fuel system problems
perna00
03-22-2004, 02:48 PM
i recently tried installing larger injectors on my 96's 2.4 with minimal success. i couldn't even get it to stay started for 30 sec. i actually inverted the fuel rail w/ injectors to see if the injectors were faulty and found that they were not spraying(atomizing) like they should. all of them. i figured that i wasn't getting enough fuel pressure/volume for these injectors and am wondering if i need: a) a new performance fuel pump? b) an adjustable fuel pressure regulator? c)a larger fuel rail? any info on this problem will be greatly appriciated. i can't even find a better pump or regulator. thanks
Three_Fingers
03-22-2004, 05:50 PM
OK, from what I know-
If yer gonna install bigger injectors:
A.) You'll need a beefier aftermarket pump (racing type)-Bosch/Holley/etc.
B.)you'll need an aftermarket fuel pressure regulator (again, variable/racing type).
C.) You'll most likely need to get the ECM's fuel maps and sensor data values remapped.
Otherwise all you're doing is flooding it (so the ECM thinks and it'll be trying frantically to compensate for what it thinks is a faulty fuel pressure regulator.
You'll prolly need a different O2 sensor as well as it is only an averaging device-it'll compensate for the richest/leanest injector and throw things severely the other way.
Are those injectors ya tried new?
If not are they clean? (internal screens, etc.)
If not-hang just the ends (inlet/outlet) in one of those cheap 'ultrasonic jewelry cleaners and be amazed at the crap that falls out of even good injectors.
Then you can make an adapter fitting to fit a bicycle pump or air compressor and clamp a piece of 1/2" heater hose off an airline water separator full of injector cleaner and test fire 'em off 12v to further clean them and check the spray patterns.
I used an old portable drill press stand to do this so I could clean and test fire my injectors-I made a firing switch out of a salvaged injector plug and a momentary switch.
I also tried the bigger injector swap and all the ECM did was try to narrow the pulse widths to compensate for what it thought was leaky injectors.
I reckon part of the problem was I forgot to tell the ECM that it was supposed to be that way.
If yer gonna install bigger injectors:
A.) You'll need a beefier aftermarket pump (racing type)-Bosch/Holley/etc.
B.)you'll need an aftermarket fuel pressure regulator (again, variable/racing type).
C.) You'll most likely need to get the ECM's fuel maps and sensor data values remapped.
Otherwise all you're doing is flooding it (so the ECM thinks and it'll be trying frantically to compensate for what it thinks is a faulty fuel pressure regulator.
You'll prolly need a different O2 sensor as well as it is only an averaging device-it'll compensate for the richest/leanest injector and throw things severely the other way.
Are those injectors ya tried new?
If not are they clean? (internal screens, etc.)
If not-hang just the ends (inlet/outlet) in one of those cheap 'ultrasonic jewelry cleaners and be amazed at the crap that falls out of even good injectors.
Then you can make an adapter fitting to fit a bicycle pump or air compressor and clamp a piece of 1/2" heater hose off an airline water separator full of injector cleaner and test fire 'em off 12v to further clean them and check the spray patterns.
I used an old portable drill press stand to do this so I could clean and test fire my injectors-I made a firing switch out of a salvaged injector plug and a momentary switch.
I also tried the bigger injector swap and all the ECM did was try to narrow the pulse widths to compensate for what it thought was leaky injectors.
I reckon part of the problem was I forgot to tell the ECM that it was supposed to be that way.
perna00
03-22-2004, 07:53 PM
so in summary, if i change x, then i have to change y, then z, then reprogram q. . . ha, they were venum fuel injectors(new) and they "are compatible with stock fuel system, no modification required" ha! bunch of $&#* i got an intake, header, free-flow cat, and cat-back system. do i need anything to increase the amount of fuel or will the computer compensate for all the modifications?
Three_Fingers
03-27-2004, 08:39 AM
Sounds like the comp is already trying to compensate. Trouble is-you screwed up the fuel aspect of the equation.
You need to keep as close to a 14.7:1 fuel/air mixture to get the maximum outut and an efficient burn.
If you change one of those proportions-you gotta change all the others, too.
You put bigger fuel holes in it-the computer which is still thinking stock says "WRONG!" and tries like hell to lean out the mixture it knows is wrong.
Blame your O2 sensor for this and your ECM's internal fuel map data.
The O2 sensor reports to the ECM that the mixture is too rich now-the O2 sensor is a stupid bird really-it's just an averaging device. Which means that the ECM will take that O2 info and compensate for the richest/leanest injector and shove things hard the OTHER way to try to compensate.
Al the ECM knows is what it's programmed to to keep a stock motor running.
X amount of time opening an X sized fuel aperture =X amount of fuel delivery to keep running efficiently. (This is called injector driver pulse width-the amount of time the computer holds a certain sized injector open)-the computer is programmed with values for this under stock conditions.
You make that fuel hole bigger and you've just gone beyond what the comp is programmed to compensate for.
You can add the bigger injectors-if you have the proper and proportionate air intake/exhaust size increase as well,(try breathing thru a soda straw underwater and you'll see what I mean-if the motor can't breathe right-it won't run right..) and then you have to reflash the PROM with new fuel data for all the conditions it will encounter with the bigger fuel/air holes.
Then there is the reprogramming of the cold start maps. ("Open loop data")
The O2 sensor doesn't generate any voltage until it reaches 600 degrees F, so the ECM ignores it and goes by coolant temp sensor and IAT sensor data until then or until about 2 minutes have passed, so meanwhile it refers to a pre-programmed pulse width map that is supposed to support efficient combustion until the O2 sensor comes online-sending the ECM into "closed loop" mode where it controls every aspect of the engine's operation.
"Power chips" will accomplish this-but you gotta know the numbers you are looking at-ECMs talk in hexadecimal.
Each hex value stands for a pulse width under a given condition-the conditions change rapidly and everything in between has to be accounted for to fill in the spots between conditions. Other hex values speak of ignition timing, possible sensor data combinations, crank position, cam position, throttle position, knock sensor data, IAC valve position, vehicle speed/load data, gear position, RPM-it's a lotta damned stuff that ECM has to think about-nevermind the values that are programmed in there for when it has to guess.
You're talking more numbers than you can look at in one day.
Usually performance setups come as a matched set.
The injector size is based on the chip's fuel data maps-the air intake is matched to the anticipated fuel delivery and the engine's displacement, cam overlap, ignition timing, etc.
In the old days it was more guess work, but carbs made it easier because all you had to do was turn some screws and listen. We got some serious power out of those old setups, but they were still horribly inefficient. Fuel injection is exact. Change one value without changing the others in direct proportion screws things up.
Ya just can't guess anymore.
That's why serious tuners have all that computer equipment and software to monitor and change stuff around-it's necessary.
You need to keep as close to a 14.7:1 fuel/air mixture to get the maximum outut and an efficient burn.
If you change one of those proportions-you gotta change all the others, too.
You put bigger fuel holes in it-the computer which is still thinking stock says "WRONG!" and tries like hell to lean out the mixture it knows is wrong.
Blame your O2 sensor for this and your ECM's internal fuel map data.
The O2 sensor reports to the ECM that the mixture is too rich now-the O2 sensor is a stupid bird really-it's just an averaging device. Which means that the ECM will take that O2 info and compensate for the richest/leanest injector and shove things hard the OTHER way to try to compensate.
Al the ECM knows is what it's programmed to to keep a stock motor running.
X amount of time opening an X sized fuel aperture =X amount of fuel delivery to keep running efficiently. (This is called injector driver pulse width-the amount of time the computer holds a certain sized injector open)-the computer is programmed with values for this under stock conditions.
You make that fuel hole bigger and you've just gone beyond what the comp is programmed to compensate for.
You can add the bigger injectors-if you have the proper and proportionate air intake/exhaust size increase as well,(try breathing thru a soda straw underwater and you'll see what I mean-if the motor can't breathe right-it won't run right..) and then you have to reflash the PROM with new fuel data for all the conditions it will encounter with the bigger fuel/air holes.
Then there is the reprogramming of the cold start maps. ("Open loop data")
The O2 sensor doesn't generate any voltage until it reaches 600 degrees F, so the ECM ignores it and goes by coolant temp sensor and IAT sensor data until then or until about 2 minutes have passed, so meanwhile it refers to a pre-programmed pulse width map that is supposed to support efficient combustion until the O2 sensor comes online-sending the ECM into "closed loop" mode where it controls every aspect of the engine's operation.
"Power chips" will accomplish this-but you gotta know the numbers you are looking at-ECMs talk in hexadecimal.
Each hex value stands for a pulse width under a given condition-the conditions change rapidly and everything in between has to be accounted for to fill in the spots between conditions. Other hex values speak of ignition timing, possible sensor data combinations, crank position, cam position, throttle position, knock sensor data, IAC valve position, vehicle speed/load data, gear position, RPM-it's a lotta damned stuff that ECM has to think about-nevermind the values that are programmed in there for when it has to guess.
You're talking more numbers than you can look at in one day.
Usually performance setups come as a matched set.
The injector size is based on the chip's fuel data maps-the air intake is matched to the anticipated fuel delivery and the engine's displacement, cam overlap, ignition timing, etc.
In the old days it was more guess work, but carbs made it easier because all you had to do was turn some screws and listen. We got some serious power out of those old setups, but they were still horribly inefficient. Fuel injection is exact. Change one value without changing the others in direct proportion screws things up.
Ya just can't guess anymore.
That's why serious tuners have all that computer equipment and software to monitor and change stuff around-it's necessary.
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