Write-Up: Fuel Pump Re-Wire Modification

I'm looking in my 1997 FSM about the fuel pump module that supposedly runs the fuel pump at 2 different speeds, as commanded by the PCM. There's two things that don't make sense to me about all this.
For one, the wiring diagram shows a separate wire for high vs low speed going from the module to the pump (doesn't explicitly show the fuel pump's ground either) but I know for a fact there is one hot and the other wire is the ground (plus 2 more for the level sensor but that's totally separate. I guess the wires are B (black I assume) that apparently turns gray on its way to the fuel pump module and a pink. It could be a mistake but the only way it makes any sense to me is if there is no high vs low wire but just a + and ground that both come from the module. Anyone know what's up here?
The other thing is the operation of this fuel pump module seems ludicrous. My FSM says it normally runs the fuel pump on a 33% PWM duty cycle and doesn't change to 100% until the PCM sees a value higher than 90kPa from the MAP sensor. That's like 13psi... This things saying the PCM doesn't let the stock fuel pump run higher than 33% duty cycle until the boost hits almost double what it's ever supposed to see? I'm missing something here.

I did a quick test. I used HPtuners VCM controls to command low and high speed to the fuel pump and you can clearly hear it running at two different speeds when you switch it. It commands full current to the pump for the pre-start prime. I also looked at my fuel pressure with the car idling and I read 40psi with the fuel pump on low speed and then when I commanded high speed fuel pressure actually went up to 42psi. I went back and fourth a couple times just to make sure. 2psi is considerable, in this circumstance. It takes a big bump in fuel pump output to make a small change in regulated pressure.

I also took a look at the fuel pump module which I'll post soon.

The whole point of this is I'm finally getting around to re-wiring the fuel pump in this car and installing the magnuson fuel pump booster. The complicated nature of this fuel system is slowing me down but I think what I'm going to end up doing is running heavy gauge wiring from the fuel pump module (which is directly where the fuel pump hot and ground both come from) for the s/c rivieras (not the case with n/a cars) to the pump for the ground and then run run heavy gauge from the + side of the module through to the booster where I'll then connect to the fuel pump with heavy gauge. So far, that seems like the only way to do it and keep the stock variable speed system. The fuel pump booster has its own dedicated + and ground sources so the whole thing should behave like a normal fuel pump rewire and then when the booster kicks in, the fuel pump then get's about 17 volts to it. It'll kind of be like a 3-speed system once it's in and working. This, of course, is assuming I'm understanding this whole thing right. It'll probably turn into a write-up as I make progress.

The fuel pump module has some pretty heavy wiring on it already that goes to the pump so just looking at that, it doesn't look like the car could benefit from a rewire but then when you look at the actual pump side, it's smaller. I guess it must change to smaller wire at the looms where the wires pass through the shell of the car.

MAP is not the same as boost, it's one atmosphere (~100 kPa depending on barom) + boost pressure. So typically you'll see a lower number at idle (vacuum), usually ~40 kPa. As you apply throttle, MAP climbs until 101 kPa, above which you're in boost. 90 kPa is a point just before entering boost.

At full stock boost, MAP should read about 143 kPa.

AA wrote:

MAP is not the same as boost, it's one atmosphere (~100 kPa depending on barom) + boost pressure. So typically you'll see a lower number at idle (vacuum), usually ~40 kPa. As you apply throttle, MAP climbs until 101 kPa, above which you're in boost. 90 kPa is a point just before entering boost.

At full stock boost, MAP should read about 143 kPa.

Right on.
I knew I wasn't going to be up all night with insomnia reading technical manuals without forgetting how basic physical measurements work.


So I have the back half of the car ripped apart granting access to everything I'm dealing with. I've got all the fuel pump wiring found and accounted for. Unfortunately, I cannot get the magnavolt unit to function. I might have to call tech support for it this week since they don't really seem to have any universal install, operation manual for it on their website.

As for the fuel system, help me understand. Does "PWM" mean to reduce the overall current to the pump and run it slower without lowering voltage? I ask because In my testing the pump, connected as stock, was running at full charging voltage while the engine was idling but it was still running at the slower speed. I need to fully understand how this works so I can figure out if the magnavolt is going to work the way I want.

PWM stands for pulse width modulation. It's the premise behind such attenuation devices as lamp dimmers and motor speed controllers. The idea is pretty simple. The PWM unit sends a square wave signal to the pump, much like an amp sends an audio signal to a speaker, except the PWM is more "on/off/on/off". Since the duty cycle of the pump is now less than 100%, it will run at a lower speed, but still it's getting full voltage, just not 100% of the time. Another way to see it, the pump is being switched on & off several times per second. If it's "on" 50% of the time, and "off" the other 50%, the effect is similar to being powered by 1/2 the voltage. The advantage to PWM is that voltage sensitive equipment can operate without compromise at varying speeds.

After studying all the wiring for the Riv's fuel system, I've come to the conclusion that factory wiring is quite a bit different than what W-body cars have and a fuel pump re-wire is a completely different job. I'll also point out right now that the pre-made re-wire harness that you can buy for the grand prix, regal, etc isn't really going to work on a Riv either.

Here's a simple wiring schematic I drew.

The wire colors are all accurate to real life except for the purple wire going from the fuel pump relay to the PCM - I didn't check the color of that one.

I'm going to cover how a re-wire can be done on a Riv though. Since no one has done a write-up on this that I can find, I cannot report results until I've completed and tested mine. I'm making changes only to the parts of the wiring that I'm observing to be likely quench areas. A good way to observe voltage drop for the fuel pump is to compare voltage coming out of the fuel pump module pins (red wire and grey wire) to the voltage at the fuel pump harness pins (solid black wire and grey wire) with an accurate volt meter. If the difference is .2 volts or more, the industry would consider that excessive. In the interest of a re-wire, I'd say any more than .1v drop makes a re-wire worthwhile. If you running a Walbro or some variation, I'm told it's even more sensitive to voltage drops as it draws a little bit more current than a stock pump does.

Reference shot of the Fuel pump module and it's harness

As you can see, they were nice enough to label each pin.
+B : hot wire from fuel pump relay
FPC : control wire from PCM
FP+ : hot to fuel pump
FP- : ground to fuel pump
E : ground for fuel pump module


As shown in the above illustration, the high-current wires at the fuel pump module harness are all thick 12gauge wiring. There's no need to improve that. The harness passes through the floor under the rear seat on the driver side and then there's a connector where the wires change to a smaller 16gauge and the red wire becomes a black wire. That is the harness that snakes up to the fuel pump assembly at the top of the gas tank. If there is anything to improve on, it's that harness underneath the car. The procedure is to de-pin the 2 wires at each end of the harness and replace the wires with 12gauge wires with new pins. If you are comfortable with crimping these pins, this is a relatively easy mod to do. You need to gain access to the fuel pump harness so you need to pull up the carpet a little bit and remove the access cover to the fuel pump. The connector on the other end of this harness is pretty much in plain sight if you're under the car. If you drive the rear tires up onto ramps, that should give you plenty of room to do this. Supplies needed are the two lengths of 12gauge wire and both types of new pins to crimp the wires to. You can purchase small spools of wire from any auto parts chain. Unfortunately grey is not an easy color to find. I'll get back with where I find mine though. I'm going to try napa and if not them, I'll start looking at Fry's electronics and the big hardware chains. As for the pins, The only store that carries a decent selection is Pep Boys. I'll report back with part numbers that work as well as crimping techniques (since they may or may not be rated for the gauge we want to use).


There's a shot of the fuel pump access cover-off from the cabin side.

As another installment of this write-up, I'll be putting in a Magnavolt which is Magnuson Superchargers' version of the better known MSD "Boosta-pump". It is just a switching transformer that bumps fuel pump voltage up to about 17 volts to increase fuel pump output.
Why? This unit comes along with some of Magnuson's add-on supercharger kits as an alternative to an upgrade fuel pump to get the necessary amount of fuel from the stock (otherwise underqualified) fuel pump.
Frankly 97% of people who mod an L67 probably don't need this. Fortunately for us the stock fuel pump goes a long way. The walbro and perhaps a re-wire will get some more, still.
I want to use it for my setup because I'll have uniquely high fuel pump demands in short bursts once finished. WIth ethanol, the fuel volume required jumps up 30% across the board. On top of that, I'll be using a nitrous system that solely relies on the primary fuel system and with slightly boosted fuel pressure at that. Fuel pump flow decreases with more fuel rail pressure so you really start to run out of fuel pump fast when you get to that point when you need lots of flow and pressure at the same time.

A few technical notes about the Magnavolt (since Magnuson doesn't have any clear functionality instructions)
Even when it's not energized and passing normal voltage through it, it still needs to have its own ground and power leads connected - It's not strictly pass-through.
There are two triggers. The white wire triggors the magnavolt when it sees 3000rpm. The vac/boost hose triggors is when you hit 3psi. Either/or will trigger it - doesn't need both.
Another thing to note is that with a 3psi trigger point, it will step up voltage only when the fuel pump is in full duty cycle via the PCM (which is a good thing), provided you don't use the rpm trigger. If you utilize the rpm trigger, it is possible to trigger high voltage while the PCM is still commanding modulated (reduced) fuel pump current. Aside from the fact that this doesn't really make any sense to do, I suspect the modulated current pulsing through the magnavolt with stepped up voltage might be bad. It sounds like there's definitely at least one solenoid in this thing which I don't think would react well to pulsed current. This is something I plan to contact Magnuson tech support about before I complete the install.

Here's what I'm starting with.

This is the basic on how to wire the Magnavolt up to the Riv fuel pump. There's other wires coming out of the magnavolt harness but they have to do with triggering and tuning, not the fuel system so I left them out for this. The magnavolt should not have any affect on the stock variable fuel pump speed functionality as long as it is wired as I've illustrated above. If you want to, you can also wire this to bypass the fuel pump module and eliminate the PCM's fuel pump modulation but I would suggest against this as it will affect your base tune a little bit and more importantly, shorten the life of the fuel pump unnecessarily.

So far, I have done a quick test with the unit to make sure it works and I've found a good place and method to mount it. No drilling or hacking to the car




I added these two brackets.



That's where it mounts. I looked pretty closely all over the car searching for a good place to put this and this is by far the best spot I could find. The wires are all close to their destinations, there is no drilling or hacking necessary (with the brackets pictured) and most importantly, the Magnavolt is in a place that allows it to breath with no danger of heat-related problems and it stays dry. Being it is a transformer, it will produce some heat and I would not recommend putting it in contact with carpeting or anything of that nature. The unit is supposed to be sealed but there's no reason to chance it. I have heard of these failing due to getting splashed constantly, mounted under the hood. The only downside to this location is that you need to run a good length of vac/boost hose to the engine. The hose as about the thickness of an 8gauge wire so routing it through the car is not too bad.

Now I'm waiting to get hold of some grey wire and 25ft of silicone 4mm hose so I can get further on this but I'll continue the write-up as I make more progress.

Some reference pictures of the Magnavolt harness

top

bottom

I tested the voltage drop between the fuel pump module and the fuel pump and found right about .1v difference on average. I did the test on full duty cycle. I also observed about .11v difference between the voltage coming out of the fuel pump module and the input voltage on leads to it (the green wire coming from the fuel pump relay and the ground). The results are not bad but I think I can get it better. I'd be interested to see what W-bodys test for voltage drop on stock vs rewired.

My readings on 100% duty cycle
14.25v at pump avg
14.34v at module output avg
14.45v at module input avg

33% (idle-cruise) duty cycle
14.44v at pump avg
9.00v at module output avg
14.62v at module input avg

The measurements under full duty cycle make perfect sense. I also tested under the reduced duty cycle but the findings are worthless.

Thanks for posting. It's good to see the improvement, but I have to wonder how much difference results from .1 volt. These wiring upgrades always make me question the value of the kit and the installation time. I think one vendor sells a rewire kit for $50. I'd like to see a test: someone take off their existing pump wiring, clean up all the connection points and connectors, then just reinstall those original wires. How much of that .1 volt comes from replacing the wire itself vs. the age & quality of the connections.

Still, every little bit helps, and there's no doubt your new wiring job will likely outlast the old!

Hey turtle, nice Kawasaki. Do you ride? I just bought the wife an 08 Suzuki GS500F instead of me buying some sqrivi bumper covers.


and on topic:
turtle, I'm glad to see you're not taking fueling chances with your setup. All the time and effort to do things right will pay off.

Karma wrote:

Hey turtle, nice Kawasaki. Do you ride? I just bought the wife an 08 Suzuki GS500F instead of me buying some sqrivi bumper covers.


and on topic:
turtle, I'm glad to see you're not taking fueling chances with your setup. All the time and effort to do things right will pay off.

It's an 87 Ninja250. It's a pretty awesome bike if you don't need to ride on the highway. It's pretty gutless above 40mph or so but just cruisin around town to get to work/school for cheap, it's great. That's all I do with it.

Just to officially post, I finally got everything done with this. As of 1/31/12 (205,402mi on the car) The Magnavolt is hardwired in for full time use and I upgraded all the wiring for the fuel pump. A few things I'll point out is the factory ground for the fuel pump module (and therefor the fuel pump) is pretty terrible looking. The actual ground wire that goes to the module is a good thick 12g wire but if you trace it down to the source its actually one of 5 or so other ground wires that are all being shared (not unusual) but the main wire that they are all sharing is like a 16g wire. I have a picture of this I'll dig up at some point. I didn't bother to check what the other ground supply wires go to but I'd assume/hope they are devices that don't need much current. Anyway, I ran a new ground for the module. The fuel pump assembly has an external connector and an internal one. The external connector uses pins that support no more than 14gauge wire max. Factory wiring there is 16gauge. I ended up just using a re-wire harness like ZZP's so I wouldn't have to crimp the pins since I don't have the few-hundred dollar tool that does it nicely. I ran the new wires through the access cover with wire grommets and then sealed off all the original wires with shrink tubes. It could all be returned to stock if necessary.

There are some options for how you can wire this but I did it just as I showed in the diagrams I made in the above posts, keeping all the functionality of the factory fuel pump speed control. So far it's working great. With the factory speed control, The PCM runs the fuel pump at low speed until you hit 90kPa manifold pressure which is a little bit before you enter boost. Pretty much if you're hitting the throttle to do any more than an easy acceleration, the PCM is enabling full speed to the pump. With the magnavolt connected like I did, it's kind of making it a 3-speed deal. The factory speed control works the same but as soon as you get on the the throttle more and hit 4psi, the magnavolt kicks on and you get ~17volts to the pump and obviously it'll flow a lot more fuel then. So in summery, between idle vacuum to 3in/hg vacuum the pump is at low speed, between 3in/hg vacuum to 4psi of boost the pump is at full speed, above 4psi pump is at extra high speed.

turtleman wrote:

the factory ground for the fuel pump module (and therefor the fuel pump) is pretty terrible looking. The actual ground wire that goes to the module is a good thick 12g wire but if you trace it down to the source its actually one of 5 or so other ground wires that are all being shared (not unusual) but the main wire that they are all sharing is like a 16g wire. I have a picture of this I'll dig up at some point. I didn't bother to check what the other ground supply wires go to but I'd assume/hope they are devices that don't need much current.

Here's the pic


And some more pics of everything dealing with the install


the bracketing I put together to mount the magnavolt without drilling any holes into the car at all


mounted and wired up. Only thing not done here is the loom for the wires running to the seat area. The thick red fused wire is the main power for the Magnavolt, the black that's sorta going up is the ground. The loom in going left is the wire from the fuel pump module. I routed that one through the trunk upper beams. The light blue wires that are just tied together is just something for the Magnavolt its self. I'm guessing some setting for something. You can't even really see the silicone boost hose but that's routed up to the back seat area and then through the floor sills and stuff all the way to the engine compartment through the firewall passage where the main battery line goes through. I'm putting all my added wiring through that.


neat view of the right rear quarter panel caves. Actually this is a pretty damn good place to have the Magnavolt as it is protected from the elements and is still able to breath. I don't know how hot the transformer gets but I'm don't think it's too much anyway. Magnuson's instructions have it mounted onto plastic fuse boxes and stuff so I'm not worried.


Here's where the battery power (red) and fuel pump supply wire (blue) wires come into the back seat area. You can also see the black silicone hose coming in. The group of black wires are all for the nitrous bottle warmer.


another shot of that wiring. The relay is for the n2o bottle warmer.

Onto the other side of the car

Routing of the new wiring to the fuel pump module is basically the same deal as the Magnavolt side. Side note. I searched and searched and searched for new pins for this connector for the fuel pump module and never found any so I ended up getting the whole mess of wires for this from Alex's riv as a spare to use. That worked out fine in fact I didn't even actually need to extend anything. So here, the thin brown signal wire and thick green wire from the relay are untouched. The thick red is the new ground going straight to the pump and black is a new ground for the module. The wire you can't really see inside the loom kinda going up is that wire going to the magnavolt.

another cave shot


There's the new ground for the fuel pump module


and the new fuel pump ground (the red wire i just mentioned) You can also see where the fuel pump ground and the module ground split up at the right


just snaked that fuel pump ground in there


and finally at the pump area. I looked for a fancy terminal setup to integrate into the access cover for these two new wires but nothing really panned out. The terminals themselves would have added bulk and complexity to it which could cause worse fatigue problems and whatnot than just having wires pass through with grommets like I have so this is my solution.


connected with the carpet and padding down, everything seems perfectly happy

All updated with pics now. The only other thing I might post at some point soon is a test video or something to explain the function a little bit.

As promised here's the demo video