jeeps2creep

OK , been messing with some ecms, 7747s, 7746s and numerous others but cant seem to figure some stuff out. I put a post or two on here about what I was looking for as far as a cold start idle prom goes but got lost during my quest.

Now for my new gouge questions; is there really any difference's between ecms besides location of wiring pins? And do you have to have the same limp home chip in ecm as prom chip?So if I have a $AO prom ID do I have to have a $AO limp home chip? Are these matched up too? If so what ones match up? I called up and after market company and they told me 2 or 3 different serial numbers for the limp home modules that I could use with a 7747 ecm but I only asked about a 6 cyl and that "specific" ID number too.

You see I had a good trial and error day with ecms but also got more confused when trying to get the cold start stuff fixed that I was originaly working on. I have 3 bin files that I work with, 2 are for a jeep 4.2L/258 motor that run off of a GM 4.3 liter / 6 cyl. tbi and harness that run fuel only to my motor(howell type system). I also have 1 bin file that runs the same system 4.3 liter harness that runs a jeep 360 motor ,it also has the same 4.3 liter set up but with a 360 programmed chip and has 350 injectors?????.

Now some more gouge help needed? How come I can put the same program from the "lets say a store bought chip" for the 360 on another chip and when I run it in any ohter ecm that it just goes straight to limp home mode no matter what ecm I used(I did leave the limp home chips in each ecm as they were in stcok form as well as used the $AO program for every ecm prom ID too no matter what ecm I installed it into). But when I take a stock 1227746(ecm,prom chip,limp home chip) which was for a 6 cyl /4.3 liter motor and plug it into the 360 harness that it runs just as good if not better than the supposedly 360 setup chip/ecm......HMMMMM.........this gets better......Now I took the same 1227746 ecm pluged it into my 4.2 liter system and besides a touch of hesitation on the low end it runs 10x's better than the "store bought chip set up" for the 6 cyl motor as well. I'm not sure if I am figuring anythng out or if I"m just digging a deeper hole????? There seem to be to many variables out there. If there is any help or more write ups on how to understand or figure out ecm and proms please let me know the link. I think I read almost all of them that I can find but they dont cover this, lol. As always thanks in advance for any info.

dimented24x7

iTrader: (2)

I wouldnt go into alot of depth in trying to figure out all that is in the actual prom. Itll be too confusing.

The best approach would be to pick an ECM and chip (preferably a 4.3L chip, or something similar) that works the best and take it from there.

The only major difference between a V6 and V8 chip is the cylinder count. This is needed to correctly calculate the RPM from the time between cylinder firings. The actual fuel thats needed is calculated for just one individual cylinder as there is one injector firing per cylinder firing, so it doesnt matter how many cylinders it has when fueling is concerned.

Rather then compare and try to find something that works, or get lost comparing bins, Id concentrate on the cold start parameters, like the choke air fuel ratio, decay rate, AFR tables, etc. and just tune the computer for your motor. After that move on to other items and work on things one at a time and take it slow.

Theres no timing control by the ecm so about a third of the work has been eliminated.