Michael's V8Y62

[V8Y62]

Point 1.. I find it hard to believe you drive a VK56 and rarely exceed 1600rpm. The pleasure of hearing that puppy sing at 3-4k rpm is worth the fuel outlay!

I have done 1 1/4 mile drag test and heard the induction roar and exhaust rumble making a beautiful cacophony of ICE noise. I actually took my foot off at about 1/8 mile because the steering felt to loose to continue safely. The steering was one of the things I first noted in this thread and while I am getting used to it I still think it is to light.

Points 4 & 5: So many things can affect the fuel trim (the long term I suppose is more interesting). But what exactly does the percentage indicate? I.e. what is the 6% figure a reflection of? And why is 6% way too high?

The % indicates what the ECU is doing with regards to fuel, it will either take it out or add more in. Normal petrol, not ethanol blend, has an "optimum" (Stoichometric) AFR (Air Fuel Ratio) of 14.7-1, E10 is 14.08-1, LPG (Propane) is 15.5-1. There is another scale that tuners use called Lambda and it doesn't matter what the fuel is the optimum Lambda is always 1.00. The ECU calculates how much fuel is required based on inputs from the various sensors, with all else (e.g engine is at operating temp, ambient air temps are "normal", intake air temps are "normal", oil temp is at operating temp, etc etc etc) being equal on a MAF system the MAF tells the ECU how much air is going into the engine in grams per second (g/s). The ECU then calculates how much fuel to inject and then gets told by the O2 sensors if it injected the right amount or to much or not enough. The % is an indication of the difference between Lambda 1.00 and what the O2 sensors report back to the ECU and on the new information the ECU "trims" the fuel by the % difference. If the O2 sensors report 0.94 (which is rich) then the ECU needs to remove 6% fuel, if the O2 sensors report 1.06 (which is lean) the ECU needs to add 6% more fuel. Scaling the MAF to get fuel trims to within 2% means changing the reference values (g/s) so that the fuel trim is more accurate to within 2%.

Point 6: Adjusting the MAF will obviously have a bearing on your fuel trim. Do you know, or is there a factory standard setting, frequency, voltage or whatever? How do you know the MAF is working per design specs?

Brilliant question. So the VK56 has a system that uses MAF and also MAP. When tuning MAF the MAP system must be turned off and vice versa so one does not influence the other during tuning. How do I, personally, know the MAF is working per design specs? If it isn't it would trip a fault code and the dash should alert me to this with the CEL (Check Engine Light). The thing with all this though is manufacturers specs cover a huge range of tolerances, some of these are there for a reason 1 being the catalytic converters require fuel to cycle a couple of percent either side of stoichometric to help the cats burn off and not deteriorate prematurely. Generally 2% variation either side of stoichometric is the maximum required for a cat to work efficiently and have a long service life. If the variation is more than 5% the cats burn up, break down, crumble and block exhaust systems.

Do you have the factory exhaust system still fitted? There are 4 x O2 sensors in the exhaust system. Each side has one located pre-cat and one post-cat. It is my understanding only the pre-cat sensors have the authority to alter fuel trim. The rear sensors are for error coding only. If you have an aftermarket exhaust system installed, and have subsequently altered the O2 sensor offset from the exhaust flow, you could negatively affect the fuel trim via changed sensor configuration from factory design parameters.

Pearl is bog stock in everyway. As soon as anything is changed on the intake or exhaust of an EFI engine the fuel trims will change, the change may not be much but there will be a change anyway. I am aware of the 4 sensors, most modern cars that are Euro 4 and above spec have 2 sensors per cat. The first is to control the fuel trim and the 2nd is to make sure the cats are functioning as required.

Edit: the aftermarket exhaust system comment really only relates to an aftermarket cat replacement, not a cat-back exhaust replacement. I have aftermarket high-flow cats still in the shed until I pluck up the courage to mess with the O2 sensors!

Actually the greatest effect on an engine from an exhaust system is the increase or reduction of back pressure. Reducing back pressure generally causes an engine to run leaner until the ECU adjusts the LTFT to accommodate the change. My intent with Pearl is to work through all these things in a logical scientific manner so that people can see if the difference a modification makes it worthwhile for performance and/or economy reasons rather than just having a nice sound. I should probably say I have a genuine HDT Commodore and had a genuine 1977 Bandit Trans Am. I love the sound of a V8 at WOT (especially the roar of a Quadrajet at WOT) or even just burbling along (the HDT Commodore has the nicest exhaust note I have ever heard at cruise) but I see young fellas throw on huge systems that are loud yet the engine is no more efficient than a smaller system that costs alot less.