1984 4.9L engine diagnostics

[1986F150Six]

I have looked, but have not found a description of the function of the white wire which is connected to the end pin of the test plug connector.

Thank you in advance.

 

[1986F150Six]

I just found this and I will study it.

https://www.garysgaragemahal.com/electronic-engine-control.html

[Gary Lewis]

I just found this and I will study it.

https://www.garysgaragemahal.com/electronic-engine-control.html

David - I think you found an error in the EVTM!

The link you gave takes me to this page, and you can see the W/BK wire in the lower right and then the notation that the group of wires go to Start/Ignition on pages 27 and 30. And yet I cannot find Ckt 4 W/BK on those pages.

However, I did find it in the Charge/Power Distribution section on Page 15, and it is the stator wire from the alternator to the choke and to the Electronic Engine Control. Does that answer the question?

[85lebaront2]

David - I think you found an error in the EVTM!

The link you gave takes me to this page, and you can see the W/BK wire in the lower right and then the notation that the group of wires go to Start/Ignition on pages 27 and 30. And yet I cannot find Ckt 4 W/BK on those pages.

However, I did find it in the Charge/Power Distribution section on Page 15, and it is the stator wire from the alternator to the choke and to the Electronic Engine Control. Does that answer the question?

One minor item, you are looking at the 1986 EVTM, not the 1984 EVTM. 1986 was the last year for the 4.9L FBC system and it was an EEC-IV unit. I am looking at my information right now.

Circuit 4, the stator 7.5V output for the choke, does not actually go to anything on the FBC system other than being in the test connector. I assume that was done so the 7.5V can be easily verified on the 1G alternator without having to get at the alternator connections.

 

[Gary Lewis]

One minor item, you are looking at the 1986 EVTM, not the 1984 EVTM. 1986 was the last year for the 4.9L FBC system and it was an EEC-IV unit. I am looking at my information right now.

Circuit 4, the stator 7.5V output for the choke, does not actually go to anything on the FBC system other than being in the test connector. I assume that was done so the 7.5V can be easily verified on the 1G alternator without having to get at the alternator connections.

Good points, Bill. We don't have all of the '84 EVTM online so I can't speak to what it shows. But it is interesting that Ckt 4 only goes to the test connector, not to the ECU as implied.

[85lebaront2]

Good points, Bill. We don't have all of the '84 EVTM online so I can't speak to what it shows. But it is interesting that Ckt 4 only goes to the test connector, not to the ECU as implied.

I can scan what I printed from AllData today so you can add it if you want to. BTW, how is the scan of my owners manual coming?

[Gary Lewis]

I can scan what I printed from AllData today so you can add it if you want to. BTW, how is the scan of my owners manual coming?

I might get started on the scanning tomorrow. It has taken a back seat to the show and the trip.

But remind me what I can take apart and what I can't?

[1986F150Six]

I might get started on the scanning tomorrow. It has taken a back seat to the show and the trip.

But remind me what I can take apart and what I can't?

Thanks, Gary and Bill, for your input.

Here is the deal... my son is out of country and I am looking after his truck [an original 1984 feedback system 4.9L equipped F150]. On my first drive, it ran poorly. It had an intermittent hard miss which was not dependent on engine speed. At first, I thought possibly a bad spark plug wire as it seemed worse while under load, but after stopping for awhile, when restarted, the truck ran well for the return trip. I raised the hood with the engine idling and performed a "jiggle test" of the wiring harness. When the wire [it looks white to me, with no other markings] on the passenger side was jiggled, the engine stumbled. Upon closer inspection, this wire which is small gauge has numerous cracks in the insulation. I suppose this is due to age and the fact that this wire resides above the exhaust manifold.

[85lebaront2]

I might get started on the scanning tomorrow. It has taken a back seat to the show and the trip.

But remind me what I can take apart and what I can't?

The 1990 can be taken apart, the 1996 one no, it's the only copy I have. I believe you said you have a 1986 one.

1984 4.9L EEC, charging and ignition pdfs along with a corrected EEC pinout spreadsheet are on their way to you.

[85lebaront2]

Thanks, Gary and Bill, for your input.

Here is the deal... my son is out of country and I am looking after his truck [an original 1984 feedback system 4.9L equipped F150]. On my first drive, it ran poorly. It had an intermittent hard miss which was not dependent on engine speed. At first, I thought possibly a bad spark plug wire as it seemed worse while under load, but after stopping for awhile, when restarted, the truck ran well for the return trip. I raised the hood with the engine idling and performed a "jiggle test" of the wiring harness. When the wire [it looks white to me, with no other markings] on the passenger side was jiggled, the engine stumbled. Upon closer inspection, this wire which is small gauge has numerous cracks in the insulation. I suppose this is due to age and the fact that this wire resides above the exhaust manifold.

That is probably the W/BK wire and goes from the "S" terminal on the alternator to the choke cap. It provides the 7.5V to heat or assist in heating the choke.

It may have originally been sheathed and in some clips on the valve cover bolts to keep it off the exhaust manifold.

While you are doing a "wiggle test" grab the top portion of the carburetor and see if it is loose on the throttle body as this is a common problem on the carbureted 4.9L engines.