Thread: Fuel Pump Resistor Upgrade

Prj Performance - Racetronix Fuel Pump Kit

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Originally Posted by scootcoupe91

The PRJ hotwire kit still runs the fuel pump in high speed mode all the time which puts unnecessary strain on the pump. I'm looking to keep the stock two speed mode AND improve the reliability of the system already in place.

The only unnecessary strain it puts on the pump is the overall lack of voltage to the actual pump.

99% of cars don't have a fuel pump resistor. There's really no need for one and running a pump at full speed shouldn't do it any damage. However..

GTP does

do the regal gs have this resistor?

Originally Posted by jim97regalgs

do the regal gs have this resistor?

Yes, my 98 Regal GS has the fuel pump resistor. And I don't recommend running this fuel pump in high speed mode either. My fuel pump resistor went bad so I bypassed it for a week while waiting for the new one to come in. I replaced it and a month later, the fuel pump went bad. After running it in high speed mode for that week till a month later when it died, the fuel pump sounded louder than usual.

i told you you do jorge lol....my word isnt good enough

In reality the 3800 V6 SC engine seldom uses nor requires the full 55psi fuel pressure under most circumstances in all normal driving. If you run it with the resistor bypassed it actually runs dirty, worse, more roughy and at reduced power and fuel efficiency. The problem with all wide range fuel injection systems is one of dynamic control.

Stop and think about it. A fuel injector is simply a small electromagnetically activated "fuel-squrter" solenoid valve. It does not use a spring to close it, the fuel's pressure does. This fact means higher fuel pressures also make it more prone to stick or to open slowly, too. The exact amount of fuel it injects (open timings) is thus the product of three variable factors:

The current fuel pressure at the rail (including help from intake-stroke cylinder vacuum)
The length of the timing of the "on" pulse controlling it (managed by O₂ sensing/calculations of ECM)
The voltage/current available to power the valve (DC voltage regulation)

The third factor is the least issue, since a properly sized coil-solenoid combo will behave right under most power (and normal load and lubrication) conditions. The most important then, are the first two.

Aside from cylinder wear/piston-ring or valve issues, cylinder intake vacuum is pretty much a constant value, though oil type and condition may improve or worsen it, it is generally unaffected by mere speed/rpm. Any actual longer-term physical cylinder compression/vacuum changes would be gradual and/or minor in nature, and most such small or bigger, dynamic engine vacuum-load changes can be compensated for dynamically in operation by the mechanical regulator, or the ECM's air flow, O₂ detection and "tweaking" of the fuel trim values. Since the ECM cannot undo what it has done, it must make it's timing calculations, + or - adjustments and decisions ahead of time, for each cylinder, every four strokes, based upon estimates it can tweak from "fuel trim" tables pre-programmed and stored within it. The largest single other (externally controlled) variable factor that affects this pre-calculation "guesswork" is the current fuel pressure. Unfortunately mechanical fuel pressure regulation valves have a limited range of functionality, especially when you want to be able to adjust their pressure-output set-points "automatically".

This engine employs two methods to control fuel rail pressures.

The first and biggest (coarse) one is controlled by the high-low fuel pump pressure relay. It comes on almost immediately after start-up and stays on most the time unless the engine is in supercharged boost-phase (throttled out) mode or running over 3500 RPM, where fuel demands will soar. This high/low pump speed control drops/changes the fuel pressure/flow by about 20%. What is happening here is a sudden. sharp drop (or rise) from 55 psi to 44 psi, created by adding a 1.1 ohm 35 watt resistor into the 14 vdc fuel pump motor circuit, which suddenly and abruptly drops the pump's voltage to around 10-11 volts. The pump speed relay thus causes a severe and abrupt change in fuel pressure which the ECM always "assumes" is happening and quickly tries to compensate for. This means it will always immediately begin to squirt more gas when it turns the low pressure relay on and only (maybe later on) try to squirt (somewhat) less gas after (or if) it (later) "sees" some bad (O₂) results from the exhaust sensors

The other (fine) more dynamic and graceful "mechanical" automatic fuel pressure regulation valve controls a somewhat smaller 15% (or so) range of pressure irregularities. It's ever-present mechanical "further attenuation" functions rely upon general intake manifold vacuum (an all-important engine load indication somewhat hampered by all the air hoses' integrities, not to mention steering and brake system vacuum-demand fluctuations) to further "hold back" excessive fuel pressure, (thus increasing fuel pump motor loads) releasing more fuel pressure into the injector rails as vacuum decreases, in a sort of a dynamic-demand adjusting "balancing act". This means that at idle under no load your engine can run on as little as 36 psi of fuel pressure, though it always uses 55 psi to start, race like a banshee or belatedly attempt to recover from a stall.

So, if your fuel pump is running on "high" all the time the engine will seem to work, but not actually hardly ever be "working right" at all. With no (a shorted) fuel pump resistor you are imposing massive pressure burdens on the regulator the pump and the injectors, and fooling the ECM into wasting gas. (most people do not remove and bypass the relay so the ECM knows it's not there/malfunctioning.)

Now, let's consider the high pressure fuel pump and it's electric motor like any other appliance. This is a very continuously hard working tool that (at full power) consumes about 80 watts, and like any electric tool it has to be well-powered, thermally protected and fused correctly to prevent overheating and/or catastrophic burn-outs. The biggest load problems it is likely to encounter in it's well filtered liquid hard-pumping existence are sludge (blocking it or it's intake capillary sponges), excessive load pressures/blocked lines (or upstream fuel filters), chronic low RPM drivers and poor DC power conditions that may overheat it, it's connections or wiring. Like any power tool you never want to run it on something like an old, cheap, worn-out 100 foot extension cord, right? -- Wrong. -- GM does exactly this by using the "speed" resistor!

Let's consider an electric table saw as an example.

Most of them run on about 5 amps and also consume about 10 amps to start-up with a full, strong 115 volt power source. Once a table saw motor is running at full rpm it's high-power "starter coil" turns off. When it's blade is cutting or cutting harder, the lower current induction winding draws more current producing more heat and assuming a good 115 volts, when cutting really, really hard, or during a stall, it can draw over 15 amps, quickly blowing the fuse or circuit breaker. Inside the motor it has a thermal protector that based upon standard rate of rise and heat dissipation assumptions, cuts out at a certain temperature from which it is assumed the motor can, later, safely cool down from, enabling it to run again later if it fails to blow the fuse. The engineer knew how long the motor could sustain using 14.5 amps without permanent damage and at what temperature point it would need to be heat-protected

What people fail to understand is that fuses and circuit breakers are not current (ampere) sensitive, they are wattage (voltage X current) sensitive. If you use a 100 foot extension cord you will only be running it with 100 volts, due to line-losses. This means (at lowered rpm) it could draw 13-14 amps to start, and 7 or 8 amps just to run with no load. Unfortunately these things blow no fuse, far, far away, back at the 115 volt source where the fuse box is. In fact because the extension cord is also heating up, the fuse thinks it's using less power (overall wattage), and probably won't even blow even when the motor is drawing 16 or 17 amps @ (only) 90 volts (since the whole long cord has also heated up). Current (amperes) is what produces heat in a motor winding, thus the stored heat-floor (standing operating temperature) in an underpowered tool can be far higher than it would be at full power (lower current and higher voltage) with full rpm running it's rotor's cooling fan. The tool's thermal protection is also fooled because it assumed a faster rate of rise on the coil temperature and a cooler motor chassis to cool the coil down later. These reasons are why it's easy to blow or burn out a power tool with low power due to a long or bad extension cord.

A fuel pump resistor then, is like a bad extension cord that should have a much smaller fuse on itself to protect the motor from overheating under any heavy load. It seems that GM neglected to use a durable DALE-type high power ouside wound ceramic heat sinked power resistor with a secondary 8 amp fuse for safe low power fuel pump operation, electing to use the (now unreliable) slim-wound ceramic-potted TRW type resistor itself as the "secondary" low-voltage operation "fuse". This is why they "blow".

So after a bit of experimenting (including a rather complicated 2n3055 based adjustable current-sensing cathode-followr bypass regulator I scrapped) after I had to replace my fuel pump a few years back I came up with a simpler solution. It seems that a $2.00 12VDC 75Watt MR16 quartz halogen track lighting bulb is the best and a nearly ideal replacement for the not so cheap huge $30-40 TRW ceramic encased thin-wound fuel pump resistor/fuse thingy that so often blows out leaving you stranded on the highway when the fuel pump gets overburdened while running at low pressure.

A sealed 12v quartz halogen bulb just goes full brightness (and lower current) whenever/if ever the fuel pump motor stalls at low speed, and restarting the engine will clear the blockage with full power to the pump motor. (it also doubles as a nice fairly useful engine compartment light that informs you of valid low fuel pressure pumping mode) When the quartz halogen is functioning in resistor (low fuel pump power) mode it simply, slowly, glows-up to cool soft yellow and cherry red, (10 watt brightness) rather than fully incandescing, and it also has much higher cold resistance (.65 ohm) giving a more gradual and gracefully delayed fuel pressure drop which the mechanical vacuum fuel pressure regulator handles more gracefully. Unlike a resistor that stays at the same power the lamp's power sharing not only ramps down gracefully upon warmup, but varies with loads, so that if the pump encounters problems the lamp will just get brighter and actually draw less current, lowering pump power further. Once the pump draws less current the lamp cools supplying it with more power.

Halogen lamps exhibit three modes; a (usually very quick) high inrush current "start-up", a (also usually brief) "warm-up" mode (which we use here, constantly) and then (highest temperature, lowest rsistance) "operating" mode. Each phase draws different, progressively diminishing currents. It thus shares power with the fuel pump in three ways, providing a 1/2 second "graceful power down" pressure drop, a constant "passive warmed-mode" steady resistance and finally, if needed, an "activated hot mode" further power reduction under overloading of the pump motor. So basically this one component provides the best of most worlds, "sinking" excess current and heat from the pump and allowing it to "wander around" as needed while still short of being an entirely acceptable substitute for a smaller fuse that we should also be insisting upon.

It also provides for a bit lower than stock low-fuel-pressures, meaning quicker, more accurate injection, broader trim control range and better mileage.

So the alternatives are three:

Buy another primitive $40 TRW fuse-resistor thingy from a GM dealer because most parts places can't and won't warranty them.

Buy a better quality DALE type resistor with integral heat sink but be sure* to add an additional, smaller 10 amp fuse.

Buy a $2 MR16 75 W, 12 V quartz halogen bulb at a dollar store and a socket for it from Home Depot. For absolute safety* augment it with a 12 v inline automotive minifuse holder and a 10 amp minifuse from Walmart for $5 more.

(*the standard factory-GM wiring circuits generally provide only one 20 amp fuse for both power modes, which never blows, because the low power mode is always when the fuel pump dies)

Unlike the undependable original TRW potted-ceramic $40 resistor-fuse thingy, the 75 Watt bulb will last you indefinitely (at 10 Watts), can be found in most dollar stores and only costs you $2 to replace. If it ever goes on you, you can quickly get the engine going again with a bypass switch or single, bared-wire twist-tie...

I've been using mine for 6 years now, on my 2000 GTP - it works like a charm and great under the hood light for adding washer fluid on the highway at night, GM even included enough cable on the old resistor harness to put it anywhere you like. You can also just crimp and heatshrink-tube some standard spade lug clips to hold on tightly to the two bulb pins if you (like me) don't feel like buying an official MR16 socket, since it doesn't ever run as hot as a 75 watt recessed pot-lamp would.

The car runs better (seems like much better torque) and gets better mileage with it than with an original OEM resistor. I tried both, and the lamp definitely seems to provide an uncanny boost to the low end power, smoother all-out acceleration and deceleration and an additional small boost to the mileage.

What I like most about it, by running really lean, is it makes it easier to tell exactly when to add a fuel injector treatment, since the engine idles just a wee bit less smoothly with lowest fuel pressures upon a cold start. As it was before I could never tell when/if they were getting dirty.

^^^awesome read. Any pics of the bulb thibg

Android Fire

Agent...you have a lot of good knowledge there, however I feel you make it much more complicated than it needs to be.

The pressure regulator will keep the car at the proper fuel pressure with the pump in high speed mode. The pressure increase we see with throttle from the regulator doing it's job. Let's keep in mind that the pump has nothing to do with pressure if the supply and ability to bleed off the excess supply are adequate.

Pumps and saws are designed to run at a certain voltage. When running higher or lower they will work harder and cause excess heat etc. One of the items I didn't see you mention is that your extension cord is not adequately supplying the power to the saw, because the cord is undersized, like stock W body wiring.

Injector sizing has a lot to do with how a motor runs. You can get a much better running car from the right sized injector that will have a higher duty cycle and atomize fuel versus a large injector running a low duty cycle that can not atomize as well

Very cool to hear about the bulb, interesting to see how you thought outside of the box.