I recently picked up a 1991 f150 with the 4.9l. I was told it had a bit of a backfire when I purchased it. Drove it 110 miles home and since then it has gone downhill severely lots of backfiring, bucking loss of power and angry drivers behind me as it began acting up the next day. Going uphill or above 30mph or so it starts bucking and popping, the smell of gas floods the cab and smells like gas coming out exhaust. The previous owner replaced the wires with "v8" wires- I replaced with proper I6 wires and routed properly so no crossfire. The distributor is brand new but I discovered they had never tightened down the bolt so I was able to move it while pulling the wires, also said to have replaced plugs (on my list of things to do in between rain). I found a long crack in the egr exhaust line and have since repaired that crack. I have made sure all vacuum lines are connected. I will upload a couple pictures as it appears according to the other photos ive seen of this truck that I should have a tube running under the manifold that connects to the combo air/vacuum pump. This is my first ford and im already frustrated with it. I have taken pictures from all different angles of the vacuum system as it appears by the codes I got that it points back to vac. KOEO 114,116,565 KOER 116,126,213,311,332,522,565. I did not have a second person so the clutch was not pressed and the goose test probably didnt work right. So far I have replaced the wires, positioned the distributor as close as possible while I await a new timing light, replaced o2 sensor and flushed coolan.

 

I am aware you have another post going and being assisted by Hayapower.
Will try not to interfere with his directions.
Do you have any type of multimeter available to use.
I ask this because it seems some of the codes indicate a problem that is common to a few of them and it could be a ground connection left off or missing or possibly a 5 volt reference voltage that should be available to some of the components and may be absent. Those years had loads of emission stuff on them and when working correctly were OK. On the other hand the more stuff the more opportunity for things to go wrong.
If you become confused, don't feel frustrated they drove us nuts too. Some of the controls were electrically controlled after the temp controls worked then the vacuum controls were allowed to work.
I usually try to tackle the problems one at a time, it takes a little longer sometimes, but prevents duplicate efforts.

 

Yes I actually just picked up a brand new autoranging multimeter.

 

I know this goes back awhile , but is the vacuum diagram still under the hood and readable>\?
I can't tell you exactly where the ground connections are located, but there should be a ground (make a separate wire if necessary) coming from the battery negative post to the sheet metal (pick a good clean spot), then one to the engine (sometimes they used the thermostat housing for that one, There is of course a ground cable going to the starter mtg at the engine.. There needs to be a good ground for the computer case that is mounted in the vehicle.
There should be an Orange wire with a white tracer going to the MAF (mass air flow) sensor, the throttle position sensor (on the throttle body) and EGR valve (Exhaust Gas Recirculation) position sensor (mounted on top of the EGR valve)
That wire should with the key on have 5 volts and it is called vehicle reference voltage. It is supplied by the computer (ECM).Pin #26
Those 2 items (power & grd) will keep you busy for a while , but now you will have confirmed if those 2 items are good and working.
Key power and vehicle power are the same 12 volts supplied by the battery. Let us know what you find.
Don't forget to check all the fuses, easily done with the meter. If you have 12 volts on one side you must have 12 volts on the other side of the fuse. Some fuses will require the key to be in the on position to make sure power is there.