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No power jeep holding back

Tonyt22

NAXJA Forum User
Location
California
My 93 XJ 4.0 is completely dogging out if I put my foot in it it will get up to 45 and 3k rpms and hold it will shift in and out of OD but wont go past 45 unless I'm going down hill I've replaced the fuel pump, fuel filter ,injectors, tps,headers, map sensor checked trans the fluids fine shifts fine kick down has been adjusted any one have any ideas I'm all ears

Ordered a new compression tester just to test it also checked cat getting a back pressure of 1.5 psi and idle and 2.5 at 2k ordered a cat just in case but dont wanna throw anymore parts at it
 
Good fuel pressure? Seems like you're already started throwing parts at it.

I was already addressing other issues over that last few months the tps and map were the only two I've changed chasing this problem
I'll check it tomorrow morning figured with a new pump and regulator it wouldnt be a issue but I guess you never know
 
How many miles on the engine ?
If the timing chain skipped a tooth it would not only screw up the cam timing but take the ignition timing with it.
Those two combined can make for a real funky running engine.

Just some forensics, sounds like you have already thrown enough parts at it.
 
167k it idles fine and trails just fine it's only going past 50 that is the problem when I get some time I'll pull everything to check the chain
 
I know you said you replaced the fuel pump, but did you check the fuel pressure at the rail? Really sounds to me like a fuel delivery problem.
 
I know you said you replaced the fuel pump, but did you check the fuel pressure at the rail? Really sounds to me like a fuel delivery problem.



Just finished checking the fuel pressure 30-33 at idle when I rev it about 2k shows about 31 unplugged the regulator shot up to 40 so I think that's all good
 
Just finished checking the fuel pressure 30-33 at idle when I rev it about 2k shows about 31 unplugged the regulator shot up to 40 so I think that's all good

The best check would be at WOT and the pressure should be 39psi.
 
So compression numbers are 90.110,110,115,110,115
Did a wet test on cylinder 1 brought it up to 115 so I'm thinking time for a rebuild all those numbers seem pretty low
 
Compression numbers are pretty low, but not low enough to cause what you are seeing all by themselves. Do a manifold vacuum test and post up the results.

What do the plugs look like? Oil fouled? Wide Gap?

Does it run smooth? Is there more power when the engine is cold vs hot?

My thoughts are probably a bad O2 or clogged cat first. Personally I have seen a CPS that simply would not perform at high rpms and the same for a coil going bad.

Do the tests first and that should tell a lot before throwing $$$ at it.
 
Compression numbers are pretty low, but not low enough to cause what you are seeing all by themselves. Do a manifold vacuum test and post up the results.

What do the plugs look like? Oil fouled? Wide Gap?

Does it run smooth? Is there more power when the engine is cold vs hot?

My thoughts are probably a bad O2 or clogged cat first. Personally I have seen a CPS that simply would not perform at high rpms and the same for a coil going bad.

Do the tests first and that should tell a lot before throwing $$$ at it.
Did a vaccum test the other day was 15 lbs at idle and stayed the same at 2k it runs great idles fine and has power until you jump on the highway all plugs looked good save one that had some oil on it from the valve cover leaking I did a exhaust back pressure test and got 1.5 psi at idle and 2.5 at 2k didn't think it was bad but now thinking there might be a slight clog in the cat o2 is new changed that a few months back when I changed the exhaust manifold I'll look into testing the CPS thanks for the input
 
Did a vaccum test the other day was 15 lbs at idle and stayed the same at 2k it runs great idles fine and has power until you jump on the highway all plugs looked good save one that had some oil on it from the valve cover leaking I did a exhaust back pressure test and got 1.5 psi at idle and 2.5 at 2k didn't think it was bad but now thinking there might be a slight clog in the cat o2 is new changed that a few months back when I changed the exhaust manifold I'll look into testing the CPS thanks for the input

I think Old man is on the right track, my first guess would be O2 sensor. For the first couple of minutes after a cold start, the engine runs on presets (mostly) after the O2 sensor heats up (after a couple of minutes) the O2 sensor regulates fuel (mostly). I honestly could tell the difference between a O2 sensor issue and a CPS issue, except the limited RPM only showed up after a couple of minutes after starting a cold motor. Another reason is you obviously have an issue and O2 sensor can be way bad before they set a CEL code. Many other sensors set a CEL (key) code way earlier while failing.

Another possibility is you may be running out of advance, sensor related.

The simplest would be a weak spark. Pull the number two plug, ground it on something good, have somebody turn the motor over, The color and sound of that spark may tell you something.

Something a little more exotic is the CPS shares a sensor input voltage, with other sensors, the cam position sensor for one. A failing sensor can suck down that input voltage (partial short) and cause iffy CPS function.
 
Have someone check your catalytic converter while you're at it. Do a before the cat pressure test.

Unless you have no cat...

Normally the CAT makes that tin can full of rocks sound before the Ceramic filler gets broken down enough to clog the screen. I guess, though I've never seen it, the screen could get clogged with soot and/or carbon and make no noise.
 
Normally the CAT makes that tin can full of rocks sound before the Ceramic filler gets broken down enough to clog the screen. I guess, though I've never seen it, the screen could get clogged with soot and/or carbon and make no noise.
Not always the case. Especially if something caused the cat to go bad.
 
So I cut the cat out today was pretty clogged had a new one welded in soo much better now guy at the shop said that .5 psi over at idle is enough to rob power at speed and wot and cause my issues
 
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