Fuel pressure question. Insufficient flow?

[TheRadBaron]

I’ve been reading up extensively on converting to an electric fuel pump. I know the subject has been beaten to death but I have a specific question about fuel pressure that I haven’t seen addressed.
Lots of people talk about installing various electric fuel pumps and report along the lines that they have 6psi at idle and light load but the pressure drops to 2psi at full load.
This is usually said like that’s not a problem and they don’t make it sound like the engine is starving for fuel.
But doesn’t this suggest that the flow of the pump is insufficient for the fuel demand at WOT?

I like what I’ve been reading about the Walbro FRB5 and I’m thinking about installing it with a return style regulator. But I’d like a system that can deliver steady fuel pressure across all operating conditions.
Or am I overthinking this?
Thanks.
(‘94 F350 IDI-T with mild performance upgrades).

 

[IDIBRONCO]

But doesn’t this suggest that the flow of the pump is insufficient for the fuel demand at WOT?

Not really. I do think that you're overthinking this. The electric pumps put out their pressure and flow whenever they're running. The engine needs more fuel at higher RPM/load, which is how any internal combustion engine operates. The mechanical lift pumps put out more volume/pressure at higher engine RPM because they're being worked faster. Simple as that.
how often are you planning to operate at WFO and for how long?
From what I've read, the Walboro pumps generally only have about the same volume as the mechanical lift pumps are rated at. If that suits your engine, then they're fine. If you are thinking about bigger pumps, injectors, and turbos, then they won't give you enough volume.

 

[DirtyWood]

I have spent way more time reading about various pump options than I care to admit. A lot of pumps don't seem to deliver the volume and pressure that we need even though the listed specs appear to be adequate. To ensure enough volume at the desired pressure at WOT it seems we need a pump that is more than enough at lower RPMs/loads. I have a Mr. Gasket 105P that will get installed soon, and although it's rated at 105gph free flow it's only rated 70gph at 9psi. And yes I am thinking about bigger pumps and injectors.
But FWIW, if you have 6psi at idle and 2 psi at full load/WOT then you're actually doing okay on a stock-ish setup. I can't recall if the spec sheet was from International or Ford but the IP is only required to have 1psi at the inlet at 3000rpm.

 

[TheRadBaron]

I’m not planning on operating at WOT very often or for very long. It just seems odd to me that a pump that's rated at 8-11psi, and regulated to 6psi, would drop to 2psi under heavy demand unless the pump lacked the volume of flow necessary to meet the demand.

My setup will be pretty mild. Stock injectors, stock injection pump turned up a bit, stock turbo with the wastegate tweaked for maybe 12psi max.

Do you know the GPH rating of the stock mechanical pump?

That's good to know that the IP only requires 1psi.

 

[DirtyWood]

I don't know how the stock lift pump is rated but the real complaint is lack of quality more than lack of fuel. 1psi may be a minimum on a spec sheet but my engine seems, no dyno runs for me, to run better with at least 3psi. I am not knowledgeable about the inner workings of the IPs but inlet pressure is supposed to affect dynamic timing advance. I had a brief online discussion with Justin from R&D and he related an instance where he gained a little power on the dyno by reducing the pressure to 7psi from 9psi, so there must be a sweet spot somewhere for optimum performance.

I tried the now infamous Facet Dura-Lift and though it's rated at 9-11psi I had about 6psi at idle and it would quickly drop to 1psi or less when heavy throttle was needed. Some manufacturers offer a flow chart that gives a crude idea of what flow can be expected for a given pressure. Other factors like clogged pickup screens, clogged FSV, or clogged fuel filter will drop the performance even further. It's easy to blow some low-psi compressed air back through the lines and into the tank just to help clear out any crud, but do remove the tank cap before doing so.

 

[franklin2]

I do not care if you bought the largest electric fuel pump known to man, it will not develop any pressure if there is no restriction in front of it to build against. It's about flow, not pressure.

Someone can correct me, but I think the injection pump has a small pump inside of it that supplies the rear of the injection pump. This is where the rubber meets the road, all you have to do is keep the injection pump supplied with enough fuel. Believe me, if you start running out of fuel, you will know it. The engine does some crazy surging and actually seems to run better for a instant when you are running low on fuel. Something to do with the timing mechanism inside the injection pump which is actuated with the fuel supplied to the pump.

 

[TheRadBaron]

I found a few references that list the factory mechanical fuel pump at 30gph. The Walbro FRB-5 is listed as 45gph so that seems like it would be a decent choice for a mildly upgraded fuel pump.

They have a good reputation for reliability and long life from what I can see. That appeals to me.

 

[TheRadBaron]

I've also seen a few discussions where guys are talking about using '99-'03 Powerstroke Bosch inline electric fuel pump on an IDI. Also, CDD is using a Walbro GSL396 in their E-fuel kits for IDIs with big IPs.
These are both high pressure pumps. Approximately 50psi and 80psi, respectively. This seems excessive but I'm sure a return style regulator is used to get them down to the 5psi or so that's needed for the IDI. Still.... seems kind of excessive.
The Powerstroke Bosch fuel pump sounds like a very well made and reliable unit. Not terribly expensive, either. Is there any downside to regulating a high pressure pump like this down to a much lower pressure for these engines?

 

[DirtyWood]

I think if you're using a return regulator then it shouldn't stress the pump. It seems plenty of people have had good luck with Holley Reds but then others say the opposite. Personally I would try a Holley Red on a non-turbo or stock turbo setup since they don't require a regulator. A good pre-filter is necessary with any of these electric pumps.

 

[TheRadBaron]

I've heard of enough bad experiences with the Holley pumps that I don't think I want to mess with them. Reliability is at the top of the list of priorities for this truck. I have a pretty nice return regulator sitting on the shelf already that might pair well with a Bosch Powerstroke pump.

 

[IDIBRONCO]

It just seems odd to me that a pump that's rated at 8-11psi, and regulated to 6psi, would drop to 2psi under heavy demand unless the pump lacked the volume of flow necessary to meet the demand.

That pressure rating is probably at max pressure. That's without a large demand of fuel, or maybe without any demand for fuel. When the fuel flow is restricted in any way, including to a lesser pressure, then you'll never have the full, unrestricted flow which results in less pressure. You can generally keep the fuel pressure really close to the rated pressure with a gas engine with a carb on it. All the pump has to do is to keep fuel to the carb and nowhere else. Think of that as a dead end fuel system. Our engines have a continously circulating style of fuel system. The fuel is constantly being pumped to the engine and then returning to the tank while the engine is running. That makes it more difficult for any fuel pump to maintain a constant fuel pressure.

Do you know the GPH rating of the stock mechanical pump?

I believe that it's around 42 gallons/hour from what I've seen on here. If it is around 30 gallons/hour like you said, then I'm wrong and the Walboro will be enough pump. Most of what I see are talking about volume at cranking speed (with the starter). Kansasidi can run his Walboro out of fuel, but I'm not sure what his set up is other than a Hypermax turbo. Either way, it's not big enough for him.

my engine seems, no dyno runs for me, to run better with at least 3psi.

Mine seems happier with 4PSI and higher.

 

[Clb]

There's a lot more technical issues with fuel delivery and the i.p. 's internal timimg, so rather than pimp/bang on a holley ( red in my case) we should be quoting discussions from the builders here.
If to much delivery psi will cause an advance in timing, then it stands to reason that the low psi delivery rate will have problems.
The supply chain being shoved down our throats is what we should be lobbying our backsides off about.
Op search some more topics for more perspectives.

 

[IDIBRONCO]

If to much delivery psi will cause an advance in timing, then it stands to reason that the low psi delivery rate will have problems.

Yes it will. That's why mine seems to like 4 PSI and higher fuel pressure to keep the timing advanced enough.
One thing I did notice was that he only mentioned the fuel pressure being regulated to 6 PSI. I saw no mention of the being 6 PSI at idle, at highway cruising speeds, WFO throttle, engine not running, or something other than what I mentioned.
Another thing here is that, at least for me, the fuel pressure goes back up when I let off the throttle. Sometimes to 7 or even 8 PSI so throttle position makes a HUGE difference in fuel pressure.

 

[DirtyWood]

There's a lot more technical issues with fuel delivery and the i.p. 's internal timimg, so rather than pimp/bang on a holley ( red in my case) we should be quoting discussions from the builders here.
If to much delivery psi will cause an advance in timing, then it stands to reason that the low psi delivery rate will have problems.
The supply chain being shoved down our throats is what we should be lobbying our backsides off about.
Op search some more topics for more perspectives.

IIRC, didn't Agnem post that ~5psi regulated was his preference? From reading a ton of older posts on the fuel pressure subject it sure seemed that a lot of info pointed to something between 5-7psi with 9 or 10psi being about the point of too much pressure. I can't quote scripture on this but I do not recall much of a variance in recommended fuel pressure except for the Ford or International spec claiming 1psi@3krpm was adequate.

 

[Ruffnek7tree]

Currently I have a fuel pump for an early 24v cummins, not the in tank one, it was a huge difference from the 35-40gph parts store pumps, it works ok for the most part, it's loud though..

Whenever it takes a dump, I got a used powerstroke pump, gonna try that with a return style regulator, seems like some have had the return tee into the suction side with success..

I can attest to the bosch powerstroke pump longevity, I've had my 01 powerstroke 13 years now and a few hundred thousand miles without ever having to replace it