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  #1  
Old October 17th, 2020, 17:11
gmcchamp99 gmcchamp99 is offline
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96 XJ Hesitation when hot & cant rev

I just picked up a second 96 Jeep Cherokee with the 4.0L & its having issues with reving and accelerating once warmed up. Tonight, its about 50 degrees and I changed both O2's, cleaned the IAC valve, throttle body and replaced the throttle body gasket. I took it for about a 15 mile drive. First 8 miles, I could WOT and it would accelerate no issue. I got off the highway and looped around to head in the opposite direction and after sitting at a red light for about 2 minutes, I began to accelerate and at around 3500rpm it started to cut out and sputter. I was able to get it up to highway speed but couldn't press the accelerator past half throttle. I did manage to coax it upto about 75mph by feathering.

Came home and checked fuel pressure. It varies and averages around 45-50 PSI. In drive, it remained the same and while going down the road at 25mph, same pressure with little variation. When it was hot again, i checked it while in park with the same pressures. At WOT while driving hot, 52 PSI was the peak and the low was about 46 PSI. The cat looks to have been cut open and possibly gutted. Would a hollow cat cause these symptoms?

What's your thoughts?
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  #2  
Old October 17th, 2020, 19:36
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Anak Anak is offline
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Re: 96 XJ Hesitation when hot & cant rev

I would wonder if someone gutted the cat thinking they had an issue with a plugged cat. I cannot imagine how a hollowed out cat would cause this problem. However, if the guts of the cat wound up in the muffler I can see how that could relate.

However, I would be more inclined to think that you are having an electrical issue of some form. I could easily see it being a sensor or a coil. Something is probably increasing in resistance when hot.

You probably need access to a scanner that can show you readings for each sensor. Compare readings cold to readings hot. See if something is changing that should not be. I am not sure how you test a coil, but see if you can find differences between hot and cold for the coil.
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Old October 17th, 2020, 20:55
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Runnin'OnEmpty Runnin'OnEmpty is offline
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Re: 96 XJ Hesitation when hot & cant rev

Good suggestions from Anak.

I might add the cam position sensor inside the distributor
might be faulty, or a wire could be opening up when hot.
It's very easy to check visually on a 96, just pull the cap
and rotor off to access.

The CPS is a notorious fault point too...
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Old October 18th, 2020, 04:04
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Re: 96 XJ Hesitation when hot & cant rev

Just a guess but it sounds like an O2 sensor. I wouldn.'t assume the wiring for the sensor is OK. The rear sensor wire can cook on the exhaust,many have trouble with the wire holder.
The front sensor, more likely, could be a problem. Look closely behind the power steering bracket. It can be hard to see there, you have to figure out a way to inspect all the wiring.
O2 sensors are notorious for not setting a CEL code until they are completely dead.
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Old October 18th, 2020, 05:02
gmcchamp99 gmcchamp99 is offline
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Re: 96 XJ Hesitation when hot & cant rev

I followed the wiring loom for the front 02 sensor from the connector straight up to where I enters the bulk of the electrical wiring behind the power steering pump. I opened the loom, non of the wires appear pinched or burned. The rear 02 was the same look with no visible issues withnthe wiring. I have replaced both sensors with NTK branded 02's. I do have access to a good scanner with live data. The STFT B1S2 is at 99.2%. Ive never seen that before. The two 02 voltages range from 0.380 to 0.942.
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  #6  
Old October 18th, 2020, 08:42
Unclewolverine Unclewolverine is offline
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Re: 96 XJ Hesitation when hot & cant rev

Always start with tps, notorious failure point. Gutted or no cat causes NO problems. Don't ask me how I know. May even improve gas mileage and acceleration
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Old October 18th, 2020, 10:12
RCP Phx RCP Phx is offline
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Re: 96 XJ Hesitation when hot & cant rev

Since you just bought it and don't know the history I would start at square 1 and do a compression test.
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Old October 18th, 2020, 11:11
Unclewolverine Unclewolverine is offline
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Re: 96 XJ Hesitation when hot & cant rev

Also fuel filter
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Old October 18th, 2020, 14:24
RCP Phx RCP Phx is offline
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Re: 96 XJ Hesitation when hot & cant rev

Quote:
Originally Posted by RCP Phx View Post
Since you just bought it and don't know the history I would start at square 1 and do a compression test.
You need to pull at least one plug anyways because with that fuel trim your plug is either going to be soaked if your having fuel management problems or if it looks dry you have a fuel starving problem.
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Old October 18th, 2020, 17:05
gmcchamp99 gmcchamp99 is offline
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Re: 96 XJ Hesitation when hot & cant rev

I haven't finished everything I wanted to do today with it but I have replaced the TPS, MAP, ignition coil, plugs, distributor, cap, rotor wires and plugs. Plugs were spanked but dry. Theynl weren kind of sun colored, white mixed with orange. Two had cracked porcelain. I just finished up the exhaust. Everything behind the down pipe is new and in place. Fingers crossed for tomorrow morning. I need to out the serp belt back on, change the fuel filter and we shall see if it lives and if its all resolved.
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  #11  
Old October 18th, 2020, 18:16
Unclewolverine Unclewolverine is offline
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Re: 96 XJ Hesitation when hot & cant rev

Boy, with all that I would be super surprised if it wasn't fixed!
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  #12  
Old October 19th, 2020, 17:18
gmcchamp99 gmcchamp99 is offline
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Re: 96 XJ Hesitation when hot & cant rev

The new distributor that I purchased from O'Reilly's was defective right out of the box. I happened to have another fromnl a different 4.0L and the jeep fired up. So far, 50 miles round trip and no loss of power or inability to rev. Seems like a regular old spunky 192k 4.0. It does rev a bit high, it stays around 1,100 or so hundred RPM. Im suspecting the throttle position sensor and or map is the culprit. I checked all vacuum lines as well as the intake/exhaust gasket and the exhaust manifold. Oddly enough no cracks in the manifold. Looks like someone patched it but did a real bang up job.
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Old October 19th, 2020, 18:25
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Re: 96 XJ Hesitation when hot & cant rev

Well, congrats on fixing it.
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  #14  
Old October 20th, 2020, 15:41
gmcchamp99 gmcchamp99 is offline
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Re: 96 XJ Hesitation when hot & cant rev

Well, I spoke too soon. We are just coming up on 200 miles and she sputtered out again and lost about 95% of throttling ability. You can slightly feather the gas pedal and get it to crawl but until it cools down, she's barely drivable. I did get another Spectra distributor CH15 is the part # and installed that the night before last. Fuel pressure holds steady at 48-51 PSI after the filter change. Engine temp stays just under 210 the whole time. No CEL and no codes even when scanned. Im thinking either CPS or the ECU itself? All the wiring & connectors look good.

Once it sits and cools down for about 20-30 minutes, it will drive just fine for another 20-30 minutes until it does it again.
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  #15  
Old October 20th, 2020, 15:42
gmcchamp99 gmcchamp99 is offline
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Re: 96 XJ Hesitation when hot & cant rev

Or possibly compression difference. I dont have a compression tester that I can screw into the #1 cylinder.
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