Fuel injector pounds per hour?

[ecgreen]

How do I know what pounds per hour to choose when buying new injectors for my 2.9?

 

[rusty ol ranger]

IIRC factory are 14lbs/hr

 

[ecgreen]

Rusty for the win! Thanks

 

[ecgreen]

I am assuming 15.4 wouldn't matter?

 

[rusty ol ranger]

I am assuming 15.4 wouldn't matter?

No cause the ECM controls how long they stay open. But maybe @RonD or @adsm08 could chime in. EFI isnt my forte.

 

[danielp3344]

I don't know offhand what the flow rate of the stock injectors are but using any other flow rate (even a little different) could easily cause problems if you don't also tune your ECM. The ECM can only control how long the injectors stay open and uses the flow rate to calculate how much fuel that is. So if you change the flow rate and don't tell the ECM you'll have issues.

It looks like stock injectors are 14.8 lbs/hr? (https://www.injectorplanet.com/products/bosch-0280150710)

 

[ecgreen]

I don't know offhand what the flow rate of the stock injectors are but using any other flow rate (even a little different) could easily cause problems if you don't also tune your ECM. The ECM can only control how long the injectors stay open and uses the flow rate to calculate how much fuel that is. So if you change the flow rate and don't tell the ECM you'll have issues.

It looks like stock injectors are 14.8 lbs/hr? (https://www.injectorplanet.com/products/bosch-0280150710)

How does the ECM know the flow rate? There is no sensor to collect that info and send it back to the ecm that I know of.

Or are you saying that it uses the number 14.8 to open the injector for a specified amount of time.

If it's the later, than the more pounds per hour, the more fuel you let out pernpwriod of being open?
Learning a lot about injectors here, thanks guys.

 

[danielp3344]

Most ECMs as part of their configuration(tune) have a value for the flow rate of the injectors, so when the ECM needs X units of fuel it checks that value to figure out how many milliseconds to leave the injectors open. So yes, if you install larger injectors without tuning the ECM it will just add more fuel by leaving them open for the same amount of time. Now technically most ECMs also have two modes of operation, open loop and closed loop. When the engine is cold generally it runs open loop, meaning the ECM reads all the sensors (map, air temp, tps and rpm generally) and uses precomputed amounts of fuel. once the engine is warmed up and ready, it will start to use feedback from other sensors (in this case the o2 sensor(s)) to tune exactly how much fuel to add to keep the engine running at the correct AFR (air fuel ratio). So it's *possible* that larger injectors would only make the truck run rich when cold and then normally once it warmed up, but I wouldn't recommend it. (also I believe most ECMs limit how much fuel trims can be adjusted in closed loop, so it can only correct so much).

 

[ecgreen]

Most ECMs as part of their configuration(tune) have a value for the flow rate of the injectors, so when the ECM needs X units of fuel it checks that value to figure out how many milliseconds to leave the injectors open. So yes, if you install larger injectors without tuning the ECM it will just add more fuel by leaving them open for the same amount of time. Now technically most ECMs also have two modes of operation, open loop and closed loop. When the engine is cold generally it runs open loop, meaning the ECM reads all the sensors (map, air temp, tps and rpm generally) and uses precomputed amounts of fuel. once the engine is warmed up and ready, it will start to use feedback from other sensors (in this case the o2 sensor(s)) to tune exactly how much fuel to add to keep the engine running at the correct AFR (air fuel ratio). So it's *possible* that larger injectors would only make the truck run rich when cold and then normally once it warmed up, but I wouldn't recommend it. (also I believe most ECMs limit how much fuel trims can be adjusted in closed loop, so it can only correct so much).

Do you have experience with injector planet? Last time I bought injectors that cheap half of them didn't work.

 

[RonD]

Yes, each PCM(ECM) is indeed programmed with engine size, injector size and Fuel pressure expected

And when cold it does run without O2 sensor feedback, Open Loop
Once the O2 sensors are hot enough(650degF), 3 to 4 minutes of run time, the PCM will go into Closed Loop as it now has Feedback on the air/fuel ratio needed for calculating best fuel mix

In closed loop the PCM would calculate open time for each injector, that calculation is 0 STFT(short term fuel trim)
Calculation is based on RPM, load, MAF(air weight), fuel pressure and injector size
If O2 shows "rich burn" not enough oxygen, then computer reduces injector open time
If O2 shows "lean burn" too much oxygen, then computer opens injector longer
This takes 2 or 3 seconds once Closed Loop starts

If injector open time is 20% lower or higher (-20stft, +20stft) then computer will set a rich or lean code, but engine was never actually running lean or rich, except at FIRST COLD START

The computer also has LTFT(long term fuel trim) this is an average of STFT, so if you had larger injectors, and computer needed -20stft to get correct burn, then LTFT would be -20
So at NEXT cold start computer would use -20stft to start off

LTFT allows vehicle to age gracefully in normal use, lower fuel pressure, small air leaks, lower compression, all effect air/fuel ratios, so -10 to +10 LTFT allows computer to run engine better as it gets older, it doesn't have to constantly re-learn the failings of an aging system
If LTFT gets 15% low or high it will also set a code

So wrong size injectors, within reason, would just set lean or rich codes, but engine would run fine after FIRST start up/warm up

 

[rusty ol ranger]

Yes, each PCM(ECM) is indeed programmed with engine size, injector size and Fuel pressure expected

And when cold it does run without O2 sensor feedback, Open Loop
Once the O2 sensors are hot enough(650degF), 3 to 4 minutes of run time, the PCM will go into Closed Loop as it now has Feedback on the air/fuel ratio needed for calculating best fuel mix

In closed loop the PCM would calculate open time for each injector, that calculation is 0 STFT(short term fuel trim)
Calculation is based on RPM, load, MAF(air weight), fuel pressure and injector size
If O2 shows "rich burn" not enough oxygen, then computer reduces injector open time
If O2 shows "lean burn" too much oxygen, then computer opens injector longer
This takes 2 or 3 seconds once Closed Loop starts

If injector open time is 20% lower or higher (-20stft, +20stft) then computer will set a rich or lean code, but engine was never actually running lean or rich, except at FIRST COLD START

The computer also has LTFT(long term fuel trim) this is an average of STFT, so if you had larger injectors, and computer needed -20stft to get correct burn, then LTFT would be -20
So at NEXT cold start computer would use -20stft to start off

LTFT allows vehicle to age gracefully in normal use, lower fuel pressure, small air leaks, lower compression, all effect air/fuel ratios, so -10 to +10 LTFT allows computer to run engine better as it gets older, it doesn't have to constantly re-learn the failings of an aging system
If LTFT gets 15% low or high it will also set a code

So wrong size injectors, within reason, would just set lean or rich codes, but engine would run fine after FIRST start up/warm up

See? This is why i called Ron.

 

[ecgreen]

See? This is why i called Ron.

Dude...this is some knowledge!

 

[ecgreen]

Yes, each PCM(ECM) is indeed programmed with engine size, injector size and Fuel pressure expected

And when cold it does run without O2 sensor feedback, Open Loop
Once the O2 sensors are hot enough(650degF), 3 to 4 minutes of run time, the PCM will go into Closed Loop as it now has Feedback on the air/fuel ratio needed for calculating best fuel mix

In closed loop the PCM would calculate open time for each injector, that calculation is 0 STFT(short term fuel trim)
Calculation is based on RPM, load, MAF(air weight), fuel pressure and injector size
If O2 shows "rich burn" not enough oxygen, then computer reduces injector open time
If O2 shows "lean burn" too much oxygen, then computer opens injector longer
This takes 2 or 3 seconds once Closed Loop starts

If injector open time is 20% lower or higher (-20stft, +20stft) then computer will set a rich or lean code, but engine was never actually running lean or rich, except at FIRST COLD START

The computer also has LTFT(long term fuel trim) this is an average of STFT, so if you had larger injectors, and computer needed -20stft to get correct burn, then LTFT would be -20
So at NEXT cold start computer would use -20stft to start off

LTFT allows vehicle to age gracefully in normal use, lower fuel pressure, small air leaks, lower compression, all effect air/fuel ratios, so -10 to +10 LTFT allows computer to run engine better as it gets older, it doesn't have to constantly re-learn the failings of an aging system
If LTFT gets 15% low or high it will also set a code

So wrong size injectors, within reason, would just set lean or rich codes, but engine would run fine after FIRST start up/warm up

Would a 15.4 injector throw a code then, if it is looking for 14.8? I wonder if 15.4 injector would make it rich enough to make the o2 sensor open 20% longer. I doubt it. Hopefully I am understanding.

 

[racsan]

so, having injectors in my 2.3 that came from a 302 really didn’t gain me anything?

 

[Curious Hound]

N

so, having injectors in my 2.3 that came from a 302 really didn’t gain me anything?

Not unless your 2.3 injectors were broken or severely dirty.