2.5 engine help needed

[mbz]

i have a 97 TJ with a 2.5 engine, it back fires through the intake upon exceleration. i put the scanner on it and has no codes. please give me some suggestions of what it could be.

[aw12345]

Check the sparkplugs and wires

[mbz]

Check the sparkplugs and wires

i changed the plugs, cap, rotor, mass air flow sensor and it still does it

[aw12345]

Fuel pressure where it ought to be?

[mbz]

i will check that. maybe change the fuel filter too, where is the filter located??

[scherf68]

filter is in the gas tank, one of those lifetime jobbers, rarely go out.

[Roger]

Isn't backfiring a symptom of the timing being off? I'm no mechanic, but that's one item I would look at.

[Jason]

I'm with you Roger. With today's engines though, you would think that the computer would adjust them. I can't even remember the last time I have used my timing light.

[OU812]

i changed the plugs, cap, rotor, mass air flow sensor and it still does it

Are you sure you didn't get your wires crossed?

[chris142]

Does it just do it ocasionally or a constant popopopopop that gets worse as the revs go up?

[aw12345]

Timing is deemed, not adjustable, it should time of the crank sensor. It could be a whole slew of things.
Got to start with the basics compression, ignition, fuel delivery

[mbz]

didnt cross the wires, it did it before and after the plug change. it gets worse as it revs up, gets a little better once the engine warms up.

[chris142]

Since it gets worse as it revs up it's a valvetrain issue.

Broken intake valvespring or flat exhaust cam lobe or a non sealing intake valve.........Last is very,very rare.

Pull the valvecover off and start it. See if all the rocker arms are moving the same amount.

[mbz]

thanks guys for your help. i will check it out this weekend

[mbz]

going to check the fuel pressure today, can anyone tell me what the fuel pressure should be at??