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Go Back JeepForum.com > Models > Jeep Grand Cherokee & Commander Forums > ZJ Grand Cherokee Forum > Common ZJ Problems / Tutorial On How To Fix Them

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Unread 12-04-2013, 09:37 PM   #136
JasonStebbins
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1997 ZJ 
 
Join Date: Jan 2009
Posts: 3,138
Quote:
Originally Posted by OCDComputing View Post
I may have missed it...but best practices for flushing a heater core.
Hmm. I linked a write up to replace it, but not flushing. I'll edit it now. You basically just need a garden hose and whatever type of cleaner you choose.

Edit - Added a flushing link.

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Unread 12-05-2013, 10:36 AM   #137
OCDComputing
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Thanks for that! Great link.
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Unread 12-07-2013, 09:53 AM   #138
housedl
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wow.. we can delete the forum and just read this.
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Unread 12-07-2013, 10:00 AM   #139
SpectralZJ98
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1998 ZJ 
 
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Location: Louisville, KY
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Just thought of something. Rear liftglass defogger grid repair. Have to take pictures, now
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Unread 12-07-2013, 10:22 AM   #140
Edwardmiller221
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I've got a tough one. When I accelerate with the pedal more than half way down and rpms pass 3300 I start to backfire through the intake. No vacuum leak. I've replaced the crank sensor, tps and map sensor. The overall problem got slightly better with tps but still having backfiring. Only codes are misfire codes for different cylinders. Have disconnected battery for 8 hours. No difference. What should I try next? The tps and crank sensor are mopar parts. Map and iac are aftermarket. Forgot to add also misses at idle sometimes.
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Unread 12-07-2013, 10:58 AM   #141
SpectralZJ98
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Quote:
Originally Posted by Edwardmiller221 View Post
I've got a tough one. When I accelerate with the pedal more than half way down and rpms pass 3300 I start to backfire through the intake. No vacuum leak. I've replaced the crank sensor, tps and map sensor. The overall problem got slightly better with tps but still having backfiring. Only codes are misfire codes for different cylinders. Have disconnected battery for 8 hours. No difference. What should I try next? The tps and crank sensor are mopar parts. Map and iac are aftermarket. Forgot to add also misses at idle sometimes.
Clean your fuel rail, replace your fuel injector basket filters, and check your fuel line
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Unread 12-07-2013, 11:30 AM   #142
Edwardmiller221
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Quote:
Originally Posted by SpectralZJ98 View Post

Clean your fuel rail, replace your fuel injector basket filters, and check your fuel line
I forgot to include 97 5.2. Basket filters, I'll have to look that one up. Thanks. Also must state that she will do 80 on the highway with no problems.
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Unread 12-07-2013, 11:54 AM   #143
SpectralZJ98
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Quote:
Originally Posted by Edwardmiller221 View Post

I forgot to include 97 5.2. Basket filters, I'll have to look that one up. Thanks. Also must state that she will do 80 on the highway with no problems.

4.0, 4.2, 5.2, 5.9, same difference. You did your electrical components. Only thing left is the fuel system. You'd be surprise how overlooked the rails and basket filters are. Ebay has kits for fairly cheap, and its cake to clean them and the rails.
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Unread 12-07-2013, 12:02 PM   #144
JasonStebbins
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Quote:
Originally Posted by Edwardmiller221 View Post
What should I try next? The tps and crank sensor are mopar parts. Map and iac are aftermarket. Forgot to add also misses at idle sometimes.
Check all these things to track down the misfire.

• Worn spark plugs
• Cracked distributor caps
• Out of Phase distributor/rotor
• Shorted rotor
• Leaking plug wires
• Low fuel pressure
• Low compression
• Sticking valves
• Broken valve springs
• Worn cam lobes
• Incorrect valve or ignition timing
• Leaking EGR
• Vacuum leaks
• Leaking Injectors
• Clogged Injectors
• Contaminated fuel
• Low fuel tank level
• Excessive EVAP purge
• Low ignition system primary voltage
• Cracked coils
• Plugged exhaust
• Excessive PCV flow
• Wiring Harness
• Faulty PCM
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Unread 12-07-2013, 12:15 PM   #145
SpectralZJ98
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^^^^^^ Yeah, what he said.
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Unread 12-07-2013, 12:37 PM   #146
Edwardmiller221
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Quote:
Originally Posted by JasonStebbins View Post

Check all these things to track down the misfire.

• Worn spark plugs
• Cracked distributor caps
• Out of Phase distributor/rotor
• Shorted rotor
• Leaking plug wires
• Low fuel pressure
• Low compression
• Sticking valves
• Broken valve springs
• Worn cam lobes
• Incorrect valve or ignition timing
• Leaking EGR
• Vacuum leaks
• Leaking Injectors
• Clogged Injectors
• Contaminated fuel
• Low fuel tank level
• Excessive EVAP purge
• Low ignition system primary voltage
• Cracked coils
• Plugged exhaust
• Excessive PCV flow
• Wiring Harness
• Faulty PCM
Thanks for the list. Most is done. New coil cap rotor wires champion plugs. My confusion lies with the fact it will red line and not misfire until pedal is pushed beyond half way down. So if I don't pass half throttle will not misfire and will red line with no problem. Once dip farther into the pedal from past halfway to floor misfires passed 3300 rpm or so and of course will not red line and then throws the misfire code. So since it will red line prior to more than half throttle and drive at any highway speed with no problem leads me toward some sensor or possibly the pcm. But with no codes I'm pulling straws. Since it only effected by throttle position leads me to believe that all mechanicals and fuel system is good or I would see and issue passed that rpm across the board, ie any and all throttle position, correct?
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Unread 12-07-2013, 12:54 PM   #147
JasonStebbins
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Quote:
Originally Posted by Edwardmiller221 View Post
Thanks for the list. Most is done. New coil cap rotor wires champion plugs. My confusion lies with the fact it will red line and not misfire until pedal is pushed beyond half way down. So if I don't pass half throttle will not misfire and will red line with no problem. Once dip farther into the pedal from past halfway to floor misfires passed 3300 rpm or so and of course will not red line and then throws the misfire code. So since it will red line prior to more than half throttle and drive at any highway speed with no problem leads me toward some sensor or possibly the pcm. But with no codes I'm pulling straws. Since it only effected by throttle position leads me to believe that all mechanicals and fuel system is good or I would see and issue passed that rpm across the board, ie any and all throttle position, correct?
So after half throttle, it starts to misfire? Is your catalytic converter original? Upstream oxygen sensor? Have you checked fuel pressure? Sounds to me like an exhaust restriction or fuel delivery problem.
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Unread 12-07-2013, 01:07 PM   #148
Edwardmiller221
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Quote:
Originally Posted by JasonStebbins View Post

So after half throttle, it starts to misfire? Is your catalytic converter original? Upstream oxygen sensor? Have you checked fuel pressure? Sounds to me like an exhaust restriction or fuel delivery problem.
Yes after somewhere past half throttle. Will red line and drive normally unless I get heavy into the pedal. Cat and o2 sensors are original. But like I say will red line and run like a Swiss watch until push to far into the pedal.
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Unread 12-07-2013, 01:33 PM   #149
JasonStebbins
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1997 ZJ 
 
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Quote:
Originally Posted by Edwardmiller221 View Post
Yes after somewhere past half throttle. Will red line and drive normally unless I get heavy into the pedal. Cat and o2 sensors are original. But like I say will red line and run like a Swiss watch until push to far into the pedal.
When you're really on the pedal or downshifting, it's moving a lot more and air fuel. That's why I'm guessing CC or o2. You can try unplugging the oxygen sensor and go for a drive to see if the symptoms go away. Can't really test the CC without a heat gun, but if it's original it's probably not in great condition.
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Unread 12-24-2013, 05:30 AM   #150
AAA
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Nice thread. You should also include the elusive rear clicking sound under acceleration or deceleration. I kept hearing a click coming from the rear of the vehicle when I would accelerate of hit the brakes either from a stand still or driving at low speeds, but I could never pinpoint where it was coming from. I had a friend drive the vehicle so I could listen on both sides, and I could never quite figure out what was clicking. Finally, I noticed that the Rear Upper Control Arm mounts had started to break away from the frame, and that was the source of my clicking. If your ZJ is lifted with short arms, check your rear UCA mounts for any signs of breakage, splitting or tearing. It's a fairly common problem. The fix is either to remove the mounts, repair the split or hole in the frame, then either replace the UCA mounts with aftermarket ones, or re-attach the stock brackets. This will take a good welder to fix this, as the ZJ frame is very thin and easy to burn through.
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