4.0 backfiring ?

[alx]

ok i have got my hands on a 94 ranger with a 91 explorer motor in it ...
started out with a code reader got all codes cleared and fixed so it now has no issue's other than at 1200 to 2100 rpms it starts backfireing and has no power put new exhaust on it as well as changed the fuel filter and mass air all good ... but i cant figure out the backfire ?

also i replaced the intake gaskets all of them still have the issue

 

[n_grimm]

While waiting for someone with actual 4.0 experience to respond, I'll throw out a couple things that are always good to check. Fuel pressure and blocked air box. I think flat cams and weak/broken valve springs can also cause backfiring at higher rpms but those would be a little harder to verify.

 

[Big Jim M]

First we need to know is it backfiring from the intake (front) or from the tail pipe (rear)?
Ya see one man's backfiring isn't always the same as another man's backfiring.
Big JIm

 

[feellnfroggy]

If hes got low power then hes most likely backfiring from the intake. Which can be caused by the timing being off. backfiring is backfiring, it means one of the valves are open during or just before the combustion cycle allowing the fuel/air to burn without full compression, it explains all the problems. Given teh year of the truck, with an engine swap having been done, its surely a possibility that the crank/cam timing is off.

 

[alx]

ok got back on it it backfires tru the intake it has 32 psi at idile 40 when you rev er up and steady 36 under load..

 

[Big Jim M]

Ok!

ok got back on it it backfires tru the intake it has 32 psi at idile 40 when you rev er up and steady 36 under load..

1200 to 2100 is where the timing starts coming up. Check the timing to make sure it is correct and not too advanced.
Big JIm

 

[feellnfroggy]

He has a exploder motor which means its 4.0 and EFI. SO im guessing with his timing chains its not off too far(didnt read this before) Imm thinkin maybe stuck valve or something similar. If hte timing is off it happened when the motor was rebuilt or swapped and its been this way along time.

 

[alx]

well not a timing issue and its not mechanical.... only does it after its warmed up .

first 10 mins of the day runs out perfect

 

[kunar]

double check that all 6 spark plug wires are in the proper order. i had a 2.9 that did the same exact thing, turned out that 2 wires were swapped. i guess i didnt know firing order off the top of my head like i thought i did....

 

[alx]

been there done that , it actually turned out to be a bad coil pack
the number 2 spot on the coil melted the new plug wire in there
worked fine when cool but would start acting up the warmer it got

 

[kunar]

been there done that , it actually turned out to be a bad coil pack
the number 2 spot on the coil melted the new plug wire in there
worked fine when cool but would start acting up the warmer it got

i was close

glad you got it figured out though