buddyantunez1

CLIFFNOTES:

-Have to prime ignition 3-4 times before engine starts.
-1st acceleration after engine start, at 2000rpm it wants to die and backfires.
-Runs great afterwards for the rest of the drive/day.


-Off road, the truck misses and runs on 3-4 cylinders after being restarted after sitting for 5-10 mins.
-Usually clears up after driving 100 feet or so, but has gotten worse lately.
-Once off the trail, it runs on all 6, but runs like a pig, with a good bit of power loss.
-Crank it up the day after wheeling and it goes back to running great after priming the ignition, like stated above.


-Replaced CPS 4 months ago.
-O2 sensor circuit fuse blows from time to time.
-Plugs and wires replaced 2 months ago.
-Cap and Rotor will be replaced tomorrow (2/5/13).
-FUEL PRESSURE AT 43-50PSI AT IDLE.
-Fuel pump assembley/bucket replaced this past week.
-Plugs look great, no signs of lean or rich conditions, and no oil on them.

I've done a good bit of research and nothing has solved my erratic problem with my 98' XJ. It's a 4.0 with 128k on the clock. Auto trans. Ever since I bought it, I've had to prime the fuel system by keying it on and off 3-4 times and after that it fires up great. Every now and then after letting it warm up, and on the 1st acceleration after starting it, it will get to about 2k rpm and then act like it's going to die, backfire, and then I'll put it in neutral, tap the gas, put it back in drive, and then it'll act perfect the rest of the drive. Figured all this was a check valve issue, until I replaced the whole fuel pump/bucket assembley and still have the same problem. Fuel pressure at idle is between 43-50psi.

Now onto a weirder problem. The truck has great street mannors, but as soon as I get it off road to go wheeling on the weekends, it acts crazy. Once I shut it down, sit for 5-10 mins and try to start it back up, it will miss and only hit on 3-4 cylinders, backfire, and act crazy until i drive it 100 feet or so and it straightens up. But this past weekend, it got even worse, and never cleared up until I got off the trail. And the whole way home it felt like a pig, couldn't make it up small hills without dowbnshifting after backfiring.

I've also seen where people are saying to check the TPS and CPS, O2 Sensors, injectors, and possibly the coolant temp sensor. I replaced the CPS about 4 months ago or so. I've also replaced the plugs and wires about 2 months ago, and checked the plugs a few days ago and they look great. No signs of running too lean or rich, no oil or anything on them. I've ordered an Accel cap and rotor since it was a fairly low price. The O2 sensors and wires look great, although it will blow the O2 circuit fuse from time to time. Check Engine light is on for a transmission slip code, which is only noticeable if driven when not properly warmed up. And the coolant temp looks great and never gets above 210.

After checking the fuel pressure and seeing it was fine, I'm leaning away from a fuel delivery issue, although I haven't checked the injectors yet, but they're not leaking externally. A neon injector swap will be in the near future.

Any opinions on what might cause my issue? It's stumped a few other local jeep guys as they all think it's a fuel issue, until I show them that the rail has 50psi.

Thanks for any help in advance, as this problem is embarassing on the trail and getting very frustrating.

-Kyle

Radi

Any sign of trouble with wiring harnesses, particularly that to the fuel injectors?
Ever replaced the TPS?
I'd find the short in the 02 circuit and repair it. Shorting that line can affect other sensors powered by the PCM.

What code are you getting for the transmission?

buddyantunez1

I haven't spotted anything out of the ordinary from the injector harness, or where the CPS and TPS all come together at the harness. As far as I know the TPS is still from the factory. Need another pair of hands to be able to test it. I'll start to track down the O2 circuit and see if I can find anything.

I'll double check the codes on my scanner and get back to you. I know it's for the torque converter, and it does slip when driven cold, so I normally let it warm up pretty good before driving.

It just seems like I'm having a combination of errors and I can't quite pinpoint what is causing it.

buddyantunez1

The codes are as follows:

P0123
P0135
P0700
P0740
P0141

Bought a TPS from Advanced with a lifetime warranty. I know OEM is better, but not at 3x the price.

The o2 Heater Circuit fuse was blown, so I replaced it, cleared the codes, and drove it probably 10 miles without an issue so far. It usually comes back within a few days, so I'm sure a downstream o2 will be the next purchase. All the wiring for the o2's look in tact and still have the OEM loom on them and look great underneath it.

Radi

P0123 TPS voltage too high
P0135 O2 sensor heater circuit fault- Sensor #1
P0700 Transmission control malfunction
P0740 Torque Converter Clutch circuit malfunction
P0141 O2 sensor heater circuit fault- sensor #2

TPS voltage too high is often a failed TPS or a shorted harness.
O2 heater faults are either bad sensors or damaged wiring
TCC malfunction is damaged wiring or a failing solenoid in the trans
I'd go over the appropriate wiring harnesses again, even opening them up to inspect the wiring. Plugs on both ends too.

KCXJKID

I see you've checked the fuel PSI. I had the same problem and had a weak fuel pump. It sometimes would show 50 psi and sometime 35-40psi. Chased the problem for months and finally replaced the pump and never had a problem after that. Good luck

buddyantunez1

So far so good with just replacing the blown fuse for the heater o2 circuit. I bought a new TPS along with a cap and rotor, so I'll relace both and take a good look at the harness for the o2's and hope everything is straightened out.

The trans codes are true, it does slip when cold but clears up very quickly. I'll rebuild it later on.

Hjkjohn

When I first got my XJ I did a full rebuild and replaced dist. Cap, rotor, plugs, wires and starter. I has to proem the fuel pump by cycling the key 7-10 times. Rough idle at first but smooths out completely in about 30 seconds. Has 290k. Use to run great once started. Recently have very poor acceleration and a backfire up near the engine if I try to accelerate too fast. I know I probably need a fuel pump assembly and plan to order one this week. Just got some less used injectors and plan to install those too as I'm sure mine leak. I get codes 12 21 23 21 55 when I cycle the key 3 times. I replaced the IAC sensor and no change. Any help would be great! Could it be a wiring issue near the o2 and iac?