Stealthy injector kill switch, 6th Generation Civic

[California98Civic]

Originally Posted by PaleMelanesian

That tells me what I need to know. Thanks. It's a simple-ish mod, I may have to try it in the near future.

Oooh... Does it leave the fuel system pressured up? That's a problem on my car when it gets low - I have to cycle the ignition several times, to run the fuel pump, to get the pressure high enough to actually start the engine. I'd guess this would help with that issue by not running down the pressure.

I don't KNOW the answer, but I have run the tank down to its last two gallons probably four times since the mod, maybe more, since this mod. I have never had to do what you describe, suggesting I may have better pressure in the fuel system.

Originally Posted by Old Tele man

...I don't know how "physically" compatible they are with the HONDA, but the shift-quadrant selector handle on 2003-2008 Pontiac/Toyota Vibe/Matrix with automatic transmissions has a button on the side--just like you're re-inventing--that's used to "lock-out" (disconnect) the Over-Drive (OD) 4th-gear.

This is exactly the sort of idea I had. My goal was a shifter that was stock in appearance, so I got a stock 1998 Civic auto shifter knob! Fits the interior styling perfectly.

[brucepick]

Originally Posted by PaleMelanesian

...
Oooh... Does it leave the fuel system pressured up? That's a problem on my car when it gets low - I have to cycle the ignition several times, to run the fuel pump, to get the pressure high enough to actually start the engine. I'd guess this would help with that issue by not running down the pressure.

I'm pretty sure there's an anti-backflow valve in the fuel line, intended to maintain fuel line pressure when the pump is off. I'd suggest web searching to learn how the fuel line and pump system are configured and where is that valve etc. Likely a mechanic who works on lots of Hondas will know exactly where it is and related tips. I haven't yet had the pleasure(?) of learning about the Civic's fuel pump details; I had to learn re. our old rear drive Volvos which had electronic fuel injection and pumps all by Bosch.

[bestclimb]

on my 5th gen when I am down really low I bump start it and if I try to add power immediately I get a momentary hesitation. If I wait for about 1-2 seconds after bumpstarting then releasing the clutch and adding power I get no hesitation. If I have more than 2 gallons in the tank I get no hesitation. That may not be useful information as your 6th gen may not be wired and plumbed the same.

[PaleMelanesian]

That's exactly the behavior I'm talking about. If this mod keeps the fuel system pressurized, it could eliminate that.

When you key off with the ignition, it's the spark you're removing. The fuel continues to flow until it's used up, or at least until the pressure is fairly low so not much is injected. If you interrupt the injector signal instead, you immediately stop the injectors and keep the system pressurized.

I'm going to have to try this and report back.

[some_other_dave]

When you turn the key to "off", the spark is cut and the signal to the injectors is cut. The same ECU controls both, and if only the spark were cut the engine would be able to diesel on for a while.

On older Hondas, I believe that the fuel pressure regulator is on the driver's end of the fuel rail, where the fuel return line comes off of the rail. That should hold pressure when the pump is off. I do not know if there is a separate check-valve elsewhere that holds pressure in the other end of the system, or if the pump itself serves as the check-valve. (I know that some older systems which have pumps mounted outside of the tank do that.)

-soD

[brucepick]

Originally Posted by bestclimb

on my 5th gen when I am down really low I bump start it and if I try to add power immediately I get a momentary hesitation. If I wait for about 1-2 seconds after bumpstarting then releasing the clutch and adding power I get no hesitation. If I have more than 2 gallons in the tank I get no hesitation. That may not be useful information as your 6th gen may not be wired and plumbed the same.

Thanks, bestclimb.

I also get a hesitation occasionally after bump starting. I hadn't connected it to a low tank but I will watch for that. Or possibly the fuel system pressure drops for another (occasional) reason that we haven't yet identified.

[California98Civic]

An update on the use of this injector kill switch. I find it is important to wait until the rpms hit about 1000 or lower to cut the injectors. Doing that ensures that a short cut of the injectors, which will not shut off my Ultra Gauge, is possible without unwanted engine restart when the power to the injectors is re-engaged due to relatively higher rpms. Also, there is a significant difference between alt-on and alt-off in terms of the time it takes to reach this rpm reduction. With the alt engaged, the engine slows more quickly (predictably).

[SentraSE-R]

FWIW, I believe Brucepick's explanation of the fuel injector relay in message 9 of this thread is incorrect. Most automotive relays are either four terminal (as he described) or five terminal. Both four terminal and five terminal relays connect the two "switched" or "power" side wires in Normally Closed (NC) position by default. This is a fail-safe mode, so if the relay fails (its triggered electromagnetic contacts don't move), your fuel injectors will still work when untriggered. When you power the "control" or trigger side terminals, you open the "switched" or "power" side circuit. In a four terminal relay, the switched/power side circuit opens, and there is no continuity - the opposite situation to what Brucepick said. In a five terminal relay, the same thing happens to the switched/power side NC terminals, but the fifth NO terminal connects to one of the NC terminals, so you make a connection between those terminals in the switched/triggered Normally Open (NO) position.

[California98Civic]

Originally Posted by SentraSE-R

FWIW, I believe Brucepick's explanation of the fuel injector relay in message 9 of this thread is incorrect.

So you are saying that his description of how the switched and powered side of the relay works is incorrect. But I don't think it changes the general import of the message, does it? He wrote:

Originally Posted by brucepick

By temporarily severing the ground wire you disable the relay's internal switch, and it sends out no current from the switched side....

This modification just adds one more place from where the relay's status can be controlled. I can't tell from here whether the computer switches the power to the relay's control side on and off, or whether it severs the control side's ground, basically like this mod does. Either way would disable the small coil, which ultimately means no power going out to the injectors.

The injectors themselves receive constant power as supplied via this relay. They are controlled on their ground side. Each injector has its own ground wire going to the computer. The individual grounds are completed by the computer for small fractions of a second at a time. Each injector will squirt fuel only when its individual ground path is completed by the computer.

I have been wondering if there is any possibility of squirted and unburnt or partially burnt fuel in this scenario. Would show-up as fouled plugs, but would also mean piston damage over time. That's why this update. I want the injectors shutting off more cleanly, and that seems to work best when the revs are dropping, not arcing-up from a 75% load pulse at the moment of cut-off.

[SentraSE-R]

I was wrong. Most of the Bosch four terminal automotive relays I'm seeing are NO. You can find almost any configuration of relay to suit any application, but I'll go with what's standard in the industry.

I don't know Hondas, but Brucepick's explanation sounds reasonable.