Would low fuel pressure trigger the computer to create a rich condition?

[SanDiegoOverland]

Low fuel pressure = not enough fuel.
Computer detects too much air = increases fuel/decrease air thereby creating rich condition...

Possible? Unpossible? Am I way off in my understanding of what the ecu can prompt everything to do?

Thanks a bunch

 

[Demonoid369]

Hmmm I'd like to know that also, I have some 21lb injectors for my jeep and would like to know if that does do anything.
Spec: 97' 4.0l

 

[Digger87xj]

SanDiego: in short, no.

too much air, or too little fuel is a lean condition. It can't increase fuel if the fuel pressure is not there.

Demoniod.. you will see no difference with 21lbs/hr injectors if nothing else is done. The computer will only allow as much fuel in as required to keep the mixture as close to stoichiometric as possible. Increasing the injector size will give a temporary rich condition until the computer learns that it needs to reduce injector pulse width.

 

[98stocker]

Low fuel pressure = not enough fuel.
Computer detects too much air = increases fuel/decrease air thereby creating rich condition...

Possible? Unpossible? Am I way off in my understanding of what the ecu can prompt everything to do?

Thanks a bunch

Maybe? How about if the low fuel pressure leads to poor atomization which leads to partial burning which leads to lots of leftover o2 which leads to the sensor telling the pcm to widen the pulse width which leads to lots of unburned fuel which you will smell at the tailpipe and...

i dunno

 

[Ecomike]

Low fuel pressure will not atomize well, thus it will not burn well, and may not always ignite, thus causing a rich condition in the exhaust based on unburned fuel, but to confuse matters further, it also has unused air, O2, that reads as lean on the O2 sensor, when in fact it is excess unburned fuel and air!!!

 

[Ecomike]

Yes that is possible, that is why diagnostics requires looking the spark plugs (signs of rich or lean conditions on each and every plug), injectors for atomization pattern and flow and O2 sensor live data!!! And if the ECU gives up after reaching the fuel trim limits, it will switch to open loop rich limp mode!!!

Low fuel pressure = not enough fuel.
Computer detects too much air = increases fuel/decrease air thereby creating rich condition...

Possible? Unpossible? Am I way off in my understanding of what the ecu can prompt everything to do?

Thanks a bunch

 

[Ecomike]

SanDiego: in short, no.

too much air, or too little fuel is a lean condition. It can't increase fuel if the fuel pressure is not there.

Demoniod.. you will see no difference with 21lbs/hr injectors if nothing else is done. The computer will only allow as much fuel in as required to keep the mixture as close to stoichiometric as possible. Increasing the injector size will give a temporary rich condition until the computer learns that it needs to reduce injector pulse width.

It can increase fuel feed rate, pulse width, by keeping the injector open longer.

 

[Demonoid369]

It can increase fuel feed rate, pulse width, by keeping the injector open longer.

So will that happen with 21lb flow injectors? Sorry for thread jacking but I can't seem to get info from certain people who recommended the injectors I have. I know for 97' and up the injectors have 23lb flow on stock so I've been trying to figure what that 2lbs difference is going to make

 

[Ecomike]

So will that happen with 21lb flow injectors? Sorry for thread jacking but I can't seem to get info from certain people who recommended the injectors I have. I know for 97' and up the injectors have 23lb flow on stock so I've been trying to figure what that 2lbs difference is going to make

I thought 97 and up was 19 lb stock? Renix and OBD-I , HO was 21 lb stock. Renix and OBD-I runs at a lower pressure!!! If you truly have 23 lb, and they work, 21 lb should be fine. Is yours stock?

There was a thread with a link to a chart on that question here 2-3 weeks ago.

 

[hubs97xj]

96-99 should be 23.2lb/hr.

 

[Demonoid369]

96-99 should be 23.2lb/hr.

Yup on a 49 pressure rail. Which is why I'm curious as to what 21lb/hr on 49 would do? Mines a 97 with a k&n cold air intake and 2.5 exhaust.

 

[Ecomike]

It should be fine, read this thread:

http://www.naxja.org/forum/showthread.php?t=1020795&highlight=fuel+injector+flow+rate&page=2