on whether your IDI is properly optimized for timing. So many factors play into the variability of how that particular IDI is "timed," that the arbitrary number is cool to know, but it's not likely the best performance for your engine.
Several factors can alter the "timing" of an IDI: how an IP was rebuilt, the inlet fuel pressure, injector pop pressure and rebuilding, cam and crank variations, different turbo variations, fuel screw rotation, injector line radii, etc. Slapping a ferret meter on and timing it just tells you that you have it to a specific BTDC degree, but depending on your setup, that might not be optimal. When you rotate your IP, you are altering that number, and just because it reads the stock (or turbo) timing spec, doesn't mean that it's done. Sometimes a neighboring timing degree might get the turbo to spool up better. A lot of factors come into play on these imprecise and mechanical diesel engines.
For the most part, getting it close to stock spec would be ok for the average IDI owner. But if you have modified or repaired your engine or fuel system (and who in this group hasn't), then I'd recommend "timing it by performance." This means to time it with a gun to get it to stock spec, then conduct several 0.5deg - 2deg timing variations and drive it, recording MPG, boost, EGT, and other performance data, while carefully recording fuel usage. Eventually, you'll find the
optimal timing position for that particular engine. The optimal performance timing might end up being the stock spec, but it might not. It'll take some work to investigate the neighboring degrees relative to the spec.
The timing gun is also good for returning the timing (to the respective previously-tested "optimal" position), if you ever had to remove the IP or do a repair that required you to tear down your injection system. But if you buy new injectors or a pump, then you are back to timing by performance to find that optimal timing position. That's why I don't really take the digital timing spec as gospel. Stock spec might be close to ideal, but with more testing, you might find even more power, boost, or efficiency.
