t4m0 vs. j4j1???

Discussion in '1994 - 1995 Specific Tech' started by Blackened302, May 22, 2007.

  1. alright, it's time for me to get back on this tuning thing now that my engine swap bugs are taken care of (finally! thank god!)

    i was thinking today... i know i have the t4m0, but i do, essentially, have a 94-95 cobra engine now---does that mean i should run the j4j1?

    luckily, i had the following tunes loaded on the selector:
    1. t4m0 -- changed fan temp switches, changed idle
    2. t4m0 -- changed fan temp switches, changed idle, added 5* global timing
    3. j4j1 -- same as #1, but w/ the t4m0 injector settings (size, pulse width)
    4. j4j1 -- same as #3, added 5* global timing

    i tried using #3 today, but the idle was at the stock setting (left it that way cause i wanted more lope) which is a little too low and the car almost stalled.

    what is the difference between the two eec's aside from the injector stuff?

    lastly, i don't have the r/t which i know is a huge set-back. i really want to get the fuel maps taken care of--will a couple pulls on the dyno w/ afr plus my cam specs help in figuring out what the fuel map/curve/whatever should be?

    thanks, guys :SNSign:
  2. I used the j4j1 as a base tune, but ive changed everything that made it a cobra tune, The main differences between the two is the injectors and the MAF curve, although the same MAF, the curve is a little different. There are other odds and ends like high speed fuel enrichment, ect.

    the j4j1 is probly a good place to start for you tho.

    Just get your timing and AFR down to whatca want on the dyno and your tune will be close, but to do all the other tuning such as idle tuning, injector stuff ect. the R/T version is a must.
  3. The problem your going to run into, even with the dyno time, is that once the adaptive kicks in and starts doing its thing...is when you will be at a dissadvantage. You know this from what you posted. I just dont want you going into a dyno session and thinking your all around drivability is going to be knocked down...WOT probably so but you may end up with alittle hickup here and there non-WOT.

    The kinda good thing is that atleast you can get the car to RUN with the base model. When you have more cash you can always buy the upgrade.

    IIRC on the J4J1 there are some much deeper (deeper than the tweecer will go) programming changes over the t4m0. The theory is that Roush had a short time to get the eec setup and working. They are believed to have shut down some parts and changed the way some other are calculated. I dont know if the posts are still there but I remember someone who had the ability on eectuning to look DEEP at the code. I am also preaty sure the load is calc. diff./or a diff. kind of load. The breakpoint and slopes are kinda screwie as well from other eecs.

    The changes are also thought to be the reason its a good base and more adaptive as far as how it reacts to tunes...so its kind of a mixed blessing being a "hack" job.
  4. For na 302 h/c/i combos ... many t4m0 peeps have found the j4j1
    to be a way to make most of their drivability issues go away with
    nothing but a quick upload.

    Most of those peeps got 24's or larger and after market meters
    They are gonna get into their tune to perfect their drivability.

    Why anyone would wanna move a bunch of that t4m0 stuff over
    to the j4j1 :shrug: they will end up changing much of it anyway
    to work specifically for their combo ;)

    One thing I like about the j4j1 is it does less + or - to spark and fuel
    with the act and ect and there are other things but that is the biggie

    True ... the j1j4 does add fuel at 90mph but its a snap to null that out

    Yes ... You need the RT unit for the best results

    Yes ... I'd tell you to use the j4j1

  5. thanks, gentlemen. my reasoning (however basic, hehe) was that because i have a cobra engine, i should use the base cobra tune.

    of course, all i kept from the t4m0 was the injector #'s as i'm still running the stock maf and stock injectors (19#ers, hopefully i'll get some 24's soon).

    gonna borrow a laptop today so i can raise the idle on my #3 & #4 settings to where it needs to be and drive it around for a couple days and see how the car runs that way.

    i appreciate the responses--thanks.
  6. J4J1 , stock idle is 672 up that to about 704 and it should be good
  7. thanks, Sniper. that's actually where i have my #1 and 2 settings at: 700-750rpm and it idles great.
  8. Paul

    One thing that is very different between the two is in the area of the various
    values that are associated with injectors.

    Here are just the main ones :D


    high slope ..... value chosen
    low slope ...... high slope value x 1.46
    breakpoint .... value chosen
    inj offset ....... [email protected] volts


    high slope ..... same value as low slope
    low slope ...... same value as high slope
    breakpoint .... na if high/low same value
    inf offset ....... [email protected] volts

    The 4 parameters form a relationship with each other ;)

    Notice the HUGE difference in the one and only offset I listed

    The t4m0 uses an offset more than double the value of the j4j1

    I spent a lot of time with those relationships and found you can obtain
    a nice stable Closed Loop tune with just about any slope value within
    reason such as:

    high low same
    [email protected] high x 1.1
    [email protected] high x 1.2

    You can see the lower offset value is present in the file where the
    slopes are the same

    Here is where I saw a rule of thumb come into play with slope values
    after all my hosing around with trying different values

    The larger the offset used ... the larger the difference between the slopes
    will end up needing to be ;)

    These days, EEC Analyzer can help with inj values tremendously :nice:

    Another big difference between the two is the scalar ... load scaling switch

    T4M0, U4P0, W4H0 use a value of 2
    J4J1 uses a value of 0

    Tons of info written about load scaling so I won't get into it but
    I use the default value of 0 in my j4j1 based file :D

  9. you are welcome I just did a chip for a guy that did an auto to manual conversion on a 95GT , I used the J4J1 tune to reference for changes I did to his , I cant remember everything I changed but I tweaked his timing in a little faster than the J4J1 in the upper load levels and the car runs as if it has a set of GT40 heads on it and its bone stock , he is looking to get some heads and stuff soon , so I will get more experience with these computers as he gets more money to mod his car , he could not believe the difference it made, I am hoping to get some track times soon , we are going to pull the chip and run it and then put the chip back in a run it again to get some comparisons