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Old 01-27-2014, 09:32 PM   #1
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shiwnath's Avatar
AKA: Trevor
Join Date: Jun 2011
Location: Kitchener, Ontario
Age: 28
Posts: 168
Vehicle: 2000 Olds Alero Sedan
shiwnath Gettin' there
Injector timing tuning for Aftermarket Cams

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:

Link the calculator that I downloaded and modified for my own cam vs stock specs:

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)
2000 Silvermist GL2 Sedan w/ LX9 3500 V6
TCE 65mm throttle body, ported 3400 upper intake manifold, ported 3500 lower intake manifold and heads, WOT-Tech Strip performance cam 276/264 adv duration .536"/.520" lift , COMP Cams 26915 Valve Springs, 28# Trailblazer Injectors, TOG headers, Custom PCM tune and 4th Gen Camaro front calipers
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Old 01-27-2014, 09:50 PM   #2
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Location: Naptown, IN
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So in short, you were still fueling when the cylinder experienced blowdown, and the resulting HC dumped into the exhaust accounts for the unexpectedly low economy?

How was this translating into an actual rich condition at idle? Reversion? Carbon in the chamber soaking up the fuel injected after exhaust opening, allowing it to richen the subsequent intake charge?

I never considered timing injection events relative to exhaust opening; common thought always relates it to intake closing and just assumes you can hang the injector open as long as it takes to complete fueling.

Thanks for sharing this!
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