Bought the car back in Aug. Took it on the highway for the first time a few weeks ago and noticed 2 things.
1. Speedo reads about 10 mph faster than actual speed.
2. Manually downshifting to 3rd gear causes the car to either completely stall or the engine sputters around 500 rpms and does not respond to throttle input.
In either case if I pull off, shut the car down, & restart it the car runs fine.

A couple things to note:
I have the dreaded abs & traction failure warnings on the dash. No other warnings or codes.
The other possible contributing issue is the previous owner changed the rear end gears to 3.58 and installed an LSD.
The car does seem to downshift a little hard into 2 & 1.
Car sat for about 2 yrs before I bought it, but previous owner did change trans fluid just before I bought it.
I've also swapped out the custom 19" wheels/tires for stock asteroid wheels w/correct size tires.
Going to try the "shift adaption process" to see if that helps. Just wondering if there anything else I should check. Thanks in advance.

 

Until the diff gear ratio gets changed back to 3.08, you will always have that abs light.

If you only stay in D, will everything drive and shift fine?

 

Do a code read from ecm, abs and tcm atleast. Then gearbox oil level check. Different gear ratio will mess things up.

 

if the C1175 or P0730 code is flagged it won’t upshift, because you have a 3.58 rear it thinks it’s getting bogus data from the left rear abs sensor. had this same problem when i destroyed my hub carrier and it took out the abs sensor wiring. you need to use an obd reader and clear codes every so often and you can force it into 5th

when you have time take a picture of your driveshaft setup, need to copy it for my build.

 

Jagustar, can you please post a
semi-close picture of your hood? I have always wanted an XKR (X100) hood scoops on either one of my R’s.

Also, you may want to PM XJR99 and/or Avos for assistance with reprogramming ECM/TCM for your differential situation.

 

So I double checked my dash warnings and it's actually "traction control failure" & "stability control failure."
If I stay in "D" it's fine around town, but if I'm on the highway and slow down too quickly on an off ramp it will do the sputtering thing until I come to a stop, shut it down, & restart it.

 

Thanks man. Will do!

 

Hey thanks a lot man!

Well def get you a pic of the driveshaft soon as I have time to get it up on ramps.

 

Awesome! Thanks for the info.

Will get hood close up tomorrow. Those hood scoops are actually from a 1988 Trans Am GTA. Will get a pic of the underside so you can see how the previous owner fabbed them in.
Interesting side note, the front lip spoiler is actually for a 68 Camaro.

 

Sounds like a broken wire from the left hand rear wheel sensor. This drives the speedo, so will create all the warnings you are getting. It may affect the gearbox, because not getting the correct speed readings.

 

LH wheel speed sensor isn’t the only thing that gives the speedo data on the 308, I still had a speedo with cut wires.

The reason the gearbox is going into limp mode is because the rpm doesn’t match the predicted speed ->P0730 incorrect gear ratio flagged

 

freddo60 Thanks for the info! Will check that wheel sensor wire.

 

xalty, do you know where else it might pull a reference signal for speed? I don't have any PCM or TCM codes just warnings for traction & stability failure.

 

only other place could be the speed sensor on the transmission.

there should be a C code logged when you get the trac fail warning. kinda weird that you can’t go into 5th but don’t have a gearbox fault or incorrect gear ratio code

 

Looks like your PO figured out how to bypass the incorrect gear ratio fault....

Quote:

Originally Posted by greverrr

The "incorrect gear ratio" fault haunted me for months!!!! Gotta love a whiney diff