help me diagnose fuel pressure prob please..

[ninetythreez]

1. at the turn of the key with no cranking the engine the pressure jumps up to 40, then 3 seconds later, falls off to 20 lbs.

2. at cranking the engine at idle, pressure is running 32-35 lbs at idle.
93 Z28, LT1 w/ 24lbs/hr injectors.
bad pump? fpr? both? the fuel pump has a pressure baffle in it also right?
what kind of $$$ is a pump gonna cost.
any recommendations for a good pump for the street with bolt on mods?
Thanks!!!!

[TraceZ]

1) FPR is cheap. Replace it and the filter. Test again.

2) It may be a leaky injector. Lift the fuel rails with injectors off the manifold and pressurize the system using the over ride wire for the fuel pump. Look for drips.

3) If all the above tests well, and you still cannot maintain ~42LBS pressure... replace the pump.

[ninetythreez]

.

I just happen to have a good fpr I got from Lingenfelter and a set of injectors extra here. I will try this idea of yours.
Question: How do you "lift" rails with injectors on attached? do the injectors just pull right out of the intake?
If I were to need to change injectors. how are they removed from rail? there's a clip holding them or sumthin right?
Sorry for so many questions. This is just one of those things I haven't had to do before.
THANKS!!!

[ninetythreez]

,

the car.

[Craig 94 TA GT]

OK, I have all the experience when it comes to the fuel system now. (Started when some punk $%#@ kids poured sugar/syrup in my tank). Anyways, to diagnose each one:

To check if the injectors are leaking, remove the 4 screws holding them down. Both sides will lift up as one piece as they are connected by hard lines. The injectors might be a bit tight in the intake, so make sure you lift up firmly, but don't yank it. Make sure the O-rings are still on the injectors, as well - especially when you put them back in. Once it is lifted, pressurize the system and look under each injector to see if any are wet.

To diagnose the FPR, you can simply install your new one and see if the pressure still bleeds. If you want to avoid that, then you can check the system by using a simple method: remove the vacuum line from the FPR and see if it's wet. If it is, your diaphram is ruptured and is causing your leak. Another test is done by using a fuel line shut-off valve. What you would do is remove the return line (5/16") from the regulator and install the valve in between. Pressurize the system and then close off the valve. If the pressure still bleeds, then you have a leak that's coming from your pump (only if the injectors are OK). If the pressure doesn't drop, your FPR is bad. What you can also do with a shut-off valve is start the car and watch the pressure gauge. Slowly close off the fuel line shut off valve. If the pressure rises above 47 psi, then your regulator is bad. Make sure you do not attempt to shut the valve off all the way because you will grenade your injectors with 80+ psi.

To check the pump, install a fuel line shut-off valve in the supply line (3/8"). Simply pressurize the system and close the valve. If the fuel pressure does not drop, then your leak is from the pump.

Let me say that it was a PITA to diagnose these things for me. Turns out I needed a new pump, new injectors and a new regulator. Good luck.

[TraceZ]

Re: .

I just happen to have a good fpr I got from Lingenfelter and a set of injectors extra here. I will try this idea of yours.
Question: How do you "lift" rails with injectors on attached? do the injectors just pull right out of the intake?

Yup. The injectors pull strait up and out while still attached to the fuel rail.

If I were to need to change injectors. how are they removed from rail? there's a clip holding them or sumthin right?

They fit into the rail with an O-ring and a clip. Here is an illustration of a 93 fuel rail.
http://shbox.com/1/fuel_rail_93.jpg

Sorry for so many questions. This is just one of those things I haven't had to do before.
THANKS!!!

No problem, man!
Good luck.

[AmericanZ28]

I got my fuel pump from Summit as a Granetalli kit for $127 I believe. The Pump is a Walbro unit, and works pretty much as a drop in replacement, although minor modifications are necessary.

[ninetythreez]

i

I saw that Granatelli pump in the Summit catalog. So are you pleased with it so far? what kind of modifications are you talking about?

Ahhhh, a burnout pic!
Lite em up!

[AmericanZ28]

So far, the pump has worked flawlessly. Ive had it in for about 3 months already. I had originally changed it because my old one went bad, but its good to know that im going to have a pump that will keep up with future upgrades. The modifications are minor, its just kinda tricky getting the pump to sit properly, and the upper sleeve that it comes with wont fit right into the housing, so I had to cut it to make it fit. The hardest part is the install, especially when doing it in your garage with jack-stands

[ninetythreez]

f

do you have to drop gas tank and rear axle to access it? I have heard of guys cutting thru trunk floor to access the pump also. kinda risky near gas with cutting metal i think.

[Trans Am]

i have done the cutting thru tank thing and i recommend it, just in case the fuel gage doesnt work, or other problems after the pump is in place do a search and yoou will find even pictures and mesurements how to do it

good luck

[AmericanZ28]

Re: f

Originally posted by ninetythreez
do you have to drop gas tank and rear axle to access it? I have heard of guys cutting thru trunk floor to access the pump also. kinda risky near gas with cutting metal i think.

Yes, unfortunately you do have to drop the tank and axle ! But its all worth it in the end. I was thinking about going the the route and cutting through from the inside, but its a "hack job," as many here told me. I wanted to do things right, so I went the hard way out. Theres nothing wrong with doing it the other way, it saves you a whole lot of trouble as well as cuts and bruises. It's up to you how you want to do it.......

[fastTa]

I was able to drop the gas tank in my 1997 WS6 without dropping the rear axle whatsoever. It took a little coaxing but I got it out.

[Detroit_Bird]

I was thinking about going the the route and cutting through from the inside, but its a "hack job," as many here told me

I can see why people would think it was a hack job, but did you know that most import vehicles where it is hard to access the tank (300ZX comes to mind) this is a stock feature?

There is no increased danger or structual problems as long as this is done correctly, and it makes a 8 hr R+R into a 2 hr breeze.