DualSportDad

Posting this up to see if anyone else has ever come across this.

The jeep: 1997 XJ complete correct 5 speed swap (everything, hanesses, PCM, all of it) , 4.0, ax-15,np231, stock engine, air intake, stock new design exhaust manifold, no cat, 2.5" dynomax exhaust.

The problem: when tipping into the throttle under load the Jeep starts to stumble, lose power etc. I have verified it goes lean with a wide band o2. I will post a video below.

This Jeep has ran like this since the day I bought it but you can feel it much worse with the 5 speed. The lean condition ended up burning the exhaust valves.

When I did the 5 speed swap I bought a donor jeep and was able to drive it for a year before I pulled it apart. It ran fine and now most of the engine management, sensors etc are in the jeep.

So far I have replaced both o2 sensors, crank sensor, tps sensor, distributor (complete assembly) , fuel injectors, map sensor, timing chain and gears, exhaust manifold and gaskets, ignition coil, had head rebuilt, new head gasket and I'm sure there's more I'm forgetting. Most of these parts were swapped off the great running donor jeep so o know they were good. O2 sensors are new, distributor assembly new, manifold new, ignition coil new.

I've looked it over for vacuum leaks, can't find any. The only thing I can even remotely think of is the cat converter. Its the only thing that this jeep doesn't have that the other one did. I have tested fuel pressure and its good. Fuel tank, pump etc are also from the donor jeep.

My jeep is mainly a trail rig so I've never really worried about getting a replacement cat, esp at $150 and not knowing if that would even cause my problem. I've read plenty of threads where people have removed their cats and the jeep runs fine.

I'm at the point right now that if I can't get this fixed I'm going to swap the 4x4 stuff into my daily driver 2wd 99xj and scrap the trail rig.

Here's a awful video of my lean problem. When its acting up I'd say I'm about 25% into the throttle around 2,000 rpm.

1997 XJ running lean:

DualSportDad

It seems I solved the problem. Yesterday when I took the downstream o2 sensor or to put the wideband in I put the downstream back in without the spark plug non fouler ( I had the o2 in a non fouler so the PCM wouldn't throw a code for no converter). I guess the downstream o2 was adjusting the upstream goal voltage to a lean value.

I just took the jeep for a 20 mile drive through town and it seems to run much better. I'll throw the wideband back on at some point and see where I'm at.

CCKen

What's with the "wideband". Why not just state what O2S ou are using.

DualSportDad

Not sure I understand what you mean? You want to know what wideband I was using? It's a innovate lm-1. I was using it to monitor my exact air fuel ratio.

Radi

That's a handy monitor to have, you can see the system lean right out when it stumbles.
Interesting confirmation about the rear O2 setting the goal for the front. A few of us have made that point before (Hi Ken) only to watch the torches and pitchforks come out...
Glad you found the problem, good info to know about the fouler adapter causing the issue.

DualSportDad

There are several different wideband monitors you can buy. I believe the price has come down a lot on some. I bought this one years ago so I could street tune my turbo civic before I hit the Dyno. Saved lots of money in Dyno time since timing was the only thing that needed to be touched up when I got onto the Dyno.

This particular wideband is a bit more expensive than most (at least it was when I bought it) because it has outputs that can be sent back to your fuel management for data logging. There is also a "aux box" add on that can be purchased which allows map, tps, etc to be temporarily installed on a carbureted engine and then data logging can be done through the wideband controller itself. If I had the aux box I would have been able to press the record button on the controller and then upload that file here so you could see exactly at what tps percent, map value, air intake temp etc that my problem came up.

As far as people bringing out the pitch forks etc about three downstream o2, I have seen it happen on here once. I'm sure where those people get the idea where the downstream doesn't affect the way the engine runs. The way the PCM is set up to monitor the converter is so as the converter ages it changes the tune in the engine so the converter lasts longest and the engine runs properly. I mean if you have a slightly plugged cat and you're still dumping the same amount of fuel as you would with a new converter the engine will be down on power and the cat will continue to get worse and worse faster and faster.

While right now my jeep runs much better it still feels like it's lot on power compared to my 99. My 99 is a stock 2wd auto and my 97 is lifted with 31's and is a 5 speed but since I have auto axles (3.55 vs 3.07) I would think they would be similar. I think if I add a cat I'll get some more low end power. I'll add one in the future after some other repairs that need to be done.