Installing new engine and converting it from carb to TPI. Have the injectors (Bosch III) and fuel rail installed and did a pressure test. Using a power probe to run the fuel pump, system immediately builds pressure - I set my AFPR to 47 psi. When I remove the 12v from the fuel pump relay, the pressure begins dropping fairly quickly, ending up around 10 psi. I did not see any leaks in the lines from the tank to the intake.

The fuel pump is a Deutschewerks 200.

Is the drop off in fuel pressure when the pump is not powered normal? Did some checking here on TGO and it sounds that the factory fuel pumps had a check valve while aftermarket ones do not.

Any guidance would be much appreciated! Don't want to keep assembling the intake if there are problems somewhere.

 

What happens when you pinch the return line? I'm assuming the schrader valve is before the fpr, so the fpr should be holding pressure there. Also, what brand afpr are you using?

Further conjecture: 43.5psi is factory spec. 47 is the recommendation in Holley's paper that is shipped with their afpr. I think the idea there was to bump the pressure for a safer nitrous hit, and if you're running just a normal n/a deal, 43.5psi is more appropriate. I ran my system both ways, found no improvement at 47, and ended up settling on 43.5psi.

 

Your pressure regulator is most likely leaking fuel back into the tank.

 

The pump should have a check valve. Reg probably just leaking off down to 10 psi. Honestly dont think its a concern as long as pressure rises quickly on key on priming and cranking, and is controlled at set point through operation.

 

in general,
1. as with any fluid system the lowest pressure possible is generally the least wear/stress on the system overall. This goes for blood, oil, air, fuel, etc
Ex. I run my fuel systems at 34-38psi of baseline fuel pressure, with 1000cc injectors in V8 application this is good for approx 800rwhp even mixed with Alcohol fuel.

If you are not able to tune the system yourself, you will need to initially use the default factory fuel pressure setting of approx 44~psi
From there, using a wideband, you can add or subtract pressure if needed to fine tune the entire a/f curve without any computer based tuning efforts.
Setting a custom fuel pressure to match your engine's needs is part of tuning the entire setup. Tuning just means adjusting as needed; for example tuning the suspension. It doesn't always have to do with electronic controls.

2. Fuel drainback through the fuel pump or fuel regulator is common and nothing to worry about, as long as it isn't leaking out through an injector. You may wish to test where the fuel leaking is happening to ensure it isn't one of the fuel injectors. Fuel systems that hold pressure are simply easier to prime before starting. If the fuel pressure drops off when the system is turned *off* then it will need to re-prime before starting. Pay close attention to the fuel pressure before cranking the engine; don't try to crank until you see the full fuel pressure build. Some systems will take longer than others to prime, and it may even become more difficult to fully prime as temperatures rise and heat soaking of fuel system components occurs. For example any tiny air pocket will expand when heated causing more fuel to leave the system and de-prime while off, causing extended cranking times if you are not aware of the low fuel pressure lack of prime.

 

Thanks guys! Really appreciate all the info. I powered up the pump this morning, then pinched off both the main and return lines. Pressure held fine, so I'm considering that as no leaky injectors at this point.

From what I've read above, I might back the fuel pressure back down to 41-42, then start tuning with my wideband and Autoprom for higher pressure if needed.

I've tuned my TBI system I installed in my Vette, but this will be my first TPI setup.

Thanks for the info!!

 

Something else I forgot to mention if you have old injectors, get them cleaned and flow tested, never rely on or install old/used injectors unless you have them cleaned first, especially used and especially if they sat,

good luck

 

I am currently guilty of both counts, used injectors that have sat for a few years at least. I have been troubled with that for awhile and should have sent them off before starting my conversion. Think I'll be calling South Bay on Monday about testing or buying a new set. No need for additional headaches.

 

People make too much of a deal with fuel pressure. Fuel tuning is done thru fuel control tables in the efi, whether thats ve table, a fuel mass table, pulse width table, or mass air flow parameters, or also some sort of enrichment factors. Fuel pressure is just for injector size imo. You can up pressure to get more out of too small injectors. Or turn pressure down to get too big injectors to work better at low pulsewidths. As long as they have enough to spray somewhat good patterns, which by oem standards seems like 38-58 psi is most common and well used. We have turbo guys running base pressure at 80-90 psi to make large injectors. As long as injector is rated for it, it doesnt matter. I just never liked tweaking fuel pressure as a method of tuning fuel when i have access to the actual controls in efi.

then again, if not tuning it yourself, sure you can get it running close enough with a wideband and a screw driver on the regulator lol

 

It might seem negligible or ridiculous, we are talking a very small percentage of efficiency and power on the table here in this topic of regulators.
However, in a setup overall, as a whole, every bit counts. I take my 1% extra cooling or power wherever I can get it safely, easily, if its truly free. 1% or whatever it is worth, is extra longevity, worth when its free to us.
very few snipes in efficiency and longevity are actually free, but the fuel pressure is a easy free way to gain these increments.

reasons to
Run the lowest fuel pressure possible with a referenced regulator because
1. Keeps fuel cooler
2. Pump will last longer
3. Pump flows the most fuel
4. Easier to idle tune large injectors
5. Takes stress off all fuel system components
6. Allows low base pressure to be adequate for boost setups
7. ____________________ <--- there has to be more


You throw all of that away by using high pressures unnecessarily or counter intuitively. Using high pressure instead of upgrading the injector for example, results with hotter fuel, less overall fuel pump flow, more strain on the pump and parts associated. And is completely avoidable when the system is designed properly.

sorry i get carried away this is one of my enjoyable hobbys, I should really be writing something about tissues

 

That is great info, thanks for taking the time to write it down! Terrific points and seem spot on. I need to swap out my #10 Phillips head for a hex bolt so I can turn it with upper plenum installed. I'm running Bosch III 19# injectors on a stock rebuild. No need to get crazy on FP.

Plus, anything that keeps the fuel pump running longer is a good thing in my book. Don't want to drop the tank again to swap that piece out again!

 

i dont disagree with the reasons but again, making a bigger deal out of it than necessary lol fuel heats up much more from heat soak in engine bay than pump. Its really a non issue. I run twin pumps 100% all time and dont see a heat issue. There really isnt a lot of stress on the system…its designed for it. Most pumps will outlast a performance motors maintenance schedule. As long as you are within design range, typically 30-60 psi, they will last. But yeah, getting away with the lowest pressure and smallest injectors typically works well.

 

Well it depends on the situation, future plans, level playing field, the necessity of economy, etc...
I appreciate you taking the time to read and respond so please take my response as a way of thanking you and hopefully having fruitful discussion topic.

There are times when its fine to throw away 1% or 2% efficiency
and there are times when that 1% can win a race (either by being faster or being more conservative with fuel and energy)

I get the feeling that we Americans with large V8 engines tend to be 'fat with overcompensation' - we take for granted blatant excess fuel/food use, we trash more than we should and just say 'its fine' to ourselves. Kind of a crude comparison which even I am guilty of, I hate to throw food away but it happens from time to time.

In an engineering sense, it could go both ways. An engineer can be 'sloppy' or extremely precise with decisions. For example say I am sizing a turbocharger for a setup. As a novice I might be tempted to go for the larger compressor with the huge center island and not really understanding what I am giving up in terms of spool or efficiency, economy, etc... Just concerned about the number and the turbo being large enough to do the job.
But as an efficiency connoisseur- especially in terms of engineering applications, there is a narrow range of turbo selections which will work superior to all other choices- despite the final resulting power figure to the tires being similar between those possible selections. Efficiency islands we are talking 1% here and 2% there- it may seem negligible to casual observers but it has a massive affect on area under the curve and even kinetic energy available during cruise and throttle transitional situation.

Now- when purchasing the turbo in question, the prices may be similar. In other words it might not cost extra $$ to get the 'perfect' turbo as opposed to one that just works.
In light of the effort vs cost of this situation, it makes sense to go with 'perfect as possible' since the difference in cost is negligible.
In other words, take your free lunchs wherever you can get them.

That thought plays out here entirely too well. It is essentially free to reduce fuel pressure and attach a reference to the system. Even if they only bring 1% extra longevity and 1% additional lifespan to some components, wasn't it worth the cost of being 'free'?


Here is some popular individuals weighing in their thoughts...

https://ls1tech.com/forums/forced-in...ml#post8866697

https://ls1tech.com/forums/forced-in...ml#post8867985

https://ls1tech.com/forums/forced-in...ml#post8930762
https://ls1tech.com/forums/forced-in...ml#post8863503

So lets recap. LOWER fuel temperature. REDUCE The stress on fuel pump and "make it happy". EASIER to tune idle and low rpm conditions. REDUCE Injector duty which keeps the driver board and injectors cooler, "happy".

There are MANY BENEFITS to reference regulators, low pressure setting, free gains is free

It ain't hot smoke

 

Lol again while its mostly true what you are saying, its a insignificant factor for the most part

heres a fun test for you…

hot wire your fuel pump on, engine off and let the fuel pump pump 15 gallons thru rails and back at no pressure, 30 psi, and 60. Let it run for an hr. Let me know the fuel temperature in tank

now do it again with car running engine 180-200 deg. For 30 and 60 psi since 0 wont run. Let me know what the gas temp is then when rails are 150 deg lol

we are talking a simple street car setup, naturally aspirated. How many hrs can you say 10-20 psi of diff will make on a car that had oem pumps running for 10-20 yrs at 43 psi? Is 30 psi gonna make it 30-40 yrs? Is the engine gonna last that long?

im an engineer so i get where your heads at. But im also PRACTICAL in application.

Side note: what happens when your 1:1 regulator actually references more like 1.2-1.3:1 as boost rises? Lol nothing…you just adjust your ve table to allow for the tolerance

 

Fuel pump overheating can happen to any car
https://www.thirdgen.org/forums/tpi/...regarding.html

Toolbox, do calcs to find how much heat produced by fuel pump
https://www.engineeringtoolbox.com/p...ase-d_313.html

In a daily driver application, the tank may only have 3 or 5 or 7 gallons. Not everybody can keep 15 gallons all the time in the tank to absorb heating.
It is an issue for daily drivers especially with low fuel condition and large fuel pumps.


Modern manufacturers recognize and make quality parts for this 'practical' application (fuel pump heat control) for high power fuel pumps
https://www.motortrend.com/reviews/t...mp-controller/


Its a common problem when using powerful fuel pump
https://www.corral.net/threads/how-t...tor-x.2505786/

https://www.gtr.co.uk/threads/using-...essure.564893/


https://www.msextra.com/forums/viewtopic.php?t=73337

DIY arduino project PWM fuel pump control discussion
https://forum.arduino.cc/t/arduino-a...roblems/432190
Practical application?
In 1995-2002 Toyota Supra came with about 400hp capable engines. Thus it requires a higher flow fuel pump from the factory than typical daily drivers.
The OEM engineers recognized the increased flow rate (remember this is 1995) of the fuel pump would create unwanted stress, or unwanted heating, or both for the vehicle.
So in 1995 the Toyota Supra comes factory OEM with a PWM fuel pump controller to reduce fuel pump heating/stress at low speed operation.
It is a good example from truly 'practical application' scenarios where engineers from other countries, specifically Toyota in Japan, recognize and engineer a solution for this apparently common issue that goes unnoticed or unheeded in novice installations

I think the confusion here revolves around the term 'practical application' and its potential for misuse. Two to Four fuel pumps running in a fuel tank to support 800-1600rwhp is not 'practical' by any stretch, especially for a daily driver with 5gallons of fuel in the tank idling in traffic. I believe the scope of this argument should be separated into actual practical daily drivers, which require the use of fuel pump PWM controllers, lower pressure, single-pump running only for traffic, etc... VS practical "racing" applications where running two or four pump with a full tank of fuel for a single 'run' of some kind, and it never will see idle in hot traffic heat soaked 600rpm for extended periods with low fuel level.

To put it another way, when I setup a fuel system for 1000hp or 2000hp destined for daily traffic duty and extended idle periods, I would naturally use a single primary fuel pump with PWM controller that runs for the daily driving stuff. And then gradually bring online a second, third, fourth pump as needed for wide open throttle situations, using appropriate control trigger. I can see no other 'practical' method; I wouldn't do it any other way. There is no other good solution. Letting them run all the time or using the full force of fuel pump for idle in traffic is... not a smart way or well engineered method. Even if it does work for some amount of time... it isn't optimal. When we design a generic part or typical application it may be fine, like for a normal car 250hp using a tiny pump, that can fool us into thinking the same rules apply to 2000hp pumps but they do not. For our OWN cars, it should be the best. I want the best thing in my car, my fuel system, my turbo, my engine, etc... The BEST. Not just something that 'works fine'.
Average isn't what I'm going for
"works fine" isn't a target .... "works the best" is the target

 

You basically confirmed what i was saying, fuel heating is mostly from volume of fuel passing thru hot engine bay rails. Not necessarily the pumps themselves. I also read studies on gas tank temps that ambient air temp outside also plays a major role, as expected.

no where did i say you should run multiple pumps at the same time all the time. Running two small 255’s does not seem to be significant when some cars have 340-400 lph pumps stock. If you can modulate the pump then do so. Stage the others as needed. For me i prefer mechanical pumps for serious power

 

Hmm
The speed of water flowing through a cooling system will not change the rate of fluid heating done by an engine
Removing a themostat = high flowing water = same temp rising rate overall due to closed loop

likewise the speed of fuel flowing through a fuel system will not change the rate of fluid heating.
It may return more quickly with less temp, but more fuel overall returns per unit time which adds up to the same energy input.
Fuel system has advantage it can get rid of some of the heated fuel mass by injecting it, but that amount is constant for each example.


The pressure has nothing to do with the flow rate in this case. High pressure = more heating (more pump heat + constant engine heat) = more pump wear = same flow rate

Again its an efficiency thing. I'm more concerned with pump wear than fluid heating anyways. Aeromotive particularly addressed this issue and say that using PWM or lower fuel pressure will extend pump life. Nobody can argue that. And its a 'free lunch' to reduce the pressure overhead. Thats all I really need to point out to novices- often they don't know the benefits of running a reduced pressure and tend to immediately simulate the factory overhead of 60psi which is ridiculous and will reduce pump flow overall at peak flow demand. You lose pump life AND max flow potential. Loss/Loss from high pressure. Plus the "negligible" heating component. So, loss/loss/loss

thanks for reading
Maybe Some novices can use this
I agree that twin 255's is a joke, I don't consider that a high flow or high demand situation, but still I'd rather run a parent pump and keep the secondary off and healthy, one day the primary will fail and I will flip a switch and use the secondary to get home with, plenty of life left, I can continue to drive around for a good while on the second still full of life pump. Saves money and time

 

idk if its your reading comprehension or if im not clear enough but you seem to make up/bring up things that are not being discussed.

im am talking about closed loop fuel system. The heat source to the fuel is the hot engine. Yes some heating of fuel comes from the pump but it is less significant than the fuel rails. We dont need to know flow volume that’s irrelevant to the discussion so why bring it up?

just like a coolant system. Run water pump for an hr engine off, does water heat up? Run pump for an hr with engine on and hot, does water heat up? Lol. Same with fuel

 

Yes of course it will. All types of pumps input heat to their fluids. It is universal, natural law. The idea behind selecting appropriate pumps is generally based on their fluid heating efficiency.

What I am getting at with the coolant example is, we can't control the engine/rail heating done in a return style system easily. But we can control the pump wear, pump heat input, pump efficiency, etc... pump stats. And in my car I want the best pump stats, longest life, least heating... and that means minimum pressure, but not necessarily minimum pump speed. Depends on the type of pump and fluid. Some pumps are extremely inefficient at low speed. But now I am being too general, most fuel pumps these days are PWM compatible and don't mind low speeds. I am only address the wide issue of pumping in general.

Interesting 1 vs 2 pump heating
https://ls1tech.com/forums/fueling-i...ts-inside.html

Regardless of whether 1 or 2 pumps is an issue;
Bottom line: fuel pumps heat the fuel even with engine off
...So do water pumps. All pumps will input heat to their fluids.

Not sure its my reading comprehension
https://www.vaporworx.com/resources/...-systems-work/


Some people having the similar arguments
https://forums.nasioc.com/forums/sho...1&postcount=14


https://www.ls1gto.com/threads/twin-...3/post-6229460

 

That ls1 tech test shows what i am talking about

fuel rise was only 10 deg more with two pumps vs 1. Thats less variance than you may see in summer time temps from morning to mid day to evening lol

everyone always says it, fuel pumps heat fuel. But noone has the actual data of how much and is it even a factor when engine bay temp and ambient temps have greater fluctuations and influence.

 

IDC about 2 vs 1 pump. The test wasn't done very well we have very little to go on.
The point is fuel pumps heat fuel, even just 1 of them, it is a concern, a control point, an efficiency pivot, an engineering consideration.

The temp just goes up and up whether its 1 or 2 pumps doesn't matter. Two just heats it faster.