a reasonable assumption, but an untrue one all the same.
with a hot wire maf like this, in low to midrange the increased reversion from your cam will cause non-linear airflow, throwing off the calibration. that will cause it to read more air than actually exists. enrichens idle and light throttle.
to make matters worse, that 'cam lope' you hear is pumping some amount of unburned air into the exhaust at low airflows, causing the o2s to read excess oxygen... computer adds more fuel.
of course if you have no maf and are tuning speed density, you also remove low to midrange fuel, as larger cams have less volumetric efficiency at lower rpm.
at heavier throttle and higher rpm, the airflow becomes more uniform and the maf reads airflow a bit more accurately with the stock calibration, but in power enrichment, since the stock tune is set way too rich to reach peak power, again, you are removing fuel when you tune these cars, not adding it.
trust me, i've tuned a lot of LT1s... you're pretty much always removing fuel with cams your size.
Ah I gotcha, pretty much all of what I've dealt with is MAP, so I have little understanding of how MAF reacts, but I thought you'd have to add fuel in the top either way. What you're saying makes sense for the lower revs, but why is it still too rich at peak revs? I would expect with the much higher VE it'd be pretty on-point. Is that just because it uses the same correction % across the board?
Originally Posted by BALLSS
didn't know obd 1 does not have IM monitors. The Ca. smog site says:
"Gasoline-powered vehicles model-year 1999 and older will continue to receive Smog Checks using a tailpipe probe as well as the OBD test"
so whatever they read when they plug in the OBD 1 cars
I think he's right, that there's no I/M monitors in OBD-I cars. Either way, that piece you quoted is kinda misleading/inaccurate. Maybe it means only for '96-'99 where you have the plug & play OBD-II scan? If that's not the case then it's completely inaccurate. I've never smogged something in that '96-'00 window. Prior to that you needed the proprietary connectors for each manufacturer. I'll have to let you know in a year when I smog my g/f's '99!
2000+ OBD-II cars
: No dyno, no sniffer, just plug it into OBD-II diagnostics, computer must respond, no CEL's, no I/M monitors in the "NR" (not ready) state.
cars (latest OBD-I I've smogged is '94, I assume it's the same for '96-'99, but they might do something different for the OBD-II in '96-'99 - maybe they sniffer AND scan them
): Dyno+sniffer at 10 & 15mph, CEL if existed in that year/car must come ON when you start the car/stage 2 ignition and then turn OFF when the car has been started. Then they do the gas tank fume test (EGR) where they have a special gas gap with a hose and they pinch the line going to the charcoal canister and pull a vacuum and see if there's any leakage.
Originally Posted by terminal_crazy
He has a '94 he wants to test, which is OBD1 & I think don't have the monitors like his '96 OBD2.
Yeah I think you're right that that OBD-I did not have I/M monitors, but regardless they do no computer scans for '94, I've brought 94's to get smogged before. They do verify that the CEL comes on during stage2 ignition/start and that it shuts off when the car is running, but that's just visual. They don't do any electrical testing/interacting on '94's. All mechanical/visual.
Originally Posted by BALLSS
Having pre 02 exhaust leaks is the biggest reason you don't pass. 02 sees more air and PCM commands more fuel so you will run pig rich eventually killing CATS and 02's
I have a 383 H/C, header car and pass Calif emission testing......and I get the full colonic....plug in, tail pipe & visual
If you have un-plugged the battery or cleared codes in the PCM you will need to do regular driving for about 200 miles so the IM monitors read ready. Now in Calif you are only allowed 1 to show not ready vs the 2 it used to be. This is not a check engine light thing....the smog test plug in checks to see if IM's are ready.....a good tuner can set them to show ready all the time
Yeah, that's what the smog guy told me after I failed, given which values were high. I thought maybe a gasket was missing or header crack or something but then I found that there was only half the bolts holding one of the headers on - so I purchased the ARP bolt kit. Been lazy and haven't installed yet, though.
Yeah, I know about the I/M monitors, as terminal_crazy said I don't think OBD-I has monitors, and even if it did CA doesn't do any computer scans on OBD-I (on '94's and earlier at least, I'm guessing they do OBD-II scans on '96-'99). Though regardless I didn't unplug the battery. I didn't swap the computers, I was GOING to. Now that I understand there's some incompatibilities I won't. No point if it's just gonna throw a bunch of CEL's. They verify that the CEL comes on and then shuts off for '94's, so that needs to work properly.
Next steps for me:
1. Replace the header bolts so the header is now [hopefully] sealed
2. Take for re-smog and at least figure out where I stand with that.
Based on that I'll see if I should look for somebody to tune it or what.