I need some help

Scrambler

Scrambler

Member
My 1997 Jeep Wrangler with a 4.0 is giving me fits and I can't figure out what the problem is. Let's start off with the symptoms: It has no power, sputters, and "backfires" from under the hood, not the exhaust. If I get it under enough load it will smooth out until I switch gears and then I have to go through this throttling dance again until I can get it under enough load to smooth out in the next gear.

Parts replaced: Crankshaft Position Sensor, Upstream 02 sensor, all spark plugs, distributor cap, rotary button, and the ignition pick up coil.

It has been hooked up to 2 different OBDII readers and the big ass machine that shows the electrical pulses, with no indications of a problem. At idle, this thing purrs like a kitten, but as soon as you want to drive it down the road it goes full retard. I'm stumped. If anyone has any suggestions on what I should replace next, I am all ears. By the way, I have already added the attenuater and put my last oil change's oil in the frame rails, so I know it isn't that. :cheesy:
 
Scrambler said:
My 1997 Jeep Wrangler with a 4.0 is giving me fits and I can't figure out what the problem is. Let's start off with the symptoms: It has no power, sputters, and "backfires" from under the hood, not the exhaust. If I get it under enough load it will smooth out until I switch gears and then I have to go through this throttling dance again until I can get it under enough load to smooth out in the next gear.

Parts replaced: Crankshaft Position Sensor, Upstream 02 sensor, all spark plugs, distributor cap, rotary button, and the ignition pick up coil.

It has been hooked up to 2 different OBDII readers and the big ass machine that shows the electrical pulses, with no indications of a problem. At idle, this thing purrs like a kitten, but as soon as you want to drive it down the road it goes full retard. I'm stumped. If anyone has any suggestions on what I should replace next, I am all ears. By the way, I have already added the attenuater and put my last oil change's oil in the frame rails, so I know it isn't that. :cheesy:
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Surprised the oil on the frame didn't fix it.... Sounds like an ignition module or crank sensor problem. Also check to make sure dist hold down bolt is tight. You could check fuel pressure too but everything sounds more like ignition system especially with no codes.
 
Scrambler said:
My 1997 Jeep Wrangler with a 4.0 is giving me fits and I can't figure out what the problem is. Let's start off with the symptoms: It has no power, sputters, and "backfires" from under the hood, not the exhaust. If I get it under enough load it will smooth out until I switch gears and then I have to go through this throttling dance again until I can get it under enough load to smooth out in the next gear.

Parts replaced: Crankshaft Position Sensor, Upstream 02 sensor, all spark plugs, distributor cap, rotary button, and the ignition pick up coil.

It has been hooked up to 2 different OBDII readers and the big ass machine that shows the electrical pulses, with no indications of a problem. At idle, this thing purrs like a kitten, but as soon as you want to drive it down the road it goes full retard. I'm stumped. If anyone has any suggestions on what I should replace next, I am all ears. By the way, I have already added the attenuater and put my last oil change's oil in the frame rails, so I know it isn't that. :cheesy:
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Did you change all your control arm bolts to 9/16 yet.
 
Backfiring has to be timing issue. If it were valve timing, it would likely always be there and never smooth out and would most likely set codes. My gut feeling is that it's somehow related to ignition timing.
 
WJCO said:
Backfiring has to be timing issue. If it were valve timing, it would likely always be there and never smooth out and would most likely set codes. My gut feeling is that it's somehow related to ignition timing.
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That's what I am thinking. I've never seen a 4.0 jump time, not to say that it hasn't ever happened, but I highly doubt it in this case. I'll start going down the ignition route. I hate electrical related problems....
 
Before this happened, any unusual circumstances? Like driving through water or mud? Or any electrical mods installed?
 
WJCO said:
Before this happened, any unusual circumstances? Like driving through water or mud? Or any electrical mods installed?
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It stalled out at a red light. I cranked it right back up and then had to limp it home, but after all these new parts were installed I could drive it after fighting the backfiring and loss of power. When I pulled the spark plugs the rear spark plug was completely black and became increasingly white/brown to the forward spark plug. it looks like it isn't firing correctly.
 
Scrambler said:
It stalled out at a red light. I cranked it right back up and then had to limp it home, but after all these new parts were installed I could drive it after fighting the backfiring and loss of power. When I pulled the spark plugs the rear spark plug was completely black and became increasingly white/brown to the forward spark plug. it looks like it isn't firing correctly.
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I would look at your coil and ignition module. There should be info online on how to test both of those.
 
Just a little update. I replaced the ignition control module and nothing. I started tackling fuel delivery and found that when hooked up to a proper diagnostic machine that the computer was reading 25PSI on the fuel. This is way out of the range the pressure is supposed to be at. I'm going to drop the tank and test the fuel pump and the fuel regulator. I'm still not totally convinced that the problem lies in fuel delivery.
 
Any additional check engine lights? How does the Jeep idle when it starts? how does the jeep start if you pour some gas directly on the intake?
 
Tag92yj said:
The backfiring may be a lean misfire. You will get bad gestation and a definite lack of power.
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geberhard said:
Any additional check engine lights? How does the Jeep idle when it starts? how does the jeep start if you pour some gas directly on the intake?
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The dealership I bought it from took it in today to diagnose and fix it at a discounted rate(I guess trying to do the right thing) and reiterated the 20 PSI fuel pump issue. Seems all these issues stemmed from a bad fuel pump, but the fat lady hasn't sung yet and I won't believe it until I actually drive it down the road. I'll update tonight or tomorrow and let you guys know if this was the true cause of my 4.0 woes.
 
The fat lady has sung and the fuel pump was the issue. I just brought it home. The dealer basically did the work for parts cost. I would have done it myself, but if someone is going to drop the tank for free, then I'll let them do it. :thumb: Maybe now I can start my axle fund.

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cwmt3 said:
Nice combo :-D I just picked up an old green 97 tj to go with my commando green renegade.
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Shweet. We love the renegade and the TJ has grown on us, but we have been spoiled because we are coming from a JK that we absolutely loved. Once we get this one built and 100% reliable i am sure we will love it as much as the JK.
 
Scrambler said:
Shweet. We love the renegade and the TJ has grown on us, but we have been spoiled because we are coming from a JK that we absolutely loved. Once we get this one built and 100% reliable i am sure we will love it as much as the JK.
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No way, had a '13 jk sport before the renegade too. My wife just had to have twins last october. :doh: needed 4 doors and mpg these days. Ive sub'd, keep it coming
 
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