AFX issues exhaust leak?

[383]

Come to think of it when I was starting out I had this same issue with a cammed vette. I went about it in a wrong way by setting stoich rather rich "high 13's" then readjusting MAF to keep the fueling right to get rid of some horrible bucking the car was having. At light throttle and idle it was running 15.1 to 15.5 AF. After doing the stoich and MAF "the way that is wrong", I wound up getting rid of all bucking and running at a constant perfect 14.6 to 14.7 AF. I only learned later to adjust injection timing to do the same thing the correct and non fuel wasted way...

SO set your injection timng by adding to the boundary, then recheck...

I will thanks, the cars on jack stands right now for delrin bushings but Ill try to add 12 to the EOI vs ECT when I can. It was bucking a bit (about 11-1200 rpm) in low gear.
The reason I was subtracting was because of the GB DVD I learned from said to inject AFTER the exhaust valve closes, but now Im thinking that if the cam has an intake valve event thats radically different, you might need to add to try and finish injecting before the valve opens.
Thanks for the input guys Ill try to add and report back soon.

[GHuggins]

Adding to the injection boundary retards the injection event - in other words after the exhaust valve closes to keep it from "short circuiting" or sending the fuel straight out the exhaust. In Greg's DVD (anyone please correct me if I'm wrong here) he explains how to keep the injection timing more to stock timing - injecting onto hot closed intake valve. Or atleast that's how I remember taking it when I watched it - (moving the ect table in the same direction it's already going)... That will work great for minor cams, but... Well it's already been proven that as long as emissions aren't the only objective more power and torque can be gained by injecting afterwords. There was someone who had experimented with this and found best low end torque and power gains could be achieved by injecting just before max intake valve opening where the most turbulence took place. This also supposedly kept the fuel from washing the cylinder walls... Don't know. I just stay right around 10 to typically no more than 25 degrees retarded for the injection timing. Makes for great out of hole throttle response, fuel economy and really helps to dial back needed fueling durring WOT which further helps fuel economy if you spend more time playing than driving...

You will probably need to add a min 10 degrees to start noticing a difference, but I would highly recommend using fuel trims and idle "smoothness" along with smaller adjustments to dial this in. Think 12 to 15 is good rule for turbo cars with stock cams, then somewhere closer to 20 for a NA with more radical cam... Atleast that's what I typically use to go by then add or take from there.

[383]

I added +12 to the inj timing normal ECT and started it. I noticed that the cold start enrichment is commanded but not delivered, then once it warms up ve gets closer
I also added +4 on top of the +12 to see if I could notice a difference. Both short logs are attached
Thanks for looking

[GHuggins]

So it runs slightly richer than commanded when hot, but fairly leaner than commanded when cold... This is because injection timing is quite a bit more advanced at colder temps in hopes of it vaporizing on the colder valve if it's allowed to sit there longer. Try setting your colder injector timing values in your ect timing table closer to your hot timing number then re-evaluate... I also personally use the boundary table to retard the injection timing simply because the ect tables can go either way depending on build and year model, whereas boundary is pretty much always retarding the timing if you add to it.

Hope this helps.

[383]

So Im back to subtracting then? My cam has 20* more intake duration and about 20* more overlap. should I go back to -20*? Should I just do it to the cold side?

[GHuggins]

Your overall goal here is to (retard) the injection timing... This is why I stated to "add" or raise the boundary number, then "lower" the normal ect numbers in their colder temp zones... Injection timing is very confusing, but worth every second spent to get it right.

SO, in as simplest terms as I can make it. "ADD" your 20 to the injection boundary. Re-evaluate your idle and running quality (may require more to be added - may require less). THEN "subtract" from the colder operating regions in your ECT injector timing table. Once again re-evaluate for idle, cold start and running quality.

Intake valve timing is important, but no where as important as what's happened to your exhaust valve timing and overlap, which is the whole reason for needing to change all of this. If it helps - think of it that way. You don't want raw fuel being wasted out the tailpipe...

Hope this somewhat helps to clarify.

[383]

Your overall goal here is to (retard) the injection timing... This is why I stated to "add" or raise the boundary number, then "lower" the normal ect numbers in their colder temp zones... Injection timing is very confusing, but worth every second spent to get it right.

SO, in as simplest terms as I can make it. "ADD" your 20 to the injection boundary. Re-evaluate your idle and running quality (may require more to be added - may require less). THEN "subtract" from the colder operating regions in your ECT injector timing table. Once again re-evaluate for idle, cold start and running quality.

Intake valve timing is important, but no where as important as what's happened to your exhaust valve timing and overlap, which is the whole reason for needing to change all of this. If it helps - think of it that way. You don't want raw fuel being wasted out the tailpipe...

Hope this somewhat helps to clarify.

Ahh I get it now. I may get a chance to drive it tonight so ill try then.
Thanks for the help.

[383]

If I add to the boundary table it gets LEANER but idle smooths out, if I subtract from it fueling gets close enough but idle roughens up. startup fueling commands richer than l1. but all I get is l1. why is start enrichment not giving me any more than stoich?
It kinda diesels a little when I shut it down, that means its lean right?
Im going to add the 20* and then add the needed fuel in the bluecat tool and return...41115boundry+18 hot start.hpl

[GHuggins]

Have you tried knocking your cold ect injector timing values down closer to the hot engine values yet? Finally, it is possible that you went too far with the injector boundary. I would set your boundary to just where it smooths out the idle and not try to go much past there. You can always go back later and retard it more via your rpm injection timing table if need be to take more timing out in the mid rpm ranges. Finally you may also need to multiply out your open loop tables to get fueling just right when colder but get the hot running values right before worrying about this.

[383]

I moved the cold side down 15% and nailed it. Thanks for the help. Now my VE is pig rich. Im going to MAf only till I can dedicate some time to do VE over.

[GHuggins]

Yes, I don't think most people out there realize just how much away from OE the tunes need to be when "we" throw things like cams and other modifications into the equation... Glad to hear it worked out for you... Of course it is the simple things that we never think of that bites us the most in the end You can thank JasonS5555 for coming up with the timing correction when colder. Don't think I would have ever tried it myself if he had never mentioned it to me when we were discussing injection timing... Now I do it for this very reason on most cam and turbo setups.