joeCor Posted May 6 Share Posted May 6 Hi I have a 87 2.5l base model, long bed, 5 speed 4WD. A while back after driving for a bit it used to start to buck but if I turned it off and on it usually stopped. I then changed the oil, coolant temp sensor for the ECU and topped off the coolant. The first drive after that after about 5 minutes it starts to buck then lose power. The engine does not shut off I just get nothing when hitting gas. If I turn it off and let it sit for a while it will drive for another 5-10 minutes before happening again. I then replaced water pump, fan clutch, thermostat, all radiator hoses added an inner spring to lower hose, serpentine belt, both coolant sensors, crankshaft sensor and MAP sensor. Still having the same problem. I’m inexperienced but love the truck and have enjoyed working on it but very frustrating having nothing work. Any help is appreciated Link to comment Share on other sites More sharing options...
89 MJ Posted May 6 Share Posted May 6 What happens if you cycle the key to prime the fuel system a few times immediately after it does some of its bucking? I wonder if your fuel pump is on its way out. Link to comment Share on other sites More sharing options...
joeCor Posted May 6 Author Share Posted May 6 I have not tried. So you’re saying once it starts to buck. Turn it off and cycle the key. And if the bucking stops it’s a fuel pump problem? Link to comment Share on other sites More sharing options...
89 MJ Posted May 6 Share Posted May 6 Correct. Maybe cycle it 2 or three times. Just to make sure you’ve got fuel at the injectors. Link to comment Share on other sites More sharing options...
joeCor Posted May 6 Author Share Posted May 6 Ok thanks I’ll give it a try. If that doesn’t work any ideas of what to check next? Link to comment Share on other sites More sharing options...
89 MJ Posted May 7 Share Posted May 7 If that doesn't fix it, next time it happens, check for spark. It is getting air, so it either must lose fuel or spark. Link to comment Share on other sites More sharing options...
pizzaman09 Posted May 7 Share Posted May 7 This sounds very similar to an issue my parent's ZJ had back in the day. Turned out to be a bad O2 sensor combined this a cracked exhaust header (4.0L). A new O2 sensor fixed it. Link to comment Share on other sites More sharing options...
joeCor Posted May 7 Author Share Posted May 7 Find it weird the bucking worsened and loss of power after the oil change and swapping the coolant sensor. Thats why I flushed and did all the work to the cooling system. Thought maybe I got air trapped or something. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 7 Share Posted May 7 Oil nor coolant changes would cause the engine to do this. Something electrical would do this related to the fuel and sensors. now you changed the coolant sensor. Which one? Now the only way coolant could do this is if the head gasket has failed and is getting into the combustion chambers. Link to comment Share on other sites More sharing options...
joeCor Posted May 7 Author Share Posted May 7 6 minutes ago, eaglescout526 said: Oil nor coolant changes would cause the engine to do this. Something electrical would do this related to the fuel and sensors. now you changed the coolant sensor. Which one? Now the only way coolant could do this is if the head gasket has failed and is getting into the combustion chambers. At first I replaced the one for the ECU. Since then I replaced the one for the gauge because the temp gauge did not work and still doesn’t after changing. Ok glad it shouldn’t have anything to do with that. At least flushing the coolant made me see the metal shaving from the water pump. That’s why I replaced it. The pump was in bad shape Link to comment Share on other sites More sharing options...
joeCor Posted May 7 Author Share Posted May 7 2 hours ago, pizzaman09 said: This sounds very similar to an issue my parent's ZJ had back in the day. Turned out to be a bad O2 sensor combined this a cracked exhaust header (4.0L). A new O2 sensor fixed it. Replaced most sensors already might as well give that a try. Thanks Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 7 Share Posted May 7 For the gauge, did you get the ‘sensor’ or did you get the one labeled as ‘sender’? Link to comment Share on other sites More sharing options...
joeCor Posted May 7 Author Share Posted May 7 7 hours ago, eaglescout526 said: For the gauge, did you get the ‘sensor’ or did you get the one labeled as ‘sender’? Sender, Crown Auto 53005309. the rpm gauge the temp gauge and the odometer don’t work. Everything else on the cluster does. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 7 Share Posted May 7 You need the sensors for the gauge not sender. Sender is for the lights. tach gets its signal straight from the coil and the Speedo is cable driven. Speedo itself could be busted or the cable is messed up. Or the gear in the transmission and or transfer case could no longer be making contact. Link to comment Share on other sites More sharing options...
joeCor Posted May 7 Author Share Posted May 7 2 hours ago, eaglescout526 said: You need the sensors for the gauge not sender. Sender is for the lights. tach gets its signal straight from the coil and the Speedo is cable driven. Speedo itself could be busted or the cable is messed up. Or the gear in the transmission and or transfer case could no longer be making contact. Where do the sensors for the gauge go? The one I replaced is on the top of the block back driver side. Do you know a part number? Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 7 Share Posted May 7 Sensor goes in the same spot as the senders for oil and temp. I don’t have a part number at the moment. Link to comment Share on other sites More sharing options...
Tex06 Posted May 8 Share Posted May 8 If these don't fix it, I have an idea what it could be. It's a PITA to diagnose but if you have a multi-meter I can show you what my 4.0 with these symptoms was. Link to comment Share on other sites More sharing options...
joeCor Posted May 8 Author Share Posted May 8 22 minutes ago, Tex06 said: If these don't fix it, I have an idea what it could be. It's a PITA to diagnose but if you have a multi-meter I can show you what my 4.0 with these symptoms was. I got a multimeter and I’m all ears Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 8 Share Posted May 8 3 hours ago, Tex06 said: It's a PITA to diagnose but if you have a multi-meter I can show you what my 4.0 with these symptoms was. OP has a 2.5L, but I’m curious if you’re experience will translate Link to comment Share on other sites More sharing options...
Tex06 Posted May 11 Share Posted May 11 On 5/8/2025 at 7:29 AM, joeCor said: I got a multimeter and I’m all ears I basically had a bad solder joint that fed both my tps and map in my main wiring harness. Was able to track it down using a wiring diagram after seeing my TPS +5V was dipping to 1.7-2.7V while the engine was running (and only while plugged it....unplugged there was no electrical load on the solder joint so I measured 5VDC every time I unplugged the connector. When you changed the coolant sensor, you probably moved/jostled/pushed on that wiring harness if it's like the 4.0 in any way. Feel free to call me, I have every manual made for the 91 & 92 model year Jeeps bc of this issue.... not sure how much the 2.5L changed after the switch to Chrysler but I've got ADHD and a decent internet connection if the manuals don't cut it. Link to comment Share on other sites More sharing options...
Tex06 Posted May 11 Share Posted May 11 On 5/8/2025 at 10:58 AM, eaglescout526 said: OP has a 2.5L, but I’m curious if you’re experience will translate Not 100% sure but this definitely sounds like an electrical issue and I've gotten pretty good at those 😁 Fix is page 5 of this thread. I was a little inactive for a while and it kinda got hijacked but the info is in there. Link to comment Share on other sites More sharing options...
joeCor Posted May 13 Author Share Posted May 13 On 5/11/2025 at 2:21 AM, Tex06 said: I basically had a bad solder joint that fed both my tps and map in my main wiring harness. Was able to track it down using a wiring diagram after seeing my TPS +5V was dipping to 1.7-2.7V while the engine was running (and only while plugged it....unplugged there was no electrical load on the solder joint so I measured 5VDC every time I unplugged the connector. When you changed the coolant sensor, you probably moved/jostled/pushed on that wiring harness if it's like the 4.0 in any way. Feel free to call me, I have every manual made for the 91 & 92 model year Jeeps bc of this issue.... not sure how much the 2.5L changed after the switch to Chrysler but I've got ADHD and a decent internet connection if the manuals don't cut it. thank you I’ll try to give it a shot this week. I read the whole thread and it very interesting. Seems very similar. Just wondering if the 2.5l renix will be different. Does this look similar to your harness? Link to comment Share on other sites More sharing options...
joeCor Posted Wednesday at 10:57 PM Author Share Posted Wednesday at 10:57 PM Also, does my system have a IAC? Or is it just the ISC? Seeing contradicting info. Link to comment Share on other sites More sharing options...
eaglescout526 Posted Thursday at 12:06 AM Share Posted Thursday at 12:06 AM 2.5L Renix has an ISA. It’s different from the 4.0 and later HO set up with the IAC. I love when everyone assumes the 2.5L shares the same set up for 4.0 Renix when they were never the same to begin with. Also grinds my gears too. Link to comment Share on other sites More sharing options...
joeCor Posted Thursday at 01:53 AM Author Share Posted Thursday at 01:53 AM 1 hour ago, eaglescout526 said: 2.5L Renix has an ISA. It’s different from the 4.0 and later HO set up with the IAC. I love when everyone assumes the 2.5L shares the same set up for 4.0 Renix when they were never the same to begin with. Also grinds my gears too. Thanks yea it’s hard to find solid info Link to comment Share on other sites More sharing options...
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