Put in my 42# injectors and ngk TR6 plugs and now its missing

Blk003GT · 05-05-2009, 10:37 PM

i just put in my frpp 42# injectors and put in new TR6 plugs gapped to .32" and now the car is missing and it sounds like it has a big cam and is billowing out smoke out the exhaust. i just put the s/c on it and haven't had a tune yet but it was running fine just before i changed the plugs and injectors. why is it doing this?

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sxynerd · 05-05-2009, 10:41 PM

Hmm, imagine that, you put in bigger fuel injectors without having tuned for it and your car runs like crap. :01

Take out those injectors, duh.

SilverNGrey4.6s · 05-05-2009, 10:42 PM

^^^^nailed it

Obsequious1 · 05-06-2009, 05:47 AM

Before I even installed my supercharger, I installed the 42lb injectors and started it up to see if it would make a difference and it did. The car barely ran and it smelled like gas out the exhaust.

Blk003GT · 05-06-2009, 12:26 PM

ok. i just thought i read somewhere that the computer told the injectors to put a certain amount of fuel in so it didn't matter but i guess not. thanks guys taking them out until i go to get it tuned on monday

WhiteFoxGT · 05-06-2009, 01:26 PM

Quote:

Originally Posted by Blk003GT

ok. i just thought i read somewhere that the computer told the injectors to put a certain amount of fuel in so it didn't matter but i guess not. thanks guys taking them out until i go to get it tuned on monday

Your MAF is calibrated to the injectors. If you swap in big injectors and dont tell the computer, its going to freak out and run like crap...

cliffyk · 05-06-2009, 07:08 PM

MAFs are not calibrated to injectors. A so-called "calibrated" MAF has had its output voltage curve altered to lie to a a particular tune (typically a stock tune), AND allow THAT stock tune to run with larger than stock injectors.

Calibrated MAFs are a kludge, left over from the days when OEM tunes could not be changed conveniently, or at all. In these modern times a "calibrated" MAF is never necessary and can really foul things up if the MAFs real transfer function is unknown.

The transfer function is the relationship between mass air flow and sensor output voltage. To do things right, the MAF transfer function (whatever it might be) is programmed into the tune, along with the selected injector's capacity (the amount of fuel the injector can "inject", if energised 100% of the time).

The tune uses this information along with load, rpm, throttle position, IAT, and a bunch of other inputs, to determine how long it needs to energise the injector to deliver the desired amount of fuel--this is the injector pulse width.

"Calibrated" MAFs work by lying to a tune (generally a stock tune used with larger than stock injectors) about how much air is being ingested. At lower airflows a "calibrated" MAF tells the tune that less air is flowing, than is actually flowing. The tune then calculates a shorter injector pulse width, which when applied to the larger than stock injectors causes the proper amount of fuel to be injected.

At higher airflows the "calibrated" MAF lies less and the tune calculates longer injector pulses causing more fuel to be injected (with the larger injectors) than the stock injectors could deliver. In extreme matchups a calibrated MAF will screw up the tune's load calculations and can create very lean mixtures at high real loads.

It get worse--mixing a calibrated MAF with an unknown transfer function, with a custom tune, and injectors of a different size then the MAF was "calibrated" for (or a different transfer function than the stock tune the MAF was "calibrated" to work with) will make a nearly untunable mess.

All that's needed is a MAF, any MAF capable of accurately measuring the amount of air a particular engine will need, and its transfer function--and injectors capable of injecting enough fuel to go with that amount of air (at 80% maximum duty cycle). You then program the MAF curve into the tune, set the low and high injector slope values, and breakpoint, and tweak things from there...

pcs · 05-06-2009, 11:26 PM

so just get your car tuned or it will run like poop

WhiteFoxGT · 05-06-2009, 11:58 PM

Quote:

Originally Posted by cliffyk

MAFs are not calibrated to injectors. A so-called "calibrated" MAF has had its output voltage curve altered to lie to a a particular tune (typically a stock tune), AND allow THAT stock tune to run with larger than stock injectors.

Calibrated MAFs are a kludge, left over from the days when OEM tunes could not be changed conveniently, or at all. In these modern times a "calibrated" MAF is never necessary and can really foul things up if the MAFs real transfer function is unknown.

The transfer function is the relationship between mass air flow and sensor output voltage. To do things right, the MAF transfer function (whatever it might be) is programmed into the tune, along with the selected injector's capacity (the amount of fuel the injector can "inject", if energised 100% of the time).

The tune uses this information along with load, rpm, throttle position, IAT, and a bunch of other inputs, to determine how long it needs to energise the injector to deliver the desired amount of fuel--this is the injector pulse width.

"Calibrated" MAFs work by lying to a tune (generally a stock tune used with larger than stock injectors) about how much air is being ingested. At lower airflows a "calibrated" MAF tells the tune that less air is flowing, than is actually flowing. The tune then calculates a shorter injector pulse width, which when applied to the larger than stock injectors causes the proper amount of fuel to be injected.

At higher airflows the "calibrated" MAF lies less and the tune calculates longer injector pulses causing more fuel to be injected (with the larger injectors) than the stock injectors could deliver. In extreme matchups a calibrated MAF will screw up the tune's load calculations and can create very lean mixtures at high real loads.

It get worse--mixing a calibrated MAF with an unknown transfer function, with a custom tune, and injectors of a different size then the MAF was "calibrated" for (or a different transfer function than the stock tune the MAF was "calibrated" to work with) will make a nearly untunable mess.

All that's needed is a MAF, any MAF capable of accurately measuring the amount of air a particular engine will need, and its transfer function--and injectors capable of injecting enough fuel to go with that amount of air (at 80% maximum duty cycle). You then program the MAF curve into the tune, set the low and high injector slope values, and breakpoint, and tweak things from there...

Dude, did you seriously just type all that out because I told him his MAF wasnt set to work with the injectors? Like I said in my original post, the MAF is directly related to the injectors... if you swap injectors and dont tell the computer, it wont run right..

cliffyk · 05-07-2009, 12:13 AM

Yeah, I got carried away.

I spent the day yesterday with Pat at Delta Force Tuning, and at lunch we were discussing the general lack of knowledge of MAFs that is out there, and the customer support problems caused by that lack of knowledge--particulaly concerning calibrated MAFs and MAF housings that use the OEM sensor.

They and their use are a major cause of tuning problems encountered by users of handheld and other entry level tuning systems such as Special Forces.

Guess I saw this as an opportunity to try to spread some knowledge, I wasn't jumping on you...