So I have a very strange problem happening with my 99 gs300
this is a NA-T build, using the stock intake and throttle. I had to hand make the harness as the original harness was destroyed by mice or something. Using the EMU black and pnp harness with the stock ECU. I’ve loaded my base map and adjusted timing so the car starts and runs/ idles fine. I have a check engine light for the VVTI but no other codes. The thing is when I have the car running for a little bit and then I turn the ignition off and pull the key out, the fuel pump does not turn off and the throttle motor stays running too. I waited a few minutes and neither shut off. I tried unplugging the fuel pump relay (I have the pump, since it’s larger than stock, wired to the battery and starter so it comes on when I turn the ignition on) and it turns the fuel pump off but the throttle motor stays on still and when I plug the relay back in the fuel pump turns on again. Also if I put the key in again and turn the ignition to the on position without starting I can hear the injectors firing randomly. In the EMU black software, it shows my RPMs are at about 90 when the car isn’t even running, but the throttle motor and fuel pump are on (current issue) I assume the ECU sees this RPM reading and is firing the injectors trying to start the car without me even turning the key to start it? Weirdly enough, if I unplug any of the connectors on the throttle body (tps sensor, accel. Position sensor, throttle motor) everything that stays on, turns off. Including the fuel pump. I’ve checked the ohms of each thing on the throttle and they were all within repair manual specs. I also checked if the main fuse could possibly be stuck, but I can hear it click on and off when I test it by supplying 12v power to it. I’m at a loss of what it could be. I’ve also tested continuity from connector to the corresponding ECU terminals and they all are under 1ohm, most are 0. If anyone has an idea of what could be wrong I’d love to know because I hate having to constantly unplug the throttle connections just to make sure everything is off. I’m hoping it’s not a wiring issue as I’ve searched everywhere for a stock engine wire harness for my car but no where sells one and if the do they want me to buy the motor with it.

 

In the future you should post your repair questions in the regular 2GS forum and use the builds forum to show the work your doing to your car over the time you own it. These are long term threads to let other members follow along with the work you do to your car. If you post questions about general problems in the regular threads you'll get more responses much more promptly. The answer to your question is the fuel pump is designed to be powered different than other automotive components, usually all automotive electrical components are designed to receive a constant 12-14 volts. A fuel pump needs to vary the pressure depending on engine RPM, HH igher the RPM, the higher the voltage, the higher the fuel pressure. It's designed to get full voltage when the key is turned on, and then it shuts back off until the engine is started. I don't know what kind of swap was done or what was done to the wiring but you really should just return the wiring back to stock. Even a larger fuel pump should work just fine with the original wiring set up. you can find good, unmolested wiring harnesses for your car on eBay for low pricing, probably $100-$150. You need to find the part number for your wiring harness, so you can get exact replacement for it. Then before you install you can give it a good restoration, pull off all the crusty old tape and coverings, so you can can replace them with new, fire resistant covers and inspect all the plugs and replace any that are damaged, also you can inspect the wires for any damage. It’s much easier to do while it’s out of the car.

 

I looked them up on ebay and my previous price mentioned was a little low, looks they are listing for about $300 currently, but it looks like you could buy a good one and then sell whatever is currently in your car for about half what you spend on the good one. There are several damaged harnesses listed for about$150, so you won't have to spend to much money and it will be worth it to get a good harness, you'll just continue to have problems that are hard to diagnose you ntil the wiring is sorted out.

 

The reason why your injectors are cycling is because they aren't designed to hold back full pressure indefinitely. They are usually cycling for the brief time the fuel rail gets maximum pressure from the fuel pump. Typically the engine gets started right after the pump powers up, but if you don't start the engine right away, the power gets shut off to the pump, so the pressure can relax, and once u start the engine the pump will get the appropriate amount of power for the rpm the engine is running at. If you just have full battery voltage at the fuel pump then it's running at fuel pump at all times and the engine doesn't that much, so your quickly going to wear out your fuel pump and the injectors unless you get the wiring returned to it's original design, I wouldn't be surprised if it also blew a fuel line. Typically when an engine swap is done that requires more fuel, you will run full battery voltage to the fuel pump but you will add a return line from the fuel rail so that excess fuel is just returned back to the tank, having that excess pressure just build up the fuel line and rail is probably dangerous.