Fuel pressure confusion

[No disintegrations]

going back to the beginning. During engine braking situations there will be extra intake vacuum. That will lower the fuel pressure the same way it rises when in boost ( but the opposite, lol)

 

[TurboDetroit]

Return line is dumping in the back right of the fuel cell. Feed line is in the right side of the sump front of the cell....

 

[No disintegrations]

under braking when the fuel pressure dips what happens next? Stalls or near stall?

the pressure with vac line off is....?

 

[NY Twin Turbo]

According to the electrical "experts", a DC circuit should have all critical items like fuel pumps and ECM's with a ground back to the battery using the proper size copper stranded wire, not through a crappy low carbon steel frame or a body with many bolted-on parts which are old and corroded.

On all our builds, the fuel pump wiring is using copper wires directly back to the battery.

With a performance build, we set base fuel pressure close to 50 psi with gas, and 55 psi with e-85.

My opinion is to have more pressure at the injector as I do not trust gauges, and I would rather have more fuel available at the injector than less fuel.

2 things I'd like to mention here.

I don't think much about good or bad grounds to the frame or body. Why? Because first I cleaned and brushed multiple points all over the car.I ran a bare #8 copper wire from the battery all around and along the entire length of the car from front to back and zig-zagged it off the frame and body and engine. Fastened it with screws and copper straps at all the clean spots. Problem solved. No more issues grounding to anything! Easy 2 hour modification that anyone can do to a race prepped Buick.

Nick, I'm not sure I agree with the 50psi fuel pressure thing. Seems like a lot of overcompensation for an inaccurate gauge. I'd get a better gauge.

But I guess it depends a little on what engine management your going with. I use an XFI and I prefer to set fuel pressure exactly what the injector is flow rated at. This, along with every other little detail about my combination is entered accurately before the tuning begins. Then, later when tuning the maps, let the numbers fall where they may.

 

[dank GN]

As far as grounds go . I have my main ground tobthe motor I also have acouple attached to the body . But if I'm not mistaken the main is supposed to be attached to the engine block

 

[achalmersman]

As far as grounds go . I have my main ground tobthe motor I also have acouple attached to the body . But if I'm not mistaken the main is supposed to be attached to the engine block

It is. In a frame car like ours the block is the "main ground" which is distributed from there. In a unibody car it's the body

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[NY Twin Turbo]

But if I'm not mistaken the main is supposed to be attached to the engine block

Yes.

But as you have done also, it's always cool to add auxiliary grounds to the other major pieces that make up our cars. They never hurt.

 

[turbo nasty]

The body of a Gbody is the ground plane...NOT the frame.

 

[achalmersman]

The body of a Gbody is the ground plane...NOT the frame.

Actually its the engine block.

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[turbo nasty]

Actually its the engine block.

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Good point on block but.....thats the engine harness, alt, starter it is Biggest point in my post if the FRAME is NOT the ground plane. Block is tied into it as well but block isnt the "sole" plane. Firewall (body) to intake, Firewall to Trans bell housing, Dash harness,Taillight harness, Head light harness, look at the inner fender by battery, etc grounds all tie into the body in several spots. These gnds are NOT ran straight back to the block for EVERY ground so the Body is used. Cut it how you want .....body is used.

 

[achalmersman]

Good point on block but.....thats the engine harness, alt, starter it is Biggest point in my post if the FRAME is NOT the ground plane. Block is tied into it as well but block isnt the "sole" plane. Firewall (body) to intake, Firewall to Trans bell housing, Dash harness,Taillight harness, Head light harness, look at the inner fender by battery, etc grounds all tie into the body in several spots. These gnds are NOT ran straight back to the block for EVERY ground so the Body is used. Cut it how you want .....body is used.

You are absolutely right about the frame. And I am not trying to get into a pissing match here, but the body is not the primary ground plane. It is the engine block. The body is primarily grounded via the engine block not the other way around. The body is not the primary ground. Sensitive / important grounds such as sensors, ecm etc all should be grounded at the engine block.

In a unibody car this is different and the body IS the primary ground "plane"

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[turbo nasty]

You are absolutely right about the frame. And I am not trying to get into a pissing match here, but the body is not the primary ground plane. It is the engine block. The body is primarily grounded via the engine block not the other way around. The body is not the primary ground. Sensitive / important grounds such as sensors, ecm etc all should be grounded at the engine block.

In a unibody car this is different and the body IS the primary ground "plane"

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Agreed. My angle was for people not using the body for a ground on electrical pieces that could use the body tub for items say mid way or rear on the car.

 

[Nick Micale]

Without getting in to a "pissin" contest, the simple fact is the best circuit for power and ground for critical items like the fuel pump and computer is directly to the battery.

For lights, horns and other non-essentional items, they can function ok with body or frame grounds, but for my fuel system and computer I want pure power, as well a consistent power source for these components, especially in a performance build.

 

[achalmersman]

Without getting in to a "pissin" contest, the simple fact is the best circuit for power and ground for critical items like the fuel pump and computer is directly to the battery.

I don't have the time to conduct this test. It would require taking amperage readings and voltage measurements under load. But I am pretty certain that with the engine running, the fuel pump circuit has the potential to perform better if the positive is provided off the alternator stud, and a dedicated ground ran to the block. I believe this will perform better than if the positive and dedicated ground is both on the battery. And almost certainly better than if the positive is on the alternator and the negative on the battery. This would change if the alternator was not able to keep up with the load under WOT but this shouldn't be the case. In that undesirable condition the battery would be better.

One thing is for sure you are right that a dedicated ground is an advantage.

Please don't take my replies as being argumentive. I enjoy technical discussions. When I install my double pumper setup perhaps I will take the necessary measurements to validate or disprove what I'm saying. When the car is running, the battery is still not the "ground plane". The engine block is.


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[Nick Micale]

......Nick, I'm not sure I agree with the 50psi fuel pressure thing. Seems like a lot of overcompensation for an inaccurate gauge. I'd get a better gauge.

You may not agree, but what really counts is the car likes the higher pressure!

Most of the turbo cars using e-85 respond better off-idle at the higher pressure, my 4.1 street car on e-86 likes 55 psi best.

Some gas cars like slightly higher base fuel pressure as well, all cars are not equal, so we set it to what the car likes best, as I like to have more fuel rather than less.