WH Hemi Transmission investigations

[Windex]

Hi guys,

Have just finished my first round of mods to my 2005 Hemi and have put a few kms on it now and have noticed a few things that I want to try and confirm and gather the information here if I can. The specs of the car are below:

2005 WH Grand with the Hemi
CRDSTU ~2 inch lift
245/75/R17 BFG Mud terrains
Roof racks / flat cage


I've had a few occurrences of the ETC light coming on along with a few persistent MIL (engine light) triggers. The MAP and ERG have both been replaced and now have 4 oxygen sensors that I am going to replace as two (separate banks) have thrown codes in the past 2,000kms.

I drove from Melbourne to Sydney via the coastal route over two days, unfortunately while I had a MIL (oxygen sensor), the code has now cleared itself (as it must have gone through the required number of warm ups without fault to clear it). At the start of the trip I reset the fuel consumption computer to have a look at what I was getting for the journey and over the course leveled out at 16.5L/100KM (not factoring in the changes to tyres). It dropped in the last 50kms into Sydney but for most of NSW it was in the 17.5-18L/100KM (non adjusted) range. While I suspect most of the extra consumption was due to sitting on 100km/h with a dodgy set of oxygen sensors and as such not getting MDS (need to confirm) and not getting 5th gear (need to confirm).

To be confirmed

1. Confirm distance traveled and calculate fuel use manually 17.4L/100KM
2. 5th gear availability during MIL / O2 MIL
3. MDS activation blocked by MIL - Does not block MDS
4. MDS activation blocked by oxygen sensor MIL

Confirm distance traveled and calculate fuel use manually
This was following the Princes Hwy (A1) from Melbourne to Sydney with a few little detours for lunch and such, so representative of easy country driving mostly @ 100 km/h. Few hills in the south coast of NSW but nothing to trouble the Hemi.

5th gear availability during MIL / O2 MIL
I noticed during my driving on the second day that I didnt appear to be getting 5th gear. I could set the cruise control or apply light throttle and get it settled in ~2k RPM, then nudge the gear leaver to the '-' and drop from D into 4 with not change to RPM. I could also play with the TOW/HAUL button and get the same results (it would jump at at first then settle down to the same rev range). This lead me to suspect that due to my MIL I might be getting locked out of 5th gear but I've yet to validate that this is actually the case.

MDS activation blocked by oxygen sensor MIL

[wjlimited]

Although my WH hemi is a 2010 I have had a Mil for "low system voltage" and the MDS functioned correctly (I have a louder exhaust so can confirm it's working because it sounds like a wrx when the cylinders shut down) so number 3 on the list can be ruled out.

Also the MDS only functions in "D", tow haul or using the gear selector shuts my MDS off.

When I push the gear selector once "-" my indicator goes from "D" to "5" and the rpm goes up 200rpm or so and with it in top gear, converter locked at a Gps 100kl/h I'm at 1750 rpm with 265/70r17s, and get mid 11l per 100.

[Windex]

Originally Posted by wjlimited

Although my WH hemi is a 2010 I have had a Mil for "low system voltage" and the MDS functioned correctly (I have a louder exhaust so can confirm it's working because it sounds like a wrx when the cylinders shut down) so number 3 on the list can be ruled out.

Also the MDS only functions in "D", tow haul or using the gear selector shuts my MDS off.

When I push the gear selector once "-" my indicator goes from "D" to "5" and the rpm goes up 200rpm or so and with it in top gear, converter locked at a Gps 100kl/h I'm at 1750 rpm with 265/70r17s, and get mid 11l per 100.

Thanks for the reply mate, from what I've been able to dig up is that the newer WHs (not sure when it started, perhaps with the VVT) have the D-->5 movement but the older ones are D-->4. I'd guess that the 200 RPM is torque converter difference when you kick it down manually so it might have been that the torque converter wasn't locking up for me. The difference between our tyres is ~0.4% in diameter.

[slippery]

your consumption doesn't seem too great, even when considering the muddies, roof rack and stuffed oxygen sensors

I get 13L highway with overtaking, 110km/hr speeds with 31.5 all terrains, 3 inch lift roof racks and a P0133 code (exhaust leak). I have an exhaust too and can confirm MDS isn't on very much at all at 110km/hr

Im interested to see if new sensors do much to your figures

[Windex]

Well did my first decent trip ~ 800kms and I got it down to a ~16L average since the new sensors fitted which was mostly on the Hume Hwy from Sydney to Gundagai, at times I saw the trip computer give me 14.7L/100.

The good news is that my 5th gear / TC lockup is back as I was seeing the tacho drop to ~1850RPM when cruising on the hwy. I've been doing a bit of monitoring with a OBD2 scanner and noticed a few things which I'm going to have to do a bit of googling on.

1. Load value - This seems on average quite high (ie. above 40 when cruising)
2. Absolute throttle position - Always reads high (at idle is ~15%)
3. Relative throttle position - Again reads high but a bit less than above
4. Coolant temperature - Ranged from ~92-98 which I think is fine just not sure if it gets too cold MDS gets shut down.

Two links I had a read of to figure out what I can of the operating of the MDS. I'm wondering if I could possibly have a exhaust leak thats playing havoc with it.
http://www.jeepforum.com/forum/f309/...works-1176294/
http://www.jeepforum.com/forum/f67/wk-mds-reset-927744/
http://www.jeepforum.com/forum/f309/...works-1176294/

[slippery]

To have an exhaust leak is a very common ailment for these things. The exhaust manifold studs are just too thin and prone to snapping.

Mine have been replaced once and need to be done again

[Windex]

I just completed a 600 km round trip and saw a best of 12.9L/100km (uncorrected so real reading might be slighty better) for a chunk of the journey, it blew out over the last 30 miles or so as there was terrible traffic. A lot of this driving was @ 105-110KMH which got me onto what I think might be part of my issue which relates to the transmission... As mine is a 05 it has manual selection of only the gears 1-4, so tapping the stick to the side drops it to 4th so you can check what gear it is using when the cruise is set. So I set my cruise to a 108 kmh, which was reading 100 kmh on the dash (checked via OBD2 scanner) the cruise would hold speed but appeared to be constantly holding 4th gear, I found that by setting the cruise at the level I wanted then accelerating manually beyond that then snapping off the throttle and the car would drop into 5th. Tested this multiple times and found the behavior a repeatable way to get the transmission to select 5th. I could then see the fuel rate drop which I assume would be MDS kicking in. I am wondering if with the lift and roof rack the transmission is thinking the load is just that little bit too high.

I now suspect that I might have a fault or number of faults with the transmission, I'll get a fluid flush and filter change done then start code hunting. I've managed to pull a couple of codes out of the TCM which give me some clues but do think speedo correction may also help.

Transmission Control Module codes:
P0932: STORED - Hydraulic Pressure Sensor Circuit
P0869: STORED - Transmission Fluid Pressure High

Got a corrected average over two tanks of 14.5L/100 and 13.9L/100 for the trip with a bit of driving either side with me gaming the transmission into 5th.