WG Jeep Geek - Tinkering with Jeep Electronics

[Hoobz]

Originally Posted by Tyvokka

Hey Hoobzy, My head hurts!

I've been reading up links to pirate, Adrian's links and I'm getting a bit lost tbh. Can't see the forest for the trees lol! , so help me see the big pic please.

The WJ speed signal comes off the two rear ABS sensors to the ABS module. SpeedoDRD splices into these wires and one does the speed correction accordingly, so no worries there.

The problem is when one changes axle diff ratio and the ecu tcu is not happy, is that right? Can this be solved by as JeanLuke wrote : DRBIII Pod JTEC read/write? If there's a cheapy one that works, would that help?

I'm having problems with my gearbox, in the sense that the gear changes is a bit wonky with 5.38 and 37s. I have gone back to 33s for on road driving and saving the gnarly tyres for the bush. I do have tranny codes, not so happy front ABS sensors, ABS and handbrake lights.

I'm hoping silycr, AdrianD, Jean and Clarky might know about your model exactly and can verify. A couple of the forementioned will know a lot about the diesel regearing hassle, the other two might be right up on the 4.7s, HO or not.

For your model I think the speed sensors going off your abs tone rings, down at your back wheels, are sending the speed data to the ecu tcu. And that information is being used to diagnose and interpret what the engine and tranny should do. Then signals go out to the tranny and motor and gear changes are controlled as needed. I'm not sure if for some reason the ecu tcu system uses 'both' the transmission output speed sensor and the abs tone ring speed sensor to analyse and compute for outputs to the tranny and engine.

I'll just note down how far out your readings/parameters are from stock, anyone feel free to go over my calcs:

Standard gearing 3.78
Standard tyre diameter 29.3'' with circumference of 92"

Your gearing 5.38
Your tyre diameter A. 37" with circumference of 116"
Your tyre diameter B. 33" with circumference of 104"

Ok. To begin with if your ecu tcu is programmed to think each 3.78 turns of the tranny output sensor equals 1 rotation of the abs tone ring...it's out by an additional 44% rotations, that's not using any SpeedoDrd or similar.
Which if the computers are (I'm not sure) using both the rear tone rings readings and tranny output speed to compute what to do, 44% would surely have to be well out of any margins (if any) the electronic engineers would have allowed in the programming. Well, you'd think so.

But,
Then factor in your SpeedoDrd adjustment to get the speedo working correctly to gps.
29.3" tyre travels 92" per revolution.
37" travels 116" per revolution

Purely tone ring pulse signal changing, you are making the speedoDrd change the signal up by 25% so the speedo reads correct.

Even that 25% increase in speedo abs tone ring pulsing signal would probably be out too much still.

Then,
Compute the 44% ratio change (5.38 gears) with the 25% tone ring pulse increase from the SpeedoDrd...

The tranny output sensor is sending a 44% too fast signal than oem (compared to wheel abs tone ring rpm), but SpeedoDrd has increased abs tone ring pulse also, by 25%. 44 - 25 = 19% difference, which is still probably out of specifications of the program. You'd think. That's with 37" tyres.

Save you the reading for 33's, using the same math and logic, the end percentage outage going to the ecu tcu is 44 - 12 = 32% out. More out of spec than the 37's.

Does it change gears slightly better with the 37's than the 33's, when you use the SpeedoDrd correctly set for each tyre size?

I think it might. Only because the sensor pulse speed is closer to stock with the 37's on.

Am I right. Just a slight hunch, but let us know.


After all that. Can the pro's comment? Thoughts?

Now I have to help miss 12 with algebra

[Hoobz]

Tyvokka,

I forgot to mention. I have standard gearing, front abs disconnected, and have the same lights on as you. No SpeedoDrd, i use GPS on the dash for speed reference.

But she still changes gears real sweet.

Take the SpeedoDrd off for a bit completely. Does the tranny shift great again?

Go test for us.

[Tyvokka]

Originally Posted by Hoobz

Tyvokka,

I forgot to mention. I have standard gearing, front abs disconnected, and have the same lights on as you. No SpeedoDrd, i use GPS on the dash for speed reference.

But she still changes gears real sweet.

Take the SpeedoDrd off for a bit completely. Does the tranny shift great again?

Go test for us.

Cool thanks dude for taking the time to reply and calculate all that schtuff. You have too much grey matter and I have too much grey hair.

I'm in Santiago, Chile atm and will be back next Thursday to run the tests..

[JeanLuke]

I'm pretty sure the CRD and the petrol models are quite different in their handling of transmission slip detection. I *think* the petrol models have output shaft speed detection while the diesel does not. So, on the diesel, if gear, engine RPM and wheel RPM don't compute as expected, it throws a MIL error. Again, supposition (based on lots of reading) the error is transmission slip.

[Adrian D]

Originally Posted by JeanLuke

I'm pretty sure the CRD and the petrol models are quite different in their handling of transmission slip detection. I *think* the petrol models have output shaft speed detection while the diesel does not. So, on the diesel, if gear, engine RPM and wheel RPM don't compute as expected, it throws a MIL error. Again, supposition (based on lots of reading) the error is transmission slip.

That's correct. That why a quick and dirty method would be to intercept the ABS signals and send different signals to the ABS module.

[Tyvokka]

Originally Posted by JeanLuke

I'm not seeing any hijacking here!

The tool I was considering is one of these: http://www.ebay.com.au/itm/2017-New-...4/263124909160

Has anybody played with one of these puppies?

Here the catch:

"A separate Tech Authority Subscription is required to access to Module Re-Flash Programming, TSBs, wiring diagrams, and repair information."

I'd imagine that would cost a bit more and may NOT even work...

[JeanLuke]

Originally Posted by Tyvokka

Here the catch:

"A separate Tech Authority Subscription is required to access to Module Re-Flash Programming, TSBs, wiring diagrams, and repair information."

I'd imagine that would cost a bit more and may NOT even work...

You can get short-term TA subscriptions starting from around $50 for 3-days, I believe. The key point - does it work? I'm willing to be first to be second to try, which is why I am putting it out there - has anybody else done it?