2000Firehawk

iTrader: (248)

Ok, I lowered my "IRF", [injector tables], by 2% to get my LTFT to go negative numbers across the board.

By lowering the "IRF" tables by 2% ,the PCM thinks the injectors are smaller, so PCM commands them on longer, making my LTFT to all go into the negative numbers, because I'm running richer. It works well, I understand this....

But, what is this doing to my WOT PE ???
Did I just go richer by 2% WOT ,because I made the injectors look smaller to the PCM ??
If so, did I cause a "ripple" effect on other parts of the PCM causing other areas to go richer or leaner ???

Thanks,
Dave

AzzHauler

iTrader: (3)

Yes the pe will be richer.

Ed Blown Vert

iTrader: (2)

Good to know. I just lowered mine by 5%. Should we lean out the PE by 5%?

Also my idle is real rich till the engine warms up since I changed my IFR? Normal?

Cal

iTrader: (1)

That's because your engine is operating in open loop until it warms up. You need to scale down your VE by 60 to 80%.

Ed Blown Vert

iTrader: (2)

Thanks, I will try that. And I assume you would change just the first two columns?

Bink

NOT the whole table. ONLY up to 1200 RPM, MAP 15 thru MAP 105. Monitor your injector pulsewidths, shouldn't be below 3-4 msec( CAMAROHOLIC is the originator of this tweak). You don't want it too lean. Don't scale the whole table as it is used in speed density mode if the MAF fails.
joel(Bink)

Bink

PE will only be richer IF LTFTs are positive. If LTFT are negative then they will lock at zero at WOT and fuel will be strictly dependent on PEvRPM and PEvTemp.

joel

WicketMike

iTrader: (13)

agree, if you got your ltfts negative at WOT or 0, then its not adding extra fuel, so now you should be running leaner

pekkaz

Let's assume positive LTFTs directly scale WOT fueling up.

If enrichment based on originally positive LTFTs would be in the same scale as the effect of injector offset scaling at WOT then the WOT fueling would remain the same in case you succeeded dialing LTRIMs to exactly zero. They will be negative though and that means you have scaled IFR in a way that WOT will be richer as IFR is in the equation when calculating WOT fueling. So this applies if we believe the effect of LTFT caused enrichment and IFR scaling is at the same scale.

Though, I've seen some arguments against the negative LTFT theory. At least I wouldn't count on IFR scaling not affecting the WOT fueling or it becoming leaner due to LTFTs not being added on top of PE. By default I would say WOT fueling will be richer if you scale IFR down.

Ed Blown Vert

iTrader: (2)

That is what I thought. So should you scale down PE, when scaling down IFR? In the attempt to lower LTFT's?

Ed Blown Vert

iTrader: (2)

But if you lower the IFR, to lower LTFT's. Wouldn't that richen up WOT?

pekkaz

Most likely you need to do that in order to have desired or no effect on WOT fueling. LTFTs are not affected by PE according to my non professional understanding. There is probably no way of calculating compensative PE scalings to be applied though. Be very careful with scaling PE, try 1% change first and see how it affects.

2000Firehawk

iTrader: (248)

Ok you guys are really confusing me now.

Leave positive LTFTs out of the picture...

Let's say that you where already negative on LTFT & decreased "IRF" by 2%... would you be 2% richer at PE WOT ???

I say yes, because I told the PCM that I have smaller injectors by 2%, so the PCM is increasing the injector flow by 2%...

Thanks,
Dave

pekkaz

I would say yes as well but I would not count on scaling both PE and IFR tables by the same factor will keep WOT fueling unchanged.

AzzHauler

iTrader: (3)

Ok, you got me to second guess myself now. After muling it over I've concluded that wot will richen up once your ltrims go below 0, not above. Let's say you're at 0 cruise and 0 wot. You will get xx:1 afr. Now if you drop the table enough to change the ltrims to -5 at cruise, they will still go to 0 at wot, but that part of the ifr table is now ~5% richer. The pe will still add the same amount as before, so you'll get a richer afr. If ltrims are positive, then changing the table will keep wot fueling the same, until the ltrims get under 0.

Ed Blown Vert

iTrader: (2)

That is what I think too. So which is better, lower IFR to get LTFT's negative? Then tune WOT with PE?

Or leave everything alone and tune WOT only with PE?

Cal

iTrader: (1)

The way you are supposed to do it is first adjust IFRs until your LTFTs stay slightly negative all the time. Then, adjust PE vs. RPM until you get 890mv's on the O2s. If you do it any other way, it will be very difficult because what ever the LTFTs are just before you went to WOT will be added in. I believe this information is pretty good because it came from someone at GM.

Ed Blown Vert

iTrader: (2)

Sounds good to me. The only issue I have now when I lower IFR, is cold starts are really rich.

AzzHauler

iTrader: (3)

Did you lower the low rpm part of the VE table yet?

Plum Crazy Rob

iTrader: (3)

Yes, absolutely right. Then you dyno, find you are at 14:1 WOT A/F ratio and tuning by the 02 mV is only a guide, not completely accurate. Go to www.techedge.com.au and get yourself a wideband to tune it right. Save yourself time by profiting from my stupidity and learning.