Eddiebx

ah, but what about all this mess i hear about, long term fuel trim and short term fuel trim?

Basically it is to my understanding that you can't really correct too much part throttle because of the fuel trims, so if you keep your fuel adjustments on a VAFC or SAFC, or what not to just full throttle adjustments it won't affect the trim? That was what I was thinking about doing to tackle the obd2 tuning, cuz in a few weeks i have to tune this 98 lude with cams and cam gears and only a VAFC

As far as the ignition timing it corrects it to 15 BTDC automatically right? using the crank fluc sensor? I am unsure what to do when I start moving the exhaust cam around. Would it just reset itself back to 15, or is it gonna be out of whack if i don't move the dizzy along with it.

MrFatbooty

The OBD2 ECU doesn't automatically reset the ignition timing.

It has a timing map assuming a "base" mechanical setting on the distributor of 15 deg BTDC. It then adds whatever amount of advance or retard to that base setting to get the desired timing setting for any given point on the map.

If you change the mechanical setting either by messing with the distributor or the exhaust cam, the entire map willfor a little while until the ECU learns that the timing is off. It knows what the timing is supposed to be and it will alter how much it advances or retards the timing so that it gets back to the desired timing values. How long exactly this takes, I'm not sure. Also if the ECU loses power, all of these adjustments are lost. Best thing to do is to reset the distributor to 15 deg BTDC using a timing light, after you make any changes in exhaust cam timing.

As for whether or not the ECU has a learning capability on the fuel side of things, I'm not exactly accquainted with how it works. Basically an AFC would modify the voltage of the MAP sensor circuit, and I'm not sure how the ECU would figure out that it's being tricked with a fake signal. Maybe with the oxygen sensor but the stocker is a narrow band unit which means the ECU doesn't run in closed-loop operation very often. Another piece of evidence which leads me to believe that OBD2 mainly fools with ignition timing is that GReddy sells its turbo kits with electronic "blue boxes" (essentially a pre-programmed AFC) specifically for use with OBD2 Hondas. They also have kits for various other OBD2 cars (the Nissan 350Z, for example) which use a preprogrammed e-Manage. Also, the main purpose of OBD2 would be to maintain a particular a/f ratio so if it uses O2 sensor data to modify the stored fuel map, you really don't run much of a risk of the tuning of the engine being thrown out of whack. Hell it might even work to fine tune your mixture.

Eddiebx

yeah thats what i was thinking of doing, popping the lower dizzy bolt out so i can rotate the dizzy and realign it with 15 after moving the cam.

As far as the ecu fuel trims, I was under the assumption that it adjusts the fuel trims by reading the narrow band, thats why i figured i'd be safe adusting the fuel at WOT.

I've seen an s2k on the dyno, basically detune the fuel settings that we put in with the emanage in like about 2 minutes. No matter what we did it kept detuning it and the A/F ratio changing back to stock. But we were adjusting the whole range, not just at full load so that could be it. I'm not sure what was up with that car, i just assumed it was the obd2 mess, hehe.

MrFatbooty

Seems to me like this problem is more with closed loop operation as opposed to OBD2. Any car with an oxygen sensor is going to default to closed loop operation at some point. Maybe the OBD2 Honda ECU has a table of lambda values that corresponds to its fuel map as a means of checking its operation? That could be a reasonable explanation.