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Discussion Starter #1
I've spent hours looking for an answer and all I see is the same old hotwire techniques.

Question: If I were to keep the stock relay setup and just ran a larger wire, in other words, replace the #2 wire from the relay with a larger wire, bypassing the circuitous stock routing directly to the pump "should" keep the stock ECU fuel pressure control as well as providing "better" voltage to the pump. Or is the stock wiring to the relay killing the voltage right from the start?

Yeah, the car only has 37k on it but the goal is to prevent future problems. Or has this been tried and discarded long ago?
 

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I think what you are describing is what people call a "rewire" and not a "hotwire". I think there was a thread that specifically compared the two. If you search rewire you might find it.

Also, you wont really be preventing future problems if you plan to keep the stock fuel pump and/or light mods. My VR4 has 310,000 miles on it with the stock fuel pump wiring and a denso pump and is completely fine. Only recently did i find the limit of the stock wiring with that pump when running 50% ethanol and 17psi. I would honestly just leave yours alone...
 

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you pretty much answered your question yourself in your post unless you are planning to turn up the boost there is no need for the hotwire
 

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The stock wire gauge to the relay is already borderline and undersized for the upgraded pumps even to the MFI relay.

The fuel pump wire route is not as forward as it should be, due to the location of the resistor and relay"2" in the engine bay. The power comes from the ignition switched source to the mfi relay at the center console and get's passed to the fuel pump relay "2" in the engine bay codriver side and from there (over the resistor on low step operation) back to the front harness driver side(!), and side harness to the trunk, around the trunk to the codriverside pump ...
Now if you don't use the relay (or relocate it to the trunk) but remove the resistor, you can go straight from the MFI relay to the fuelpump and save around 10 foot of wire length, which helps alot even on stock wire gauge.

If you would be crazy enough to do it 100% stock style, the wire going to the MFI relay from the fusebox is just 14AWG (2mm²) - you would need to upgrade that. to around 10 / 9 AWG (6-5mm²), then upgrade the wire going to the relay and resistor to around 12 AWG - and then all the way around the car down to the fuelpump itself. Just picture completely taking your car interior out including the dash and open the harness everywhere and rewrapping it . ..OR do it like everyone else and do the rewire mod with an additional relay. ;)


As you can see to the left is the stock wire (black-blue with silver stripes) and to the right my 9AWG one in blue.
285109
 

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Discussion Starter #5
The fuel pump wire route is not as forward as it should be, due to the location of the resistor and relay"2" in the engine bay. The power comes from the ignition switched source to the mfi relay at the center console and get's passed to the fuel pump relay "2" in the engine bay codriver side and from there (over the resistor on low step operation) back to the front harness driver side(!), and side harness to the trunk, around the trunk to the codriverside pump ...
Now if you don't use the relay (or relocate it to the trunk) but remove the resistor, you can go straight from the MFI relay to the fuelpump and save around 10 foot of wire length, which helps alot even on stock wire gauge.
Thanks guys. Still not finding the information I'm looking for but Enkaio comes the closest. Why would anyone put the pump relay about as far away from the actual fuel pump and then run the wire into the next county and back to the tank in the first place makes no sense to me. Yeah, I get that it's by the relay box and all but short of pulling the relay and relocating the whole mess to the pump, I'm thinking a larger gauge wire direct to the pump through the console from the relay itself would get me better voltage to the pump itself. I'm going by the fuel pump rewire that Jeff did and the fact he didn't get any voltage increase at the pump so I thought just keep the relay and resistor and reduce the run and resistance in the first place and see if that works. Obviously, I don't want to go through the trouble if it's a waste of time. I've got this waking nightmare of fuel starvation so call me paranoid.
 

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Thanks guys. Still not finding the information I'm looking for but Enkaio comes the closest. Why would anyone put the pump relay about as far away from the actual fuel pump and then run the wire into the next county and back to the tank in the first place makes no sense to me. Yeah, I get that it's by the relay box and all but short of pulling the relay and relocating the whole mess to the pump, I'm thinking a larger gauge wire direct to the pump through the console from the relay itself would get me better voltage to the pump itself. I'm going by the fuel pump rewire that Jeff did and the fact he didn't get any voltage increase at the pump so I thought just keep the relay and resistor and reduce the run and resistance in the first place and see if that works. Obviously, I don't want to go through the trouble if it's a waste of time. I've got this waking nightmare of fuel starvation so call me paranoid.
Ok, I'll call you paranoid :).

But really, trust me (and others) from experience, you dont need to do this on such a good example of a car as you have. Keep the fuel pump and wiring stock and enjoy the car. Revisit the consideration if you plan to mod in the future. You should have absolutely no issues with stock turbos even cranking up boost.

If you are worried about fuel starvation, get a WBO2 installed so you actually know what is going on.
 

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If I had to guess the Japanese engineers mind in the late 80's, it's because of the resistor. The resistor get's really hot and as you can see on every fuel hat which had seen extensive road service, everything corrodes from the air draft back there bringing up moisture and everything light enough. Also the resistor pack was already a finnished piece in other mitsu 6g7 cars.

I never wasted to much thought about keeping or upgrading the 2 step system. Afpr + straight wire from a good power source, shortest distance possible. No resistor no relay bridged in the engine bay. Easy and simple as it gets.
 

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Discussion Starter #8
Ok, I'll call you paranoid :).

But really, trust me (and others) from experience, you dont need to do this on such a good example of a car as you have. Keep the fuel pump and wiring stock and enjoy the car. Revisit the consideration if you plan to mod in the future. You should have absolutely no issues with stock turbos even cranking up boost.
If I had to guess the Japanese engineers mind in the late 80's, it's because of the resistor. The resistor get's really hot and as you can see on every fuel hat which had seen extensive road service, everything corrodes from the air draft back there bringing up moisture and everything light enough. Also the resistor pack was already a finnished piece in other mitsu 6g7 cars.
I'll take the leave it alone advice. Just because I'm not paranoid doesn't mean there's nothing wrong. :rolleyes: And thanks, this car (aside from the bad driver door switch) is amazing. I put Meguiar's Synthetic Sealant 2.0 on it last week and it really brings out that pearl in the paint. It's still stunning to me I got this thing for the price I did.

I totally forgot about the resistor heat. My first car was a 1978 Plymouth Volare Kit Car (black valve cover) that ran 10s all day long after I got rid of the damned lean burn and put a point distributor/resistor/coil on it (along with a 1000 cfm carb, NASCAR exhaust and solid motor mounts) and burned the crap out of my hand one day on that stupid resistor.
 
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