i took the line off the fpr on my 93 z and it smelled like i took the gas cap off lol. so i put it back on and the started the car and while the car was running i pulled the tube off again and no change to the motor. dose this mean the fpr is no good? if i am right the car should rev higher, but i dont. and could this be the reason for my bad mpg.

thanks for all help on this.

 

yeah, change that out. it's no good. one of the points of a fpr is to maintain the correct pressure drop across the injector. say, fuel pressure is set at 45psi. 45psi at atmoshperic pressure. in your intake, (now think outside the box here) there is no vaccum, only less pressure. the engine has to maintain the correct pressure drop ratio across the injector. 45psi/14.7psi=3.06/1. Now, lets say your intake manifold is running 15 inches of vaccum. thats about 7.35psi of absolute pressure (take into acount the 14.7psi absolute pressure for atmospheric). The engine is still trying to maintain that 3.06/1 pressure drop ratio. So, take 3.06*7.35/1 and there is your new fuel pressure, roughly 22.50psi, at idle, with a vaccum reading of 15 inches. you are completely correct with saying removing your vaccum hose should make it rev higher, but the increased richness normally makes your engine real sluggish until enough air is entered to completely burn it. Basically, your motor is just running rich as [ EDIT ] at all times.

 

You're right, the FPR needs to be replaced. But the vacuum compensation logic is a bit confused.

The purpose of the fuel pressure regulator is to maintain a constant DIFFERENTIAL pressure (rail absolute pressure minus manifold absolute pressure) of 43.5psi across the injector. The injector is an orifice. Flow through the injector is governed by the orifice equation. Flow through the injector is proportional to the square root of the differential pressure. In your example, with a 7.5psia manifold absolute pressure, the regulator would maintain 7.5 + 43.5 = 51.0psia = 36.3psig rail pressure.

No matter how you figure it, the regulator will simply lose vacuum compensation with a torn diaphragm, and the fuel pressure will stay at 43.5psig. Yes, that does cause it to run richer when intake manifold vacuum is high (absolute pressure is low), but that's not the only cause. There's the additional issue of the vacuum line pulling raw fuel through the diaphragm and into the intake manifold, where it ends up in the cylinders.

 

and that can was out the cylinders and cause the oil to thin am i right there? and could cause gas to get in to the intake and with your cai off if you rev the car from under the hood some smoke will come out of the t/b am i right there?

yes all them numbers are to much for me lol. but thanks

 

I don't know if the 93 has the vacuum compensation line connected at the same point on the intake manifold as the 94-97 cars (passenger side, near the back). But if that's the location, the fuel is probably going to end up mostly in #6 and #8, and may wash down the cylinder walls. You would smell fuel in your oil. Don't know whether it would vent smoke out of the CAI though????

 

yea it vents in to the intake by the middle of the intake. and i do smell gas in the oil, and if i change the oil everything is ok for a while. but after about a week if i take the oil cap off there is some snoke that comes oout of it but only after a week. then i change the oil and go aroumd the block and do some wot runs and for days no smoke. so i think it is washing down the cylinders. but idk

 

Is the only symptom the extremely strong smell when you pull the vacuum hose off the FPR? Did you look at the nipple on the FPR to see if there was wet fuel present?

Pulling the vacuum line off the FPR should create a vacuum leak, and the way the engine runs should change. The vacuum line is letting in more air. If the diaphragm is working, there should be a change in fuel pressure in the rail. But your vacuum line may have a crack in it, which would mean the amount of air entering the engine does not change when you pull the line off the FPR, nor would the fuel pressure. The long term fuel corrections would already have adjusted for the vacuum leak.

You need to put a pressure gauge on the fuel system, and measure the fuel pressure at idle, with (41-47psi) and without (6 to 8 psi drop) the vacuum line connected. That will tell you if the vacuum line is doing anything.

 

i will do that but did not see anywhere that there was gas on the like. but i have looked at the line and it seems ok. and whats the best way to change this fpr. it seems to be hard to get to lol.

 

I don't know the details of changing a 93. 94 and up is totally different.

 

Injuneer, What i mean by pressure drop across the injector is the difference in terms of pressure ratio from the fuel rail and the manifold absolute pressure. thanks for correcting me about the fpr logic, though.

 

You don't control the "ratio". You control the DIFFERENTIAL pressure across the injector. Rail pressure minus manifold pressure. There is no ratio involved. It doesn't matter whether you work in absolute units or in guage units, the results will be the same.

 

Hey now.. no need for all that. i said THANK YOU for correcting me, not, "YOUR WRONG, SCREW YOU BUDDY!!". How about a, "You're welcome."? I would even settle for a, "Next time, get your facts straight." I was just explaining the twisted train of thought my mind took toward it's delusional answer.

 

Just what we need.... members with an attitude.