Redneck_jeep

okay so i got a jeep awhile back had a post up about it got it running and now it runs and drives. However when i get on the gas the rpms drop and it basicly dies then picks back up and will go it does this every time i touch the gas below one thousand rpm. very now and again it will back fire through the intake i need it running tonight im a delivery driver full time and my other jeep got wrecked.

tjwalker

Backfiring through the intake is usually a sign of a "lean" fuel/air condition.

Start with some basic fuel pressure testing; it is what would be done if you took your Jeep to a shop. You'll need a fuel pressure gauge; you must have accurate data here. If you don't have access to this gauge, they can be rented inexpensively from many parts stores; call around for availability.

At idle, you should have 31 psi of fuel pressure. Now 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 to the FPR is not wet with raw fuel which would indicate a ruptured fuel pressure regulator.

cruiser54

Pay heed^^ to this.

Redneck_jeep

okay. where is my fuel pressure regulator? and it wont unlock from four wheel drive as of today as well but we can address that later.

salad

Fuel pressure regulator is the big circular thing at the front of the fuel injector rail. Where the two hoses connect, closest to the power steering pump.

cruiser54

And when fuel pressure regulators fail, they generally go pig rich, not lean. TEST your fuel pressure first.

Tried this to shift?

Here's how the factory suggests you shift the transfer case and I've been doing this since these things were new and I worked at the dealership. Quoted from the owner's manual.

"To engage, shift the transfer case lever from 2H to 4H while the vehicle is moving at any legal speed". I let off the gas, throw the lever, and then tap the gas and let off.

4L position: " To engage, slow the vehicle to 2-3 MPH , shift the transmission to Neutral, then shift the transfer lever to the right and pull firmly rearward to 4L".

Redneck_jeep

alright its 40 psi at the rail and 36 psi at the rail running. and that didn't get it out of 4x4 and its the non vacuum actuated axle. still back firing all vacuum lines to the regulator are good and in the proper place.

highmileage

If you are not running lean you could have a sticking intake valve, bad spring or a timing issue.
I would start with unplugging the injectors one at a time to locate the cylinder causing the backfire(there will be some rough running doing this). You can also do this by pulling the plug wire as well. If you can isolate the problem to one cylinder take a look at the valve springs and work them, a sticking or stuck one should show itself, and or the bad spring.
As far as a timing issue cruiser will know way more than I do how to fix that.

cruiser54

31 at idle with the vac hose ON the regulator, 39 when the vac hose removed from the regulator.

Redneck_jeep

okay going to put it at tdc tomorrow. this is the same jeep that had the injector problem im definitely feeling a timing issue.

DFlintstone

I had backfiring out the intake. Had to feather it just so. Just a little and she might go OK, but more and it bogged and backfired out the intake. Blew the mouse nest out the front. (no sign of the mouse). Then I found if I floor-boarded it it would launch like heck. It took me a very long time to figure it out. About a year.

It waz one of the wires to my lower sensors grounding, I AM sure. .....Since I taped the grounding wire in the harness up above without checking which, I don't know which sensor wire was grounding.

You don't have a knock sensor, and your CTS is on your t-stat housing, (or is it?), so that leaves the 02 sensor.

I should un-tape my repair and look. (it was before I joined the forum). One of those three grounding can make it backfire with acceleration. (but go fine, floored, in open loop). I don't know but doubt it was the knock sensor.

My wires were routed goofy and the heat shield was cutting in. Man, was I glad to finally find that! Maybe not your issue, but in the pic below is the cause of 101 backfires!

DFlintstone

If it always goes fine floor-boarded, (more than 80% throttle), it might be a sensor issue.

The computer moght ignore some sensors floor-boarded. Your CTS is not at the back of the head. (that's a the gauge/light sender). It's not on in the radiator near the battery. If you have one there, that is for the E-fan.

I'd want to rule that one out, (and it's wiring), weather it's still down below, or now up on the t-stat housing.

Redneck_jeep

well my no pulse issue turned out to be a fire in the wiring harnes and a bad ecu. my emissions control light is on it idles fine sits at five hundred rpm. once im above a thousand rpm it goes fine besides the back fire if i rev it. i just have to have it running asap.