Injector timing tuning for Aftermarket Cams

[Shiwnath]

After meeting with Paul (MMGT1), we got talking about how my car seems to run rich on idle and how fuel efficiency has gone down the drain even for this type of build.

One of the things HPTuners does not allow for is End of Injection Timing which is vital to tune when you swap in a cam with a lot more degrees of overlap. Seeing how we are stuck using the .hpt file format that HPTuners uses, we can't use TinyTuner to help us out unless we have a DHP PowrTuner. Luckily for myself I actually bought one in 2012, but had mixed results reading/writing my PCM with it. That's why I bought the HPT Suite. Anyways, after lucking out tonight with DHP, I successfully was able to read my .bin file from the PCM and could use the TinyTuner program to tune this End of Injection table.

The Theory from what I have learned and my understanding:
How this End of Injection Table works on the V6 PCMs is that it uses the camshaft's BBDC( Before Bottom Center (Piston lowering) ) specification as a reference to command the injector pulse in order to efficiently inject fuel into the combustion chamber. BBDC is the point when the exhaust valve is about to open. This is why this information is important for end of injection. If this value is left stock, you're essentially allowing your fuel injectors to send fuel into the combustion chamber while the exhaust valve is open. In my case, while 2.5 degrees may not seem a lot, it's still wasted fuel. The BBDC value in the End of Injection table on the stock .bin file is 60 degrees.



I found a website that explained the terminology in a way I could understand as well as gave me an awesome calculator that I could use to calculate the BBDC on my strip cam. After using the calculator, I calculated that my BBDC was 62.5 degrees and I verified the stock cam is in fact 60 degrees given stock specs from Ben. Just keep in mind that if you use this calculator, you have to use the cam specs at .006" lift, NOT .050" lift.

Link to the site where I learned all about cam specs:
http://www.tildentechnologies.com/Cams/CamBasics.html

Link the calculator that I downloaded and modified for my own cam vs stock specs:
https://drive.google.com/file/d/0B1U...it?usp=sharing

Feel free to correct my if I'm wrong, I'm still learning after all! I literally JUST flashed the PCM so I'm still in the process of gathering results with this end of injection timing table. I'll update this thread when something worth noting happens. Stay tuned! (No pun intended)

[MMGT1]

There is an erogenous error on GM's part there, nothing new! The end if injection should move closer to the valve event as the temp reads colder. The whole point of the end of injection table is to account for fuel pooling on a cold valve, and to account for the overlap of a cam. An intake valve, when heated, is in the area of 400*F. This high temp keeps the fuel atomized and will allow you to move the injection timing further away from the valve event as there is plenty of room for that fuel to be atomized by the incoming charge. Heat in the head also plays a role here but overall can be mapped by valve temp. In V8's, HP Tuners gave us the table to directly tune this event. From the factory the V8's are set up much better as the temps are already mapped and all that a tuner has to do is move the entire EOI table closer to the valve event with the same percentage that the increase of cam overlap increased by. So if you added a cam that gave you an extra 20% of overlap you would in turn move the EOI 20% closer and would have you in a good ballpark and you would just "tweak it" from there.

Seeing what GM has done to the V6 there it is a blanket at best. Moving the entire table I cannot see working properly as the atomization of fuel changes with the increasing valve temperatures. If you have worked out an increase of 2.5* with the table then you would have to test the 2.5* change and see at what temp it is making the engine run best at idle, ie: least amount of fuel smell from exhaust. Then you would use that as your starting point. Colder temps would need to be moved closer to valve opening and the opposite would need to be implemented as the valves increased in temp. Now, your table is governed by coolant temp. I can tell you that a valve temp of around 130-140*F is about where the valve is warm enough to begin stabilizing the atomization of the fuel vs the incoming charge of air. Coolant temp wise this is going to happen around 60*F to 70*F. The way I would attack this is with a fully heated engine, coolant temps in the 80-100*C range in your table there. Reduce the table in that range by 2.5* and test the results. Move the factor in .5* increments until you have reduced the "smell" of the exhaust from being rich. Once you have the heated engine “tuned” this will give you a good idea as to the amount of advance or retard to apply above and below that point. Again, a steel valve will heat to an average of 400*F with an engine at full temp.

**Keep in mind because you smell fuel does not in any way, shape or form mean you are running rich in the combustion chamber and quite the opposite can be happening. You may be lean even though you smell an insane amount of fuel from the tail pipes! The pooling of fuel is being sucked straight out through the overlap of the cam to the exhaust side causing the fuel you smell to be there. Some of this fuel will ignite in the exhaust due to temperature of it and actually is how you will have a false rich reading on your O2 sensor. An O2 sensor is reading oxygen content and is not reading fuel content of the emissions at all.

Hope this helps you figure that table out buddy……

[a.graham52]

Isn't this kind of what the "transient fueling" section of hpt is?

[MMGT1]

Transient Fuel is for Tip In issues. Here is a great read if your looking at Transient Fueling, very different than EOI stuff:

http://www.hptuners.com/forum/showth...A-how-to-guide