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Unread 06-25-2012, 06:42 PM   #1
torchd
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1998 ZJ 
 
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Jeep Seems Like It's Down On Power.... BIG TIME!

As of lately, my ZJ (4.SLOW) seems like it is severly lacking power... You hit the gas and the throttle response is definitely lacking. There is 0 pick up at any speed.

I'm throwing no CEL or SES codes. I am do for an oil change and air filter change that will get done by me on this wednesday.

So I really don't know what it can be. Ohh yeah I did the Kolak ignition tune up 10/2010 (new plugs, wires, cap/rotor and ign coil)

TB, intake manifold and exhaust components are all stock.

At home I do have waiting to be installed: 99+ intake manifold, "703" injectors and will be getting an exhaust header and will prolly do a custome 2.5" exhaust from header collector > cat > muffler

So why else can my jeep feel like its lacking some major power?

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[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 06-25-2012, 07:09 PM   #2
JasonStebbins
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No codes is strange. Any sputtering/hesitation when accelerating? Any idle problems? Ever check fuel pressure or do a compression test?

Faulty upstream o2 sensor
Clogged catalytic converter
Transmission issue (Low fluid, Governor Pressure Sensor/Solenoid)
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Unread 06-25-2012, 08:19 PM   #3
torchd
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Quote:
Originally Posted by JasonStebbins View Post
No codes is strange. Any sputtering/hesitation when accelerating? Any idle problems? Ever check fuel pressure or do a compression test?

Faulty upstream o2 sensor
Clogged catalytic converter
Transmission issue (Low fluid, Governor Pressure Sensor/Solenoid)
No codes or lights

No hesitation, pinging, stalling, stuttering, high or low idle issues

Never have checked fuel pressure or done a compression test

Don't think it is an O2, no lights and gas mileage is very consistant

Maybe my OEM cat of 14 yrs is starting to go bad

Tranny is fine, no issues
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 06-25-2012, 08:30 PM   #4
JasonStebbins
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Original converter is a good place to start. Will definitely bog down the Jeep if it is clogged.

Could be fuel starvation or low compression in one of the cylinders, but you said you have no other running issues.
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Unread 06-25-2012, 08:48 PM   #5
torchd
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Quote:
Originally Posted by JasonStebbins View Post
Original converter is a good place to start. Will definitely bog down the Jeep if it is clogged.

Could be fuel starvation or low compression in one of the cylinders, but you said you have no other running issues.
Pretty soon here I am putting on the 99+ intake, the "703" injectors and while I have everything off will also do a header too. Then take it to my buddies and do a custom 2.5" exhaust using a Magnaflow metallic spun cat.
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 06-25-2012, 10:21 PM   #6
zander21510
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I would say dump a bottle of Techron (the one for 20 gal tanks) in at one-half tank...but I would wait till u do the injector swap at least. Seafoam would be an excellent idea as well, but again you could wait till u install all that good stuff.

You will notice a HUGE improvement over stock with all those upgrades...stock 4.0s after 15 years (arguably even new) just tend to have no pickup normally...
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Unread 06-26-2012, 12:50 AM   #7
torchd
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Quote:
Originally Posted by zander21510 View Post
I would say dump a bottle of Techron (the one for 20 gal tanks) in at one-half tank...but I would wait till u do the injector swap at least. Seafoam would be an excellent idea as well, but again you could wait till u install all that good stuff.

You will notice a HUGE improvement over stock with all those upgrades...stock 4.0s after 15 years (arguably even new) just tend to have no pickup normally...
I seafoam my gas tank and top end of the motor 3 times a year
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 06-26-2012, 04:37 AM   #8
torchd
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I think I am going to change out my plugs and wires for a new set, maybe go with a set of Granatelli (GMS) wires and use my same plug (Autolite Platinum Plugs gapped to ~.040".

Also I desperately need to do my intake and WHOLE exhaust!!!
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 06-26-2012, 10:12 AM   #9
4Slow9erHybrid
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I vote for partially plugged cat. Mine had no power at higher speeds. Top speed was ~ 75mph, had trouble maintaining 60-65mph on the slightest incline. Replaced exhaust starting from the cat. converter (magnaflow), much more power at higher rpm (2500+rpm) and maintains speed uphill without issues in OD. Had only ~ 90k at the time on the odometer.
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Unread 06-26-2012, 07:24 PM   #10
torchd
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Quote:
Originally Posted by 4Slow9erHybrid View Post
I vote for partially plugged cat. Mine had no power at higher speeds. Top speed was ~ 75mph, had trouble maintaining 60-65mph on the slightest incline. Replaced exhaust starting from the cat. converter (magnaflow), much more power at higher rpm (2500+rpm) and maintains speed uphill without issues in OD. Had only ~ 90k at the time on the odometer.
When I come to an incline, my Jeep DIES!! Literally falls flat on its face and it constantly shifts in and out of OD.

I think my cat is FUBAR
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 07-01-2012, 06:04 PM   #11
torchd
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Some other things I've noticed, I adjusted my TV throttle cable bc my Jeep at low speeds would not kick a gear down if you need to pass someone.

But today, I was maybe doing 20mh to 25 mph and I needed to accelerate and literally stabbed the gas pedal held it to the floor and the Jeep wouldn't down shift a gear. But my tranny is fine, shift smooth as silk, no hesitations at all.

And today I was accelerating to get onto a busy hwy, I was maybe doing 45 mph, I needed to merge and again I HELD the gas pedal to the floor, tranny down shifted a gear, then wuickly shifted again. My RPMs would barely climb even though pedal was to the medal!!!!

Any ideas?
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 07-01-2012, 06:07 PM   #12
JasonStebbins
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Replace your converter yet?

Sounds like your TPS could be failing as well.
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Unread 07-01-2012, 06:09 PM   #13
torchd
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Quote:
Originally Posted by JasonStebbins View Post
Replace your converter yet?
No.. Reason is bc I am waiting to get the time to install my 99+ intake, 703 injectors and a header. Then will take it to my buddies shop to get a custom 2.5" exhaust from the header collectors all the way out back

Where is the TPS located? on the TB correct?
__________________
[b]1998 Jeep Grand Cherokee Laredo[/b]
2" BB Pucks | SkyJacker Hydro Shocks | Rubicon Wheels | Cooper 245/75/16 Tires

[b][color=red]2002 Trans Am[/b][/color]
Cam, Full Exhaust, Stock Heads, Stock LS6 Intake and Stock 10 bolt with 3.42s
[b]420 RWHP and 382 RWHTQ[/b]
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Unread 07-01-2012, 06:11 PM   #14
JasonStebbins
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Yep, right in that area. Mine has a sticker on it.
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