Thread: fuel pressure question

i just swapped a lowport into my 92 about three weeks ago. what fun that was(sarcasm). it took me forever to get my o-rings on my injectors to seal after hydrolocking my engine 3 or 4 times. i'm not really sure if they are sealed good now. i don't smell any fuel in the exhaust and i pulled the plugs and they weren't soaked in gas or anything. this brings me to my question. i have a fuel gauge in line and my pressure fluctuates 1 or 2 psi at idle (32-34), which i think it's supposed to be 36. is that normal? i'm thinking not. also once you pressurize the line should it drop off when you cut the car off? when i cut the car off it will slowly start dropping off. i have a surge/hesitation when i gradually accelerate but if i gun it it's fine. i don't have a egr and the computer should have relearned that or whatever as i've put 200 miles on it. so if anyone has a gauge in line could they tell me how theirs reads. sorry for the long post. thanks

It is suppose to bleed off slow, if it was dropping right away there would be a problem.

ok, it does do it slowly. how about the pressure? should it fluctuate a couple psi and shouldn't it be a little higher?

The FSM shows 2 specs for fuel pressure.

1. At idle, 36 psi.
2. A few seconds after ignition switch is turned OFF to ON: 43 psi.
   

It's normal for the pressure to vary a couple psi. Keep checking to see if this is a consistent thing or the pressure is higher sometimes as well. A change of 3 psi will move your AFR about half a point up or down depending on whether your pressure increases or decreases.

When did you last change your fuel filter? If it's been a while, you might think about putting in a new one.

i could have sworn that 3 bar was around 46 psi? and 4 bar was around 58 psi? i guess im thinking bout it to hard lol.. anyways the fuel pressure should drop down slowly. My gauge has pressure for about 5 to ten minutes after i turn my car off. also you can take your entire fuel rail off and put a rag under them. turn your key all the way on but dont start it and let the rail get filled with fuel. if you have a leak you will see fuel comming out.

I thought the same too but my B14 FSM says 34psi at idle and 43 with the vacuum hose disconnected. So stock is ~2.313 bar. I forget why it is said factory is 3 bar unless it is for the DET or VE.

Doenst really matter in this case, long story short, jmix, your fuel pressure is fine.

i have changed the filter recently but thanks for the info. i appreciate it.

If your injectors were leaking real bad, check you oil for the presence of gas in the oil.
Pull your dipstick and smell the end for the presence of gas. If found, change your oil.

yeah i changed it when they did leak. i don't think they are leaking anymore. before it hydrolocked because it just flooded the cylinder then when i thought i had it fixed, and it wasn't, my exhaust was backfiring when i'd let off the gas due to the unburnt gas igniting.

Keep this in mind:

Your car is not always in vacuum. It is only in vacuum at idle. This is why with vacuum removed (under load), you should have ~43psi of fuel pressure, or 3bar. Same is said for 4bar fuel pressure. Under load (no vacuum), you should have ~58psi of fuel pressure.

That's why they say to check with vacuum removed and capped off. You need to know what fuel pressure is under normal load, not what it is at idle.