1987XJ

My 87 cherokee is backfiring through the intake when accelerating. Any ideas?

RTorrez1

How about some info about your Jeep. Such as engine and model. They are not all the same. Also did you recently do any work to it. Did it just start out of no where?

1987XJ

1987cherokee with a 4.0, automatic.

RTorrez1

What about the other questions I asked. If you are going to be so vague the best answer you will get will be just as vague. Such as, It can be a lot of things. If you're not willing to give any info it will be almost imposable help.

1987XJ

Its a 1987 Cherokee (xj), not sure what month in 1987it was made. Lije I said but fore; it jas a 4.0 with an automatic (aw4). It had an intermittent problem. It loses power and starts to backfire through the intake when accelerating.

tjwalker

Backfiring is usually because of a fuel/air imbalance.

First thing is to verify fuel pressure. Must be done with a fuel pressure gauge which can be rented inexpensively from most parts stores; call around.

For your 87, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line is not wet with raw fuel, which would indicate a ruptured fuel pressure regulator diaphragm.

There are a number of possibilities here; this is a process of elimination. Start with fuel pressure. Good luck and keep us updated!

1987XJ

A put a new fuel pump in it.im thinking it may be the cps.

tjwalker

A new fuel pump does NOT rule out a faulty fuel pressure regulator. You must consider the entire fuel delivery system and that includes the regulator. Perform the testing I recommended. Use a testing based strategy to figure out the root cause. I guarantee you that any technician worth their salt would be doing this exact testing if you brought your Jeep to a shop.

Also; a faulty crank sensor does not usually result in backfiring. I don't think that is your problem here.

cruiser54

When, and what brand? Airtex from VatoZone?

CPS is generally a crank/no start, not load related.

How long since it got new plugs, wires, cap and rotor?

Ever done Tips 1 through 5 in my Pink Link below. They address a lot of intermittent issues. But, you must do them.

Roler

When my 97 was intermittently backfiring/popping/hesitating (especially when accelerating), replacing the CPS fixed all that...must be my RHD
But I would never recommend that to the OP, because his is a RENIX, and I'm always wrong with those

cruiser54

Renix CPS has different symptoms.

More like crank/no start, complete cut-off etc.

But then again, mine is LHD.........