2point5liter

Hmm...really interesting. I'd hate to have to pull the harness out again! but if I need to at any point in the future that sounds like it'd be really helpful, thank you! Advance honored their 1yr warranty, so I got a new ECU in, and it's running great, idling as it should and adjusting as needed to keep a nice idle. I haven't gotten a real ride out of it yet though, waiting until I have some backup to call if I end up broken down on the side of the road, until AAA can get to me. However, when putting the harness back in to test the new ECU, I noticed something I hadn't noticed before. The relay connectors. I had been so focused on the actual wires that I didnt even look at the connectors. the black boxes the relays get plugged into were all melted, and the terminals had some kind of goop on them. I swapped new ones in so HOPEFULLY if I did have an issue, that was it. Thank you for your help!

Well, I checked everything in the harness. It all checked out in my continuity tests, meaning, I got sold ANOTHER bad ECU. I wish I had a friend with the TBI 2.5L wrangler so I could check and make 100% sure, but hopefully Advance Auto fulfills their 1 year warranty after I told them I had to do the same with AutoZone when I picked this one up. If not, I'll use that part number you gave me and find a more reliable source. Thanks! Ill check back in after I get my vacuum lines back on, my harness cleaned up and installed, and my new ECU in and installed. Looks like I still have a lot of work ahead of me.

Thank you! I love this Jeep, It was my first vehicle, bought it barely running for $850. It makes me mad at times, but I wanna see it up and running again. I'll keep that in mind with the grounds, because something is going wrong here. I forget if I mentioned it or not, but this will be my 4th computer actually. I get them from Advance, remanufactured from a company called "Borg Warner" I think. the issue the first time was my Power Steering Pressure Switch broke off and melted against the exhaust manifold, causing a short. it blew my ECU, the wire leading to my fusible link, and the fuel pump relay. replaced them all, before I knew that was the issue, and they blew again. Found the issue, fixed it, replaced everything, and it ran for 3 days, until the ECU itself went bad. That was a cardone reman, and when I opened it up, I was appalled at what they said had "passed". blobs of solder connecting things that werent supposed to be touching, and white powder corrosion under the board. It was an entirely new issue too, so I knew it was just the ECU that went bad. Now I had this ECU in, from Borg Warner, and it ran for about a day, started cutting out, and got worse and worse, and now it just refuses to run without flooding itself out. That's why I was so skeptical of the wire harness, maybe blowing the ECUs, but it seems to be perfectly fine. This ECU looks perfect, doesnt look or smell burned at any points. But neither does the wire harness, and everything seems to be routed correctly, even if it is super messy. Ill keep that in mind with the grounds and give that a shot. if it runs the same after I get this harness all cleaned up and reinstalled, and the grounds redone, Ill go for a new ECU.

I dont think I have a check engine light on my 89. I do have the diagnostics terminals though, and have been using them to help troubleshoot. I checked the fuel pressure and it was good, so the next thing I did was pulled the wiring harness out. I can't see much that's bad, but I can see that someone else already had this thing out, and used duct tape instead of electrical tape in all the spots where multiple wires connect. Unless it came like that from the factory? That would be awful. Anyways, im currently trying to organize this mess, using nails and rubber bands with it laid out on a large piece of plywood. So many connectors are running to the diagnostic terminals I can barely even see what's going on.

I didnt test the fuel pressure, but im positive it isnt that. It's gotta be either the wiring harness or the ECU, because high fuel pressure wouldnt cause the jeep to run well for a brief period then return to poor idle. it also would not have gone from good to immediately bad like it did. Im gonna tow it home, pull the wiring harness, pull it apart and start looking for some burned up parts. if I cant find anything, it's time for a new ECU, even though it doesnt look or smell burned at all. Maybe it still is.

I ended up re-checking my Coolant sensor and my MAT sensors. They were both open. It turns out, when I checked them, I had rushed it. They read ~4M ohms, but I had thought they read 4k ohms. Retested this time and they were anywhere from ~5.5M ohms to ~18M ohms. replaced both, leaving them outside the Jeep with the old ones still screwed into the intake. No improvements. I am almost positive that the injector isn't bad because I am now using my old one, and it's working the same as my new one did, I have swapped them a few times. I haven't been able to test the fuel pressure yet, but I will soon, It's been a busy week. Although I checked the fuel pressure regulator by taking it off the throttle body. It seemed fine, no rips and the orange gasket looked good still. Made sure I put it back in correctly. Is it operated by vacuum?

Okay, I retested the injector voltage this morning, because I was tired and aggrevated yesterday when testing it. The wire in question, is a light blue wire running all the way from pin 21 of the ECU to the injector, connecting to nothing in between. So to rule out a short in the wire harness, I cut the wires at each end and spliced in a wire of my own running outside of the Jeep, separate from the rest of the harness. No change. This is what the wire looks like now. [ECU PIN21]---|Splice1|----------------------------|Splice2|---[injector] SO, when the Jeep is off, it reads 0v at all 4 locations. when it's set to run, it reads 3.7v at all 4 locations when its idling it reads 12v, but onlyup to splice #2... Somewhere between splice #2, and the injector the reading changes from 12v to ~5.5-6.5V. the first 3 location are easy to test, because I left the splices untaped, but out of reach of anything to short against. to test the injector itself, I had to let the Jeep flood out until it was bogging, unplug the injector, which makes it run perfectly using the gas it is flooding out on for a good 5 or 6 seconds. While it was off I would stick the prong in the injector get a reading of ~6v, then immediately to the second splice next to it, 12v, and keep going back and forth, it didnt change. Im thinking I should try a nice injector connector, but im still curious why it would do that.

I tested the TPS sensor attached to the throttle body, with the throttle body off the Jeep. I brought it home and my dad used a 5V source to test it, so I know that's good. What I did today was cut the wire at the ECU pin 21, and the wire at the injector that it leads to, and soldered a wire between the two to rule out a short in the harness. It acted strangely. It still read 3.7 @ both the ECU and the injector and it was still flooding itself out. but then it started to run properly for a minute, as it had before. it tested 12v at the injector and the ecu. it then started flooding out again while still reading 12v at the injector and computer. I also checked the system ground pin of the ECU, at both ground points (pins 1 and 2) and both of them read next to nothing for voltage, so the grounds are good. Maybe the question I should be asking here is how can I convert this YJ into a carb setup.

Thank you for the replies! I wish I found this community a little sooner. but of course it's only after I make a topic that I see some progress finally! Something really odd happened when testing everything today. I had it idling with everything vacuum related plugged up, just to see if it was the intake manifold gasket. It still had almost no vacuum, and was still idling very low. However, it started to run properly, building up plenty of vacuum and everything. So I knew it was most likely not mechanical, but rather electronic. However, it returned to idling poorly and low vacuum after about 2 minutes. I then found that if I let it run until it started to flood, then took off the injector, the vacuum would shoot up, as would the RPMs, going up to about 3000rpms. Meaning the injector signal, because I have tried 2 injectors now, was pouring out gas as aggressively as it could, flooding as soon as it was started, then unplugged and being deprived, back to flooding when I put it back on. so I now know it's an electrical issue with the injector. The engine runs good when plugging/unplugging the injector, and the timing is great. The vacuum system is also fine, I'm pretty sure. Next, I tested the injector wires. 3.7V to one of them, and the other gets 0V, then 12V while the fuel pump is priming, then back down to 0V. And ~14V when it's running. The 3.7V goes directly to the ECU at pin 21. Now to me, that sounds really odd that it would read 3.7V. SHouldnt it be in the range of about 5V? SO I think the issue is either a bad ECU or a short between my ECU pin 21 and the injector. Does this sound correct?

I did test it with a gauge and got a good reading. But I just remembered that it was right before this issue was occuring. I'll have to retest tomorrow, along with a leakdown test.

a huge problem with my YJ brings me to this forum, so I'm a new member. I own a 1989 Wrangler YJ 2.5L 5-speed. It's a '94 block, with the '89 accessories/head/etc. I drove my Jeep to work one day a couple weeks ago. No issues. Went to leave to grab some lunch at a local restaurant and it started idling not well in about 20 seconds after starting it up. Tried to just drive it anyways, and the power would completely cut out as if I were idling, even though I had it almost floored. The RPMs would go from ~2500 down to ~1000 where it would stay until I got off the gas, when it would die. I started it up a couple times, but it would repeat the process. Luckily I was able to do a U-turn and coast into my work's parking lot. tried to drive it home afterwards and it would do the same thing, over and over. It seemed to run well off of the gas I used to start the Jeep with, bringing itself up to ~3000rpms, and I would be able to quickly get it in gear and drive it. but after that gas was used up, it wouldnt want to run anymore and would die. Luckily there were no cars on the road and I was able to make it about a mile to my grandfather's house, where the Jeep sits now, unable to even idle well. My Jeep will start fine after it's been sitting awhile, go up to 2k rpms as usual, but will quickly fall to around 600rpms and try to die. if I give it gas, it doesnt like it and ends up flooding itself out rather than gain rpms. It won't start again after that unless the gas pedal is to the floor, because it's flooding itself out. While it's doing this, it produces white smoke and condensation that leads to black all on the cement under the tailpipe. Now for what I've tried to do about it. I've done alot, so I'll try to be as thorough but organized as possible. I dropped the gas tank, dried it COMPLETELY out, because I had water in the tank before this. New spark plugs, a full tank of new gas, a new fuel filter, and jumping the fuel pump relay to flush the throttle body. No difference. I got a new injector a few days before this started, because the old one was seemingly clogged. When the throttle body bonnet is pulled off, I can hear a sort of hissing sound coming from the injector. I tried getting the old one cleaned out and trying it, but it's the same as the new one, so the problem probably doesnt lie there. However, along with the hissing, the spraying seems to mess up when it happens. However, it's flooding so I'm not sure if that is a cause or a symptom. The fuel pressure was good, the return line I blew into with my lips and heard it bubble in the tank, so it's not blocked. Tested for vacuum...5in HG if I'm lucky. The other day before I put the new injector in, it was bouncing from I think 10in HG back down to 0in HG rapidly. Now it just goes beween ~0-3. Pulled the Throttle Body off, the gasket was good and it's clean. The fuel pressure regulator is seemingly fine. the IAC is acting normally and isnt very old. The CTS is within it's range at ~70F (~3400Ohms). The MAT sensor is a little off, but I have the '91-'95 sensor, so I have to look at the ranges on that. SHouldnt affect my Jeep that massivley anyways if it's only a little off. The TPS is good and within range. The WOT sensor is working. New MAP sensor as well. Checked all my vacuum lines and they are all good and routed correctly. I plugged the brake booster, no change. Plugged the EGR/Charcoal cannister/Purge solenoid vac line @ the purge solenoid, no change. I was worried about the head, and did a compression test, passed perfectly. All of them within 120-130. the timing test also passed great. I pulled the ECU out and there are no indications of heat or corrosion. I'm not sure what else to do. I checked around the intake manifold for a leak in the gasket, but the gasket isnt very old and I didnt see anything. However, I can still do the WD-40 test, spraying around where it bolts up. I havent checked the O2 sensor, but my manual says it doesnt take O2 into consideration until the vehicle is warmed up. I may have a clogged cat because the cat is old, but would that cause effects this major? Another thing is my power steering switch broke off the line and shorted on the exhaust manifold awhile ago that blew the computer, so I got a new one. I cut the switch off, taped up the lines, and it ran great for a few days after that until this started, so I dont think it matters. But I figured I'd include it. I know this was a long post, and I'm sorry, but I'm incredibly frustrated with it, after having all sorts of issues for the past two months. This one I just can't figure out. Any help would be greatly appreciated.