Fuel leak down test?

[vancouverbc]

I lose about 20 psi in 30 seconds. Is this oK? If I pinch fuel line between fuel filter and gauge, I dont lose the pressure so I know the check valve or canister or gas tank is leaking. Not sure if this abnormal.

[Chezedik]

No, this is not normal. It is an indication of a problem in the pump. Specifically, there is a valve in the pump that is designed to maintain fuel pressure on the lines. When it fails this test is usually how you find it. The typical car will go 20min without losing pressure. Hope that helps. Try going with a known good pump.

EDIT: I am guessing that you have had a hard starting condition due to vapor lock?

[vancouverbc]

I failed an emissions test so I was testing for leaks. Otherwise , car runs well. I maintain 20 psi residual pressure for along time.

[Chezedik]

You've got it all wrong buddy. You failed the emissions test for HC, right? That isn't a fuel leak, with the exception of a torn injector o-ring. You are running too rich. This is most probably caused on the 240sx by a bad ground to the MAFS. Try installing a new external ground to it, many people have found that this clears up an overly rich condition. Particularly on older cars, because of deterioration of the quality of the grounds.

BTW, you don't have a 240zx (no such thing), you have a 240sx.

EDIT: Check your oil for fuel. If you have a torn injector o-ring, it would cause you a pressure loss like you described, while causing an overly rich condition. It will cause your cyl walls to wash down with fuel, and eventually your oil will be thinned from fuel.

[vancouverbc]

re: 1991 240sx

I failed emissions with high HO and CO2 during idle and drive. My self-diagnostic test of O2 sensor blinks like it should. My sparkplugs are not wet. However, my O2 sensor reads continuous 1.07 volts during idle which I guess indicates a rich condition. I know that nissan idle does run rich normally, though. Pinching off the injectors and orings did not stop the fuel pressure loss.

Ill check the oil and maf. thanks.

[Chezedik]

HO = Hydroxides?

I forget which way the scale goes on an overly rich condition, but I wouldn't put much stock in what the stock O2 says, it's crap. You are saying that having the gauge hooked up to the supply side of the fuel sys still showed the same pressure drop? Would indicate a pump issue or small leak.

[vancouverbc]

Sorry, high HC(hydrocarbons) and high carbon monoxide(CO).

1 volt is a rich condition and 0 volts is a lean condition for the O2 sensor.

Yes, the fuel pressure gauge is hooked up to supply side. The only way I can stop the pressure loss is to pinch off the hose between fuel filter and gauge. The gauge being between fuel filter and fuel rail.

Im cleaning the maf tonight. There was very low voltage drop on the maf ground.(less than .1 of a volt). There is continuity. The car idles terrible when maf disconnected.

[Chezedik]

Try using alligator clips to add a ground to the MAFS, see if it helps. At this point, you should know the smell, or at least be able to check and see if your 02 is pegged or fluctuating, like it should. What is the VD on the MAF ground, because on it, I would expect something below .05, otherwise it is too high. Keep in mind you failed an emissions test, not have a poorly running vehicle. LMK!

[vancouverbc]

O2 sensor does fluctuate. The reading starts off like .2 volts when engine is cold and builds up slowly to approx 1 as engine warms up. I squeezed the fuel supply line and did not see much change until car stalled and then there was a dramatic fall in voltage.

The voltage drop on the maf ground is around .002.

Do I splice the second ground into the present ground wire or do I connect to the aluminum of maf structure? Thanks for your help.

[Chezedik]

To the body is fine, but with a drop like that, you are not facing an issue like that. How does your oil smell?

EDIT: How does the car run?

[vancouverbc]

The car runs good. The idle is good. The oil does not seem to be contaminated with gas. I was low on oil but that was after about a year.I get around 22 mpg driving half in town and half on highway.

The dealer mechanic did say last year that my catalytic converter would be saturated with fuel from injector leak that I had fixed.

[Chezedik]

Well, do you guys offer Ethanol or MTBE in your fuel? If so, that will solve your emissions test issue. Otherwise, you need to find some Ethanol to put in your fuel, the car will be gutless, but it will pass.

[vancouverbc]

Turned out to be faulty computer.

[Chezedik]

Yeah, just found out I have a bad one too. Maybe we will both luck out.