HELP! Backfire/ Popping sound

[TrublesumRanger]

I'm having trouble figuring out the problem with my 91 4.0L ranger. It has a sort of bogging/ hesitation when i accelerate and then Pop!! The sound is coming toward the front end of the car.. But it only happens when im driving and accelerate around 2k rpm. The truck idles fine and doesnt stall. I've change the simple stuff so far. Ignition module, spark plug wire, spark plugs, PCV, Fuel filter. Cleaned the MAF, TPS, TB, o2 and nothing there is no CEL
It was running fine 2 days ago.. i disconnect the CAT to see if there was clogged but still did it.. I'm stuck

 

[RonD]

What did the old spark plugs look like?

Any of them blackish?

First triple check Coil firing order
3 4
2 6
1 5
Front

I mess up the 5 6 4 all the time, trace each wire back to the cylinder as well, I mess that up too, lol, surprised I still work on engines, and I think it is getting worse

Generally a back fire(out of intake) is air/fuel igniting as it enters a hot cylinder, this can be caused by a dirty injector that drips fuel instead of spraying fuel so you get a Lean mix that can self ignite before intake valve closes.
Run some cleaner in fuel system, like Seafoam

Back fire(out exhaust) is air/fuel that didn't burn or only partially burn, it is ignited by hot exhaust from another cylinder on that bank

 

[TrublesumRanger]

What did the old spark plugs look like?

Any of them blackish?

First triple check Coil firing order
3 4
2 6
1 5
Front

I mess up the 5 6 4 all the time, trace each wire back to the cylinder as well, I mess that up too, lol, surprised I still work on engines, and I think it is getting worse

Generally a back fire(out of intake) is air/fuel igniting as it enters a hot cylinder, this can be caused by a dirty injector that drips fuel instead of spraying fuel so you get a Lean mix that can self ignite before intake valve closes.
Run some cleaner in fuel system, like Seafoam

Back fire(out exhaust) is air/fuel that didn't burn or only partially burn, it is ignited by hot exhaust from another cylinder on that bank

Yes, the order is correct . triple checked before . the old spark plugs were all matching with very little blackness. They are gaped correctly.. 0.54 . I haven't checked the injector just yet . I will have to wait on the Seafoam till later tonight .. Thanks for the input! (annoying neighbors complain about everything )

 

[RonD]

Other thing is...........does it do it when engine is cold?

Or only after it warms up?

 

[TrublesumRanger]

it does when its cold and warm..

 

[TrublesumRanger]

Tried seafoam.. did nothing. The truck still has loss of power and still sounds like backfire but only when i start driving....

Might be a bad injector. or something else?

 

[RonD]

If it does it cold then can't see injector issue.

'91 4.0l uses EDIS-6 module(ignition control module), which you said you changed.

It sets base timing and can do some RPM based advance, but it really relies on the computer to give it data on spark advance.
EDIS-6 get PIP signal from crank position sensor, it passes that signal on to computer to use for injector timing.
Computer uses other sensors, like the TPS, to send the SAW(spark angle word) signal back to EDIS to advance or retard spark timing based on driver input.

So when you step on the gas, computer gets "heads up" from TPS, increase fuel AND sends spark advance data to EDIS.

If this(SAW) wasn't working then engine would be sluggish and hesitate.

I would think this would set a code unless the problem was in the computer.

If you can get a timing light you may be able to tell if you are getting engine spark advance.

 

[Big Jim M]

If that "pop" is a backfire I'd be looking at fuel delivery problems. To little fuel for the amount of air your foot is allowing will cause the "pop" of a backfire and a loss of power.
Now if you have recently changed something, like sparks, then perhaps you have installed the wrong ones and the bottom of them is getting too hot and igniting the fuel prematurely.

Big Jim

 

[RonD]

I would also check if computer monitoring is working, disconnect MAF sensor and start engine, you should get a CEL right away.

 

[TrublesumRanger]

Wont be able to get a timing light until next week.. i'll check back in next week and let you guys know how it goes. thanks for the help