Hesitation in my nonDI 2.4 Ecotec

Pescador

Member
I have a small hesitation in throttle response when shifting up and down through the gears in my non DI 2.4 ecotec, I have checked the obvious air filter, Fuel filters, etc. Anyone have any suggestions?



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dzrt performance

Well-Known Member
couple things to check.

injectors. at very small duty cycle (assuming you are lifting to shift) it only takes a tiny amount of dirt to obstruct injector flow. clean/flow your injectors or even consider replacing them. it costs almost as much to send them for testing/cleaning as it does to simply buy new injectors.

ignition. again, like the injectors, at very low coil duty a worn ignition system could cause misfires that don't manifest at heavier engine load. replace plugs, clean coil electrical connections with rubbing alcohol. could possibly be a coil "going away".

general electrical system. the type of cantilever pins used by GM are rated from the factory for a measly TEN connection cycles. The OEM never intended the electrical system to see countless connecting/disconnecting as seen in racing use. Depending on the age of your wire harness, consider removing from the engine, cleaning all connections with rubbing alcohol and good dry compressed air. Even better, cut all the connections off and re-terminate the harness or replace entirely. if the problem gets better/worse after messing with it, there are bigger electrical issue on the horizon. I have seen one faulty pin cause all sorts of havoc that "looked" ok but would only work intermittently. many think the wiring should just last forever and not need attention, but its no different than any other part on the car and in reality is more fragile than most systems on your race vehicle.

fuel pressure regulator. if your FPR has a vacuum line going to it, fuel pressure is not constant and varies with engine load. the FPR can simply (pressure changes become unstable) be going away or there could be a leak in the vacuum line.

start with these checks and see if there is any change.




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5racer

Well-Known Member
take the o-rings off the comp plugs, if they roll out of there groove it won't let good contact be made.
 

BITD_1021

Well-Known Member
A common overlooked problem with DI motors is the fuel delivery from a inline electrical pump to the mechanical pump. Factor stock in tank electric fuel pumps for DI motors provide a variation of pressure to the mechanical pump mounted on the back of the motor. All of the aftermarket ECU units don't have a connection to the inline electrical pump and therefore can't increase or decrease fuel pressure delivery to the mechanical fuel pump when needed. Which is constant.
The motor concept was built to have a regulated amount of fuel pressure to the mechanical pump between 58-63 psi that's controlled by the computer. That pressure can't be a static pressure of 60 or 59 or 62. Your hesitation could be a lack of variable fuel pressure that isn't offered by aftermarket computer systems for the DI motor. Most likely unfixable. Unless you run a stock computer with the stock electric fuel pump in the fuel tank.
We do run a stock computer and harness with an external 1.7 gallon fuel cell that houses the stock fuel pump that is regulating the delivery pressure to the mechanical fuel pump. We have a total of 3 fuel pump. A Holley electric fuel pump that delivers fuel from our 24 gallon fuel cell to our 1.7 gallon fuel cell that houses our stock in-tank factory electric fuel pump that's controlled by our stock computer. And the 3rd and final fuel pump which is the mechanical high pressure pump mounted on the back of the motor.
Never a hick-up, burp, or hesitation with our system.
 

Bert is my name

Well-Known Member
I've used a fuel pump voltage booster in the past on a supercharged raptor that had drivability issues similar to what you described. Worked like a charm.
 

Bert is my name

Well-Known Member
A lot of the newer fuel pumps use pulse width modulation to control fuel pressure. Running full voltage and full pressure helps to ensure that you have an adequate supply. Also fuel line sizing is an often overlooked problem I have seen. Pressure isn't the only factor. Volume is just as important.
 

Pescador

Member
It’s been a long time since I posted my problem but recently got to the bottom of it. I noticed a bit of wetness around my fuel regulator after changing it out the car runs like a bat out of hell. Thanks to everyone and there potential fixes. Problem solved!!!
 

Bert is my name

Well-Known Member
It's easy to go down a rabbit hole when bench racing. Check the easy stuff first. G.m. regulators are not the best. I would carry an extra with the car. Glad you got it figured out.
 
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