Need help: engine cuts out when cold. stops when o2 sensor unhooked.

I have a 1997 jeep cherokee with the 4.0. I have had several mechanical issues since I bought it a couple months ago. So far this is what has been replaced. Plugs, wires, and cap. Map sensor, TPS, CPS, o2 sensor by headers. Also cleaned throttle body and IAC.

Now here is the issue. The jeep started acting up, when the engine is cold and I first take off it will start sputtering and cut out for 10 seconds or so. Once the engine warms up a little the issue goes away. I had a new o2 sensor but heard that could be an issue caused by bad o2. I unhooked the o2 sensor for over a week and it never did it once but seemed to get worse gas mileage. I ordered a ngk sensor because I heard they were better for the 4.0. Replaced that and hooked it back up. The issue continued once again...
Any ideas what could cause this?
Also the jeep sat for about 5 days and went to start it yesterday and the battery was dead. I recent put a brand new battery. Could these be related?

Is the Check Engine Light ON ?

The starting symptoms are probably a faulty check valve on the fuel pump. If you have an excessive amp draw you will need to test for, locate, and fix it.

Yes I have had the codes ran twice and nothing is showing up. It starts fine it's just when you first start driving. I thought it was something with the fuel pump so tried priming it before I started for awhile but it didn't help.

So for the third time i had the codes ran. This time the code P0135 came up. The code is for the oxygen sensor. Possible explanation could be defective o2 sensor (its brand new) poor connection at sensor or circuit fuse. Would anyone know where the fuse for that is? I had checked all of the fuses recently and none were blown but may check again to make sure.

Anyone have any ideas??

P0135 relates to the heater circuit of the O2. they are heated to get the system to closed loop faster.
Dropping a sensor can break the heater element, so it could have been faulty from the get go.

Looking at the sensor, the 2 wires that are the same color are the heater circuit. You can check for them continuity. They will have some resistance but as long as continuity is shown then it's likely ok. If there isn't any continuity, the element is broken.

The highest probability of failure is the harness to the sensor as it passes close to the exhaust pipe behind the p/s pump. I've repaired failures there many times.

The fuse you are asking about is in the PDC, #23 a 15 amp

I'm pretty sure the front and rear O2 sensors share the same fuse and wiring for the heater circuit.

You may have a short in the rear O2 sensor or the rear sensor wiring. Pretty common for the wiring to the rear O2 sensor to be ripped out while wheeling. And/or some lazy mechanic to fail to route the wiring back into the wire hanger after replacing the sensor. The wiring can cook on the exhaust.

The O2 heater fuse may get hot even before it eventually blows if the system has low resistance, partial short or a partially melted O2 heater . It can get pretty hot, not enough to blister a finger, but nearly that hot.

I haven't looked at the rear sensor so may have to check that out. I will also check the wiring near the exhaust. I am pretty sure it's not the actual o2 sensor bc I have had 2 brand new ones of different brands and it still continues. Does anyone know what fuse would be connected to the o2 sensors?

workman13 said:

I haven't looked at the rear sensor so may have to check that out. I will also check the wiring near the exhaust. I am pretty sure it's not the actual o2 sensor bc I have had 2 brand new ones of different brands and it still continues. Does anyone know what fuse would be connected to the o2 sensors?

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Well I am pretty sure that fuse is missing in my fuse box. The fuse just not being in wouldn't cause that would it?

I believe that fuse is missing in my jeep. The fuse not being there wouldn't cause the issue would it? Hopefully it wasn't removed because someone didn't want to fix the issue.

It most certainly will cause the code and cold drivability problem you are describing

If you install a fuse and it blows you'll have to examine the O2S wiring for chafing/shorting together or to chassis/engine structure.

Well I noticed the plug that hooks to the o2 seems to be a little loose when I plugged it in. May try the fuse then check into that if it doesn't fix it.

Sidewinder CC said:

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This helped me out, I had my rear o2 sensor wires get caught up in the drive shaft. I replaced the o2 sensor(wasn't able to salvage the old one) but was still throwing a p0135 code and had rough idle after first starting. Checked the fuse and it was burned out, I'm sure when the wires got ripped apart it blew. Hopefully this fixes it for me.

Now I also know not to rely on a zip tie to hold the o2 sensor wires in place. Made sure to attach the harness to the mount this time around and tuck the wires better.

You're getting lots of sound advice here, but one more quick and easy item to check is the quality of the air intake boot. If there is a crack in the boot allowing false air in on cold acceleration that could cause your symptoms. When the engine warms up, the rubber expands and the crack is sealing temporarily. This dogged me on an old Toyota Celica until I looked closely and found the crack in the boot. The symptoms were identical to what you describe. Just a quick and easy item to check while you're hunting for the root cause. I suspect as others, the problem lies in your O2 circuit, but it never hurts to check the easy items too.

98NWCherokee said:

You're getting lots of sound advice here, but one more quick and easy item to check is the quality of the air intake boot. If there is a crack in the boot allowing false air in on cold acceleration that could cause your symptoms.

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This is incorrect information for the Jeep EFI. A cracked intake tube would cause a problem on a MAF fuel system. On the Jeep's MAP system it wouldn't be a problem as the MAP reads off manifold vacuum.

Talyn said:

This is incorrect information for the Jeep EFI. A cracked intake tube would cause a problem on a MAF fuel system. On the Jeep's MAP system it wouldn't be a problem as the MAP reads off manifold vacuum.

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I concur with that, and that is one thing I thought of that might deserve checking.

The MAP sensor. The EFI should be able to run the motor with O2 sensor disconnected, it will just put it into open loop mode. The O.P. stated he had disconnected it in the past and it ran fine, although he got poorer gas mileage, and that is exactly what the O2 sensor does, provide feedback as to the A/F ratio, to adjust the calculated values from all the other sensors.

I.e. the PCM calculates how much fuel is needed at the moment based off all the sensors, the sensors can't tell the PCM how much air actually went into the engine, that is how a MAF system works, measuring how much air is sucked into the engine. The Speed Density System (you called MAP) just calculates how much air the engine should be sucking based off the rpm, throttle position, temperature, vacuum in the intake manifold, and thus calculates how much fuel to inject. This is open loop operation, the PCM just calculating how much fuel it should need.

Of course real life is messy, and theoretical calculations tend to be off some, that is where the O2 sensor comes in, by measuring how much O2 remains in the exhaust, the PCM can calculate what the actual A/F ratio that resulted from its earlier calculations and make adjustments to get the A/F ratio right. Its a feedback loop on how the PCM is actually performing, and its called closed loop operation.

So, now the O.P. has stated the motor won't run with the O2 sensor disconnected. Hmmmm, that says to me, the motor won't run in Open Loop. If there is something wrong with Open Loop operation, its possible in closed loop operation the feedback from the O2 could correct for the incorrect calculations resulted from something wrong in open loop. He's pretty much confirmed it by disconnecting the O2 sensor and forcing the PCM to operate in open loop.

This is sounding like a sensor to me. He doesn't have any codes for sensors, other than O2 heating element (which seems like an aside problem, NOT a cause). He's replaced most of the sensors, but NOT all, and NOT one that often can malfunction and NOT set a code, and that sensor has such a huge effect on the PCM calculations it can really throw off the engine operation if its feeding erroneous information.

That's the MAP sensor, Manifold Absolute Pressure Sensor. And on the XJ its on the firewall, with a vacuum line running to it from the manifold. On a 20+ year old Jeep, that line might be cracked or dry rotted, leaking vacuum and giving an erroneous signal.

At the very least its a simple check for the vacuum line to eliminate it as a possible cause. I've heard, NOT sure how valuable a trouble shooting technique it is, if you disconnect the MAP sensor, either or both, the Vacuum Line and electrical connector, the PCM will take it out of the calculation. Like disconnecting a bad O2 sensor, it will get the motor running better, but it won't get it running totally right. Again, a simple thing to try, if makes a noticeable change, that might be your problem, it makes no difference, then move on to something else.

Rick Anderson said:

That's the MAP sensor, Manifold Absolute Pressure Sensor. And on the XJ its on the firewall, with a vacuum line running to it from the manifold. On a 20+ year old Jeep, that line might be cracked or dry rotted, leaking vacuum and giving an erroneous signal.

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On his 97 the MAP sensor is attached to the throttle body with a 90* rubber elbow. It is worth checking if the passage into the throttle body is clear as well as the elbow. And verify that the elbow is attached and has no cracks.

my 97 has been running with no O2 sensors hooked up for over a month now because the harness is boned. It runs fine, just rich.

I too have issues with a key off draw, and electrical randomness.

Check the junction block in the passenger side footwell.
pull that big connector that's held in with the ten mm bolt. Have a look in there.
Mine is/was badly corroded from a leak from the radio antenna wire grommet.