1niceturbols

I have a 95 turbo ls. I had the engine completely re-worked while I was in Kuwait in the military to include cams, pistons, rods, springs, ect. The only thing that I have yet to upgrade is the things that I know nothing about, fuel injectors and ecu. I had a machanic tell me that I needed at least 550 cc injectors and a resistor box. So I bought a set of RC 550 and when I fired the car up it wouldn't run it was so rich. If anyone can help before I waste more money I would appreciate it. By the way if anyone want some 550cc rc injectors let me know. Or trade for the right ones. mikemccullough@aol.com

SRT_Andy

Did you install the resistor box?? You didn't mention, so I thought I'd ask. You need the resistor box for them to function properly. The 550cc injectors are fairly large and need some sort of control unit to trim the fuel supply down (such as a V-AFC for VTEC equipped cars or S-AFC for non-VTEC).

1niceturbols

yes I did but when I fired up the car would just barely idle and would shut off when you tried to push the gas

inspyral

You tried to run 550s with an AFC, or with your stock ECM? Either way, the 550s are too large to idle properly with either setup. You'll need a standalone unit to run them properly. You can run up to 310cc on a stock ECM, and up to 450cc on a stock ECM with an AFC.

MrFatbooty

You may be able to get it to run all right with a piggyback fuel computer such as an A'PEXi S-AFC but more likely you will need a means of tapping into the fuel maps within the ECU itself, for example a Hondata.

Do you have working knowledge of how the ECU operates, or do you need an explanation of the basic principles of fuel injection so we can get ya up to speed?

crxb16er

you can get me up to speed, i understand all the basics just hoping you can elaborate and explain exactly how the ecu goes about getting the info it runs on what that info is and what it does with it. i know o2 sensors let u know if ur running lean or rich and the ecu will compensate accordingly to some extent and controls the fuel injection system. what else? give me a run down. of all u know

MrFatbooty

The ECU has a "map" program for both fuel and ignition timing. Each map is based on RPM and MAP sensor voltage (MAP = manifold absolute pressure, sort of how much air is going into the motor). So for any given combination of MAP voltage and RPM, the ECU has a stored value of injector duty cycle. This is the signal sent to the injectors which tells them how long to stay open. The injectors always flow the same amount so the way you change how much fuel is injected is to change how long it is spraying fuel. Some of the time, the ECU uses the oxygen sensor to adjust the base duty cycle values but that's not all the time.

So what happens when you just change the injectors to a higher flow rate, is that the ECU doesn't know this and sends the same duty cycle signal to the injectors. But since the injectors flow a lot more fuel for the same given duty cycle compared to the stock injectors, you run way rich. Also since the ECU does not actually read the oxygen sensor most of the time, it doesn't compensate for the rich condition. What you need to do is get a lower duty cycle signal sent to the injectors so they get the right amount of fuel into the motor.

One other thing you have to deal with is preventing the ECU from throwing a check engine light from boost. The MAP sensor itself is capable of reading up to about 12 psi of boost, but if the ECU sees a voltage indicating any sort of boost it goes into a limp mode and throws a check engine light because the duty cycle table does not include MAP voltages that indicate boost.

What people typically do with an AFC is run 450 cc/min injectors and set it to lower duty cycle by 40% across the board. The AFC then reduces the MAP voltage by 40% so the ECU doesn't think it's reading boost. It then sends a duty cycle signal to the injectors that is 40% less than is actually needed. Since the higher flow rate injectors flow more fuel for the same given duty cycle compared to stock injectors, they automatically "multiply" the duty cycle signal to get the right amount for the actual amount of air going into the motor.

With 550 cc/min injectors, that is too much of an increase over stock for the AFC to compensate for. So you need to get a replacement ECU where you can change the actual duty cycle table itself, instead of use a device external to the ECU to trick it into giving you the duty cycle that you want.

If you need any sort of clarification let me know.