Just finished a build up that had taken about 5 months. Drove it down the street yesterday and couldn't get the vehicle to run above 2000 RPM.

I have recently replaced the fuel filter, fuel pump and O2 sensor. This weekend I plan to disconnect the exhaust to verify the cat isn't clogged.

Take a look at the video and let me know what you guys think.... If there is more of a smoking gun thant someone more experienced with Cherokees might know of.


As always thanks for your guys help this is a great resource.

 

What year? and a build sheet would also be helpful. I will say that it sounds like its reving past 2000 might just be video quality. did you do anything with the ignition, cam or crank sensors. It almost seems that the tach isn't accurate but it does seem to be reading a correct idle. you may be on to something by checking the exhaust. you could just pull an upstream 02 sensor if its easier than the flange.

 

Sorry... Yeah I left a few things out.

It's a 1992 XJ

The build had included an engine rebuild rough country 4.5 lift. Sye kit etc

On the engine side I have replaced the crank sensor, new plugs, new wires, dist cap, rotor.

The 2000 rpm number is a pretty rough estimate but it gets to about that and what you see the tach doing is about what the engine feels like it does. It stutters and hesitates and makes a lot of noise until I back off. It does this in both drive and neutral.

 

pop the air hose off and have a friend sit down and press the throttle pedal all the way down, and make sure the throttle is opening all the way. (i'm sure it is based on the hesitation.) but process of elimination.

Check the codes in the OBD i'm not sure exactly how but i know there is a quick test method where you can get the codes to flash out on the CEL.

could be something as simple as a TPS not being adjusted properly, i believe those older renix's had an adjustment that could be made. unfortunately my knowledge on the renix system is limited, hopefully one of the veterans will pick this thread up and offer some suggestions.

 

Thanks for the info

I will check the butterfly valve and look into the TPS.

CEL codes:

12 - battery disconnected
15 - no speed signal ( fixed I believe)
21 - oxygen sensor (replaced but problem still occurs)
55 - end of codes

 

i can see oxygen sensor causing a running issue, but not what you are experiencing...

some general info on your speed sensor...
Because so many systems use the speed, a faulty speed/distance sensor can generate codes other than code 15. It can cause the engine to lose control of RPM to race the engine or cause it to stall at idle, and can cause an automatic transmission to go into limp mode, and not shift above second gear. If the speed sensor fails, the speedometer and odometer will stop working in vehicles which use electrical signals to drive the speedometer (phased in during the 1990s), while the tachometer will still work. (Many cars had both a speed sensor and a physical speedometer cable. In the Shadow this was changed in 1992 or 1993.)

when was the last time you disconnected the battery or reset the faults and read zero fault codes? (other than code 12 and 55)

 

It has been a while since I have disconnected the battery to reset the faults but I have also been busy working on the suspension.

Tonight I tried the following:

Removed exhaust from the cat back (exhaust header is new)
Replaced TPS
Checked fuel pressure at the rail (consistent reading at idle and while revving and getting the hesitation around the 2000 RPM range)

I have a new dist cap and rotor but what about the distributor or cam pos sensor ? I can possibly look into the speed sensor as well. I know the video might not be the best but it also sounds like when the engine hits that RPM range it backfires out of the intake.... thoughts?

On another possibly unrelated issue I am getting coolant leaking from the transmission housing. I think a freeze plug didn't seat right so I will possibly be pulling the transmission this weekend to look into that issue as well.

If anyone has anymore ideas for me to try this weekend let me know I am really running out of ideas. Thanks!

 

any other ideas?

Dist and coil pack maybe?

 

i could see a failing coil being the culprit. unfortunately my in depth knowledge on these renix jeeps is fairly limited to conventional auto knowledge. if its backfiring through the intake which i did hear. it could indicate timing is going off or the valves need to be checked again. but considering it sounds more like its bouncing off a rev limiter than anything else i'm more inclined to stay focused on the distributor and coil.

 

I tried a new ignition coil this evening. Didn't solve the issue. Distributor comes in tomorrow.

Any thoughts on PCM or Possibly Valve Float?

 

"Code 21-Oxygen sensor signal-neither rich or lean condition is detected from the oxygen sensor input."

If you have no oxygen sensor signal, how could your engine run properly? Regardless of upstream or downstream I would very heavily look into this code first and foremost.

 

O2 sensor has been replaced. All is well with code 21. Still no changes with the engine though.

 

If the ecm doesn't register an o2 sensor reading if defaults to default/safe mode/limp home mode settings. It will use the adaptions that it is programmed to know are safe and the car will run relatively fine. These adaptions are similar to what it runs at when the computer is in open loop, aka a warm up cycle when the computer isn't adapting the fuel per the o2. You will notice a drop in gas mileage without the signal as this adaption tends to be on the richer side of the spectrum but it will still run.

Now when it is getting a faulty signal from the oxygen sensor it can cause some weird running issues once the computer enters closed loop and its relying on the sensor for an input. if that sensor is reading that the AF is extra lean(when its not) it will try and dump fuel, causing an over rich condition causing the engine to run poorly. one common trick to check this(with out the use of a full function scanner or dvom) is to disconnect the oxygen sensor and see if the engine runs better. if it does it generally implies that you have a bad oxygen sensor.

 

so maybe it is the ECM not reading the signal properly from the various sensors and putting the system into limp mode. I keep swapping out sensors with no change. I will swap out the dist and cam sensor today. If there is not change then I would suspect the ECM next.

 

I dropped a new distributor in the vehicle last night. It was lined up exactly the same as the old one ( it seems you can either install the dist with the rotor pointed in the same direction as when you pulled it out or 180 degrees off due to the flat screwdriver part on the bottom). After installing the vehicle wouldn't start. It sounds like the timing is off not allowing it to start. I am taking this as a good sign since it wasn't working properly with the old dist.

I am hoping that if I bring the engine to TDC and reinstall the dist and check the plug wires to be in the right spots that the engine hesitation will be gone.

Any thoughts?

Thanks!