Bad fuel injector?

[SolidState]

Hey guys,

So, I am chasing a random lean code from my 94 ATX. A little backround history: New O2s, newer plugs/wires, clean intake, functioning EGR, decarboned.

I was running a stock fuel pump and 73mm C&L MAF/K&N filter. I had been getting a random 172, and then a random 176 from time to time after about the third or forth WOT session in a short period of time.

I pulled the (really) dirty K&N, replaced the C&L with a stock MAF and replaced the fuel pump with a Walbro 155LPH unit. The fuel pump made the biggest difference, but it still seems to lean out from time to time.

Oh, and my fuel lines bleed off pressure very quickly....I still have the 'leaking check valve' symptom, but the pump is brand new.

So, what I am thinking here is that I have a leaking FPR and/or a leaking/lazy Fuel injector.

Is my train of thought correct here?

TIA

 

[NotSoSlowSHO]

What are your fuel rail pressure readings? Numbers and duration?

How fast does it loose pressure when the engine is turned odd?

Also, do you hear any noises from the tank besides the normal pump hum?

 

[SolidState]

haven't actually taken a fuel pressure reading, as I don't have the necessary tool

The engine will loose pressure quickly after the car is shut off. Upon hot restart, I still ge that 'gurgling' noise of a tell tale bad check valve.

 

[NotSoSlowSHO]

was the check valve replaced when the fuel pump was?

You need to get some pressure readings.
If the pressure falls flat when the engine is turned off, the check valve is failed.
A slower drop in pressure would point to something like a fuel injector leak.

 

[Mr Anonymous]

The check valve should be integral to the fuel pump outlet -- although they can fall out if the pump is dropped or mishandled, and the FPR is the other half of the equation for holding and regulating pressure. Getting hold of a fuel pressure tester would be the next logical step.

Did you try running a cylinder balance test to see if any particular cylinder wasn't pulling its weight?

Oh, and any chance you're running an LPM?

 

[SolidState]

Kenny,

The fuel pump has a integral check valve in it that was replaced at the same time. Pressure doesn't seem to drop sharply, but gradually over, say, 20 minutes.

Chris,

I was especially careful with the pump to avoid damaging the valve or its 'tube' when handling and installing. The new pump DID help with the hard start/stumbling issue on warm restart, even when there is the telltale gurgling.

I ran a cylinder balance test, and everything came back okay. The problem does feel intermittant, though. I can FEEL when the car leans out, and then sure enough, CEL.

No LPM.

Thanks

 

[PhysicsSHO]

Is there a separate check valve on the return line in the tank, independant of the check valve on the pump line?

For the possibly weak injector, you'll want to run the cylinder balance test, all three passes, at different times -- engine cold, hot, just after driving, etc. Maybe you can catch the intermittent injector. I've had two clog on me.