Fuel Injectors

[_ethrty-Andy_ 2122]

A mate of mine asked me last night about fuel injectors. I didn't know the answer to the question and would like to know.

If you have stock injectors, and upgrade to ones that flow more (lets assume supporting fuel pump too) but otherwise leave the engine stock, what happens? will the engine run richer because it flows x% more fuel? more/less power?

btw: This would be on a EFI car with no oxygen sensor.

Edited November 10, 2013 by _Ethrty-Andy_

[Eagle 1515]

Assuming you talking about a stock engine? If so id say the engine would run rich or even flood, loose fuel economy and probably loose power depending on the flow increase.

[_ethrty-Andy_ 2122]

so the flow would increase by the same percentage as how much bigger the new injectors would be over the old ones?

so in turn the only way to balance it out would be by either adding forced induction or remapping the car?

[jeffbebe 1559]

so in turn the only way to balance it out would be by either adding forced induction or remapping the car?

Yep. Not even sure a remap would work that well with natural aspiration. High flow for FI is what I've heard but I'm no expert.

[BreakMyWindow 1870]

My theory is that the FI's are controlled by the ECU, so the ECU, or possibly an aftermarket ecu would need to be programmed to allow the injectors to pulse shorter, or regulate their flow as per the stock injector's. Allowing more air in to the engine (cams, or adjusting cam timing) together with a re-map should definatly give it some more ponies.

Edited November 11, 2013 by BreakMyWindow

[thorburn 120]

so the flow would increase by the same percentage as how much bigger the new injectors would be over the old ones?

Pretty much. Different injectors have different characteristics. One that plays a small factor is injector dead time. Injectors take longer to open when the voltage is low(some longer then others). Dead time is the time it takes for the injector to start flowing after it has received a signal from the ecu.

so in turn the only way to balance it out would be by either adding forced induction or remapping the car?

Adding forced induction isn't going to help. The injector squirts for a time based on how much air is going in. It has no idea that it is now squirting a larger amount of fuel into the amount of air it thought was going in.

[handgrenade 189]

The computer will have a set map. For the air detected coming in through the air flow meter the ECU will fuel to suit. If you turbo or FI without tuning then it is likely that the factory ECUs will not understand a flow rate higher than atmo and flip directly to a safe mode.

If you install larger injectors you will most likely over fuel according to the amount of increase in the injector size.

The signal to the injectors will be to open x time per air intake. If your injector is larger the same signal is sent but due to the larger injector more fuel will go in. Not the best situation.

[aja540i 1896]

If it had an o2 sensor, and the injectors werent much bigger it MIGHT be ok, but with no o2 sensor it will be running rich and down on power. Even if you did a remap, the injectors may be too big for the motor, i.e. the ecu might not be able to cycle on and off fast enough to get the small amount of fuel required at idle.

[_ethrty-Andy_ 2122]

cheers guys, think ive got the picture

[yng_750 247]

Alot of cars you can.change in jectors and tune by adjusting thr fpr. Not flash but within 50% flow rate its ok. Stops factory ecus hitting 100% duty cycle

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[handgrenade 189]

if you increase the size of the injectors, you will overfuel.

The ecu will send the appropriate signal to the injectors to fire (shoot fuel) for x amount of time depending on what the airflow readings are. which means that the ecu is still thinking that it has the smaller injectors, the same signal is being sent, however much more fuel is being dumped in because large injectors open for the same time as small injectors obviously mean much more fuel.