99 Explorer EFI fuel pressure question

[rjrobin2002]

I have the 99 explorer efi that is supposed to run at 65psi.

I am running the corvette filter regulator that is supposed to give me 59psi which EFIGuy and others have said 6psi low is not a big deal and the computer can compensate for that.

When I am idling I have 49psi, but it idled perfect and no cutting out when revved in park.

i went for my maiden voyage and it was cutting out once I got to cruising speed and when I got home I did more testing.

At idle I have 49psi, when I rev the engine to say 3000rpm it drops to 30psi.

Should fuel pressure stay constant with RPMs?

I'm already looking at switching to a regulator that will give me my 65psi.

 

[bigmuddy]

Well thats not good news, I just ordered that corvette unit... Ugh!

 

[rjrobin2002]

Well thats not good news, I just ordered that corvette unit... Ugh!

Good news is they are dirt cheap.

I first thought my harbor freight guage was a little off with the 49psi instead of 59psi.

My pump may be bad with the pressure drops indicate a volume issue I'm assuming.

Waiting for the experts to chime in if pressure should stay the same with RPM.

 

[bigmuddy]

No so much worried about pricing but rather longevity. How long and how many miles on the one you are running?

 

[rjrobin2002]

No so much worried about pricing but rather longevity. How long and how many miles on the one you are running?

Today was first drive.
I actually have an extra one I am gonna slip on and see what happens.

Mostly curious if fuel pressure should stay 60 with rpms.

 

[bigmuddy]

Funny you say extra one. Amazon just delivered me two and I only ordered one! Maybe its the universe talking to me

 

[Rox Crusher]

Howdy guys, I can’t say Im an expert but for sure have lots of experience.

I had an 97 Explorer 5.0 with the return style rail. Swapped in a 5.8 with 2000 Explorer stuff including “return less” style rail. I have fuel pressure gauge on rail as well as fuel pressure gauge in VHX digital cluster. Since I had a return line with the 5.0 set up, I installed an adjustable fuel pressure regulator in the engine bay.

https://www.summitracing.com/parts/aei-13129

When I first put the 5.8 in, it would hold 68 psi at idle and drop to 62 psi when in lead foot mode. No run issues and the rail would hold the pressure for a good while after engine turned off.

then on a couple long road trips in height of summer heat it would be at 62 at idle and steadily drop down as low as 52 when really hot (110F ambient with engine at 205F). Would still run most of the time but occasionally would drop down to 40 PSI where it would quit running. Rail will no longer hold pressure, as soon you shut off the engine, pressure drops to zero. When starting, I have to cycle the key a couple times to build pressure to start it. I’ve replaced injectors (thinking they might be leaking), replaced the in tank pump twice, replaced the fuel pressure regulator without resolution. i got a 78 Freewheeling that has been taking my attention lately so the 77 doesn’t get driven as much. It’s reliable enough in normal temps, but I would like to get it resolved before my son starts driving it (it’s now his).

my understanding is that fuel pressure should stay relatively constant regardless of RPM.

So I’m watching this thread to see if I can learn something that helps me and offering my experience hoping it might help others.

 

[SLOWnEASY]

Today was first drive.
I actually have an extra one I am gonna slip on and see what happens.

Mostly curious if fuel pressure should stay 60 with rpms.

Yes your fuel pressure should stay fairly constant between idle and under load. I've heard of systems losing a few PSI under load, but losing 10 PSI is probably a problem. It's even more concerning when you look at it as you are actually losing 16 PSI (65-49=16)

The computer makes injector pulse calculations based on many things like throttle position, air flow MAP pressure etc These calculations are made with assumed preset parameters like injector flow rate (ie. 19lb/min injectors) and fuel pressure like 65 PSI. There is some tolerance built into the programming for still running with a partially clogged fuel filter. So I wonder if that is what EFI guy is referring to. Yes your Bronco should still compensate and run at 60 PSI fuel pressure. But that might be on the low side of the compensation range. Your truck on the other hand is trying to run at 49 PSI which is probably just not enough flow.
Yes a regulator that gives you 65 PSI could help. But this to me sounds like a flow volume problem and I would be more concerned with why It's dropping to 49 PSI.

 

[rjrobin2002]

Yes your fuel pressure should stay fairly constant between idle and under load. I've heard of systems losing a few PSI under load, but losing 10 PSI is probably a problem. It's even more concerning when you look at it as you are actually losing 16 PSI (65-49=16)

The computer makes injector pulse calculations based on many things like throttle position, air flow MAP pressure etc These calculations are made with assumed preset parameters like injector flow rate (ie. 19lb/min injectors) and fuel pressure like 65 PSI. There is some tolerance built into the programming for still running with a partially clogged fuel filter. So I wonder if that is what EFI guy is referring to. Yes your Bronco should still compensate and run at 60 PSI fuel pressure. But that might be on the low side of the compensation range. Your truck on the other hand is trying to run at 49 PSI which is probably just not enough flow.
Yes a regulator that gives you 65 PSI could help. But this to me sounds like a flow volume problem and I would be more concerned with why It's dropping to 49 PSI.

It's dropping to 30psi with 3000rpm, half of the 65psi goal.

 

[SLOWnEASY]

Yeah that sounds like a problem.
There's some interesting stuff in this thread especially post #32.

https://classicbroncos.com/forums/t...-return-less-fuel-system-requirements.327024/

 

[EPB72]

It's dropping to 30psi with 3000rpm, half of the 65psi goal.

That’s absolutely a problem ,, actually under load on a system with fuel pressure with vacuum control will bump pressure up 5-7psi with low to no vacuum ,, at idle high vacuum would have less pressure ,, most OE if you dead head the pump should jump up to 100 psi there about ,,, so can you put the pressure gauge before the filter/ regulator and report pressure as well as dead head the pump as to know pump potential.. the filter/ regulator can fail so testing it … fwiw if it’s been running lean fuel trims adding fuel,,, after making any changing to correct condition you need to reset KAM to reset adaptive.. or can still have drivability symptoms till PCM corrects itself.

 

[rjrobin2002]

That’s absolutely a problem ,, actually under load on a system with fuel pressure with vacuum control will bump pressure up 5-7psi with low to no vacuum ,, at idle high vacuum would have less pressure ,, most OE if you dead head the pump should jump up to 100 psi there about ,,, so can you put the pressure gauge before the filter/ regulator and report pressure as well as dead head the pump as to know pump potential.. the filter/ regulator can fail so testing it … fwiw if it’s been running lean fuel trims adding fuel,,, after making any changing to correct condition you need to reset KAM to reset adaptive.. or can still have drivability symptoms till PCM corrects itself.

I have an extra corvette regulator, gonna install it tomorrow and see if anything changes.

Next I will test pump pressure with no regulator and see what it can create dead headed to my guage.

Tha ks for the inputs.

 

[Rox Crusher]

I have an extra corvette regulator, gonna install it tomorrow and see if anything changes.

Next I will test pump pressure with no regulator and see what it can create dead headed to my guage.

Tha ks for the inputs.

I have an extra one of these that works just fine if you decide you need one for your system. Just pm me your address and I’ll mail it to you.

https://www.summitracing.com/parts/aei-13129

 

[rjrobin2002]

I have an extra one of these that works just fine if you decide you need one for your system. Just pm me your address and I’ll mail it to you.

https://www.summitracing.com/parts/aei-13129

How much you want for it?

 

[Rox Crusher]

How much you want for it?

Nothing, just building up my karma bank

 

[fordguy]

Why are you guys running the external regulator. I went with the stock pump assembly and let it handle the return and regulation. “Returnless” has a damper on the fuel rail not a regulator. Works well and the install is really clean.

 

[Rox Crusher]

Why are you guys running the external regulator. I went with the stock pump assembly and let it handle the return and regulation. “Returnless” has a damper on the fuel rail not a regulator. Works well and the install is really clean.

For me, I had a return style rail so went with in tank pump. Didn’t want to convert to the in tank pump with regulator as I would have to modify tank.

having said that, I’m saving my nickels to get a new tank with Explorer set up and different sender so we don’t have to guess at how much fuel is left.

 

[bigmuddy]

Why are you guys running the external regulator. I went with the stock pump assembly and let it handle the return and regulation. “Returnless” has a damper on the fuel rail not a regulator. Works well and the install is really clean.

With the upper intake on the 5.8 I am running I don't have room for the return style rail. Too, I am running the BCB rear tank and there isn't room to install a stock pump and regulator. Trust me, if I could, I would.

 

[bigmuddy]

For me, I had a return style rail so went with in tank pump. Didn’t want to convert to the in tank pump with regulator as I would have to modify tank.

having said that, I’m saving my nickels to get a new tank with Explorer set up and different sender so we don’t have to guess at how much fuel is left.

I just installed the Tanks Inc sender in my BC tank and from what I am hearing it's quite accurate for fuel reading. Fingers crossed.
Also just missed out on an SS Kincer fuel tank for a good price. Damn those things are like works of art!

 

[fordguy]

My aero tank is not pretty but takes the stock pump. I put the tanks sending unit it that matches the ohm range of stock Guages (no external float). It is a little short, so I should be able to adjust to how it reads on gauge. Works well, easy install. If a did again, would probably go longer and make a spacer.