It would be worthwhile to check pressure in the return lines as it can affect your timing and fueling as much or more as the inlet pressure.
Biting the bullet: Converting to electric fuel pump
- Thread starter Cubey
- Start date
Oh? Would checking it just at idle be sufficient? I can easily use that brass tee to check it down at the frame rail.
Or would I need to check it at speed? It wouldn't be hard, there is a return hose connection right at the bell housing, but I'd need buy another tee, and a long piece of vinyl tubing or something to run it up to the cowl for the gauge.
Checking at idle would be good than no data, but if you can rig up a way to read it when driving even better.
Ok, I will see about that in the next few days.
What pressures would be normal at idle and at 40-45mph?
IDIBRONCO
IDIBRONCO
At idle, it should have more return pressure than while driving since you're using less fuel at idle, but both should be as close to nothing as possible. With pressure defined as being the resistance to flow (may not be completely accurate), any pressure means that there is a resistance (restriction) to flow. To add a little bit more, I'd also lean towards the advanced timing. My timing was advanced too far and Wes set it back to 9* last year. I gained top end power that I hadn't had before. Since you say that you lost top end power, I'd think something similar may be happening for you. By saying top end power, I mean high RPM power.
Spec is less than 5 psi is acceptable for return pressure
Idle with cold advance on, the gauge is saying exactly 2psi on the return line, branched off of the 3/8" PEX tee.
Booyah45828
Full Access Member
Well how bout that. I'm with others in the belief that the closer to 0 your return pressure is, the better.
Try measuring it with the throttle wide open and see what you have. Me thinks that might be your lack of power at high speeds issue.
Booyah45828
Full Access Member
That pex tee is towards the rear by the tanks right?
It's probably never going to be zero with an electric pump and higher pressure at all time.
It might be lower when at highway speed since filter head pressure drops by 2. I will have to get about 20-25ft of vinyl tubing to run it to the front so I can see it while driving.
Yes. Right in front of the front tank, right by the Holley.
Look right below the bolt shoved in the rear tank return hose.
I pulled the hose from the transfer pump and tested pressure from there.
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Oh, and what if return pressure stays at 2, or goes higher? What could really be done? Nothing, I suspect.
A bypass regulator set to 5 or 6 with a 14psi pump (such as Holley blue or black) would make things worse, pushing the excess fuel into the return line, drastically increasing pressure. It would need it's own separate return line to avoid that problem.
A standard, non-bypass regulator (such as the one included with Blue) would keep the pressure stable to the IP, but that might cause more problems, since the IP usually sees a range of pressure based on rpms/throttle position.
I probably won't waste $5 on 1/4" vinyl tubing to check return pressure when driving, because nothing can be done about it anyway. Why bother?
Gonna probably just go get timing done in the next couple weeks and see how things are after that.
We know the pressure is higher (7 idle, 5 even when floored) vs typical mechanical pressures, so we know timing must be effected. There was no missing top end power issue with the mechanical pump, so we know it was switching to electric that caused it. Nothing else has been touched, such as the IP.
The IP regulates the amount of fuel going to the injectors as I understand it, so the amount going to the injectors is the same, just the IP is getting higher pressure now. Once the injectors dump the excess for returning, its probably not hardly related to the IP inlet pressure after going through the IP and injectors. Correct me if I'm wrong?
The return line has had no major change except the 3/8" pex tee, but that probably isn't the problem. I could try a proper 5/16" hose barb tee instead to see if the pressure goes down, but I doubt it would change much, if at all.
A bypass regulator set to 5 or 6 with a 14psi pump (such as Holley blue or black) would make things worse, pushing the excess fuel into the return line, drastically increasing pressure. It would need it's own separate return line to avoid that problem.
A standard, non-bypass regulator (such as the one included with Blue) would keep the pressure stable to the IP, but that might cause more problems, since the IP usually sees a range of pressure based on rpms/throttle position.
I probably won't waste $5 on 1/4" vinyl tubing to check return pressure when driving, because nothing can be done about it anyway. Why bother?
Gonna probably just go get timing done in the next couple weeks and see how things are after that.
We know the pressure is higher (7 idle, 5 even when floored) vs typical mechanical pressures, so we know timing must be effected. There was no missing top end power issue with the mechanical pump, so we know it was switching to electric that caused it. Nothing else has been touched, such as the IP.
The IP regulates the amount of fuel going to the injectors as I understand it, so the amount going to the injectors is the same, just the IP is getting higher pressure now. Once the injectors dump the excess for returning, its probably not hardly related to the IP inlet pressure after going through the IP and injectors. Correct me if I'm wrong?
The return line has had no major change except the 3/8" pex tee, but that probably isn't the problem. I could try a proper 5/16" hose barb tee instead to see if the pressure goes down, but I doubt it would change much, if at all.
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IDIBRONCO
IDIBRONCO
I see something that may have affected your return. Looking at your picture, the return from the engine goes into the T and straight into the your transfer pump. From the factory, your return goes straight into the tank. By forcing it to make a 90* turn, you're making the flow slow down which increases pressure. By changing your transfer pump hose so that it makes the 90* instead of your returning fuel, you may be able to lower the return pressure a little bit. A better option than the 90*, may be a Y where the fuel from the engine goes straight through and the fuel from the transfer pump comes into it at an angle going toward the tank. I may be way off on this, but I just have this gut feeling.
Booyah45828
Full Access Member
I'm going to wait for wes to comment on this. He knows more about pump then I do.
But I'm thinking your return is an issue. You wouldn't need to drive it per se, just bring it to governed rpm in neutral/park. The fuel bypassed by the injection pump should increase with rpm, loaded or unloaded, and I'm thinking that increased volume will show up at your higher rpms with higher return line pressure.
But I'm thinking your return is an issue. You wouldn't need to drive it per se, just bring it to governed rpm in neutral/park. The fuel bypassed by the injection pump should increase with rpm, loaded or unloaded, and I'm thinking that increased volume will show up at your higher rpms with higher return line pressure.
That's easy enough to change. I can let the engine return go straight through the tee and use the side connector go to the transfer pump. I just gotta dig put a longer piece of scrap hose from my stash to change it. I will only run the transfer pump with the engine off so it can't cause problems.
Oh, I see. I looked up a diagram. The IP itself pushes returning fuel too, not just injectors.
My thought is that yes more fuel will be flowing to the IP, but at a lower pressure, so the return pressure might go down too since the IP will be getting less pressure.
The engine will be using 4-5x fuel as much fuel than at idle so that will probably eat up the extra flow.
But, I was wrong about pressure/flow from the Holley, so maybe I am again.
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Really return volume at different loads and rpms comes down to the pump, especially the advance piston wear. You may see the most at idle or the most at low load but high rpm, or high load high rpms, just depends on the pumps condition and efficiency.
