car won't start. it wouldn't start after sitting for a few days. occasionally it will start and just die instantly. when turning over, it sounds like it is trying to start, as in chugging a bit, but it just won't. i checked for spark and fuel. the fuel pump primes, though i haven't gotten a read on pressure. has spark all the time. i thought that the MAF didn't affect idle or start up but someone told me to check it so i did. i checked the pin for voltage that the FSM said to, while it was plugged in with the ignition on. got 11.5-12 volts. not sure that i did that right. seemed like it was just getting the strait current from the wire sending power TO the MAF.

anyway, since this started all at once, i don't really know what to to look at next. i think idle control might be suspect. i guess i can go back and test the IACV valves. does this sound like a good idea?

any other ideas? did i do the MAF test right?

 

ECU codes?

 

His codes read 55

 

yeah. lol

 

Turn ignition to "on" position and test fuel pressure, come back with results.

 

dude we ran around for half a day trying to get a fuel pressure gauge to test it with but came up empty handed. we're trying to diagnose it with the multimeter if possible.

what we did find, is that if you take the hose off and prime it, it does pump, but we don't know to what pressure. not sure if that's much help....

 

If the pump is turning on, it is not your fuel pump control unit. When they fail, the pump won't turn on.

You'll be hard pressed to find an inline fuel pressure testing gauge for fuel injected vehicles anywhere... it's easier to just make it. Get any liquid pressure gauge that reads up to 100psi and get the fittings to T into the fuel system after the filter.

http://www.jegs.com/i/Aeromotive/027/15633/10002/-1
+
http://www.jegs.com/i/Mr.+Gasket/720/2975/10002/-1

 

ha damn i was actually thinking about doing that with an oil pressure gauge but wasn't sure if it would hold up to the gas. perhaps i'll give it a shot. thanks.

so you're sure that the fpcm can't just cause a problem that allows prime but not regular run time pumping? after working on it more i notice that there seems to be a slight beep coming from the fpcm or maybe the fuel pump when it primes.

 

Neither has the ability to "beep." Could be the fuel pump whining, and a fuel pressure test would tell if the pump was straining to do its job.

And when a fuel pump control unit goes bad, it *fries.* It's not some minor problem.



As for the oil pressure gauge not working for fuel... they're both made of petroleum. It would work fine.

 

yeah i thought it might be the fuel pump whining. well i'll go back out and grab that gauge and see what's up.

 

update: i got a pressure gauge all set up and checked the pressure. primed to around 60 and dropped pretty quickly to 0 strait away. i clamped the return fuel line, primed, went to 60, dropped to about 38, and held. i took the clamp off, and the pressure kept holding. i primed again and it stayed the same. turned the key, it started right up. pressure stayed around 38 and jumped up to 50 or so when revved. it looks just perfect now. i turned it off and started it again a few times with no problem.

yes, you read this right. i clamped a line, primed it again, took the clamp off, and it started. that is all. i changed nothing.

could this have been a fuel pressure regulator? is that the one on the passengers side of the engine? should i go ahead and change that?

 

The fuel pressure regulator is what maintains fuel pressure in the system. It's not supposed to drop to 0 ever, so it's clearly bad.

It should read about 35psi at idle, so that's fine (there must always be a 43.5psi differential between manifold pressure and fuel system pressure, and this is the job of the FPR), but the fact that it wasn't holding pressure tells you that the pressure in the fuel system during cranking was not large enough for the injectors to spray the correct amount of fuel, thus the sputtering without starting. By blocking the return line and letting it build pressure, you allowed the injectors to spray enough fuel to start (and I suspect you also "un-stuck" the FPR).

See? I told you it wasn't your control unit. Fuel pressure testing can tell you so many things about the health of your car.

By the way, while running, how steady was the needle? If it was bouncing around, replace the fuel damper, as well.

 

yeah i looked into that. it was pretty steady. the gauge was not really good enough to tell though. the vibe of the engine was allowing a very fast 5 psi shake. too fast even to be caused by injectors though. the needle was a blur.

thanks though man. lol i'm constantly reminded to NEVER doubt a word that you say. so i'm thinking it's a pretty good idea to go ahead and replace the fpr? it may not come un stuck so easily next time...

43.5 psi difference is just how a z prefers to run? or is that some universal number?

 

Uh, that shake wasn't caused by the engine... it was caused by a malfunctioning fuel damper (actually, it's caused by the fuel pump and is supposed to smoothed out by the damper). The fuel pump is exactly that... a pump... the pressure it puts out fluctuates through each pump cycle. The fuel damper's job is to smooth that out.

Replace both the FPR and damper and you will (seriously) be surprised at how much more responsive and lively your car is.
It's even recommended in this writeup for pepping up a higher mileage Z:
http://www.twinturbo.net/nissan/300z...pages/pep.html

And most modern EFI systems require 3bar (3*14.5) fuel system to manifold pressure differential.

 

ok. i can check that out by holding the gauge in my hand then. it was sitting on the plenum when i saw the shaking. thanks.