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ECU changes effecting diff 

 

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Posted: Sun Mar 19, 2006 7:34 pm 
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i have argued this with people before, i agree that the ecu reads tailshaft rpm not axle/wheel speed, so unless theres a ratio change between the crank and the tailshaft, how possibly can changing the axle ratio affect shift points??

it knows to change gears at say 2000 tailshaft rpm, which may be 80kmh road speed, if you alter the final drive ratio, it will still shift at 2000rpm of the t/s which will be the same engine rpm as before, but me be a different road speed

 

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Posted: Sun Mar 19, 2006 7:43 pm 
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ebs_4l wrote:
i have argued this with people before, i agree that the ecu reads tailshaft rpm not axle/wheel speed, so unless theres a ratio change between the crank and the tailshaft, how possibly can changing the axle ratio affect shift points??

it knows to change gears at say 2000 tailshaft rpm, which may be 80kmh road speed, if you alter the final drive ratio, it will still shift at 2000rpm of the t/s which will be the same engine rpm as before, but me be a different road speed


thats exactly right. but most people when changing diff gears also change the speedo gear and thats where the problems start

 

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Posted: Sun Mar 19, 2006 8:35 pm 
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The ECU shifts based on road speed, which it figures out assuming a known diff ratio (which is set in the ECU's code).

I know this cause I've spent the past 8 months hacking though ECU bin files in an effort to make chips for them... The tables in the ECU, are based off load and speed, NOT RPM.

The ECU gets the speed from the dash - so yes, if you just change the diff, everythign will be fine, but you're speedo will be wrong. If you then change teh speedo gear so the speedo will be right - bam your shifts will then be wrong. So change ECU to match.

 

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Posted: Sun Mar 19, 2006 10:01 pm 
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data_mine wrote:
The ECU shifts based on road speed, which it figures out assuming a known diff ratio (which is set in the ECU's code).

I know this cause I've spent the past 8 months hacking though ECU bin files in an effort to make chips for them... The tables in the ECU, are based off load and speed, NOT RPM.


The ECU gets the speed from the dash - so yes, if you just change the diff, everythign will be fine, but you're speedo will be wrong. If you then change teh speedo gear so the speedo will be right - bam your shifts will then be wrong. So change ECU to match.


so the speedo signal goes straight to the dash then to the ECU??

 

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Posted: Sun Mar 19, 2006 10:02 pm 
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yup

For some harmless fun, pull the INST_BATT fuse from the fuse panel, the cluster will go dead, and your ECU will go into limp mode because it's not getting a speed signal. Auto will be stuck in 3rd unless you manual shift it.

 

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Posted: Sun Mar 19, 2006 11:48 pm 
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Ok data, but can you tell me how to fix the signl to the Auto computer as the V8 has a sepearate computer. I have fixed my speedo form a ratio change form 3.45 to 3.93, by using an XD transducer and a 21tooth cog. This was mal woods advice, but as a s***, it now shifts into the next gear in econ mode at 5800rpm, where as previously it shifted at 5400rpm. I have yet to use full throttle with the econ turned off. This is not good. I have the jaycar speedo corrector, and would like to get acurate speedo and correct shifts, so can i change the signal back to normal using the corrector and sending it to the auto comp. If so, which bloodly wire do i need to hack.
Brett

 

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Posted: Mon Mar 20, 2006 1:26 am 
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I'm not sure how the auto controllers work on the EA's and V8's. Wanna loan me you'rs to play with for a bit...

I'd say (just speculating), the auto box would get it's speed signal from the dash as the 6's do. Just a matter of ensuring the signal IT get's is appropriate for teh shift points you want, and the dash gets the right signal to show the correct speed. You'd need the speedo corrector on the wire bwtteen the dash and auto controller. Cause would'nt a EF fairmont 8 ECU be expecting a 3.23 diff (you've gone very wild on it)?

edit: As for wiring, I'd be looking for a pin labeled VSS possibly. But I dunno having not played with a e-series 8.

 

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Posted: Mon Mar 20, 2006 6:37 am 
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Not too wild, went from 3.45 factory fitted to 3.93. Lets just say that it is now very snappy. Would be happy to lend it to you, but then what do i do for wheels
Brett

 

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Posted: Mon Mar 20, 2006 9:39 am 
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Just did some number crunching.

With a 3.45 stock diff, you're ECU would be programmed for redline changes @
86, 141, 180 (205 speed limited)

The 3.93 ratio gives you maximum speeds in each gear of
76, 124, 180

So you need to knock 10,20, and 30KM/H off each shift point.

(that's road speed assuming 235/45R17 tyres, but if you're tyres are sized right, it'll be very close).

One thing I found with mine when I had a mismatched ECU (3.08 ECU with a 3.45) was it'd change when you hit the rev limiter. So I don't think you'll do any damage in the mean time.

Oh, and once you get the 427 I'll swap you with mine for a bit.

 

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Posted: Mon Mar 20, 2006 10:39 am 
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data_mine wrote:
yup

For some harmless fun, pull the INST_BATT fuse from the fuse panel, the cluster will go dead, and your ECU will go into limp mode because it's not getting a speed signal. Auto will be stuck in 3rd unless you manual shift it.


thats interesting. i'm assuming the the jaycer converter will still work if fitted after the dash

it would be interesting to fit one and play with shift points at the drags after making a few mods like cam shafts. although still being limited the ver limit, there would be some interesting results.

 

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Posted: Mon Mar 20, 2006 12:05 pm 
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So in my el ghia what would happen if i changed from a 3.23 to a 3.45.

i would have thought that i change the speedo sensor gear and everthing would be ok but after readinghtis thread im now confused LOL easily done
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Posted: Mon Mar 20, 2006 12:53 pm 
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Hmmm.. and what would happen in my case.. I'm not spozed to have the xr6 ecu in my ghia but i do and im running a 3.23. Does this mean its shifting to early or late?

 

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Posted: Mon Mar 20, 2006 1:20 pm 
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lol atleast im not the only one confused. what advantages is ther of having the xr6 ecu instead of the ghia one?
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Posted: Mon Mar 20, 2006 2:05 pm 
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No, bro, i dont have a Speed limiter, got an EF XR8 ECU, which doesnt control the shift points as it is an 8. Also the V8 does not have a revlimiter, because i have been known to rev it past the limit of the tacho once or twice whilst racing. And as for the 427, this wont make any difference, as the EMS will be in control of the Motor, and have a conservative redline of 7000.But i would like to sort it out now before the biggun goes in
Brett

 

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Posted: Mon Mar 20, 2006 2:07 pm 
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seems to run better, i have cam, zorst, pacemakers, filter, Motor only done 20,000. Idles alot better and shifts diffrent cause mine's only a 94.. didnt have a xr6 motor in her

 

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