HOrnbrod Posted August 11, 2017 Share Posted August 11, 2017 Whenever you disconnect the battery to do some maintenance, the ECU "learning process" has to start from scratch again on reconnect. This is normal. During this learning time my truck idles very low, sometimes stalling when stopping unless you feather the throttle, and it's a PITA until the ECU gets smart again and starts behaving normally. I usually hook up a 9V battery across the positive cable and battery post air gap - if I remember - and this retains the ECU memory. But I forget to do it more than I remember. My question is: How long mileage-wise does it take your truck to complete the ECU learning process? Mine takes about 30-40 miles minimum of driving around until it's back to normal. Link to comment Share on other sites More sharing options...
Green Mesa XJ Posted August 11, 2017 Share Posted August 11, 2017 Reset our 91-2 XJ 4.0 Never had them idle so low after reset the throttle had to be feathered, it does take a drive or two to get back to normal. This last spring I rest the 91 took two drives to feel normal, I figure it was the full operating temp back to cool cycle that did it. I thought reset was set over a certain number of start and stop cycles, but the only info I can find is for the OBDII jeeps and those are like 50 start and stops. everyone else I know who has reset the early HO ecu notice it driving differently for the first few drives, but it doesn't seem to be milage driven reset, or operating time, my guess is once the full range of operating temps and conditions finishes the rest, I could be wrong about this reset voodoo. Sent from my iPhone using Tapatalk Pro Link to comment Share on other sites More sharing options...
Minuit Posted August 11, 2017 Share Posted August 11, 2017 If the battery is disconnected for a long amount of time mine runs kind of off for about the first 2-3 drives. Never threatens to stall, but just doesn't quite idle right. The weirdness is usually only really noticeable when stopping to go from reverse to drive. Doesn't seem to depend on mileage for me, no matter how long the drive is it's usually back to normal pretty quickly. That's if the battery is out for a REALLY long time - I suppose long enough for the capacitors to naturally discharge. If the terminal is off for just overnight or for a few minutes it seems to have no effect. My battery's been out for almost a month now. If I can remember I'll try to record how it acts and how long it takes to go back to normal. Link to comment Share on other sites More sharing options...
FrankTheDog Posted August 12, 2017 Share Posted August 12, 2017 Never really noticed. But I was running a 1994 XJ ecu. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 Interesting. I can have the 12V disconnected for a second or a week, and it still acts the same - 30-40 miles before it drives normally again. Tried two ECUs also, samo-samo. Link to comment Share on other sites More sharing options...
8valvehero Posted August 12, 2017 Share Posted August 12, 2017 I usually hook up a 9V battery across the positive cable and battery post air gap - if I remember - and this retains the ECU memory.I'm having a hard time visualizing this, but it's very intriguing. Please elaborate. My question is: How long mileage-wise does it take your truck to complete the ECU learning process? Mine takes about 30-40 miles minimum of driving around until it's back to normal.I was expecting it, but my '91 has not done this once to me since I bought it in February. Maybe 10 disconnects.This is also a thing that early-mid 90's Volkswagens do. I've got a fair amount of experience with those vehicles and I have found that the severity of this occurrence varies from one vehicle to the next. Not sure why, but even when running perfectly, some systems just seem to take longer to settle. We used to blame gremlins. Link to comment Share on other sites More sharing options...
fiatslug87 Posted August 12, 2017 Share Posted August 12, 2017 ...it's a PITA... Almost makes you want a RENIX, doesn't it? :) Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 I usually hook up a 9V battery across the positive cable and battery post air gap - if I remember - and this retains the ECU memory.I'm having a hard time visualizing this, but it's very intriguing. Please elaborate. It's a variation of the lighter receptacle battery adapter below. It supplies 9VDC to "keep alive" the ECU and retain it's memory when the battery is disconnected. I just hook my 9V battery to the - battery post and the disconnected + cable using alligator clips. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 ...it's a PITA... Almost makes you want a RENIX, doesn't it? :) I was expecting a comment like this from some lowlife in the Renix peanut gallery, but never thought it would be you Mikey. I'm shocked, and deeply hurt............ Link to comment Share on other sites More sharing options...
fiatslug87 Posted August 12, 2017 Share Posted August 12, 2017 No you're not, it's just good natured ribbing. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 I know. :yes: Link to comment Share on other sites More sharing options...
Minuit Posted August 12, 2017 Share Posted August 12, 2017 Hey, with a Renix it's easier. Don't need to disconnect the battery for it to forget how to run :D Link to comment Share on other sites More sharing options...
Ωhm Posted August 12, 2017 Share Posted August 12, 2017 My question is: How long mileage-wise does it take your truck to complete the ECU learning process? Mine takes about 30-40 miles minimum of driving around until it's back to normal. Depending on all the vehicle changes from the factory settings (engine wise), short and long term fuel trim strategies would require miles of driving to re-learn their values. Link to comment Share on other sites More sharing options...
cruiser54 Posted August 12, 2017 Share Posted August 12, 2017 ...it's a PITA... Almost makes you want a RENIX, doesn't it? :) Really. What a kludgy design.................. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 ...it's a PITA... Almost makes you want a RENIX, doesn't it? :) Really. What a kludgy design.................. There's the comment I was expecting from a Renix peanut gallery lowlife. :rotf: Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 My question is: How long mileage-wise does it take your truck to complete the ECU learning process? Mine takes about 30-40 miles minimum of driving around until it's back to normal. Depending on all the vehicle changes from the factory settings (engine wise), short and long term fuel trim strategies would require miles of driving to re-learn their values. That's what I'm thinking too Ωhm. With the stroker engine, bigger injectors, throttle body, etc. I have maybe it takes longer because it's so different than the stock ECU trim settings it causes a lengthier learning process. :dunno: Would be nice if we could flash these old OBD1 computers.......... Link to comment Share on other sites More sharing options...
8valvehero Posted August 12, 2017 Share Posted August 12, 2017 I just hook my 9V battery to the - battery post and the disconnected + cable using alligator clips. Hmmm. Still having a hard time. I can't visualize what's happening here. The + cable is disconnected from the vehicle batt, and the 9v is connected between the + cable and vehicle batt. - terminal? Also I figure that I should hook it up before i disconnect the + cable. Thanks Link to comment Share on other sites More sharing options...
Gene Posted August 12, 2017 Share Posted August 12, 2017 Hi 8valve, I have not done this, but I'm familiar with this theory. If the system is without voltage for even a brief period of time, the stored memory will be lost. So you have to connect the 9 V battery, essentially in parallel to the vehicle battery, while the vehicle battery is still connected. The 9 volt pos to the positive CABLE, the 9 V neg to the neg CABLE. Then disconnect the battery cables. I would connect it immediately before pulling the battery cable, I imagine keeping the 9 V battery connected to the 12 V would try to "overcharge" and probably rapidly heat up the 9 V battery. You don't have to make the connections right at the battery, in fact I think it would be easier to connect elsewhere. The negative could go to any good ground, the positive could go to any "always hot" terminal, not sure about the HO, on the Renix it would be at the solenoid. Gene Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 12, 2017 Author Share Posted August 12, 2017 Good explanation Gene. I picked up the 9V battery adapter like in the pic for the lighter socket, but it didn't fit the Jeep socket. So I cut off the lighter plug-in and added some longer wires and alligator clips. Then you hook it up in parallel before discoing the battery cables. There's no overcharge problem from the little 9V battery and it holds the memory for hours. Link to comment Share on other sites More sharing options...
Gene Posted August 12, 2017 Share Posted August 12, 2017 . There's no overcharge problem from the little 9V battery and it holds the memory for hours. The overcharge concern would be only if the 9 volt were connected in parallel with the 12 volt Jeep battery for a while. The 12 volts might cook the 9 volt battery. Once the vehicle battery is disconnected this is not a concern. Gene Link to comment Share on other sites More sharing options...
Minuit Posted August 12, 2017 Share Posted August 12, 2017 My question is: How long mileage-wise does it take your truck to complete the ECU learning process? Mine takes about 30-40 miles minimum of driving around until it's back to normal. Depending on all the vehicle changes from the factory settings (engine wise), short and long term fuel trim strategies would require miles of driving to re-learn their values. That's what I'm thinking too Ωhm. With the stroker engine, bigger injectors, throttle body, etc. I have maybe it takes longer because it's so different than the stock ECU trim settings it causes a lengthier learning process. :dunno: Would be nice if we could flash these old OBD1 computers.......... I think this is probably the right answer. My engine is 100% stock so my "learned" map is probably not so different from the ECU's base settings. Yours on the other hand... Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 13, 2017 Author Share Posted August 13, 2017 You don't have to make the connections right at the battery, in fact I think it would be easier to connect elsewhere. The negative could go to any good ground, the positive could go to any "always hot" terminal, not sure about the HO, on the Renix it would be at the solenoid. Gene Good point. There's an constant hot terminal on the HO diagnostic connector that's easy to get to, so I'll use that in the future when I disconnect the + battery cable. Sometimes I just disco the ground cable from the truck battery, so a good ground point for the 9V battery is easy to find. Then the 9V + battery lead goes on the + battery terminal. Link to comment Share on other sites More sharing options...
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