Recently I discovered that my 1999 C5’s stalling issue is caused by low fuel pressure. The mechanic suggested that I get a new fuel pump. Does any have any suggestions on which fuel pump I should buy?

 

I think your mechanic should do a voltage drop check on your fuel pump circuit…it may not be getting good power or ground…when was your filter changed last ??…he should also see how many amps the pump is drawing…without testing he is just guessing !!

 

Its really rare for a fuel pump to produce low pressure. usually they just stop working. Sounds like more investigation is needed.

Low pressure can be caused by a few things
1. bad or stuck fuel regulator
2. internal tank pressure hose leaking rupture
3. no fuel in the tank
4. fuel sock damage / clogged / related
5. Clogged fuel filters (Some cars have two of them , one by the engine and one by the tank, and there is also a sock in the tank #4)

Additionally the quality and robustness of the electrical connections, relays, fuse, the pump attached wires, wire diameter, age, birttleness, grounding, etc... all influence potential changes in pump output

And finally, care must be taken when measuring any pressure, that you verify the pressure measurement is accurate. For example using a high quality mechanical pressure tester gauge is desired. A cheap , rented, used gauge can easily give incorrect results. Also electrical gauges can be way off depending on situational.

So,
A. ensure measurement is done correctly, verify the fuel pressure using quality mechanical gauge
B. perform return line based tests, e.g. clamp the return line to see what fuel pressure does increase, indicating poor regulator performance
C. inspect the wiring and electrical conditions, consider replacing any wiring that looks old or brittle or thin, measure the voltage at the fuel pump and compare with alternator output voltage
D. Finally if the regulator seems to be working, and pressure is verifiably low, and the voltage at the pump is good and wiring is good, fuel filters are replaced, then, inspection of the pump and associated pump filtering inside the tank and it's lines (inspect feed line and fuel sock basically) and the wires that extend into the tank to the pump itself, and if everything is good then maybe just maybe the pump really is bad.

I've seen them fail like that before, but its just rare is all
I remember the walbro in my sr swapped car did that once, fuel pressure just dropped to like 20psi, i jacked up the fuel flow to the injectors to make it home

 

So I bought the car 4 weeks ago and have no idea if the filter has been changed.

All I know is that the fuel pressure drops from 58-35 while the car is idling.

thank you for the suggestions on fuel pump circuit. I don’t think they checked that.

 

So I just changed the battery and that helped the car run and not stall for the first time. So maybe the problem is electrical. I did hear a little screeching noise from the rear of the car, so I assumed that was confirmation that the fuel pump was going bad.

but thank you for sending this over.

 

Yes, you’d want to do a voltage drop check just to make sure the wiring is OK…the pump draws about 5-6 amps…if your mechanic doesn’t know how to test this he should be selling hot dogs and not diagnosing cars…just don’t want you to change the pump and have the same problem.

 

Even if the pump was getting 9.5v it would still produce 60psi at idle i would think

In fact thats kinda how PWM control works at the end of the day, the total sum or area under the curve of time spent *on* adds up some voltage less than system total

1995-02 Toyota Supra has a very powerful fuel pump that perhaps the engineers felt would overheat the fuel or wear and tear excessively if run full voltage all time so there is a module that drops the pump to I think around 10v for idle and cruise

The issue in this case with electrical is the heat and danger produced by brittle damaged connectors so it is absolutely 100% necessary to check and indeed on the list I posted for that reason regardless of voltage as measured

 

The C5 fuel pump is not PWM if that is what you’re saying…there is no fuel pump control module.

 

Oh dear, of course not. Neither does the Supra, it just drops voltage there is no PWM. That wasn't what I meant. What I'm really doing is some kind of statistics. The customer stated fuel pump is still working, so there is some electrical connection for sure intact somehow. Now probability wise, lets say its all corroded and melted and this is causing voltage to drop 9V at the pump. Well, it would still be able to produce 60psi at idle I think, there is high probability. So the electrical wiring is not a likely failure point for this issue, and he hasn't mentioned any burning smell or plastic melting or anything that I would expect from that type of impending failure which increases probability further however little. To put that into perspective I merely used PWM as an example... and the Toyota as a realistic application for what I am suggesting is possible...

 

Would it be wise to purchase a whole new housing? I spoke with the shop and they said since the car 26yrs you might as well replace the whole housing to play it safe, as well as getting a new fuel filter.

 

Step1: Diagnose problem

You are asking me about changing a part and performing invasive surgery which may be extra-difficult due to the design of the specific vehicle (e.g. Corvette, vs say a Corolla or something easier to work on the fuel tank area)

I cannot recommend any parts shotgun without having more information, I have no idea what is wrong
You could wind up changing all the fuel system stuff and find out the problem is a fuse or wire somewhere getting hot
Or a cable isn't grounded well somewhere because it corroded (C5 Diag I believe suggested inspecting wiring - what is the result of this? Take pictures of wires and pump parts if you don't know what you are looking at )
Or maybe the pump is clogging up because of debris in the fuel tank (take pictures or look inside the fuel tank can be very difficult) You need some kind of evidence that these things are happening, the sock will show evidence for example of filth and debris since as you point out its old and could be contaminated.

All of that aside, I Agree that yes if you decide to actually go into the fuel tank and mess with the pump/wires/hoses/canister(housing) etc...
That absolutely you should replace all of that if it is within budget for general maintenance, of course its a good idea as long as the parts are OEM Authentic (not ebay or amazon) and that the quality has not degraded over time (Difficult to tell ... Search other individuals who have used the OEM Replacement to see if they complain about the quality of the 'new' parts)
Thus in theory it can be a great idea for maint. to change all these aged parts, but sometimes, as especially with OEM Axles, injectors, regulators, plastics/intakes, exhaust, etc.... the Original parts from the Original vehicle can be far more robust and valuable than anything 'new' even if its OEM due to concerns over quality over time
slippy slope for advice on a forum, it goes beyond common or practical maintenance and borders into data recovery and investigation/research

 

If you determine the pump is bad. We had luck with a Carter drop in pump assembly.

 

I 100% agree with checking out the grounds, voltage and wiring before replacing the pump, and I’m going to have my mechanic take a look at the things you mentioned.

the only reason why I asked about the fuel pump is due to the mechanic’s suggested due to the age of the car and the noise that is coming from left side rear. It’s in my budget to replace the pump and would like to get a nice pump that could handle low boost in the future.

thank you for your insight and advice on the type of fuel pump too. I wasn’t able to find an exact OEM pump for a 99 but I found a OE pump from Carter that seems solid.

 

Thank you for the reply. I just got the Carter fuel pump and was wondering if anyone has had issues with it. Seems like a nice assembly, how long have you had your Carter pump on the car?

 

What you need to decide on a pump setup in terms of performance, it is very important to get a pressure:voltage:amps data, like this



You mentioned 'boost later'. I specialize in forced induction daily drivers and that is essentially what you are getting towards.
To maintain reliability you need to compare fuel flow capability at low voltage, say 12.5volts, plus age/wear and friction losses due to hose diameter and length, to total desired brake horsepower maximum.

For example, if you wanted say 500rwhp dynojet, through a 4l60e and typical tires/rotating parts assuming 15% drivetrain losses is around 590bhp (590*.85=501rwhp)
590 brake horsepower with a Brake specific fuel consumption of .58 to .63 (take worst case scenario) on gasoline, or more like .75 on alcohol fuels,

Brake specific fuel consumption or BSFC is a conversion ratio of power to fuel consumption.
With Gasoline fuel density around 6.2lb/gal
Fuel Flow in Gallons/Hour = (BHP * BSFC) / Fuel Density
The units are (HP * lb/HP*hr) / (lb/gal) , which leaves gal/hr
For 590Brake Horsepower at a 0.63 gasoline forced induction BSFC take 590*.63 = 371lb/hr
now use fuel density to get gal/hr, 371lb/hr/6.2lb/gal = 59.9gal/hour
1gal = 3.785Liters
60gal/hour*3.785 = 227Liters Per Hour = 227LPH

Now lets look at a popular pump diagram and make observations

In forced induction we always strongly desire/need a rising rate external fuel pressure regulator in the engine bay in front of the fire wall, generally near the engine or strut tower on some kind of vibration resistant perch and protected from filth,debris,grit somehow.
If you plan to add boost at any point this means you should prioritize an external fuel pressure regulator as soon as feasible.
Unless you only plan to run a few psi e.g. 4psi to 7psi for a mild boost to the stock engine, that would be okay without a rising rate external regulator I bet.
Anyways. Most people want to run at least 1bar or 15psi of boost.
For every 1 psi of boost you add to the engine, you lose 1 psi of fuel pressure. Therefore a rising rate regulator will be needed to maintain fuel flow properly for most forced induction applications running serious boost 15+ psi.
If the base fuel system pressure is say, 60psi, and we add 15psi of boost pressure, now we are around 75psi of fuel pressure.
Look at the chart for the popular 340LPH Aeromotive and notice that it can barely produce 225LPH at 75psi of fuel pressure, and that is with 13.5V supply constant.
Next, keep in mind this is before friction, age, and any internal leaking and minor component losses of the fuel system. These parasites will take or tax approx 5 to 10LPH easily.
So we are already under fueled to start with.
Next, the voltage cannot stay at 13.5V. One day, the alternator WILL quit or have a spaz moment. You can NEVER trust alternator voltage to keep an engine alive.
Therefore this chart is entirely incorrect for our purposes because it does not show up 12V operating flow rate.
If we cannot find the correct chart, we instead must predict how far the fuel flow rate will drop instead.
Looking at the first chart, it looks like 12V will take around 20% of the fuel flow capacity from the pump in prime regions of flow. To be safe lets assume 23%.
Now, we could compare a bunch of fuel pumps and find one closely related to our pump of interest and use that data for a closer comparison. But this is just an example showing how you can keep your engine alive by addressing these issues before you buy a single part, you can plan every thing with some calculations. I specialize in this and will guide you through it
Lets do some safety factor maths now,
At 13.5V the chart claims 75psi is 235LPH~
Subtract 10~ LPH for friction and age/wear over the next 10 years (that is how long a quality pump like Aeromotive 340LPH Stealth will last , its about 2,000run hours, if you protect it correctly)
that leaves 225LPH, next take off 23%~ or so for 12V system voltage
225*.23 = 51~
Leaving us only (225 - 51) = 174LPH of fuel flow

This is one way to lose an engine by losing a cable or alternator, suddenly 10 or 20% of your fuel pump is just gone in an instant.
To keep this from happening, you need a pump that can support the engine at 12v or near 12v, say 12.5 to 13v is fine. We don't have to focus on 12.000v exactly. It depends on the nature of the system and how we manage the other variables... With a quality wideband and adequate warning system, fuel pressure safety switching from a stand-alone computer, and relatively low boost (12-15psi ranges) then alternator failure is less likely to toast the engine and we can relax some of the concerns over voltage in the long run.

moving on, lets summarize the problems and then explore some solutions
-The main problem is, performing fuel pump and fuel system changes is costly and time consuming. Lets avoid this problem by only doing it one time, correctly.
-If you plan forced induction with 8+psi of boost a rising rate regulator and return fuel line would likely be required. You should research how to accomplish this for your chassis.
-You may need to run additional return fuel line if your chassis is returnless with only a single line. I recommend hard line, not braided hose, for reliability. Riv-nuts holding OEM-style fuel line brackets which are holding 3/8" Hard line bent to perfection is ideal for up to about 900rwhp gasoline/E85 application daily driver, which can be achieved using a mostly factory 05' L33 engine fwiw for 200,000 miles when setup correctly using a turbocharger.
It is possible to use 5/16" fuel line up to about 800rwhp gasoline as well , but alcohol will be starting to push pressure losses and fuel velocity based friction
-Fuel pump flow needs to be able to support the highest power output with the worst BSFC at the lowest voltage and highest fuel temperature (fuel temp changes fuel density and it becomes significant when we compare say 70*F gasoline with 100*F gasoline, it can shift the Air Fuel Ratio by 0.5 to 1 whole point sometimes)

Now, I will share two key tuning knowledge to make most of these issues dissipate
1. Fuel pumps flow more fuel when fuel pressure is set lower and lower. For 25 years I've used a baseline fuel pressure of 32 to 38psi. With a referenced regulator this generally drops near 25 or 26psi during idle and cruise, which allows the fuel injectors to have a nice long pulse which can help deliver precise fuel at low speed conditions when using a very large fuel injector. This will make idle tuning much easier, and that is only the beginning. Using low fuel pressure will reduce fuel system stress, just like with blood pressure, everything will last longer. It will also reduce the amount of fuel heating (fuel pumps, all pumps, add heat to their fluids) that takes place, which helps slow down the fuel density swing during heat soaking conditions every daily driver goes through. Lower fuel pressure also will reduce the current draw and subsequent heating of the wiring and resulting voltage drop at the fuel pump, keeping it cooler and using less current at low pressure.
If we set the base pressure say, 35psi, then adding +18psi of boost will push that to 35+18 = 53~psi of fuel pressure. Look now at the 340LPH Pump chart, 53psi,
We have about 310LPH to play with. Now do the thing from before knock off 10 and then 23%, 310 - 10 = 300*.23 = 70 so 300-70 = 230LPH!
And this is a kind of , worst case scenario. I have tuned 600rwhp (about 750BHP) out of an aeromotive stealth 340LPH Pump with 5/16" Fuel line on Gasoline E10 fuels and taken the vehicle over 50,000 miles since. But I also run the voltage around 13.0v not 12.0v. Remember we are looking at 12.0V for that 23% loss, when in reality a healthy battery will produce around 12.85 to 13.05v when surface charged on a running vehicle with a recent alternator failure, that could drop to maybe 12.45v to 12.75v for a while, it probably won't immediately go to 12.000volts at least not for a few minutes. My ECU has a PWM control for alternator which allows me to target any system voltage during wide open throttle and you want the system voltage to be set at battery level for truly powerful setups with delicate engines, say stock engine 800rwhp setups I frequently like to tune. This ensures that we always have good fuel flow no matter what the alternator does and helps stable all electronics , taking out the subtle variations in the voltage wave form produced by noisy electronics at wide open throttle. In other words, tuning the vehicle to drop into battery voltage (13.0v~) at wide open throttle aka alternator 'cut-off' switch, is a a good way to tune the vehicle to ensure it can never suffer a sudden decrease in fuel flow due to voltage.
2. Use the largest quality injector possible around twice the required size. For example, if we need 371lb/hr of fuel (using this number from earlier above) thats 371/8 = 46lb/hr for a V8 engine. We take that number, bump it up by about 20% first, (46*.2 = 9.2) 46+9.2 = ~55lb/hr and then double it: 100 to 110lb/hr fuel injectors are ideal. Remember we came to 371lb/hr fuel for .63BSFC gasoline E10 forced inducted above earlier.
A 1050CC/min to 1200CC/min injector would be ideal here because it will give us a duty cycle of 15 to 30% for mid-range torque of a forced inducted engine, which means we can time the fuel injector on E10 especially to spray between ~285* to 230* before top dead center compression (BTDCC). This is a tuning strategy to get fuel into port injection engines after the exhaust valve has closed and during peak piston velocity which can dramatically improve cylinder filling thanks to input kinetic energy timed with the inducted fluid momentum (air is a fluid). And it will reduce 'trailer hitching' behaviors which feels like slight misfiring during a cruise, for v8 engines timed to inject fuel near overlap condition as with OEM injection timing and camshaft upgrades, which do not mix well, they need re-tuning.
This large size fuel injector will also allow us to really drop that fuel pressure down nice and low and still be able to deliver the fuel at wide open throttle. Thus, it serves multiple important purposes, everything from idle to mid-range torque tuning hangs on the size of the injector, having quality double sized high impedance fuel injectors are key to daily driver performance applications with mostly stock engines.

Summary
-The fuel system, if necessary for any upgrades, needs to plan for worst case lowest voltage, highest temperature, years of wear/age, and the highest boost pressure and fuel system pressure it will ever be expected to see, and maybe just a little higher than that.
-You will absolutely need a wideband for any forced induction, large injectors, and a return style fuel system with a referenced regulator.
-After the fuel system is finished the ECU will need tuning for the new pressure and larger injectors, injector timing will also need adjustment for any camshaft upgrade
-Strongly recommend delete the maf sensor when going forced induction for many reason (ask if you wish for another long description of every issue with maf)
The engine can run just fine with MAP Sensor only, it just takes more effort so people don't like to do it for you low cost, perhaps learn to tune yourself
-I do recommend camshaft, springs, hard thicker pushrods, however the camshaft must be LOW LIFT near the factory lift, no more than say .550~ perhaps .570" at most for these type of LS engines around 01-07. The cam ramp lobe needs to be 'slow' for example TFS-30602001 has a very slow ramp for an early LS style engine, very gentle on the valves is the key. You don't want lift or fast ramps, just longer duration to hold the valve open much longer is fine for 800-1000rwhp with a cam like TFS30602001, it doesn't take much.
-Dead head fuel rail can still be used on E10 gasoline, 5/16"+ fuel line up to 600rwhp I tested it , works great with engine bay regulator at 34psi fuel pressure baseline on LS1/2/6 style engines. This information is very important for you because I am confirming that you can use the original OEM fuel rails and OEM intake manifolds for the 600rwhp target. Part of making a reliable fuel system is keeping it simple, and less fittings and less fuel rail 'holes' (places where fittings go and can leak) is less places to leak, its that simple.
-Consider using Hose clamps on braided hose (is track legal) instead of AN fittings when adding fuel lines. Hose clamps are faster and easier to deal with in my opinion and tend to be more reliable in longevity applications, if only due to the nature of cheap AN fittings which often have some compatibility issues when they are very cheap. If you can afford to get the full set of EARLS or AEROQUIP AN fittings from a authentic distributor then that would be fine, but its going to rise the price of the fuel system from $2 hose clamps to $50 fittings each.


I know I write a lot but this information can help more than just one person and will stand the test of time here on the forum for future searching and I can even reference it in the future so I don't have to write it again.

 

My reply was for an OEM replacement and the pump has been in since 2019 with a cam only now 455rwhp heads and cam that has run multiple HPDE days in Georgia on Road Atlanta.

If you are going for boost and think you'll need more than factory with maybe a boost a pump then you'd need to spec the pump accordingly.

 

Wow, thank you for the detailed response. So, what would you recommend for a fuel system setup if my Hp goal is 550whp? I know the A&A supercharger kit comes with 60lb injectors and a boost a pump, but base on your calculations I'm unsure if the stock pump will be enough.

These are current mods on the car:

• Cam motion cam but specs are unknown (will most likely replace)
• fully renewed stock heads with LS7 lifters
• upgraded trunnions and hardened pushrods specs unknown since they were on the car when I purchased it.
• Oversized Front Oil Cooler Radiator System
• Rear Differential Cooler with Secondary Fan
• K&N Ram Air Filter System
• Oil Catch Can
• NGK TR6 spark plugs
• AEM wideband AFR gage
• Kooks Headers with Green Cats and Hooker Black heart Exhaust

 

So you got an GM OEM replacement instead of a Carter fuel pump? Sorry, I just wanted to confirm what you meant.

Also thank you for the boost advice, seems like I'll need to do a serious upgrade to the system to run boost.

 

99 was a strange year for computers of the LS engine. I'm familiar with -97 and 01+ but the 98 and 99 computers, I don't touch them. That may be your largest hurdle to having a traditionally reliable setup. Normally you would just upgrade to a 2-bar OS HPtuners and go. It should be possible with the 99 computer. Here is a post I found about the 98 computer, and you'd want to be sure you have a 99 computer or what it is exactly so it can upgrade the OS I bet.

https://ls1tech.com/forums/pcm-diagn...l#post11774169


With the ECU upgraded to 2-bar, it will read boost pressure up to around 15psi, giving you plenty of headroom to achieve 500 or possible 550rwhp with a 5.7L and mild/little modifications.
There may also be some other piggyback solutions available depending on the year and work arounds, but the most reliable way is generally to stick with the OEM computer and if possible upgrade the OS or even switch to a newer computer somehow. Maintain torque management if its automatic. The transmission if auto is a whole other issue at that level as well but I get the feeling you are 6-speed since it didnt even come up.

Lets discuss the fuel system now
500 to 550rwhp is right in the range where, there are many different ways to achieve that kind of fueling without doing too much work, and some more work but more reliable.
I'm going to list some ways people have done this, these are not recommendations they are only examples of methods you will find to meet this goal. After I will break down the pros and cons.
1. Stockish fuel system + boost-a-pump + large injectors
2. 340lph pump + returnline/regulator + large injectors
3. Stockish fuel system + Methanol injection + large injectors
Optionals:
A. water injection
B. Double size injectors, e.g. ~120lb instead of 60lb
C. PWM fuel pump controller
Requirement for gasoline fuel: Intercooling at the front of the vehicle, 10.8 to 11:1 air fuel ratio, 112*F iat maximum recommended, approx 12.5 to 13.5*btdc ignition timing

General tuning target for reliability:
~520rwhp mark at say 13 to 15.5psi of boost, 12.5* +/-0.5* of timing, 10.8 to 11:1 gasoline dynojet afr, 112*F IAT max, 9:1 to 9.5:1 compression max, less than 6,000rpm

Lets talk pros and cons
1. Boost a pumps are popular, and they work. The fuel pump lifespan is only slightly affected I think, its not bad. This is a great option to avoid opening the fuel system just to add a little fuel pump boost for a hundred extra HP or whatever.
My opinion is, I do not like them, they are not a truly reliable solution IMO. At any time the voltage boost could fail and the engine is toast. It depends how expensive the engine is, I guess, and how much work you are able to do replacing it quickly, and how robust the electrical support for the fuel system is, like how well you are in tune with the fuel system's requirements and able to observe and maintain and upgrade wires and feel connectors for getting hot and monitoring voltage drop and fuel heating etc... The more careful type of observations you are able to maintain the boost-a-pump system the more potentially reliable and long-term sort of solution it could become. But usually this is for people looking to avoid opening their fuel tank, which you seem like you are about to do, so I do not see the point of purposefully installing a too-small under sized fuel pump and then boosting it, why not just install the correct fuel pump in the first place?
Result: Boost a pump is not desirable for your situation IMO

2. This is the system we already discussed, appropriately sized fuel pump with large enough injectors and a return line and reference. Low fuel pressure as possible.
This is standard forced induction, ideal, reliable, factory setup stuff, its how you would get the vehicle if you bought it with boost. Its how all the skylines supras silvias rx7s etc... factory boost are setup and still running today same engines 30 years later 200hp/liter sometimes. This is how I've done countless vehicles for 25 years.
Advice doing it this way if possible

3. Methanol injection is a powerful octane booster and enough of it will supplement the fuel supply from a too-small pump if needed. Methanol injection would be an ideal supplemental fuel supply if the systems were actually reliable, but unfortunetely the methanol injection systems have frequently, historically, been an engine catastrophic failure for anyone thats become meth dependent and then had the delivery of methanol cut off for whatever reason. People have run it dry, had a leak, had a clog. The pumps themselves are wear items that needs replacment intervals, you have to change the pump before it fails routinely. On top of that, methanol turns to formaldehyde when it contacts human Alcohol dehydrogenase enzymes, which means if you get any on you are basically cross linking proteins and facilitating carcinogenesis. You don't want to breath the fumes because it will cross link proteins in your lungs. It is extremely toxic we use methanol for tissue fixation in my lab, it turns tissue to a sculpture preserved like embalming fluid. And to top all of that off it is explosive, it can collect as a gas from a tiny leak and suddenly explode under the hood. And it burns with an invisible flame so if there is a fire you can't even see it.
While methanol offers substantial performance boosting potential, it is not for the faint of heart and not recommended for reliable daily driver applications.
Advice: avoid methanol completely

I'm out of time rn but I will come back to discuss the PWM, over-size injectors, water injection, and some other fuel system related shenanigans optional perhaps i will think of even more , been doing this for a loooong time

 

I’m definitely leaning towards the 2nd option. I don’t want to take any chances with fuel starvation, and I’m even open to using a single-pump secondary fuel system.

Currently, I have two fuel pumps available for installation: an OE Carter with an assembly and an AEM 50-1000 340lph pump. I’m assuming the AEM will be my best option if I can get it to work. After that, I’ll look into upgrading to 120lb injectors.

I’m also running a 4L60E auto, which is the main reason why I’m planning to run low boost for now.

I have a solid local tuner who I believe has experience with 98 & 99 models, so my hope is they can help with removing the MAF setup on the car.