1997 XJ won’t rev high and loss of power

[Gabe22]

Hello everyone! I am reaching out today for some ideas on this new XJ I have recently got that’s having some issues, but first I’ll start with the background.

Background info:
I recently acquired this 1997 xj from a guy who was just done dealing with it, he just put a new motor in it, radiator, and points + plug wires on it, but it still wasn’t running right, so he gave up and sold it. Apon close inspection after I got it home, I noticed some things were half assed, such as the motor mounts not being secured, and loose bolts on the throttle body. Former owner states he did not replace gasket when installing throttle body, so he suspected it was a vacuum leak.

Problem:
The jeep will idle fine, but doesn’t want to rev up very much, it will rev up more at neutral, but not enough, it sputters backfires with the extra throttle, and barely had enough power to drive up ramps on trailer. The idle sometimes sticks and idles high, but it will not exceed 30 mile an hour before it’s about to stall. It does have an engine light and OBD 2 port, but the port is dead for some reason, and the fuses check out.

Attempted repairs:
So far, I have fixed the loose bolts on the throttle body with no improvement, and checked vacuum lines, I have done the propane test on all of the fittings and seals and noticed no changes in rpm, I also sprayed starting fluid on to the seals of the throttle body at idle and again had no improvement. I’m at a loss for what to do next, so any suggestions would be greatly appreciated, thanks!

Video of it running,

 

[Saudade]

Some things to quickly check...

Check your fuel pressure. Should be around 49 psi at idle. Then rev the engine and hold for a few seconds to see how much the pressure changes. Drop back to idle and check again.

Check your distributor indexing. Given that the previous owner changed the engine, the distributor may be off a tooth or two.

Check the air tube to the throttle body to make sure there's no blockage in it.

With the engine running, feel the exhaust coming out the tailpipe. You should feel some decent "puffing". Rev the engine up and hold for a few seconds. The "puffing" should get stronger. Visually inspect the entire exhaust for any damage (bends, kinks, flat spots).

Did the previous owner buy a "new" engine or rebuilt/salvage? There are no "points" for the ignition.

Is the Check Engine light on? Check for codes (including pending).

 

[Tim_MN]

If the Check Engine Light is ON, your Jeep is trying to tell you what is wrong. Try another OBD-II code reader and/or fix that fault first.

As suggested already, check the fuel pressure, and distributor indexing

Test the TPS. Clean the Idle Air Controller.

Inspect all the engine bay wire harnesses for chafed or melted wire insulation, failed wire splices or other damage. Make sure Bubba didn't let the wire rest on hot exhaust or sharp sheet metal edges of the valve cover. Check all the wire plugs for corrosion, and bent or pushed back wire plug pins. Don't forget the O2 sensor wires and fuses. 28 year old wire harnesses are prone to age related problems, Bubba done it repairs, and failure from rough handling during engine swaps.

 

[lawsoncl]

Since the motor was out, I would verify that the plug and injector wires are in the right places. For reference on the wire locations and indexing, see https://cruiser54.com/?p=68

 

[Anak]

You could also try removing the O2 sensor and seeing if that helps. Idea being you may have a plugged exhaust. Could be a blocked catalytic converter or could even be a shop rag used to plug the exhaust headpipe while the motor was out.