I_s2k Posted May 28 Share Posted May 28 Hey all, I acquired an '86 not too long ago (january of this year) and have yet to figure out what the problem is with it. To make a long story short, It will not start or run with the MAP sensor vacuum connected unless you hold it almost WOT. If I unplug the vacuum from the sensor, it will fire and run poorly but on its own with no assistance but starts to give out past like 1/4 throttle. If you look at my recent posts I'm sure you can see all the past topics Ive started trying to solve this but so far, no dice on everything I've tried. Anyways, what all ECU's will fit my Jeep? Its a 1986 with the 2.5 and the AX4. Ive read that there was some year ranges where there was an internal update for better fuel stability and and more HP? Also, I plan to pull the ECU this week and crack it open to look and see if any of the capacitors are shot, does anyone have a link or the know how to repair this? I can't imagine it would be rocket science haha. TIA Edit: AX-4 not AW4 Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 The MJ in your post contradicts the transmission you have in your signature. I digress. Any year 2.5L ECU will work. As far for it not running with the MAP vac plugged it, you could be having an issue elsewhere related to vacuum. Anything else you know about the MJ? Did the previous owner do their own work on it? Did they do any modifications to make it “run”? Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 56 minutes ago, eaglescout526 said: The MJ in your post contradicts the transmission you have in your signature. I digress. Any year 2.5L ECU will work. As far for it not running with the MAP vac plugged it, you could be having an issue elsewhere related to vacuum. Anything else you know about the MJ? Did the previous owner do their own work on it? Did they do any modifications to make it “run”? Oh whoops Ill edit that, typo, it is indeed an AX-4 and not the AW4. Sorry its my monday and I'm still waking up after a long weekend haha. I cannot find any vac leaks or issues any where else from bumper to bumper, all electrical connections have been cleaned from bumper to bumper per Cruiser's guide, TB was rebuilt by myself, all new gaskets and regulator, I've tried 3 new MAP sensors, new TPS and correctly adjusted, new fuel filter and fuel, no leaks(shocker, not even an oil leak) fuel pressure is unknown but I'm gonna say is fine because it can and does run/drive just very poorly I'm assuming due to the MAP issue. Unfortunately the guy I got it from had bought it from the original owner with intentions to fix it up but never got around to it and I believe it sat for 2 years before I got it. The original owner had every fuse pulled out of the box at your feet and wire nuts all over the place. I've already gone through and removed all of the wire nuts and they were all tied into the radio and some added speakers as well as some really weird hidden winch. So as of now I'm at a loss other than checking the ECU unless anything else can thought up as to why it's having this issue. It's a bizarre one for me haha. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 I feel ya haha. Has the ISA been adjusted or played with? If unplugging the map helps it run better, I’d suspect it’s not getting enough air into the engine which makes me think the ISA has been messed with. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 28 minutes ago, eaglescout526 said: I feel ya haha. Has the ISA been adjusted or played with? If unplugging the map helps it run better, I’d suspect it’s not getting enough air into the engine which makes me think the ISA has been messed with. In my ownership, the ISA has not been messed with other than unplugged just to get the connector cleaned and what not but it has been at least unplugged before as the retainer on the connector was broken off. The ISA does work as it should but I have no idea if its out of wack. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 You can get a new connector for the ISA. I’d recommend getting a weather pack pin removal tool and just swapping the new connector in place of the old one. If it has been messed with, I’d suspect the screw on it is too low and the engine isn’t getting enough air. Hence you unplugging the map. That’s my logical thinking Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 Just now, eaglescout526 said: You can get a new connector for the ISA. I’d recommend getting a weather pack pin removal tool and just swapping the new connector in place of the old one. If it has been messed with, I’d suspect the screw on it is too low and the engine isn’t getting enough air. Hence you unplugging the map. That’s my logical thinking Okay, that would make sense to me too but its confusing because of the fact that it runs with the MAP vac unplugged do you think its just forcing a ton of extra fuel to accommodate that? Obviously it does run really rich. I havent messed with the ISA just because I know how finnicky they can be. On a side note, would a bad IAT cause any issues like this? Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Yes. The ECU can see that the MAP is not getting vac and just defaults to start up values. Which is why it runs rich. If you unplug the map entirely, the ECU will kill the engine. It basically goes back into closed loop with the vac line unplugged. The ISA isn’t that finicky at all actually. It sounds like it but if you follow my ISA adjustment write up that’s straight from the AMC TBI book, it’s less daunting and scary than it seems. I dont know if you have an REM or a tach but you need one of those for the adjustment process. You can test the IAT but that’s just related to air temp. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 Just now, eaglescout526 said: Yes. The ECU can see that the MAP is not getting vac and just defaults to start up values. Which is why it runs rich. If you unplug the map entirely, the ECU will kill the engine. It basically goes back into closed loop with the vac line unplugged. The ISA isn’t that finicky at all actually. It sounds like it but if you follow my ISA adjustment write up that’s straight from the AMC TBI book, it’s less daunting and scary than it seems. I don't know if you have an REM or a tach but you need one of those for the adjustment process. You can test the IAT but that’s just related to air temp. Ah okay sweet, I'll have to look into the ISA then. I pulled the IAT the last time i messed with the jeep and the thermistor on the end looked like it was snapped it why I was asking. Like it's still attached but cracked and looking pretty rough even after cleaning it. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Sounds good. Id test the IAT. Both with the engine cold and at operating temp. It’s based on resistance if I remember correctly. So you’ll be looking for low value while hot and high while cold. I could have that backwards. Cruiser always had a picture of the how the values should be in relation to the temp. I’ll have to find either said pic or take a pic from a manual. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 3 minutes ago, eaglescout526 said: Sounds good. Id test the IAT. Both with the engine cold and at operating temp. It’s based on resistance if I remember correctly. So you’ll be looking for low value while hot and high while cold. I could have that backwards. Cruiser always had a picture of the how the values should be in relation to the temp. I’ll have to find either said pic or take a pic from a manual. Okay! Now since the Jeep will not start with the MAP vac plugged in, assuming the ISA needs adjusting, should I start it with the vac unplugged and adjust it from there and see if it starts up or runs with it plugged back in? I wouldnt have any other way to do it hence it will not run with that vac line plugged in. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Can you start it with the vac line plugged in and your foot down on the pedal? If you can, adjust the ISA until it will start. Can I get a pic of your ISA? I want to see what we are working with here. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 5 minutes ago, eaglescout526 said: Can you start it with the vac line plugged in and your foot down on the pedal? If you can, adjust the ISA until it will start. Can I get a pic of your ISA? I want to see what we are working with here. Yea, I'm gonna go mess with it a bit after work but unfortunately I can't find the picture I had of the engine bay. From what I can remember everything looked in decent shape but I don't remember how far the adjuster was pushed out but it is indeed still there. Yes, if the vacuum line is plugged in I can force it to start by holding it to the floor haha. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 18 minutes ago, I_s2k said: Yes, if the vacuum line is plugged in I can force it to start by holding it to the floor haha. This makes me think the ISA screw is too far down and the throttle is all the way closed. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 2 minutes ago, eaglescout526 said: This makes me think the ISA screw is too far down and the throttle is all the way closed. Okay, so you think I should unscrew it a bit and see if that does anything? About how sensitive are the adjustments on it? Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Give it a shot. Worst that can happen is it chokes on too much air. Not very. I’ll give ya an example. On chunk my 84 XJ, I swapped to TBI. The screw was too far in and wouldn’t idle for me. I unscrewed it enough(one or two full turns)just to get him to run and idle after two key cranks. I can’t do the adjustment since I’m still missing the down pipe for the exhaust. But there’s a real world situation of how sensitive it is. Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 1 minute ago, eaglescout526 said: Give it a shot. Worst that can happen is it chokes on too much air. Not very. I’ll give ya an example. On chunk my 84 XJ, I swapped to TBI. The screw was too far in and wouldn’t idle for me. I unscrewed it enough(one or two full turns)just to get him to run and idle after two key cranks. I can’t do the adjustment since I’m still missing the down pipe for the exhaust. But there’s a real world situation of how sensitive it is. Oh okay gotcha, I should be getting off here in about an hour or so. I'll give it a shot and report back along with pictures of the ISA. Thanks man! Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Sounds good and no problem! Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 1 hour ago, eaglescout526 said: Sounds good and no problem! Here’s some pics, this is as of right now, no adjustments made and turned off. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Not as far down as I thought it was gonna be. If you remove the air bonnet, how open is the throttle? Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 10 minutes ago, eaglescout526 said: Not as far down as I thought it was gonna be. If you remove the air bonnet, how open is the throttle? Well not very, I went ahead and adjusted it considerably going both ways. No real noticeable difference it just won’t stay running with the vac plugged in. Right now I have it running with the plunger showing maybe 2-3 threads and the vac unplugged. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 Huh. Interesting. Ok. Well only one way to find out. Is every sensor getting 5V from the ECU? Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 2 minutes ago, eaglescout526 said: Huh. Interesting. Ok. Well only one way to find out. Is every sensor getting 5V from the ECU? Before I get to testing all the sensors again, I went ahead and dropped the ECU down. I’ve heard that the reman/USA/Mexico made ones are crap or something? Or like the good OEM ones were made of France or Mexico? I might’ve misheard but my ECU has made in USA on it, so I’m thinking it’s been replaced before? Link to comment Share on other sites More sharing options...
I_s2k Posted May 28 Author Share Posted May 28 It just seems ridiculously clean to be from ‘86 to me, the connector pins on the harness side are in the exact same condition. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 28 Share Posted May 28 No that’s correct. I have seen the both as US and France manufacture. That ECU looks like it was made in 85. There should be a date code where it says made in USA. And yes it’s gonna be clean haha. It’s in the cab. Link to comment Share on other sites More sharing options...
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