Hey everyone. Just recently purchased an 86 F150 4.9. I am trying to fix it up to use as my daily driver and also to learn a bit about working on trucks.

My main issue is that I'm getting roughly 5 to 6 mpg even while light on the pedal. Previous owner installed an electric fuel pump, that runs to the carb with no pressure regulator, just a filter. I'm starting to think that's my issue. My question is, would a pressure regulator fix that? If so, what should I be looking for?

My other option was going to be converting back to a mechanical pump.

Currently has a Carter YFA 1 bbl and the fuel pump is a Carter P4070.

Any help or advice is appreciated.

 

The float in the carb acts as a pressure regulator. The pump just keeps the bowls full. If you aren't running fuel down the intake, the pump is not losing you fuel. You need to start with the basics:
1. Plugs, wires, distributor. Replace what needs to be replaced. Plugs may be fouled or otherwise garbage.
2. Clean and rebuild the carb. Mike's Carburetor Parts is great for this, their kit for the YFA is good and includes a good instruction packet. Youtube-iversity is good for help also.
3. Find and seal all vacuum leaks. This is death by 1000 cuts.
4. Set timing. The timing gear drive doesn't come out of whack much, but who knows what the previous owners were up to. If you can't find the timing marks (apparently it's an issue on the newer motors) you can get it damn close with a vacuum gage.

 

Is that engine set up for a mechanical pump?

IF so,, get rid of the electric. It probably is pushing much pressure. You don't see leaks or over-rich conditions?

Anyway, it probably does not have a safety switch wired into it anyway, so if you can, go back the the OEM setup.

 

1. So plugs are brand new, wiring looks A-ok, and distributor looks fine.
2. Carb looks to be brand new. I've adjusted the float to match my vehicle's specification and adjusted the other external screws for mixture and idle speeds.
3. Vacuum leaks was something ive been looking into. Just replaced the EGR valve (Old one was destroyed), but I have no idea where the vacuum tube from it runs to. I've capped a bunch of other tubes that look like vacuum ports on the carb that were just wide open. Still investigating possible vacuum issues.
4. I just reset the timing. My FIL let me use his timing light and that's all set now.

That's what I was thinking, but I don't know where the port for a mechanical one would be. The Electric pump on here and the switch are all definitely aftermarket, which leads me to believe that it was originally a mechanical one.

Leaks-wise, I haven't seen any overflow or drips around the carb or fuel lines, but the truck definitely runs rich. I can always smell gasoline if I'm outside the cab and it's running.

 

Newer Engine blocks didn't the hole machine in the side of the engine for a mechanic fuel pump.
Also, wire the choke full open during your testing.
Jim

 

https://www.ford-trucks.com/forums/1...p-fitment.html

https://www.f150forum.com/f13/mechanical-fuel-pump-replacement-86-f150-4-9l-388842/

Here's some photos

What are you using for an ignition system?
The original one was computer controlled, like the EGR.
Jim

 

You were right. The block isn't machined for one. See the pic.

 

I'll be honest, I don't no where to look to be able to tell you what kind is on here.

 

In the second link, first photo, you will see the ignition module on the side of the distributor. This is computer controlled ignition, which is currently locked to 10 degrees timing with no advance.
It looks like you have a square coil, not a round one.

Add some photos of the engine compartment.
Has the computer been removed?
The computer is above the gas pedal, a little towards the center.

What you are looking at is a computer delete and getting a new GM style coil over cap distributor. That will be your new ignition system. This is a common mod on 1985-1986 computer controlled six cylinder trucks.
Jim

 

https://www.ford-trucks.com/forums/1...light=computer
Computer delete info

 

https://www.ford-trucks.com/forums/1...l#post21649061

This guy used a separate controller for the fuel pump to shut it off in case of an accident.
Modern vehicle use an inertia switch to shut off the fuel pump.
Jim

 

Jim hit it on the head.
Your truck, 83 or 84 - 86, known as feedback system that a computer controlled timing & fuel even with a carb with all them wires going to it.
If any of the sensors are bad or not connected the computer goes into limp mode locking the timing and makes the carb rich and why you lack power and MPG.

The fix is to Replace the distributor with a HIE drop in off Ebay and a knock off non feed back carb off Ebay again.
Once running you can rip out the computer and wiring.
There is a lot of information on this in the 80 to 86 truck area.
Dave. ----

 

Here are some pics of the engine bay and what I think is the ecm.

 

Rambling, babbling:

- Not a feedback carb - those have a solenoid at one of the corners - so no matter what the computer is doing, if anything, it can't be doing anything that affects this.
- The head has the pumped-air inlets blocked off, FWIW.
- That looks like a grey push-start TFI ICM on the distributor, so unless the computer is controlling timing, there's no advance. I'm under the impression that those were first used with EEC-IV systems, but don't actually know.
- Is that a (broken and unconnected) knock sensor to the right of the (non-machined) fuel pump boss in reply #7? Did the EEC-III systems use those? If not, to have a knock sensor then the block is from at least an '87.
- The valve cover has the mounting bracket at the rear for the TAD, TAB, and EGR solenoids, though none of them are there - did EEC-III have those?
A clear, readable photo of the entire vacuum diagram there to the left of the hood latch would clear up some of those issues.

A guess: this is an 87+ donor engine with the TFI-mounted distributor, but a log intake & exhaust and an aftermarket (non-feedback) carb, and a partially wired up '86 ECU. Dr Frankenstein may not have put any effort into tuning the carb (jets, whatnot). If the computer isn't doing a passable job of controlling timing, then maybe swapping out the dist and ICM with a DSII ignition system (or equivalent, as previously mentioned) would be better - or whatever the aforementioned 'computer delete' thread recommends. The computer might still be controlling important things like a fuel pump relay, which would complicate just removing it; an '86 engine-to- ECU wiring diagram would be useful, or even just the '86 ECU pin list.

How did '83 or earlier systems control the EGR valve - some mix of temperature & vacuum doohickeys?

 

I appreciate all the info. It really helps out as I'm rather new to working on vehicles. Next time out there, I'll snap a pic of that vacuum diagram.

I think with all the missing parts I have that are somewhat linked to the EEC, I'll look at doing a computer delete. I'm looking through eBay for a good HEI distributor to replace my current one.