I'm assuming you mean about the two fuel pumps? In '85, this was the stock setup. There was a low pressure pusher pump in the tank and a high pressure puller pump up on the rail by the engine. In later years, they changed the system to a single high pressure pump in the tank.

In my comment above, I was saying that if I ever had an emergency, I could put a carb on and disable the high pressure front pump and just run the low pressure rear one, which would be just about right.

I also think the dual pump setup would be a good way to put a high pressure system into an older truck. Just use a sender from an 85 302 gas tank, since it's still a 2" hole. The efi sender has a provision for the low pressure pump.
Then get a stock high pressure one and mount it up front. Just needs a 12v source, which the Sniper supplies.

 

There are a few options to convert a carbed set up to a efi.

There are some really nice/expensive set ups. Including one that completely mounts under the hood. It has it own reservoir and high pressure pump. Your stock mechanical pump supplies the fuel to the reservoir and that feeds the high pressure pump and the return line just goes back to the reservoir.

Or there are set up's like the Aeromotive set up where you enlarge the hole in your gas tank and the unit goes in your stock tank.

But with some creativity you can accomplish it without spending the big bucks that the above units cost.

 

AB, that explains it. I didn't realize there were 2 pumps - LP and HP - in the stock system for '85. Thanks!

fordman, thanks for the info. I'm still far from actually doing it, but reading this thread has me interested when I get there. I'm sticking with the 300, albeit warmed up a bit with some parts I've been collecting. I also have a 4x4 ZF trans that I need to convert to 2x4, and then planned to use it as AB did, so there are some parallels to his build. Lol, he's my build guide.

 

Definitely let me know if you have any questions.

One thing that I like about having a pump in the tank is that it alleviates a lot of the problems of vapor lock.

 

This is only true for the 85+ 302 powered trucks because they were efi. Carbed vehicles got a manual pump on the block.

My 85 came to me with an additional inline aftermarket electric pump. No return. It's before the manual pump, and only operated by a rocker switch. Doesn't have to be on for the engine to run.


The next step would be swap to a Clifford manifold, and use their cast in fuel injector bosses in each runner and a throttle body.

 

That is kind of a given. Since the 4.9L didn't get EFI until 87 and 5.8L's in 88.

I think the only carbed engine that might have came with a electric fuel pump in a fullsize truck or van was possibly the 460 sometime in the 80's. I know I remember something about a 80's F250 or F350 with a 460 that had a electric pump with return line. I think I might of had that set up on a 86 F250 460 I use to own.

Running a electric pump with the mechanical pump is a bad idea. The electric pump pushing fuel thru the mechanical one can rupture the diaphragm and then fill your crankcase with gas.


If you can do some fabrication. Using the stock lower EFI intake and fabbing up a upper intake is a whole lot cheaper! I love the Clifford dual carb intake but just can't stomach spending $400-$500 for a intake manifold! I'm not sure what there single carb intake cost now.

 

Okay, pulled the #1 and #3 spark plug, since those are the closest and furthest away from the Sniper.
Honestly, if I had laid them down side by side, I would not have been able to tell the difference.

#1





#3

 

So, I found this interesting.
I had been struggling with the vacuum reading on my engine being quite low.
With all fresh intake/exhaust gaskets, space plate and "carb" gaskets, new intake, and the Sniper EFI, everything should have been nice and tight.

However... my idle vacuum was around 14 - 15. My machinist said it'd be a little lower since I have a bigger cam, but not that low.
I sprayed around with carb cleaner and everything was nice and tight.
About the highest I could get it was maybe 15.5 if I adjusted the timing into the 20's on base timing (for testing)


Anyway, I started playing around with some of the readout on the Sniper and was looking at the MAP (Manifold Air Pressure).
At idle, I'm at around 40 kPa, cruise is around 50 - 60 depending, acceleration gets upward of 70 - 100.
When I let off the gas and engine braked, it was around 20.

I looked into Holley's documentation for the direct correlation between MAP and inch pounds of vacuum.

Vacuum = 30 - kPa * 0.3


So at 40:

Vacuum = 30 - 40 * 0.3
Vacuum = 30 - 12
Vacuum = 18

I'm willing to wager that a sophisticated engine management barometric pressure sensor is a bit more accurate than an old handheld vacuum gauge I've banged around a few times.
It definitely makes me feel a whole lot better! 18hg for a freshly rebuilt, very tight engine seems much more likely than 14.

Either way, for whoever is curious:

Vacuum - kPa
0 - 100
2 - 93
4 - 87
6 - 80
8 - 73
10 - 67
12 - 60
14 - 53
16 - 47
18 - 40
20 - 33
22 - 27
24 - 20
26 - 13
28 - 7
30 - 0

 

Hello sir,

I don't want to nit-pick, but I think maybe you meant Vacuum = 30 - (kPa / (10 / 3)) or Vacuum = 30 - (kPa * (0.3)) do you agree? Probably just a typo.

I just want to clarify in case someone else tries to use the formula.

 

No worries.

No, not a typo, but you're right in that that's a more reduced way of putting it.

Vacuum = 30 - kPa * 0.3
I edited my post above.

 

I think you've mentioned that before, but I don't run the electric pump. It's just there, because the PO put it there. Its operated by a toggle on the dash.

 

Just wanted to add that with the frigid 10° - 15° mornings this week, I am thoroughly enjoying driving an engine that doesn't bog and stumble.
It's luxurious.

 

10-15* mornings... is that legal?

 

It sure seems to be, because no one's stopping them!