EFI For Big Blue

[Gary Lewis]

Yes, that is exactly what I would expect.

The 85.5/86 7.5L wiring is for a carbureted truck. I had no way to wrap my thinking around how this was to be used with EFI.

Are you thinking that you may want to modify the existing Big Blue wiring to accommodate EFI? If so, you could do away with the oil pressure sender, resistance wire and fuel pump cut off relay along with their various power feeds.You would substitute the EFI fuel pump relay output, (configured through a relocated inertia switch) for the power feeds PK/BK to the tank selector relay and the R lead to the fuel tank selector switch. This also would be the point to supply power to the frame mounted HP pump. The tank selector valve would have to be 6 port to accommodate the return lines and you still would need some sort of reservoir before the frame mounted HP pump.

Of course, if you are going to the later in tank HP FDM's, you only need to wire it like the later truck. I'm pretty sure they use the same switch on the dash and all the wiring changes would be in the harness. This does away with dual function reservoirs, frame mounted HP pumps, selector valves, etc.

I'm probably overthinking this. Best approach would be to replicate the 86 5.0 EFI wiring, (eliminating the frame mounted pump and the 85 6 port valve) and you would be good to go with the later FDM's.

Yes, I'm thinking of modifying Big Blue's wiring to go EFI. My plan is to go with the 1990ish FDM's. But I'm using the 1996 engine compartment harness, so the fuel pump relay will be in that, and I can do away with the 1985 fuel pump cut-off relay, 6-port valve, frame-mounted pump, oil pressure switch, tank selector relay, etc.

I wonder if I should get an 85.5-6 5.0L EFI fuel tank harness. Or, let me see what I have from Huck......

[Gary Lewis]

Yes, I'm thinking of modifying Big Blue's wiring to go EFI. My plan is to go with the 1990ish FDM's. But I'm using the 1996 engine compartment harness, so the fuel pump relay will be in that, and I can do away with the 1985 fuel pump cut-off relay, 6-port valve, frame-mounted pump, oil pressure switch, tank selector relay, etc.

I wonder if I should get an 85.5-6 5.0L EFI fuel tank harness. Or, let me see what I have from Huck......

Well, I just realized that there's a big difference between the 1985 and the 1986 EVTM's on the fuel system wiring. The 1985 has a 6-port tank selector valve and the 1986 doesn't. I think I remember Bill saying something about this, but it went right over my head.

The 1986 is really close to the 1996, with the obvious difference in that the '86 has a high-pressure pump and the '96 has a computer. But another subtle difference is in the pin-out on the fuel tank selector switch. So off I went to the catalog and I found that they appear to take different switches.

I wrote this up on the Fuel Systems Wiring page, and I'd appreciate it if you could take a look and tell me what I'm missing.

Here's the 1985 wiring for the 5.0L EFI:

And here's the 1986 wiring for the 5.0L EFI with dual tanks:

[NotEnoughTrucks]

Well, I just realized that there's a big difference between the 1985 and the 1986 EVTM's on the fuel system wiring. The 1985 has a 6-port tank selector valve and the 1986 doesn't. I think I remember Bill saying something about this, but it went right over my head.

The 1986 is really close to the 1996, with the obvious difference in that the '86 has a high-pressure pump and the '96 has a computer. But another subtle difference is in the pin-out on the fuel tank selector switch. So off I went to the catalog and I found that they appear to take different switches.

I wrote this up on the Fuel Systems Wiring page, and I'd appreciate it if you could take a look and tell me what I'm missing.

Here's the 1985 wiring for the 5.0L EFI:

And here's the 1986 wiring for the 5.0L EFI with dual tanks:

That is 100% clear!

Of course, there is a lot about fuel systems yet to cover, but the focus of this project is EFI for Big Blue.

I recently sent my 86 EFI wiring harness to Steve and I am pursuing later model wiring for my Frankentruck, but the actual routing of the tank wiring seems to be included in the body and chassis wiring. I think the 86 wiring is still on the chassis of my truck and the cab wiring is intact minus the EFI harness. I recall the fuel pump relay was mounted low on the driver's side firewall on the engine side and I can't recall where the inertia switch was located on the 86, but I know it's on the firewall inside the cab, just above and to the right of the transmission hump.

I'm finding a lot of the reasons I chose 87 and up components for my Frankentruck are echoed in Bill's write up on Darth. I really should start my own white paper. The fuel tank wiring on the later trucks runs in and out of the cab through the firewall connector. Relay and tanks of course are on the outside and selector and inertia switches are on the inside. The 86 has a similar layout, but wires are run through grommets in the firewall rather than a connector like the later models. I know the later model integrates the wiring into the dash wiring harness, but I think the bullnose trucks may have a separate harness because of all the variants? I will see if I can find some clues in my old cab if this weather ever warms up.

[Gary Lewis]

That is 100% clear!

Of course, there is a lot about fuel systems yet to cover, but the focus of this project is EFI for Big Blue.

I recently sent my 86 EFI wiring harness to Steve and I am pursuing later model wiring for my Frankentruck, but the actual routing of the tank wiring seems to be included in the body and chassis wiring. I think the 86 wiring is still on the chassis of my truck and the cab wiring is intact minus the EFI harness. I recall the fuel pump relay was mounted low on the driver's side firewall on the engine side and I can't recall where the inertia switch was located on the 86, but I know it's on the firewall inside the cab, just above and to the right of the transmission hump.

I'm finding a lot of the reasons I chose 87 and up components for my Frankentruck are echoed in Bill's write up on Darth. I really should start my own white paper. The fuel tank wiring on the later trucks runs in and out of the cab through the firewall connector. Relay and tanks of course are on the outside and selector and inertia switches are on the inside. The 86 has a similar layout, but wires are run through grommets in the firewall rather than a connector like the later models. I know the later model integrates the wiring into the dash wiring harness, but I think the bullnose trucks may have a separate harness because of all the variants? I will see if I can find some clues in my old cab if this weather ever warms up.

If you have the '86 tank wiring then I'd be very interested. But I'm not in a hurry. However, assuming it is the 5.0L EFI that I think it is, it would almost be plug & play. I think.

As for the later wiring, I've been combing through Huck's and found that I have all of it, albeit in pieces. I have the tank wiring, but the rear tank connector is cut off too close to allow splicing. And that harness was cut from the underhood harness, but it would be easily spliced. Then it goes through the bulkhead connector into the dash harness, so I'd have to splice at that connector. However, it then runs, along with lots of other wires, and finally comes to the tank switch.

So, with some splicing and a new tank connector I could have a the tank wiring to plug into the switch. However, if you have the '86 stuff in good shape then it should be easier and cleaner. Again, absolutely no hurry. I know it is COLD up there!

[85lebaront2]

If you have the '86 tank wiring then I'd be very interested. But I'm not in a hurry. However, assuming it is the 5.0L EFI that I think it is, it would almost be plug & play. I think.

As for the later wiring, I've been combing through Huck's and found that I have all of it, albeit in pieces. I have the tank wiring, but the rear tank connector is cut off too close to allow splicing. And that harness was cut from the underhood harness, but it would be easily spliced. Then it goes through the bulkhead connector into the dash harness, so I'd have to splice at that connector. However, it then runs, along with lots of other wires, and finally comes to the tank switch.

So, with some splicing and a new tank connector I could have a the tank wiring to plug into the switch. However, if you have the '86 stuff in good shape then it should be easier and cleaner. Again, absolutely no hurry. I know it is COLD up there!

I believe I sent you the original tank/rear chassis wiring from Darth.

[85lebaront2]

Well, I just realized that there's a big difference between the 1985 and the 1986 EVTM's on the fuel system wiring. The 1985 has a 6-port tank selector valve and the 1986 doesn't. I think I remember Bill saying something about this, but it went right over my head.

The 1986 is really close to the 1996, with the obvious difference in that the '86 has a high-pressure pump and the '96 has a computer. But another subtle difference is in the pin-out on the fuel tank selector switch. So off I went to the catalog and I found that they appear to take different switches.

I wrote this up on the Fuel Systems Wiring page, and I'd appreciate it if you could take a look and tell me what I'm missing.

Here's the 1985 wiring for the 5.0L EFI:

And here's the 1986 wiring for the 5.0L EFI with dual tanks:

Gary. I believe I mentioned that yesterday or maybe Monday. The 1985 EVTM was probably an early release before the actual EFI system was in production since it was a mid-year change, I would suspect that an update to that manual was released either by a TSB or manual update notice once the EFI production started. I have never seen a 1985.5 EFI truck without the reservoir and the system the 1985 models have. Look at your parts CD and see if the 6 port valve even shows up on the 1985 EFI engines, I will be very surprised if it does, because lack of the reserve capacity in the tank selector/filter/reservoir would have the Bosch HP pump starving for fuel. If the 6 port valve was adequate, why would the to LP pumps be needed? Mercedes used to have a Bosch pump back outside the tank that was low down where it could get fuel, I suspect the tank may have been baffled around the pickup to help make sure it didn't pull air in. FWIW, the 1987 Chevy trucks (first year for TBI) had a cup inside the tank that the pump stuck into, Chrysler did the same on their first TBI/MFI engines and had a jet on the side of the cup the return fuel went to so the cup stayed full.

[Gary Lewis]

Gary. I believe I mentioned that yesterday or maybe Monday. The 1985 EVTM was probably an early release before the actual EFI system was in production since it was a mid-year change, I would suspect that an update to that manual was released either by a TSB or manual update notice once the EFI production started. I have never seen a 1985.5 EFI truck without the reservoir and the system the 1985 models have. Look at your parts CD and see if the 6 port valve even shows up on the 1985 EFI engines, I will be very surprised if it does, because lack of the reserve capacity in the tank selector/filter/reservoir would have the Bosch HP pump starving for fuel. If the 6 port valve was adequate, why would the to LP pumps be needed? Mercedes used to have a Bosch pump back outside the tank that was low down where it could get fuel, I suspect the tank may have been baffled around the pickup to help make sure it didn't pull air in. FWIW, the 1987 Chevy trucks (first year for TBI) had a cup inside the tank that the pump stuck into, Chrysler did the same on their first TBI/MFI engines and had a jet on the side of the cup the return fuel went to so the cup stayed full.

Bill - I'm getting myself confused, but I think you are saying that all the EFI'd 5.0's had the reservoir/switching valve and not the 6-port valve as shown in the 1985 EVTM. Is that correct?

Also, wouldn't Darth's harness just be a longer version of the one that's already in Big Blue? Meaning it would be set up for the 6-port valve. Right?

That's why I'm interested in a 5.0L EFI harness since it should plug right into the tanks and the tank-selection switch.

What am I missing?

[85lebaront2]

Bill - I'm getting myself confused, but I think you are saying that all the EFI'd 5.0's had the reservoir/switching valve and not the 6-port valve as shown in the 1985 EVTM. Is that correct?

Also, wouldn't Darth's harness just be a longer version of the one that's already in Big Blue? Meaning it would be set up for the 6-port valve. Right?

That's why I'm interested in a 5.0L EFI harness since it should plug right into the tanks and the tank-selection switch.

What am I missing?

Yes, I have never seen an early EFI without the reservoir. I actually had an 85.5 to repair, it wouldn't run because the ground plug was corroded. Once I fixed that it started right up and ran fine.

Wiring, yes, pretty much so, I had actually sent that for you to use when you weren't sure what had been intercoursed with on Big Blue.

[Gary Lewis]

Yes, I have never seen an early EFI without the reservoir. I actually had an 85.5 to repair, it wouldn't run because the ground plug was corroded. Once I fixed that it started right up and ran fine.

Wiring, yes, pretty much so, I had actually sent that for you to use when you weren't sure what had been intercoursed with on Big Blue.

And I thank you for that. Want it back? Or do you want me to keep it in case you need it?

As for the 5.0L EFI harness, it is almost a slam-dunk. If you look at the wiring diagrams below you can see that I'll have to remove the power to the high-pressure pump. Beyond that I don't think there are any other changes.

[Gary Lewis]

And I thank you for that. Want it back? Or do you want me to keep it in case you need it?

As for the 5.0L EFI harness, it is almost a slam-dunk. If you look at the wiring diagrams below you can see that I'll have to remove the power to the high-pressure pump. Beyond that I don't think there are any other changes.

And, in case you are wondering about it, I realize the connections to the tank selection switch are quite different from the 1996 to the 1986 drawings. But since I'll be using a complete harness intended for the 6-pin switch, it will work - assuming Ford didn't change the connection order on the pumps and sending units.