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Hello all. I'm newly registered here, but have been snooping around for awhile. I must say, this is the best gto forum/family out there. I be an old fart learned in the ancient art of mei goh fast kung fu. Give me the basics: early 60's thru early 70's Chrysler, GM or Ford big block, a massive 4bbl, a cam, a set of headers, a curve kit and a few crude hand tools, and I'm off to the races. But todays technology baffles me (or my unwillingness to accept change :gr_jest: ). Every thing is run by computer now (ECM/PCM..or whatever its called). Anyhoo, to my stupid question of the day. I hear of a lot of different mod's people are doing to their engines...but never hear anyone address the topic of fueling. Does the computer adjust the air/fuel mix after such mod's (i.e. cam, intake, heads etc.) or is modification or replacement of fuel injectors needed? Thanks much.
 

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May I quote you on that?
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The fuel mix is set by the computer which controls duty cycle (open time) for the injectors. It relies on various sensors such as air flow, throttle position, temperature, exhaust oxygen, etc. to set the mix. Generally it will provide sufficient fuel up to the point where injector flow rate and / or fuel pressure is no longer able to keep up with air flow. At that point, you must modify the fuel delivery components to meet the increased demand.
OH, and welcome to the board! We have a few members here with cars similarly equipped as yours.
 

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13 year owner
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Generally when you exceed 80% of that duty cycle is when the injectors start getting too hot. That is when it is suggested to go to a bigger set of injectors. There is a whole bunch of tuning you can do around the injector itself. Adjustinf pulsewidths, pintle speeds and such.

As to the actual determining of the A/F ratio, it is done mainly between the MAF and the O2 sensors. We've discussed the MAF a lot as of late, so a search on that will net you the info you need in regard to it. Since our cars are duals, we have 4 O2 sensors. For each bank there are two. One pre-cat, one post cat. The O2 sensors read voltage in millvolts (mV). .475mV is considered "stoich". Anything less than .475mV is leaning, anything more is enrichment. To achieve this "stoich" mixture, the PCM using the O2 sesnors adjusts it short and long term fuel trimming. You'll hear the term "switching", this is that adjustment. It goes Rich, lean, rich, lean, rich, lean, etc. This nets a mid ground of .475mV. At WOT for power enrichment, voltage should be in the .890 - .910mV range, the O2's are ignored and no "switching" takes place.

That's it in a nutshell. I have some ASE writings on both MAF and O2's that perhaps I should post here. It is quite in depth and informative and makes for great bathroom reading. :D
 

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That would be great if you post that stuff. Questions and observations on O2 sensors:
When using a WBO2 for tuning, it seems like normal practice is to shove them up the tailpipe. But wouldn't the "real" mixture be found before the cats?

Using EFIlive to observe O2 voltage, naturally reading a flurry of digits is pretty useless, but EFIlive will show AVG voltage on the O2's. Looking at the pre-cat O2's I'm seeing about .415 on one and about .445 on the other. Sometimes the low one lags by as much as 50 mV. Am I actually running that lean? And is the difference between banks anything to be concerned about?
 

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That is true. When people dyno with the wide band, they claim the test point at the tailpipe isn't always the most accurate. Before AND after the cats just like the O2's are doing would be the most optimum, but unless you're going to drill holes and build a test bung for the probe, you're kind S.O.L.

A lot of your lag I'm sure revolves around the sampling rate of EFILive. For instance, I use a really old DOS version of AutoTap. I actually prefer it because it gives me the info I want in a tabular format, not the fancy windows layout. Anyway, A-Tap samples every 200 rpm. So there is naturally some lag in there.

As to the variance between banks, that is always possible. I wouldn't necessarily worry about 50mV. I find that most of my cars are never actually .475mV but rather .505 - .525mV. .475mV is just the technical "stoich" in a perfect world. In reality I'm sure that can move a little either way.

I really don't care about the idle level because I don't give a crap about the environment. :D I simply look at it and if it's close, I'm happy. I'm more concerned about those WOT readings.
 

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May I quote you on that?
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Perhaps "lag" was the wrong term for me to use. Actually to read average GMH02 voltage, you have to get it from a table rather than a fancy virtual gauge. EFILive will run pretty quick if you have a fast PC and aren't logging too many PIDs at once. What I meant to say is that the one bank is consistantly running 30-50 mV lower than the other. Are there geeks out there who get 02's in matched pairs? When I order my SW exhaust, I may have them weld in some extra bungholes for testing porpoises. mmmmmm......Flipper.
 

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No, mine always vary too! I think it's part of the exhaust routing design that throws it some.

Sorry, I thought you meant sampling lag. :)
 

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" '03 Crown Vic 4.6L Brown/Tan/5 pointed star/Code3 MX-7000 light bar(red/blue flashing lights)/MS100 Dynamx siren/Pro-Guard shotgun rack "

Love it!! Please don't show me tho! :gr_jest:

Welcome Billman!
 

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Speaking of which, the Illinois State Police and the Des Plaines Popo, have a killer new low profile LED lightbar that's totally ****!!
 

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Discussion Starter #10
Hey thx Mike and CMN. Was it helpful, yes :D Did it make sence to me, no :confused: It appears its time I crack a book or two. Guess this type of work is better left to the professionals. Hard part is finding a truly professional professional. In my profession I see many afolk getting screwed by some fly by night 'performance shop', very unprofessional! (ok, I'll stop now :gr_jest: ).
CMN, our department is a buch of tight wads. Lowest bidder always gets the deal. (low bidder=equipment of a lesser quality). Back in the day we could mod our own cruisers (what they didnt know didnt hurt). Now its so bad...when I take the squad in for maintanance, they know if I farted in the car and when... and want a memo as to why.

TSpeed, dont worry....I hate writing tickets. :patriot:
 

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TB,
I hear ya. I have never heard them use the term tach and dwell once. When I first started visiting here I didn't understand a frickin' thing. Now I understand enough to know that I don't know much. I spent a lot of time on the internet finding out what these guys are talking about.

:drink::drink:
 

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Very Glad to hear that, SIR! :)
 
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