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Discussion Starter #1 (Edited)
Howdy folks -

EDIT: This is on a 1996 EFI system with MAF.

I installed a slightly built 351 over the weekend and it was mostly a success. The engine runs, but it isn't getting enough fuel. I am using a BBK adjustable fuel pressure regulator because the builder said that I'll probably need to run 5psi or so above stock (still using original 19# injectors). When we put the pressure gauge on the rail last night and turned the key on, you could hear it pressurize, but the gauge didn't read. Cranked the truck up and it slowly built up to ~22 (with the BBK cranked all the way up, which should be ~75psi). Check engine light is on with a code for lean condition in both banks (which makes sense). I swapped the stock regulator back on just to see if it changed anything and it doesn't (gauge only reads 10psi with stock regulator on). I can drive around the block with no issues, but I'm lacking power.

Any ideas as to what is going on? The truck ran fine before the swap (I didn't check the pressure then). I guess it's possible that my pump is going out, but that would be a bad coincidence. I'm running without an alternator right now because it died during the swap (nut was too tight on the stud and wouldn't come off - post was just spinning in place). I had to take it apart to get it off and apparently I didn't do something right because it's not putting out any power now). This seems unrelated, but could it be causing my pressure problems from a lack of voltage?

What else should I be checking?

Pictures of the motor just for fun!
154374
154375
 

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Premium Member
84 Bronco, 351w, c6, custom doubler, np208, 5.13’s, TTB44, 9”, locked f/r
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717 Posts
Does it hold the pressure it builds when you turn the key off, or does it bleed to zero?
 

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Discussion Starter #3
Holds pressure just fine. I didn't leave it overnight or anything, but I watched it for 5 minutes or so and it held. I bought a gauge with the BBK regulator, so I'm going to put that on there when I re-install the BBK. That'll help me keep a better eye on things. Still, this should be a set it and forget it type of thing.
 

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Ford Hoarder
78 & 92
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6,560 Posts
Stock fuel rails and such as well?? If your running aftermarket be interested to see your plumbing as the regulator should be last.
It does sound like possibly a pump issue, I have also seen the socks come off the end and or get clogged up with bits of themselves. Ethenol must eat them a bit.
My other thought was maybe possible to get the return and supply lines backwards at rear of engine. I do not remember what the ends look like.
 

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Discussion Starter #5
Using stock rails and injectors. Lines are hooked up correctly (they are different sizes).

Is there any way to check the pump? I'd rather not start throwing parts and time at this thing if I don't have to. I'm so close to just being able to drive it!!!
 

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I'm sorry, I don't have any suggestions/advice to offer.
Was wondering, where did you get this condensed-line vacuum tree from?
I've removed my smog equipment and will be catching up with your engine install progress in a couple of months.
154421


EDIT: Nevermind, I understand now that it's stock equipment on the '96 Broncos. Maybe even '95?
My '94 has a massive vacuum tree with crap tubes going every which direction.
 

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Discussion Starter #7
I think this how the 5.8s with MAF came from the factory. Thankfully there really aren't many vacuum tubes on this motor.... I'll start checking vacuum once I get the fuel pressure figured out.
 

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84 Bronco, 351w, c6, custom doubler, np208, 5.13’s, TTB44, 9”, locked f/r
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If you pinch off the return line, what kind of pressure will the pump build?
 

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Discussion Starter #9
I can test that and see. Where is the best place to pinch off the return line? I put the adjustable regulator back on tonight and attached a gauge to it, so I can see the pressure all the time now (under the hood, anyway). KOEO it sits at 30psi. Engine running shows 25psi. When I turn the key off, the pressure drops about 10psi and then holds steady.

Battery is charged and is putting out 12.5v. I'll have a new alternator tomorrow, so I can test the system running at 14.4.
 

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84 Bronco, 351w, c6, custom doubler, np208, 5.13’s, TTB44, 9”, locked f/r
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717 Posts
Wherever you can get at the return line where it is rubber???? I dunno a physical location off the top of my head. It should shoot up to like 60+ psi almost instantly if you pinch the return and the pump is good
 

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Discussion Starter #11
Ok, did a couple of tests this evening while fiddling with other things in the garage. I pinched the return right behind the connection and the gauge didn't move at all... didn't react to any squeezing on the return. Does this mean that the max my pump is putting out is ~25psi?

Speaking of, at KOEO, the gauge sits at 25psi. This is the rate that it dropped after turning the key off -

0:00 25psi
1:45 20
5:00 15
10:00 11
15:00 8
20:00 6
25:00 5
30:00 4

I stopped timing after 30 minutes. What is an acceptable drop rate on these fuel pressure systems? Are they supposed to stay pressurized all the time? This is my first experience working on any EFI, so all knowledge is welcome!!
 

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84 Bronco, 351w, c6, custom doubler, np208, 5.13’s, TTB44, 9”, locked f/r
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Yeah, I think your pump has issues. In a perfect world they would stay pressurized for a day or two. But I think if it can hold 20psi for half hour or so, I bet it’s “good enough”

But start with a new pump and see what that does
 

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Discussion Starter #13
Anyone else with any ideas/advice? Are any particular fuel pumps better than others? I'd like to go ahead and get one ordered so that I have it for the weekend.
 

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1996 EB 5.8L, E4OD, 2.5" RC Lift, 33" tires, 3.55 gears
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I echo the others. You can energize the pump by directly applying 12V and see if you get different pressures at the rail. If still off, I think it’s safe to blame the pump. That’s what I did before concluding my pump was dying and replaced it with a motorcraft.

If you replace the pump, you can cut an access panel in the bed, but I dropped the tank in my 96 and it wasn’t that bad.
 

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Discussion Starter #15
I looked at the articles for cutting an access hole, and it looked like more trouble than dropping the tank. I crawled under mine today and there aren't any straps, so I'm guessing that the tank has been down before. Maybe the PO used a subpar pump and that's why it's giving me trouble now? Could it have worked sufficiently for the old motor and not for the new one?

On another note, I got my new alternator today and got it installed. Turns out, the old one wasn't bad.... I had disconnected the main alt wire with the fusible link because I upgraded and put a better one in..... I didn't realize that the exciters were tied to the old wire. DOH! Anyhow, I reconnected the old wire to the solenoid and all is well. Now I just have to decide weather to keep the sweet new PowerMaster alternator, or if I should get my money back.
 

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Discussion Starter #17
It's a 200a alt! I'm leaning toward keeping it, but I really didn't plan on dropping the $$$ right now.... as usual, the swap cost more than I anticipated. Especially now that it isn't running yet................
 

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aka: kemicalburns
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Honestly i would return the Alt... you are going to need those funds for a motorcraft pump.
 

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Discussion Starter #19
I'm still on the fence. I have picked out a Carter pump that can be here Friday.... any reason that I shouldn't go that route?
 

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i think everyone pretty much agrees that you should get motorcraft anything when available. with the fuel pump, it hink it's in part because of the effort to drop the tank to replace. of course, if you had an access panel, changing the pump multiple times would be a piece of cake. hahaha
 
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