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Injection timing pre spool

Practical Diesel Tuning

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I've got a 6.7 powerstroke with a non VGT turbo, smoke production is still well controlled by the stock smoke limit tables estimating lambda from MAF and fuel mass. However this causes 1st gear when towing heavy loads to have little to no power before the turbo spools, which really starts around 1800 rpm (because it pulls fuel rate to hit target lambda to control smoke). Without installing a higher stall torque converter I'm looking to increase power without smoke. Sure I could scrub the lamba tables and get power but I'd make a giant black cloud - no thanks.

My thoughts so far are to either use an arduino based ECU to control water meth injection at low RPM high throttle to reduce smoke production and add fuel while also massaging the lambda tables, or I'm wondering how much I can pick up with maybe increasing injection timing BTDC while under 1800 RPM, then leaning back on the timing to stock value (around 4-5 degrees BTDC) as I get closer to 1800 RPM in order to facilitate turbo spool.

I'm hesitant to retard injector timing to spool faster because it often increases smoke.

Just thought I'd get some opinions on the matter.


Well take this in mind. On part load your able to spool the turbo on a hot engine by retarding and lowering fuel pressure but chance is white smoke and popping out of the exhaust if you go to extreme.

On full load you want toque so you need the engine to run efficient and the only way to do this run decent timing but lower fuel pressure could help a bit as end of injection is more retarded dedicating more fuel to build exhaust gas but this all also within margins.

Your engine is what we call a medium bore engine so there is some space in de combustion chamber to pull of anti lag control as for not hitting the wall with diesel spray.

I might be able to enable a post main injection event to get some anti lag (usually used for regen), and lower the pressure to get a larger pulse width as you suggested.

Let me dig through the tables and see what I can find.

And yes my biggest concern is at WOT. I find that if traffic or something stops me on a BIG hill while towing 1st gear is what kills me until the turbo spools. Thankfully the tables are based on torque requested (which is directly table controlled for throttle pedal input), so I can set the injection tables to retard timing at medium torque request, and to advance timing at high torque request.

Update: there are indeed tables I can control for post injection, very few of them allow it in EOM 0 however. It seems I have to be in config mode 4 or others.

If anyone has any advice on how to control which config mode I'm in that would be super handy. It seems it's something to do with the Injection Environment table and something else I can't quite figure out.

A DOC needs diesel fuel to work and that’s why they invented the post injection.

Try this. Take off you downpipe and start a regen of your DPF and find out what feeding the DOC. White clouds of unburned fuel and some banging and popping noise but nothing that makes your turbo go wild.

Also take note that you stop the main injection and want to start a post injection with the same fuel quantity. Your post injection may not even start to burn if you retard to far from main injection and on low RPM these is load of time to burn stuff as piston speed is relative low so big chance there that main injection combustion end short after stop of main injection and all you can hope that you still have the temp in the combustion chamber to start burning diesel again. The bigger the bore size of the piston the more efficient combustion will be the harder to start a combustion up again so on smaller bore engines post injections were used for anti lag on race cars. On the bigger bore we happy to drop a load of fuel pressure still making some decent power on low end. Just try it and work out what woks best. Fuel model on your ECM or ECU is not ideal to build boost as max fuel quantity comes from a smoke table and torque demand models are slave to this getting a smoke limit only so coming out of idle fuel get you thing done with post injection or retard and drop fuel pressure and as you ask for more torque gently go to a normal injection model and hope that you get your turbo a bit up to speed. Go for big steps and data log your runs and start fine tuning using this data.

That makes a lot of sense, thankyou.

I'll simply have to experiment with timing and pressure to see what the best I can do is.

If I wanted to get crazy I think an interesting idea is using compressed air to spool the turbo by direct injection pre-turbine (no added fuel). I could use a york compressor to keep a tank full, given I only need it at under 1800 RPM, and am really only in that situation in 1st gear.

Good discussion so far. Some of it's getting pretty far out there (with the compressed air). I mean, adding 200-300 rpm worth of stall speed would likely go a long way toward drivability for a few hours labor. With the TCM's in these trucks you can be in lockup so quickly that it would likely not adversely effect drivability or heat production while towing.

Other considerations:

- Tighter A/R exhaust housing

- Quickspool-valve or similar

-Adjust 'lambda adjust by vehicle speed' table to help you get away from the stop sign

- A set of gears

What turbo configuration specifically is on the truck? What tires/gears/etc. Give us details, we're tuners!! :)


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