Catsup...
Colin: Welcome, glad you stepped up and in... I sure hope that's not the PES supercharger kit of which you speak, as I have one of those 2.8 30v SC's in my shop now with fuel issues. I'm convinced it's overrated in terms of actual HP based on MAF reading (as in a lot less than claimed), so the big injectors are drowning it. PES has sent me 3 chipsets, none of them have addressed the problem (-15% LTFT CEL)
Regarding second injectors, Audi wasn't allowed to run a second set of injectors in WRC or Trans Am. What you may be thinking of is the S1 EVO II Sport Quattro that had injectors in the exhaust manifold for antilag. That said, dual injectors can work, but at 8psi boost on an 80, I doubt it's necessary.
I completely agree that any thing less than 6 'extra injectors' are not going to work well, since rarely does upstream injected fuel enter a dry manifold runner equally. I suspect since Christo has had decent luck on the dyno without a CEL, I' ventur that Mr. T doesn't yet have crossbank fuel capability or sequential exhaust pulse capability in their application of OBDII. That said Christo, my concerns regarding those extra injectors would be that you are dialing in false fuel. I'd want all injectors to be adding xx%, because 2 is not adding even fuel to the manifold runners. This means that you are *registering* proper fuel ratio at the tailpipe or at the 02, yet you are most likely lean on some cylinders and rich on others, but the sum measurement looks ok. It's most likely not.
LT: You are getting the hang of this a bit. Yes, slightly larger injectors can indeed shift the 0 +/- 15% window up and down the scale. However, IMO/E 6% larger fuel injector on a stock fuel pressure regulator probably means that the money would be better spent on the BEGI FPR before swapping injectors. I'll also point out that the flapper style AFM can be tweeked, btdt on my 4Runner. You can lean or richen the AFM. You can also do this with many MAF's, haven't looked on the 80/100 to see if there is an adjustment for it. Since that's really opening pandoras box on a lot of fronts and variables, I will only say it can be done, and it's illegal to do so. Google search, and ALWAYS index your starting point!
Regarding the 15% LTFT window, that's in the FSM for 96> and it's in my 93 for CA equipped (but I believe dan says there was no such animal). Most OBDII systems use this, mostly because of the catalyst. Below .86 lambda, you drown the CAT, and it clogs the exhaust when it comes back on line.
Scenario trigger? Vacuum leak is the most common, but slow or bad O2's can do it as well. A slow O2 will cause a longer rich condition, which it then gets picked up by the rear O2's as too much fuel trim compensation -15% fuel trim required to 'fix' the front O2 problem. I've actually demonstrated this to customers. Reset LTFT to 0, rev car, watch STFT sticking (slow), watch LTFT slowly sink from 0>-15, then CEL
I think you guys really want to jump into WOT full boost. For those that want to move along faster than LTFT, you can start to look and datalog measuring block values of injector duration at WOT. That will give you a good idea what the FTU is programmed to do. Normally, WOT tables are fixed injector DC, with only flag inputs (WOT switch activated, temp sender within parameter, no knock sensor input present, the only real question is MAF - but I doubt it)
Whipp and Jersey mentioned that LTFT is monitored during WOT. In my understanding of it's input to OBDII systems, it's probably better said that WOT activity is a part of LTFT calculation. Basically you want .86lambda as maximum (hmm - 14% away from 1.00 lamda
) so that you don't drown the catalyst, and send it downstream, btdt.
Again, on a boosted truck (SC or Turbo), you usually want the fueling behavior to be stock under vacuum. That's probably more easily attained by fuel pressure regulator than by injectors. And here is where a larger pump could increase the complexity of your variables.
ST
