Speedo Accurate?

[SamF]

I know mine reads high...like 8-10 miles faster than it should. The odometer also picks up an extra 5 miles per 100 traveled according to a GPS unit I carried around with me for a few days.

The car has 235's all the way around (installed prior to sale by the Lincoln dealer) I suspect this may be a contributing factor and will be installing 245's on the rear soon. In the meantime is it possible to correct this with my Xcal?

[KillJoy]

Do you have stock gears?

KillJoy

[SamF]

Do you have stock gears?

KillJoy


Yes, as far as I know.

[KillJoy]

Yes, as far as I know.

Is the Tune you have for a set of 4.10's?

KillJoy

[SamF]

Is the Tune you have for a set of 4.10's?

KillJoy

I have a 4.10 tune in the Xcal but I loaded the 3.55. Actually I made this observation prior to loading the tune...the speedo I can deal with, its the extra 5 miles per 100 that is bothering me most... :down:

[ctrlraven]

245/55-18 tires are 705 revs per mile, 235/50-18 are 740 revs per mile. with the 235s your speedo should read 3-4mph faster @ 60mph than what your really traveling at.

[RF Overlord]

SamE, the 235s are about 4.8% smaller in diameter than the stock 245s. That almost exactly correlates with your 5% odometer error, so I think you've found it. :up:

[SamF]

OK fellas, thanks for the input. The difference in tire size is most likely the culprit. However, I reflashed the car using 740 rpmile and it didnt have any effect on the odo reading at all? I clocked it against a set of milemarkers (the same set) before and after. 1 mile = 1-2/10 on my odo both times :confused:

Where is the speed/odo sensor, in the rear or in the trans?

[Drock96Marquis]

OK fellas, thanks for the input. The difference in tire size is most likely the culprit. However, I reflashed the car using 740 rpmile and it didnt have any effect on the odo reading at all? I clocked it against a set of milemarkers (the same set) before and after. 1 mile = 1-2/10 on my odo both times :confused:

Where is the speed/odo sensor, in the rear or in the trans?

on 03+ panthers (98+ T.C.s) the VSS was eliminated, the OSS is now the primary speed sensing sensor. The PCM uses data from the OSS and the Multiplex vehicle network to calculate speed. THe PCM sends the speed signal to Speedo/Odo head. if the OSS was faulty you would typically notice irregular shifts as well.

Your tires are likely the culprit, and also not all tires, despite being the same sidewall listed size, are the same overall unloaded, or loaded diameter. Your 235s may be smaller than another brands. Tire pressure will effect this as well. Also make sure your sidewall height (235-xx-18) is the correct one. If the F/L/M dealer put the 235s on they *should* have already reflashed the car for correct tire size, otherwise you would likely have ABS light issues.

You should be able to correct it via your xCal without much trouble.

[SamF]

Do you have stock gears?

KillJoy

Well I fooled with the RPM setting based on tire size, tried 740, 745, 750. I didnt measure with a GPS but it "seemed" like the speedo was further off (reading higher)

Tonight I took a chance and loaded the 4.10 tune with 740 rpm and checked the speedo/odo with 2 GPS units. They both validated the indicated speed and odo readings were now correct. Seems a previous owner may have already installed 4.10's.

Looks like I'll be jacking her up this weekend to count tire/driveshaft rotations :o

I'll let you know what I find.

[SamF]

4.10's must have been installed by a previous owner, so now I won't have to :D

I jacked it up and confirmed just over 4 driveshaft revs per one wheel rev. I always felt that the car had a nice off the line pull even with the incorrect program, but now with the correct program it feels sweet. Shift schedule is improved and the speedo is within 1 mile of the GPS.

Sam

[2003DOHC]

Now buy that MMDS from D.R.!

[SamF]

Now buy that MMDS from D.R.!

I just might..I asked about it today when I ordered my proguard :D but I wasnt absolutely sure I had the 4.10's...