why everyone should rewire their fuel pump
10-19-09, 09:09 AM
#104
So, I might be the first casualty of rewiring like this. Pettit did this mod for me about 4 years ago during my 3 rotor conversion. As you know, my car hasn't seen much driving time since then (maybe 5,000 miles) but it looks like one of my fuel pumps has gone out. I had two new Denso fuel pumps installed, giving me 40 PSI. Went out to the car a few days ago and it is now 20 PSI. Barely starts. Took the car yesterday to Jesus at Kilo Racing in Orlando and we're about 95% certain one of the pumps has gone out.
Remember my earlier questions about pump longevity? Looks like we might now know more about this thru my experience. Based on my experience, running the pumps at full voltage can possibly cause them to wear out more quickly. Maybe just bad luck in my case or maybe not.
Also, note that if you do this, the AMP usage on your car will go up a lot. At idle, the Denso pumps run about 7.5 amps total but when at full voltage like this mod will do, they're at 22 amps.
So we are thinking now about another setup, one that uses the Microtech to control the second fuel pump. We're thinking about running one fuel pump "as is" (full voltage) and then turning the second one on during boost or according to RPMs or something like this. I know this won't entirely fix the problem of running full voltage but it is a start. I am also going to look into the AEM product posted earlier here as a potential solution also.
As for where to mount the relay, I have mine installed all the way in the left back of the car, behind the plastics that also hoes the rear tail lights.
Remember my earlier questions about pump longevity? Looks like we might now know more about this thru my experience. Based on my experience, running the pumps at full voltage can possibly cause them to wear out more quickly. Maybe just bad luck in my case or maybe not.
Also, note that if you do this, the AMP usage on your car will go up a lot. At idle, the Denso pumps run about 7.5 amps total but when at full voltage like this mod will do, they're at 22 amps.
So we are thinking now about another setup, one that uses the Microtech to control the second fuel pump. We're thinking about running one fuel pump "as is" (full voltage) and then turning the second one on during boost or according to RPMs or something like this. I know this won't entirely fix the problem of running full voltage but it is a start. I am also going to look into the AEM product posted earlier here as a potential solution also.
As for where to mount the relay, I have mine installed all the way in the left back of the car, behind the plastics that also hoes the rear tail lights.
What I am going to do though is rewire one of my two fuel pumps to activate under boost via the Microtech. The other pump will be the "primary" and will run off of the battery. This will allow me to use 11 amps at idle with only one pump full on and to bring the other pump on when needed.
Not quite as good as the Aeromotive solution which lowers voltage at idle like the stock wiring but should be a good compromise for my needs.
10-19-09, 09:23 AM
#105
Original Gangster/Rotary!
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David, it's unfortunate that your FD has had so many wiring issues over the years. Could this be traced back to all the hack work the guy from Wolf did when he 'cleaned up' all your oem wiring?
10-19-09, 09:32 AM
#106
This latest issue stemmed from the sensor wiring melting and then shorting out. It was wrapped in heat wrap but apparently not enough. It is being relocated away from the "heat" side of the engine and will be wrapped in DEI stuff this time around. I am taking a cue from you and am putting on additional wrapping throughout the engine bay. Can't hurt right?
02-21-10, 11:46 AM
#108
F yo couch!
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umm, i have a feeling what the answer is, but i wanted to double check
my power wire isnt red/white
its white/red
this is still the wire im splicing into right?
i just want to be sure before i do it
my power wire isnt red/white
its white/red
this is still the wire im splicing into right?
i just want to be sure before i do it
02-23-10, 02:14 PM
#109
Understanding the benefits of, and not disagreeing with the need to re-wire the FP to correct a voltage drop, I just have a question...
Can someone comment as to any ill effects of bypassing the FP resistor while still using the stock ECU? This appears to be a common mod in this thread but it seems that the ones doing it have programmable ECU's. I think there needs to be clarification that deleting the resistor is either an option for everyone or just for those with programmable ECU's.
Thanks
Can someone comment as to any ill effects of bypassing the FP resistor while still using the stock ECU? This appears to be a common mod in this thread but it seems that the ones doing it have programmable ECU's. I think there needs to be clarification that deleting the resistor is either an option for everyone or just for those with programmable ECU's.
Thanks
02-23-10, 02:49 PM
#110
This mod will make your map rich so don't go for it on a stock computer unless you have no choice due to the pump not being switched to full voltage under boost. Also don't do it on a standalone unless you retune or want to live with rich mixtures. And yes white/red, red/white. I saw red and white but didn't pay particular attention to which was the main color. There's only 1 with the 2 colors so should be easy to find.
02-23-10, 03:20 PM
#111
There is another side effect to this - your pump will be running a full voltage and thus will consume a lot of amps, even at idle. And for those of you that have more than one pump, you'll be pushing max amps. For example, I have two Denso pumps and at full voltage (like this mod will do) the pumps run at 22 amps which sucks up quite a bit of amperage on the alternator at idle. Thus, this caused a voltage drop for me that drove me crazy until I realized the cause, this mod.
I've now rethought the fuel pump wiring and have one wired this way at idle, with the other one coming on via my Microtech under boost. The result? Voltage problem solved! And the wiring is done such that I can easily swap the wires from one pump to the other, which I will periodically do to save the life of the pumps.
Finally, remember by doing this mod, you'll now have full throttle fuel which means what you don't use (most of it particularly at idle) goes back into your tank as heated fuel and we all know that hotter the mix, the worse for HP not to mention again, the issue of fuel pump life.
Just some food for thought. read this for more info:
http://www.turbomagazine.com/tech/tu...ler/index.html
But they cost more money and introduce another electrical component into the mix.
I've now rethought the fuel pump wiring and have one wired this way at idle, with the other one coming on via my Microtech under boost. The result? Voltage problem solved! And the wiring is done such that I can easily swap the wires from one pump to the other, which I will periodically do to save the life of the pumps.
Finally, remember by doing this mod, you'll now have full throttle fuel which means what you don't use (most of it particularly at idle) goes back into your tank as heated fuel and we all know that hotter the mix, the worse for HP not to mention again, the issue of fuel pump life.
Just some food for thought. read this for more info:
http://www.turbomagazine.com/tech/tu...ler/index.html
But they cost more money and introduce another electrical component into the mix.
02-23-10, 04:24 PM
#112
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ok, I'm a little confused by the last post, I just ordered a walbro, and I'm putting in larger injectors (850/1600) and was planning on doing a rewire to the pump since I'm gonna need a retune anyway, should I still do this? It's only one pump so it shouldn't be TOO much of a draw, I'm shooting for about 13.5 volts, not sure what it's at right now tho. Hot gas=not so good, so maybe since I'm just getting a new pump the rewire isn't needed?
02-23-10, 05:02 PM
#113
ok, I'm a little confused by the last post, I just ordered a walbro, and I'm putting in larger injectors (850/1600) and was planning on doing a rewire to the pump since I'm gonna need a retune anyway, should I still do this? It's only one pump so it shouldn't be TOO much of a draw, I'm shooting for about 13.5 volts, not sure what it's at right now tho. Hot gas=not so good, so maybe since I'm just getting a new pump the rewire isn't needed?
02-23-10, 10:10 PM
#114
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Not to derail this thread away from the FP mod but I have a question. I had read in another thread that you should upgrade your alternator for several reasons.
larger stereo
fancy lighting
and the stock wiring gets hot, and can limit voltage/amps to your FP.
Now if I upgraded my alternator wouldn't that just make even more current over the already crappy wiring and there by making it worse for my FP?
The reason I ask is I had a FP drop after doing this mod. After several runs on the dyno that is......Now that could be a number reasons but one of them could be from the mod itself. I had thought of upgrading the alternator but do not want to potentially make the situation worse.
Any advice?
larger stereo
fancy lighting
and the stock wiring gets hot, and can limit voltage/amps to your FP.
Now if I upgraded my alternator wouldn't that just make even more current over the already crappy wiring and there by making it worse for my FP?
The reason I ask is I had a FP drop after doing this mod. After several runs on the dyno that is......Now that could be a number reasons but one of them could be from the mod itself. I had thought of upgrading the alternator but do not want to potentially make the situation worse.
Any advice?
02-23-10, 11:32 PM
#115
F yo couch!
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it doesnt really work that way when it comes to your fuel pump
elcetricity is sort of a supply demand kind of thing
if the FP only demands a certain amount of amps, it will get that (in most cases) only that amount
having more doesnt mean the FP will suddenly demand more
a higher amperage alternator will only mean that more things can demand amps and get them..without making other systems suffer (ex. your lights dim when you turn on the huge subs you have in the trunk)
as for the wiring...thats a different story, there shouldnt be a problem..but...im not positive on that
elcetricity is sort of a supply demand kind of thing
if the FP only demands a certain amount of amps, it will get that (in most cases) only that amount
having more doesnt mean the FP will suddenly demand more
a higher amperage alternator will only mean that more things can demand amps and get them..without making other systems suffer (ex. your lights dim when you turn on the huge subs you have in the trunk)
as for the wiring...thats a different story, there shouldnt be a problem..but...im not positive on that
02-25-10, 12:03 AM
#116
Just some video and images of my experience today thoroughly wiring the fuel pump. :-)
http://www.youtube.com/watch?v=pUBAx7HuSvg
Tons of fuel pump assembly work today.
http://www.youtube.com/watch?v=pUBAx7HuSvg
Tons of fuel pump assembly work today.
03-11-10, 02:04 PM
#121
On some cars I only gained half a volt or so after bypassing the fuel pump resistor with a jumper wire at the relay and adding an additional ground at the pump. There is also a power wire at the circuit relay that can be run to the battery but I have had the best results in just wiring a relay at the pump.
So would you just say to wire as the diagram shows leave everything else alone? Will it still be at 12v even though I dont jump the resistor? I have an issue with my voltage being at 7 volts at the pump with the car on and reving.
07-07-10, 03:27 PM
#122
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FYI the relay is available at radioshack, search around in their component bin, its a 30A 12V Auto Relat part number 275-226 its a 4 post equivalent for the bosch relay
07-08-10, 01:07 PM
#123
Recovering Miataholic
About the fuel pump "speed" relay...
This is an interesting thread. Having read completely through it, I wonder why the subject of troubleshooting the fuel pump "speed" relay (the one that does or does not jumper the resistor) has not come up. For the poster above that sees only 7 volts at his pump "with the car on and revving," it would be helpful to know whether the speed relay had closed or not.
On page F-60 (and also F-108) of the 1994 workshop manual, operation of the "fuel pump relay (speed)" is illustrated. PCME terminal 1K controls the relay. Terminal 1K is the signal return for the speed relay coil. (See also page Z-28 of the manual.)
Terminal 1K "high" = "speed" relay contacts open, i.e. pump resistor in circuit; 1K "low" = contacts closed, i.e. fuel pump resistor jumpered.
The manual states on page F-108 that "high speed and heavy load" should cause terminal 1K to go low, and also activation of the PRC solenoid valve should cause terminal 1K of the PCME to go low. (Also see page F-154.)
So on a stock FD fuel system, there should be a jump in voltage at the fuel pump (also at the white/red wire at the speed relay) when terminal 1K of the PCME (blue wire with white stripe at the speed relay) goes low. If that is not seen, there is a problem with the relay itself (open coil or oxidized contacts).
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Page F-111 shows that a "high" output from PCME terminal 4M activates the PRC solenoid valve, so a "high" on 4M also causes a "low" at 1K. So under hot start conditions, fuel pressure should rise from the combination of opening the PRC solenoid vacuum hose connection to the fuel pressure regulator and the jumpering of the pump resistor by closing the "speed" relay.
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Maybe this info will be helpful if troubleshooting the fuel pump "speed" relay.
On page F-60 (and also F-108) of the 1994 workshop manual, operation of the "fuel pump relay (speed)" is illustrated. PCME terminal 1K controls the relay. Terminal 1K is the signal return for the speed relay coil. (See also page Z-28 of the manual.)
Terminal 1K "high" = "speed" relay contacts open, i.e. pump resistor in circuit; 1K "low" = contacts closed, i.e. fuel pump resistor jumpered.
The manual states on page F-108 that "high speed and heavy load" should cause terminal 1K to go low, and also activation of the PRC solenoid valve should cause terminal 1K of the PCME to go low. (Also see page F-154.)
So on a stock FD fuel system, there should be a jump in voltage at the fuel pump (also at the white/red wire at the speed relay) when terminal 1K of the PCME (blue wire with white stripe at the speed relay) goes low. If that is not seen, there is a problem with the relay itself (open coil or oxidized contacts).
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Page F-111 shows that a "high" output from PCME terminal 4M activates the PRC solenoid valve, so a "high" on 4M also causes a "low" at 1K. So under hot start conditions, fuel pressure should rise from the combination of opening the PRC solenoid vacuum hose connection to the fuel pressure regulator and the jumpering of the pump resistor by closing the "speed" relay.
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Maybe this info will be helpful if troubleshooting the fuel pump "speed" relay.
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