To The Moon: Upping economy in a 2000 Dodge Caravan

[t vago]

Well, that's mostly true.

A new ECM flash is not required, nor will it change the pinion factor. You just need a DRBIII for that. Unfortunately, my DRBIII emulator does not allow me to change the pinion factor in my minivan's computer. It will helpfully (?) show the pinion factor value once I program in one of the pre-selected tire sizes, though.

Maybe this is different for a 2000 minivan, though. Maybe the DRBIII emulator will allow pinion factor changing on earlier models. It'd be nice to find out.

I might have to set a network sniffer on that, to see what the DRBIII emulator is actually sending to the PCM. If I can do that, then I should be able to set any pinion factor I want.

[grswat]

My local dealer said they could correct the speedometer in the pcm. I assumed that meant a flash but if that one value can be adjusted that must be what they meant. I havent actually put a different gearset in a 41te other than putting the original (correct) set in when putting junkyard transmissions in. I did change the gearset on an older 31th which has the speed sensor on the output shaft so nothing had to be adjusted.

[t vago]

Originally Posted by grswat

My local dealer said they could correct the speedometer in the pcm. I assumed that meant a flash but if that one value can be adjusted that must be what they meant.

Sounds about right. For somewhat-recent late model Chryslers, the DRBIII emulator ties the 41TE pinion factor value directly to tire size, so when you change the tire size in the emulator, you're actually changing the pinion factor. That implies a table of 8 or standardized pinion factor values, for 8 or so different supported tire sizes.

Unfortunately, that also implies that the pinion factor itself cannot directly be changed (at least, not with the DRBIII emulator). Furthermore, it would appear that this table itself changes, depending on whether the minivan has a 3.8L engine or a 3.3L engine. I remember reading that the Dodge Intrepid folks had the exact same issue when they tried transplanting a shorter differential, out of a 2.7L engine-equipped Intrepid, into the transmission of a 3.5L equipped Intrepid.

Some aftermarket programmers have the ability to adjust tire size by +/- 0.25 inch (or so), which implies they can modify the pinion factor value. Unfortunately, I have not been able to find such a programmer for the Caravan.

Yep, I do miss having an actual pinion gear that could be changed. Chrysler appeared to go back in this direction with the LX platform, though. There, the speedometer is driven off the ABS controller, which takes speed inputs from all 4 wheels.

On a side note, I could finally figure out how to get my own LX (the Karen-Mobile) to accept a 2.87 differential - the stock Chrysler scan tool does not support at all changing differential ratios, since it assumes that all 2005 LXes equipped with a 3.5L engine and a 42RLE transmission, also have a 3.636 differential. There's some 4 separate values that have to be written into the on-board computers. Now, all that remains is to actually physically install the 2.87 differential into the Karen-Mobile.

[101Volts]

I've replied here to announce I retired this van from fuel economy logs on here. If anyone's wondering "Why?" it's because it's more of my Dad's van than my own, he's more of a "Fill as you go" guy with the van (or so it seems) and the van also has a fuel leak on the tank or in a hose so I'm not about to go sticking full tanks in it now. Whatever the case, It may need some work done to it or we may just sell it - I don't know. Now I may focus more on the other two cars.

Link to a thread about the highest tank I've seen on it:

http://ecomodder.com/forum/showthrea...tml#post443236