zguy36 Posted April 8, 2005 Share Posted April 8, 2005 I put up a post asking about injector firing sequences, but didn't get many replies. The reason I wanted to know the firing sequence of stock injectors is because I had an idea to increase fuel flow with smaller injectors. Yes, I did say smaller. I hooked up my meter to measure duty cycle for the injectors and the duty cycle maxes out at 42% I found this to be quite weak, but that is with a good AFM wide open. I thought that if the injectors fire in two batches, to rewire them so that when a signal is sent out to fire the injectors, that it fires all six instead of only three. This would double the fuel input, since it would be firing twice as often. The stock injectors are 2.2 ohm and higher inpedence injectors would be needed to account for running six injectors on the driver instead of three. For 19# injectors have a much higher impedance and would not overload the driver. I did not find a schematic of the L-jetronic for the turbo 280zx ('83), but every other schematic I found showed that the injectors are fired in groups of two. This could still work with wiring the driver to fire four injectors instead of 2, but diodes would be needed.. Has anyone else thought of this, or tried this? -jeremy- Quote Link to comment Share on other sites More sharing options...
Guest SpyderZ Posted April 8, 2005 Share Posted April 8, 2005 I've been thinking about doing something to fool the ECU also. Here is my finding: There are a few wires going to the ECU from the AFM and one of them ( I forgot the wire color or pin #) when increase in resistance it will cause the ECU to dump a lot of fuel into the engine. I did this by accident. In the process of swapping out the AFM I forgot to plug it back up. When I start the car thick smoke was every where, the car was running super rich. I was thinking of installing a relay ciruit that will connect this wire to a 5K (or maybe higher) resistor and use the kick down switch at the top of the gas pedal as an input to trigger this circuit. On normal cruising condition it will not trigger and will not send more fuel in. But if you floor it it will send out more fuel. This is all depends on the value of the resistor you are using. I don't know how you measure the duty cycle of the injectors but try to add some more resistance to this signal from the AFM and check the injectors duty cycles again. Sorry I couldn't comment on your injectors. Quote Link to comment Share on other sites More sharing options...
zguy36 Posted April 9, 2005 Author Share Posted April 9, 2005 I do not think that you would get anything useful out of adding a resistor to the afm circuit. The ecu will only trigger the injectors up to 42% duty cycle, and adding more resistance will not increase the maximum output of the injectors. Leaving the system as it is will provide correct fuel input up to the maximum of 42%. If you want to tweak your afm, you need bigger injectors and tighten the afm. -jeremy- Quote Link to comment Share on other sites More sharing options...
fl327 Posted April 9, 2005 Share Posted April 9, 2005 drill a hole in the flapper door. Quote Link to comment Share on other sites More sharing options...
Guest SpyderZ Posted April 9, 2005 Share Posted April 9, 2005 If you are correct that the injectors are max out at 42% there is no way any stock 280ZXT will get close to 180 HP. I forgot the formula to calculate the HP base on the 80% injector duty cycle and the stock injectors flow but I recalled that if it max out you can get close to 240 HP on a stock 280ZXT ECCS system. I will have to dig out my old notes. Fl327, Drill a hole in the flapper door will make it run leaner and it will not help the ECU to keep the injectors open longer. Quote Link to comment Share on other sites More sharing options...
fl327 Posted April 9, 2005 Share Posted April 9, 2005 Sorry about that, for some reason I thought this was a post about 370cc injectors.. Have seen good results out of 370cc, base fuel pressure with stock fpr, and a small hole in the flapper door. You can run a wb and "tune" the orifice by going up drill bits until af is in ballpark. Wouldnt suggest drilling the flapper unless you have a spare afm, this is in no means exact science here. Im just not a fan of opening afms. I do think that the ecu does more than 42 percent duty cycle, it would be impossible for most of the people running turbo setups to get even stock hp if it only ran that low duty cycle. I dont think duty cycle is something that is lacking in the zxt efi system overall. Quote Link to comment Share on other sites More sharing options...
zguy36 Posted April 9, 2005 Author Share Posted April 9, 2005 I saw the 42% duty cycle firsthand. I did not believe it either, so I double checked it on a friends car. He has a haltech and pulled up his duty cycles on the laptop. My meter was right on with the readings the haltech was showing. I have even verified this 42% on a running vehicle, 6500rpm, 12 lbs boost. -jeremy- Quote Link to comment Share on other sites More sharing options...
Afshin Posted April 9, 2005 Share Posted April 9, 2005 I certainly don't know why you are getting a max duty cycle of 42%. However, that is not correct. 260-270cc injectors at 42% duty cycle with fuel pressure in 40 psi range will max out at about 130 HP. You can't get the HP without burning the fuel, there is simply no way around it. My guess is that for some reason you are getting 1/2 the actual number and that the scope is measuring 1 out of two cycles on the z set up, so that the actual max duty cycle is 84%. It just can't be 42% and have the car run at even 7 psi. Also under load, for sure, the car fires all injectors simultaneously and not in batches of 3. Quote Link to comment Share on other sites More sharing options...
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