Speedometer adjust after V8 conversion?

[1998rollover]

I'm having the complete drivetrain from a 1998 Mountaineer transplanted into my 2002 Sport Trac.

The new combo will have 3.73 gears and 245/75 tires in place of the original 255/70's on the stock aluminum wheels. Got the nearly new tires for $200 to replace the worn out 255/70's. The 5.0 has plenty of power so it shouldn't have a problem with the bigger tires.

How far off, faster or slower, will the speedometer be? It already read faster than real speed in the Mountaineer.

How do I adjust it? I have a GPS to tell how fast it's actually moving.

 

[rmcalis]

according to tire-size-conversion.com there is about 1.4% difference in the revs per mile.
At 60 mph, you will be about 1 mph off.

 

[1998rollover]

Stock Mountaineer tire size is 235/75R15
Stock Sport Trac tire size is 255/70R16 (4.1% slower)

My V8 converted Sport Trac will have 245/75R16 or a 5.5% (slower reading) difference from the Mountaineer tires.

The Mountaineer speedometer read *faster* than actual speed, 25Mph on the speedo was about 20Mph.

 

[1998rollover]

Got the V8 swap done and it runs great. The speedometer is exactly right on according to GPS. The larger than stock for the 02 Sport Trac canceled out the error the 98 Mountaineer electronics had with stock size tires.

NOW FOR THE PROBLEM

It keeps setting a P0500 VSS error code. How do I make it stop doing that when there's is obviously NOT a problem with the VSS? I just called Hometown Motors in Weiser, ID and they're clueless.

Same for the ABS programming. The light is on but my scanner claims there are no ABS codes stored.

 

[intelisevil]

NOW FOR THE PROBLEM

It keeps setting a P0500 VSS error code. How do I make it stop doing that when there's is obviously NOT a problem with the VSS?

Same for the ABS programming. The light is on but my scanner claims there are no ABS codes stored.

My first thought is the VSS in the top of the rear differential. One electrical connector, one bolt, less than $20. I know this doesn't make much sense when your speedometer is working correctly . . . Here's something I found in another forum that might explain how it could be bad but still keep your speedometer running:

Yes, the speedo should not work if the speed sensor in the diff is toast.

But, what if the sensor was out momentarily then returned. The car would see this, you might not.

As an analogy, the wheel speed sensors can fail in a random fashion. The car is turned on, the ABS does a self check and all is well, the ABS light is off. As the car is driven, the ABS does a constant self-test, and eventually sees a wheel speed sensor that forgets to check in, and the ABS light comes on. You can turn the car off and back on, and the ABS light will go out then return in a mile or a day, you never know.

You are having this sort of failure. The sensor fails in a random fashion, and only for a second. You never see the impact on the systems that rely on it normally -- the speedo and cruise -- because they react too slowly to care that the speed signal is gone and then comes right back.

I'm not saying this is positively the problem, but I am saying that you cannot discount it yet. Just because the speedo works doesn't mean the sensor works all of the time. The sensor could drop out for a moment, just long enough to piss off the ABS/ASC systems, and this could be the trigger for the P0500.

Congrats on the V8 swap,
Dan

 

[1998rollover]

The rear sensor is brand new, changed just before the swap, hoping it might fix the 98 Mountaineer's ABS.

Nope, didn't.

There's a couple of new, complete ABS units on eBay that are supposed to be for 98 Explorer/Mountaineer. I'm going to see about getting one of those, then hopefully there's a Ford dealer with a clue around here who can program it and the GEM.

I suspect that the combo of the 98 ABS and ECM and the 02 GEM plus the larger diameter tires is throwing the error, despite the speedo reading exactly right.

I'm going to have to re-do some exhaust welds, the guy who did the swap stretched out the Mountaineer exhaust 18", could have clamped the extensions in but welded them instead. Looks like an iron bird took a **** all around the joints and one of them is full of holes.

Also, for some reason, he took the vibration weight and bracket off the Sport Trac's front diff and put it on the one from the Mounty. No wonder he had such a problem getting the exhaust in since the weight is jammed tight between the left side exhaust and the diff case! Hello Mr. Nut, meet Mr. Cutting Torch. Also going to cut off most of the bracket so it's not pushing on the oil pan, can't get at the bolts holding the bracket to the diff.

I also had to re-arrange the transmission cooler lines because rather than putting them back into the clips on the bottom of the radiator, he bent them so they'd go around the right end and they were rubbing on things they shouldn't. No @#%@%% reason to do that! It all came off the Mountaineer. All he had to do was install the stuff *exactly* as it came off the Mounty.

This is why I hate having other people work on my vehicles. I always have to redo things they did wrong. I kept telling the guy to sign up on here and ask all the questions on things he needed to know. I even gave him an old laptop so he wouldn't have to use his little old Android phone for the web.