So i have a 2000 ranger trailhead 3.0 2wd truck, just swapped a 99 3.0 engine into my truck because i broke 2 lifters and im having an issue with it running right now. It stumbles and hesitates and backfires like crazy under load but when parked in nutural it has no issues and revs cleanly.... I have replaced the plenum gasket because i swapped my plenum over, used the trucks ecu, upper intake, MSD coil pack, new plugs and wires from my truck that have less than 10k on them, what could my issue be?

 

Double check firing order on coil pack, then check it again, lol.

Could Upstream O2 sensor wires have been reversed?
Happen to me once, same connectors, left and right, and you will get what you describe, but engine will run OK cold or at Wide Open Throttle, because O2 sensors are not used then

Ford changed from 3 wire(hall effect) to 2 wire(VR) Cam sensors in late 90's they are not interchangeable, totally different signals

Double check Throttle position sensor(TPS) connector, it is the equivalent of the "accelerator pump" on a carb engine, adds an extra squirt of fuel when throttle is opened so you don't get hesitation or lean condition(back fires) when you press down on gas pedal

 

I dropped a 99 motor into a 2000, there is only a year of difference... Had to use my intake planum because there were 3 different sensors between them and i had it off anyways. Firing order should be good.... Left bank in order right bank is swapped rear on block to front on coil pack. The o2 sensors should be right because they only reached 1 way, wide open doesnt change the popping so its not that. All vacuum is in order, it honestly feels like its an intake gasket but i didnt touch the lower manifold so I'm hoping thats not it

 

The tps sensor wire is on tight.... But the truck is sucking fuel down at an astronomical rate, went for 2 trips around the block and a 3 mile drive through my neighborhood and used an 1/8th of a tank to do so

 

The 3.0l Flex Fuel engines had larger injectors for E85 fuel, and they should not be used with non-flex fuel computers, too much gasoline flows in when they open, flex fuel computer limits open time for gasoline
So was the 1999 engine/injectors from flex fuel vehicle?


Do the "Clear Flooded Engine" test

Turn key on
Press gas pedal down to the floor and hold it down all the way(this turns OFF fuel injectors)
Turn key to START

Engine should just crank and NOT start or even fire, fuel injectors are off

If engine starts then you most likely have a leaking fuel injector.

Clear flooded engine mode ends when RPMs are above 300 or if foot comes off gas pedal.

It is initiated when key is on and computer sees:
0 RPMs
TPS voltage above 4.5volts(Wide open throttle)
Computer then deactivates fuel injector pulses, until RPMs are above 300 or TPS voltage is below 4.5volts

If engine starts, then you can do the same test to ID a leaking injector or injectors
Disable coil pack, unplug wire connector, you want no spark
Crank engine over a few times with gas pedal held down, Clear Flooded Engine mode
Now pull out spark plugs and look for the WET one, all should be DRY with injectors OFF

 

My truck is flex fuel, injectors stayed in truck, just put the entire rail over by brake master when i did swap

 

Small update, still need help

So i finally got a chance to play with the truck again, swapped out my coil pack with a factory one that came with the motor, it no longer stumbles but its still backfiring quite a bit... Any ideas? It feels like its still misfiring as the power isnt there but she pulls smoothly even though its acting like it has no power

 

Re-check your firing order. Plug wires easily get reversed when reinstalling them.

 

Plug wires are in the correct order, front to back on passenger side and reversed on the driver side.

 

 

Im gonna swap the front 2 cables driver side and see if that fixes it then. I saw a different firing order that had the drivers bank simply reversed, thank you.

 

They are not in order

The firing order on coil pack for 3.0l or 4.0l has "Matched Pairs"
Each coil pack has only 3 coils inside, not 6, so 2 spark plugs Share a coil and fire at the same time, one fires for power the other fires on exhaust stroke so is "wasted"
This is called a Waste Spark system, and is used on lawn mower to airplane engines

Match spark plugs are:
1 and 5
2 and 6
3 and 4

So one side of coil pack will be 1 2 3
The other side would have to be 5 6 4, NOT 4 5 6 or 6 5 4
Pairs have to match

There are different types of coil packs and they are wire differently so you need to match connector.
Image on one kind here: https://ww2-secure.justanswer.com/up...9_050836_1.gif

You can reverse 1 and 5 or 3 and 4 wires because they share the one coil, but you can't reverse 5 and 4 or 1 and 3

Check firing order then check it again, then check it one more time.........or or until engine stops back firing

 

Thank you, i got home late so i will check it in the morning, the description you just gave me for the wasted spark makes much more sense than the one i was given from a friend and it makes quite a bit of sense now, i appreciate that very much as it helps me learn more.