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IPW questions

F

fst

New member
Really dumb/newbish question, but how does the PCM read the IPWs? Is it at the point of the injectors spraying, point of fuel entering the combustion, or after it leaves the exhaust valves? Reason im asking is because since im running alky, my IPWs are spiking to 21mS on stock injectors with the 3.2” pulley running 18* of timing. My wb is also at 10.5 but after talking with a few alky users, that’s where I should be at. I asked a few members and they say usually when running 3.0” pulley is when the stock injectors are maxxed. If the IPWs are read at the injectors spraying then my tune is bad and needs a better tune. :mad::eek:
 


A pulley really has no meaning to where your injectors should be. If you're running at 21ms to keep your afr at 10.5, then you're in need of upgrading your injectors.

The PCM commands the current to the injector milliseconds for a given air fuel ratio. If you're keeping your intake charge cooler with the methanol, then you're moving more air into the engine. If you sit and think about it, moving so much air at a certain temperature is going to differ from application to application. Just because you've read that "oh, I'll be ok down to a 3.0" doesn't mean that you can hold to it. You're moving air into the LIM from say 280* down to say 200* because of the alcohol....which equals more fuel.

I hope that I haven't completely rambled on aimlessly....
 
Reptile said:
A pulley really has no meaning to where your injectors should be. If you're running at 21ms to keep your afr at 10.5, then you're in need of upgrading your injectors.

The PCM commands the current to the injector milliseconds for a given air fuel ratio. If you're keeping your intake charge cooler with the methanol, then you're moving more air into the engine. If you sit and think about it, moving so much air at a certain temperature is going to differ from application to application. Just because you've read that "oh, I'll be ok down to a 3.0" doesn't mean that you can hold to it. You're moving air into the LIM from say 280* down to say 200* because of the alcohol....which equals more fuel.

I hope that I haven't completely rambled on aimlessly....
Click to expand...

The MAF reads X amount of air and commands X amount of fuel to reach X AFR right? If one sprays alky after the MAF I'm not seeing how this would change the IPW's to reach the commanded AFR. Regardless, I do agree the injectors need to be upgraded.
 
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Because the Alky isn't changing the air mass that passes through the MAF. It keeps it at a manageable temperature after it goes through the supercharger. Which it will still expand reasonably, but not as much as if you're trying to cram so much air into the engine that you're boost stacking. If anything, it's acting like unmetered fuel. Which is part of the reasons I've read about why it's so difficult sometimes to tune a car with alky. You can still run smaller pulleys after running methanol, but you've still got to keep your fuel trims in check regardless what size pulley you are running.
 


Reptile said:
Because the Alky isn't changing the air mass that passes through the MAF.
Click to expand...

The alky isn't changing the mass of anything, its just changing density. All air that makes it into the engine is seen by the MAF and the mass of air can't change after the MAF without additional air going through the MAF. So whatever amount of air the MAF reads is the amount of fuel needed to match that regardless of whether the density of the air changes later on.

Reptile said:
If anything, it's acting like unmetered fuel.
Click to expand...

I'll agree with you on that.
 
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Nubraskan said:
The alky isn't changing the mass of anything, its just changing density. All air that makes it into the engine is seen by the MAF and the mass of air can't change after the MAF without additional air going through the MAF. So whatever amount of air the MAF reads is the amount of fuel needed to match that regardless of whether the density of the air changes later on.
Click to expand...

You're correct. Density was the word that I was looking for. Same principle, different word. LOL
 


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