A popular mod on 3000GT's is rewiring the fuel pump to bypass the resistor and receive full battery voltage all the time. Is the FPR on my 88TII strong enough to keep the pressure down at idle?

I'm having this CRAZY porblem where if I move the shifter over to 5th gear, the fuel pump relay starts clicking really fast. Has anyone heard of this happening?

 

im not sure.. I have a constant 12v source to my fuel pump via a switch. So even @ idle I get 12v to the pump. It runs just fine, no problems... I use a Microtech Standalone. I do have it hooked through a relay that shuts my pump off, but it gets a constant 12v all the time. I suppose gas mileage is worse. The reason I did mine direct with a switch, is

#1 I have standalone and wanted to rip out all the factory wiring....which I did...
#2 Easier

 

Goodspeed, do you still have the stock fuel pressure regulator?

 

I have a setup similar to his sans the switch because I am running a Haltech. I would imagine with the programability of our computers it makes it so it can run a constant 12V because we can adjust it to where we want it.

I am running the stock FPR, well I WAS running, and it was working fine on my old engine and my new dead one as well. No it is not dead because of that

 

If you run 12V to the fuel pump all the time, then at the times when it's supposed to run on 9V (idle and low load) it'll run too rich. If these times coincide with the ECU running in closed-loop (and I think a lot of the time it will), then the ECU (not the FPR) may be able to compensate by reducing fuel injector pulsewidths to keep mixtures around stoichiometric (that's what closed-loop does). The ECU doesn't go into closed-loop at idle, so idle mixtures will definitely be richer.
The FPR cannot compensate for upstream changes in fuel pressure, because the only thing it works from is manifold pressure. If the manifold pressure remains constant, and you increase fuel pump pressure, then the rail pressure will also increase accordingly.
The other point is that rewiring the fuel pump this way will have no advantages. The voltage is instantly increased to full battery voltage any time you put any load on the engine, so there's really no point in doing this. It's a very simple reliable system, and it's easily fixed if it does have a problem.

sublimeracing, when you say the fuel pump relay starts clicking in 5th, are you talking about the relay under the steering wheel or the relay in the engine bay with the resistor? (Both are for the fuel pump). Is this while driving or just sitting with the ignition on? If either of these relays were switching on and off while driving, you'd notice the engine stumbling because of the fuel pressure would be changing too. Is this happening? Are you sure this is what's clicking?

 

Thanks for the info - the whole reason I wanted to rewire it to constant 12v is because of the relay clicking in 5th. I hoped rewiring it this way would bypass the problem of the clicking relay. I am POSITIVE the under hood fuel pump relay is clicking when the key is in the on position, I'm not sure if the relay under the steering wheel is. I will check. Also, while driving, if I shifted into 5th, the car would just die.

 

Darn good set of ear lobes if you were to ask me. And you didn't.

Car just flat all out dies when put into fifth? That's what you said, so it must be so. Do the lights stay on when this happens? Any other thing happen at the same time that you noticed?

If you wanted to see 12v at the pump all the time, it's as simple as nipping the wire to pin 1K at the ECU, or the same wire at the Fuel Pump Resistor Relay. Your choice. You can always splice the wire back together again if you don't like the results, just leave enough wire to do a splice. Or....extract the wire out of the harness plug at pin 1K at the ECU. Your choice.

Really good hearing there. Amazing.

 

hmm... if you rewired it with a constant 12v. and used the factory wire as a relay wire (which you normaly do) the pump would still die anyways... (asuming that is the problem.)

 

I'm doing some research. Who can hear their Fuel Pump Resistor Relay come and go? You know, the one up front near the right head light. With the engine running.

 

We mainly heard the relay with the engine off but the key in the on position. Also when the engine was running my friend was under the hood w/ his hand on the resistor... he could feel it clicking. The engine ground was loose and now after fixing it and adding new grounds, the relay doesn't click anymore.
I'm glad that the prob is fixed but why did it only click in 5th???When it was clicking the idiot lights and anything else on would dim.