Got an inline fuel pressure gauge, strange reading

[Mycarispurty]

I know a FI Z should read 36psi. So in order to try and fix my rich running problem, I get a fuel pressure gauge (0-100psi) from Summit Racing, along with the tee fitting and barbed fittings to fit in it so I can verify correct pressure. I hook it up between the filter and the metal fuel line on the engine and fire the car up. It's only reading 4 psi. That's exactly 9 times less fuel pressure than the car needs to run. Anyone want to shed any light on this?

[hughdogz]

I know you're going to kill me for asking this, but did you put a carburated engine fuel pressure regulator on there? It sounds like that is what's happening. Either that or you put the gauge in the return instead of the inlet, but that doesn't sound right either since you said it IS in the inlet.

 

 

Well, it won't be running too rich now! Huh...wierd. Somone will reply with more knowledge than me.

[Mycarispurty]

I didn't install the FPR that's on the car. It came on it. Even if it was one for carbs, and it actually IS running only 4psi (don't know how the car would even run like that) there wouldn't be much pressure at all, and I wouldn't imagine the car would run as rich as it is with that low of a fuel pressure reading.

[hughdogz]

Plus the FPR for SU carbs is REALLY big compared to the stock FI regulator, I think you would have noticed.

[z-ya]

Do you have the gauge on the return side?

[Mycarispurty]

It's on the feed side, hooked into the same rubber line that feeds from the filter. If I had it on the wrong line then fuel wouldn't even enter the engine. This stupid rich running problem is beginning to really get on my nerves. I'm about ready to yank the engine and set it aside and put my V8 in it.

[Mycarispurty]

Ok so I take the gauge assembly off and put air to it, it shoots right up to 35psi which is what the gauge on the air compressor was showing in it at the time, but when I hook it back to the fuel, not a damn thing. Stays constant at about 4psi, shot up maybe a couple psi once but right back down to 4. I'd hate to think there is a fuel pressure gauge that doesn't read fuel's pressure but will show other pressures.

[roger.svoboda]

back pressure regulator is shot. what ever fancy term the car guys call it that is what it does.

[roger.svoboda]

or the fuel pump is shot pinch off the return line and see what you get.

[Mycarispurty]

Could a bad FPR actually cause that low of a fuel delivery pressure?

[DuoWing]

It's hard to say if it could cause that low of a reading, but it could definitely cause a really low reading, as if it's stuck all the way open fuel would be going right through the rail rather quick. There woudln't be much there allowing it to build pressure. I agree with what roger.svoboda said. While you're running the car and watching the pressure gauge, pinch off the return line and see if you're pressure suddenly jumps. If it does I'd definitely go with crapped out pressure regulator. If not, then quite possibly fuel pump.

 

I don't know what kind of issues you have with it running rich, but you're issues would probably lie within the Fuel Pressure Regulator, the Water Temp Sensor, and the AFM. I see you're running a 77' 280Z, so the EFI system on that is really basic. If the water temp sensor hasn't been replaced, I'd say it's a good bet it needs to be as these all at some point seem to go bad, whether it's the WTS on the 280Z or the CHTS on the 280ZX. Also you could always crack open the AFM and adjust it.

[Mycarispurty]

Ok, took the fuel pump and lines off the car, and used compressed air to blow out the send and return lines. A spray of fuel shot out of the engine bay when I blew out the feed line, and a bit more junk shot out when I hit the return line, probably had more fuel in it. Anywho, I get to checking out the pump setup. Sorta jerry rigged in there. I take the feed fitting off the pump and look inside and there's all sorts of junk in there. I get some dental scrapers and pick out as much as I can and then tapping it against the garbage can lid caused some more junk to come out, but mostly it was cleaned out by scraping. I figure that, along with probably a little funk in the lines might cause my fuel pressure problem. I hook everything back up with brand new line (oil cooler line was being used for the tank to pump line) and zip everything up and go to fire it, and after the system pressurizes, it runs for a few seconds then just died. I noticed there were 3 wires by the pump. 1 of course was the red one that's wired straight to the battery through a on off switch in the cab, then there was a green wire and black wire. I hooked up the black wire as I swore the green one was the one just hanging out when I removed the pump. Maybe I have those backwards? Because after the car died and wouldn't start again, I disconnected the lines from the pressure gauge to the fuel rail and not even a drop came out.

 

Also, I was going to pinch off the lines, but there is no port on the pressure regulator with enough room to pinch before the line terminates unless you guys are talking about the vacuum hose.

[Mycarispurty]

Ok so I'm retarded. After many trial startups, a drive around the block and more startups since I've owned the car, as well as depressurizing the system several times to test and experiment and spilling fuel, plus spilling some today when I replaced all the hoses back there...the car was just outta gas. I thought the pump was making a funny noise. So I put a few gallons of fresh gas in it, and after a few seconds of cranking, it fires right up. NOW it reads 30psi constant, and even stays right at about 28 or 29 when I shut the car off. Still runs rich though and doesn't stop smoking once the fuel pump is cutoff like a previous owner said, so I'm going to depressurize again probably tomorrow and unplug the fuel line to the cold start valve and see what that does for me. I'll probably go ahead and purchase a $25 coolant temperature sensor and also order myself a new FPR once I figure out which of the 2 to get from Auto Zone. Hopefully just throwing a few bucks at it and replacing a few common culprits will fix it. Even if it is definitely the FPR, might as well replace the coolant temperature sensor while I'm in "fix the Z" mode.

[jgautosport]

I have the exact same problem, I was suspecting my guage was off. I had drained the tank, replaced my pump with a Walbro and put a pre filter before the pump. Not a lot of fuel is going through the see thru filter and my psi is not even really registering. I put 4 gallons in from an entirely empty tank. How many gallons did it take to see if that was the issue. Reason being is I dont want to fill up the tank entirely if the car is gonna be on jackstands for a good while. Oh yea runs, idles, revs perfectly fine too, just no psi. If I remove my vac line from the regulator it jumps to about 5 psi

[Tony D]

All the S30's have a drain plug. If you put in 'too much gas' you can always drain it back out and use it again.

 

FYI, you are FAR BETTER OFF completely filling a tank and using Sta-Bil fuel treatment for a long term car than leaving it half full or totally empty.

 

You will rust like crazy from condensation in the tank. It costs $30 to fill the tank today...there will be less evaporative losses from the tank (cap the EVAP line and there will be nill loss and degradation for over a year if you have good sealed lines on the vapor hoses) full as opposed to less than topped off.

 

Unless you empty the tank completely and then post purge with dry air to completely remove all traces of water (and then maybe stick a desiccant sock in the filler neck) you will get rust in any tank that isn't near full.

 

Been there, done that. Got 30 in the back yard and always have 'lawnmowergas' when bringing one out of the back 40. The alternative is more costly than the initial $30 to fill the tank and let it sit for a couple of years rusting internally.