No Fuel Pressure After Pump Primes

[Apex Eight]

Hey guys, I've got an '89 Coupe with a KA24E that is all stock except for a full emissions delete. The car has been running alright, but the exhaust smelled pretty rich and would leave black soot on my rear bumper and my gas mileage hasn't been that great. I read that getting an adjustable FPR after deleting all of the emissions stuff is a good idea.

Well, I got a used Isis FPR and installed it the other day. All is well except for a couple of things.

1) Fuel pressure drops to zero after the pump has primed which leads to a really rough start.

2) Turning the adjustment screw in to raise fuel pressure doesn't result in much change in PSI. I have the thing turned in pretty deep and it's difficult to get over 40 PSI.

3) When disconnecting the vacuum line to the FPR, the fuel pressure does not go up that much. I've read that with vacuum the pressure should be around 33 PSI and 43 PSI without vacuum, but mine barely goed up at all without vacuum.

Any help is greatly appreciated. Thanks!

Edit: Added some more information.

[Kingtal0n]

it sounds like your pump output is low, and the check valve in the pump is nonexistent/bad.

But this would be unrelated to your rich operating condition. that is more likely due to the O2 sensor being bad.

To fix the fuel pump drain back issue, it sounds like you need a new fuel pump, since the regulator you installed probably has a functional drainback "clamp" if its working correctly.

I would just a buy a cheap $30 ebay fuel pump, or another OEM unit. If you are careful with the installation it should last quite a few years on a stock N/A 4-cylinder.
And check if your O2 sensor is working, several ways to do that.

[Apex Eight]

it sounds like your pump output is low, and the check valve in the pump is nonexistent/bad.

But this would be unrelated to your rich operating condition. that is more likely due to the O2 sensor being bad.

To fix the fuel pump drain back issue, it sounds like you need a new fuel pump, since the regulator you installed probably has a functional drainback "clamp" if its working correctly.

I would just a buy a cheap $30 ebay fuel pump, or another OEM unit. If you are careful with the installation it should last quite a few years on a stock N/A 4-cylinder.
And check if your O2 sensor is working, several ways to do that.

Cool, I ordered a pump off eBay last night. I put in a new O2 sensor a couple of years ago and I checked the ECU for codes a couple weeks ago and the only one that showed was for the air intake temperature sensor (bad connector, have a new one on the way from Wiring Specialties) so I think it's good. I'll report back with the results from the new fuel pump. I really hope I didn't get a bad FPR. I got it off a guy from here and he said it was good. $90 is a lot to a broke college student like me lol. Thanks for the reply man

[Kingtal0n]

dont trust the ecu, check the O2 sensor manually. Narrowband O2 sensors in all original cars flip from .0001 volts to 1.0001 volts in closed loop. It does not need power or ground to function. Just one single wire the ecu reads changes from 1v to 0v constantly in closed loop as the ecu adds and subtract fuel to keep causing this to happen.

Yours is probably stuck on 0v so the ecu is adding fuel to bring back the 1v but it never happens so the computer keeps adding more and more fuel to maximum adjustment trying to find 1v.

You would think this would show a code but I've never seen one (I don't own alot of original computer cars.) You can change the running air fuel ratio of the engine, by adding the real O2 data from a real wideband sensor, they are $140, to show the ecu a new operating range (desired voltage per air fuel ratio).

For example, if you set the analog output for 0.998 volts as 15.2:1, and 0.004 volts for 14.8:1, your engine would run between 15.2 and 14.8 instead of 14.6 and 14.8.

[Apex Eight]

Alright so I got the new fuel pump installed, and got the fuel pressure all sorted out; it stays at a steady 33 PSI with vacuum, and jumps to 42ish PSI without vacuum like it should, unlike my old pump. So the car runs great, but it still loses all fuel pressure after the fuel pump primes which leads to rough starts. Once it is up and running though, it idles fine and pulls well. Took apart my FPR and everything seems fine; they have a really simple mechanism.

So yeah, I'm really not sure what's causing the fuel pressure loss. There are no fuel leaks to be seen anywhere. Perhaps the injectors are leaking into the cylinder when the pump primes? Idk it's weird because while the pump is priming it'll have pressure, but as soon as it stops priming it drops to 0 PSI.

[Apex Eight]

Bump ;-; I want to hear more opinions before I pull my fuel rail to see if the injectors are leaking. I don't get any code for leaking injectors though.

Thinking about the FPR design, I don't see how there is anything keeping the fuel from going into the return line and losing all fuel pressure.

[e1_griego]

Code for leaking injectors? There is no sensor or way the ECU would know that was happening.

[Apex Eight]

Idk, apparently 45 is for an injector leak.

http://www.infamousnissan.com/forum/showthread.php?t=20905