hodgepodge1983

Hey everyone, I'm hoping you can help me diagnose an issue I'm having with my stock '95 Civic, D16Z6, stick shift. When I started it up to move it the other day, I noticed that my idle was extremely low and rich, almost to the point of stalling.

As I was diagnosing, I found that the engine will continue to run if I kill power to the fuel pump. Yes, I've verified that the pump is physically not running and is also receiving 0 volts on a multimeter.

After killing power to the pump, the idle increases to about 1000 or so and then settles back down at about 400rpm.

If I open the throttle extremely slowly, the RPM will rise all the way up to whatever I want. However, if I open it normally or quickly, the engine will die.

It seems almost as if there's a siphon effect from a leaky check valve or something?

If I put a vice grip on the fuel supply hose as the engine is idling with the pump off, the engine will die a few seconds later.

Putting a vice grip on the return line hose does nothing.

While the fuel pump is on, disconnecting the fuel pressure regulator or any other small vacuum hose will bring the idle back to normal (more air in).

I've put vice grips on the lines to the charcoal canister with no effect.

There is no CEL on.

I have de-pressurized the gas tank and run with the cap off.

What could cause the engine to continue to run with the fuel pump off? I've never heard of anything like this before, haha.

ol Dusty

iTrader: (2)

you'd be surprised how long a motor like yours will run of just what's in the fuel rail.

hodgepodge1983

That's true, but that's not what is going on. My engine is always shut off by cutting off the fuel pump first (think shutting down a prop plane). Before I had this low, rich idle problem, it would take about 10 seconds before it died, either through fuel consumption or loss of pressure. Now it will run all day if I let it, with the fuel pump off.