Do bigger tires make the O/D light blink?

[kevinh]

I recently put 31s on my 95 Limited Explorer and within five minutes the O/D light started blinking. I took it to the first dealer and they told me that they would atempt to reprogram the computer for the larger tire size. They then told me that the computer in my car doesn't have the tire parameter in it, only the newer ones do and that I need to change my speedometer gear, which is what the computer reads off of. I imediatly asked how the computer could tell what my ground speed was to compare the rpms to in order for it to even know that I had bigger tires and that something was wrong. They had no answer. They suggested reseting the computer by unplugging the battery for 15 minutes which I did and everything was fine, but only for about 5 miles. I then took it to a second dealer and was told that they cannot reprogram the computer because there are no tire size parameters, they can't change the gear because there is no gear, and that it probably has nothing to do with the tires, that the timing is just coincidence. In addition to the O/D light flashing the transmission is shifting funny. It will run all the way up to redline without shifting in first gear if I do not take my foot off of the gas completely after 3500 rpm and then lightly place it back down. It has the same type of trouble shifting out of 2nd and 3rd too, but not as bad. Any thoughts on what I should do next?

 

[GJarrett]

Ok, let's settle down here and fix what we can

You've got more than one question here and I will help you with what I know from my experience. I have a '99 Eddie Bauer that now has 285/75r16 tires (33"+) which is way above what you just did. I'll help you fix what I know about.

One, you are correct that the truck cannot tell what size tires you now run. When I installed my biggies it did not set off the O/D light. I am assuming of course that ALL of your tires are the same size. Your flashing O/D light is a separate problem apart from your tire upgrade. When they switched your tires they may have accidentally done something else to your vehicle (unplugged a sensor, etc etc etc) but the tire size itself did not do this. I myself do not believe in coincidences as much as I used to, so I believe your problem may be the result of something done wrong during the tire switch even though it has nothing to do with the tire size of your new meats.

Two, I am not familiar with the '95 speedo setup but my '99 needed a tech to reprogram my computer to read the speed afterwards ($100+). It has what is known as a VSS (vehicle speed sensor) and does not have gear teeth to change. Some dealerships have no computer-savvy tech that can do this, so they will say it cannot be done. They are lying. Find another dealership.

I think you may be lucky. I believe you may have the mechanical gear setup on your '95 in which case you pull the cable out of your tranny or transfer case, count teeth, and get a different one from your local Ford dealer. One tooth equals about 3mph at 60mph. It's a $10 part instead of a $100+ computer reprogram like I had to do.

Three, your shift points in your tranny are gonna be screwed until you fix the speedometer problem you have. Our newer Explorers obtain several parameters of information from the computer to tell them when to shift. In the old days an auto tranny just shifted when the pressure dictated. Our modern supertrannies take into account several factors, one of them being mph. If your vehicle doesn't know how fast it's really going, it will shift at the wrong speed. I drove mine a week or so with the big tires before I got my speedo reprogrammed and the shiftpoints were way off until I had the reprogram done.

Hope this helps.

[Edited by GJarrett on 06-19-2000 at 08:49 PM]

 

[donkey boy]

Gerald, explain me more about the shifting point thing. This does not makes sence to me. Obviously, changing the tire size gives you a reading on the speedometer which does not corresponds to the actual speed. This we don't need to talk about.
But, as long as you don't adapt the speedo reeding, the (wrong) speed on the speedometer should correspond with the same rpm as before, no matter which tires. As you said, the car has no possibility knowing how fast it really goes. (except if the car has a windspeed meter, speed is connected to GPS or it has an additional 5th wheel as car testers use for precise data). With other words, the change of tire size changes nothing regarding the proportions of axle-rpm, tranny-rpm, engine-rpm and speedo reading. The only thing that does changes is, that due to different over all ratio with the bigger tires, the engine needs to work "harder" at same rpm. I really don't see a connection between wrong speedo reading and strange shifting points. Tell me if I'm wrong

Are there any other experiencing strange shifting in the tranny after changing from 235 to 31's??

 

[GJarrett]

You are correct

Donkey Boy you are correct. But that is precisely what makes the shift points wrong. Since I had put on much larger tires, my tranny shifted when it thought it was at a certain speed, but I was actually going much faster because of the bigger tires.

You probably have an instinctive "feel" for when your tranny needs to shift at a certain speed. It's those points at which you would shift if you had a manual transmission. Imagine your tranny not shifting at that speed, but waiting several more seconds before shifting, because it thinks you are not going that fast yet. To get an idea what it feels like, go drive a manual transmission and force yourself to NOT shift when you want to, but wait another 5-10 mph or several seconds before shifting. That's what these trannys do because the speedometer is not reading right.

Did I explain that more clearly now? Did that make sense?

Gerald

 

[donkey boy]

Gerald, very clear, and I guess we agree on that one. But this means, we still need to find an answer, why Kevin's tranny is shifting at over 3500 rpm, when taking the foot completaly of the throttle. This is not just higher speed than before the tire change, (what would be normal ) but also higher rpms (what is not normal ).
Considering this strange behavior and the blinking light, I would completely agree with you with your guess that somebody messed with the tranny and probably a vacuum hose or whatever is loose.

 

[Henry]

I've seens similar effects (didn't have OD or a light though -- it wasn't an explorer) from a disconnected vacuum hose and from a low transmission fluid level.

 

[AgExplorer]

Henry may be on the right track to your tranny problem. If it's not one of these, you may be in for a rebuild. The tranny problem may have just been a coincidence with the new tires. My '95 started doing just what you're describing this past Christmas. All the clutch plates were worn to next to nothing and I had to have it rebuilt. $1700 later, it's as good as new.

 

[GJarrett]

Hopefully its one of these simple/cheap problems and not a precursor to a tranny rebuild. Actually Donkey Boy you did have a point on the shift point; your instinctive shift point is based more on an engine's rpm and torque at that rpm than at the speed. All I can tell you is that for the new Explorers with computerized transmissions it does somehow screw up the shift points when the speedo is way off.

I do hope Kevin's tranny problem is a speedo or vacuum line or fluid level and not a major $$$ item.

Gerald

 

[98/92EB]

Hey Gerald, I have a 98 V-8 2wd. My speedo is also off. Do you know if I have to reprogram the computer or just change the gear teeth?? Do I have the VSS (vehicle speed sensor?

 

[Robert]

Re: Ok, let's settle down here and fix what we can

Originally posted by GJarrett
...Two, I am not familiar with the '95 speedo setup but my '99 needed a tech to reprogram my computer to read the speed afterwards ($100+). It has what is known as a VSS (vehicle speed sensor) and does not have gear teeth to change. Some dealerships have no computer-savvy tech that can do this, so they will say it cannot be done. They are lying. Find another dealership.

I think you may be lucky. I believe you may have the mechanical gear setup on your '95 in which case you pull the cable out of your tranny or transfer case, count teeth, and get a different one from your local Ford dealer. One tooth equals about 3mph at 60mph. It's a $10 part instead of a $100+ computer reprogram like I had to do.
[Edited by GJarrett on 06-19-2000 at 08:49 PM]

Your '99 does have a speedometer gear, even though it has a VSS! I just changed mine on my '97 5-speed Auto a couple of weeks ago. Mine has a VSS, but when you pull the VSS out it has a speedometer gear on the end of it. The gear I had to use was from a 5-speed manual transmission Ranger. My gear had 20 teeth, I needed 21 (might have been the other way around though). I wend from a black gear to a ping gear. The automatic gear was about 1/4" longer than my original one. I would pull out your VSS first and take a look. Ford may have been able to reprogram your speedometer with a computer, but I doubt it. They probably changed out the gear and hooked up a computer to verify the speed. The VSS will either be at the end of your transmission if it is a 2WD, or on the transfer case if it is 4x4.

 

[Robert]

Originally posted by 98/92EB
Hey Gerald, I have a 98 V-8 2wd. My speedo is also off. Do you know if I have to reprogram the computer or just change the gear teeth?? Do I have the VSS (vehicle speed sensor?

Just because you have a VSS doesn't mean you don't have a speedometer gear. I just change mine a couple of weeks ago on my '97 5-speed Auto with a VSS. If your 4-speed Auto is like the 2WD 5-speed auto. then your VSS should be at the end of your transmission. Instead of a cable going to it, it will have a wire harness with 2 wires with a plug at the end. Remove the wire plug, and remove the one bolt that holds the VSS in (10mm I think). Slide it out. You'll see the gear. Don't pay Ford $100 to change your speedometer. I found a link that lists all of the different gears from Ford. I'll see if I can find it and post it. Pull yours out and look at it before you take it to Ford.

Robert

 

[GJarrett]

Well, okay, we are learning that changes were made in later model Explorers between the years.

I DID pull my VSS (I have a 4wd and it was not on the tranny or the transfer case, but rather it was on the rear diffy). Trust me when I tell you I am a real cheapskate and if there was any option available to spend $10 instead of $100+ to fix my speedo I would have done it.

There are no gear teeth on my system. It doesn't read speed that way. Welcome to the new world, as told from Ford's manual:

"The vehicle speed sensor (VSS) is a pickup coil (variable-reluctance) sensor mounted on the transmission. It produces an AC voltage sine wave, the frequency of which is proportional to vehicle speed. The PCM uses the sensor input signal for several different engine and transmission control functions. the VSS signal also drives the speedometer on the instrument panel"... EMc2 etc.

I believe there is a transfer of technology in these years wherein the "early-late" models of Explorers in the '95-'97 date range may have an interim system that may indeed utilize both the early tech of gear teeth and also have late model VSS tech, but the later models do not have that luxury; they are totally VSS. Maybe someone else can shed more light on this.



[Edited by GJarrett on 06-20-2000 at 11:03 PM]

 

[Nordic-Al]

The '91-'99 Chilton’s manual shows a pen & ink rendering of a "typical VSS". The picture shows a gear on the end. However, in the description of the VSS it says, "The vehicle speed sensor is a magnetic pick-up that sends a signal to the Powertrain Control Module. The sensor measures the rotation of the transmission and the PCM determines the corresponding vehicle speed." It also indicates the VSS is located halfway down the right side of the transmission assembly.

I contacted a couple of Ford dealers today, since I just upsized my tires, and was told by both that yes they needed to reprogram my PCM. However, the first dealer I spoke to also said they needed to do programming to the ABS too and that the bill would be a minimum $200. He repeated the "minimum" routine several times. The second dealer said no problem, $75, we just need to see the circumference of the new tires and find out the correct program to use from Ford.

I don't know the right answer but I get my PCM reprogrammed Thursday (unless we have certified Ford mechanic amongst us who can give us the definitive word).

 

[Robert]

Originally posted by GJarrett
Well, okay, we are learning that changes were made in later model Explorers between the years.

I DID pull my VSS (I have a 4wd and it was not on the tranny or the transfer case, but rather it was on the rear diffy). Trust me when I tell you I am a real cheapskate and if there was any option available to spend $10 instead of $100+ to fix my speedo I would have done it.

There are no gear teeth on my system. It doesn't read speed that way. Welcome to the new world, as told from Ford's manual:

"The vehicle speed sensor (VSS) is a pickup coil (variable-reluctance) sensor mounted on the transmission. It produces an AC voltage sine wave, the frequency of which is proportional to vehicle speed. The PCM uses the sensor input signal for several different engine and transmission control functions. the VSS signal also drives the speedometer on the instrument panel"... EMc2 etc.

I believe there is a transfer of technology in these years wherein the "early-late" models of Explorers in the '95-'97 date range may have an interim system that may indeed utilize both the early tech of gear teeth and also have late model VSS tech, but the later models do not have that luxury; they are totally VSS. Maybe someone else can shed more light on this.



[Edited by GJarrett on 06-20-2000 at 11:03 PM]

2nd attempt:

Are you sure you pulled the VSS off your differential and not your ABS sensor. My Haynes manual shows the ABS sensor mounted on top of the rear diff. It only coveres through '98 though. On my '97 my VSS is mounted about 3" up from where the rear driveshaft comes out of my transfer case. Here is a picture:

Dead Link Removed

Here is a picture of where the rear ABS sensor is;

Dead Link Removed

This is my first attempt at posting pictures so they may not come out right. The ABS and VSS look very similar until they are removed. They are both held in by one bolt, and have a 2 wire connector on them. If what you pulled off was your VSS then you should still have another connector for the ABS sensor. Since my manual only goes up to '98 I don't know what your '99 would look like.

Robert

 

[Robert]

Originally posted by Nordic-Al
The '91-'99 Chilton’s manual shows a pen & ink rendering of a "typical VSS". The picture shows a gear on the end. However, in the description of the VSS it says, "The vehicle speed sensor is a magnetic pick-up that sends a signal to the Powertrain Control Module. The sensor measures the rotation of the transmission and the PCM determines the corresponding vehicle speed." It also indicates the VSS is located halfway down the right side of the transmission assembly.

I contacted a couple of Ford dealers today, since I just upsized my tires, and was told by both that yes they needed to reprogram my PCM. However, the first dealer I spoke to also said they needed to do programming to the ABS too and that the bill would be a minimum $200. He repeated the "minimum" routine several times. The second dealer said no problem, $75, we just need to see the circumference of the new tires and find out the correct program to use from Ford.

I don't know the right answer but I get my PCM reprogrammed Thursday (unless we have certified Ford mechanic amongst us who can give us the definitive word).

See my post with pictures on what your VSS looks like. It is about 3" up from where your rear driveshaft comes out of your transfer case. On the 4x4s it is not on the transmission, since the back 6"-8" is not the same between the 2WD and the 4WD. On my '97 SOHC, 5-speed auto, all I did was replace the gear at the end of the VSS to correct my speedometer to my GPS. I did it for $8.59. Mine had a black 20-tooth (C1DZ-A) gear and I replaced it with a pink 19-tooth (C0DZ-B) gear. The link that I got the part numbers from came from a Ford Ranger web site. These part numbers were under the list for a manual transmission. When the parts department brought out the first 19 tooth gear, it was a tan one. It was about 1/4" longer than mine was so I had her bring me the pink 19 tooth gear and it matched up perfectly. I went home and put it in. I had to change my gear because I was off about 4MPH since I put on my 265 75R16 tires a week earlier. Take a look at the picture in my other post. The VSS is the black item with the white plastic end. It is in the middle of the picture. The nut to the top, left of the item is the only nut that holds it on. There is a two-wire connector on it as well but you can't see it in the picture. If yours looks like this, I would remove it and see if there is a gear on it. According to my manual it should for at least up to a '98. My manual only goes up to '98 so I can't say for sure about the '99 and 2000. I did not have to have my computer reprogrammed.

Robert

[Edited by Robert on 06-20-2000 at 10:38 PM]

 

[donkey boy]

Robert, besides the speedo being off, did you experience any strange shifting of your tranny after changing to bigger tires?

 

[Robert]

Originally posted by donkey boy
Robert, besides the speedo being off, did you experience any strange shifting of your tranny after changing to bigger tires?

Only while my speedometer gear was out while I drove up to the Ford Parts department. Since my computer didn't know how fast I was going, it would wait until 4 or 5 seconds of cruising at about 3500 RPM before it would shift into the next gear. Once I put the gear back in, it shifts normal agian.

Robert

 

[98/92EB]

Okay, both Nordic-Al, Robert, and Gerald's answers appears to be 90% right. Man...is there a person who actually calibrated a 98 V-8, auto, 3.73limited slip, 2wd? Did Gerald put out the ABS sensor? Is there a gear at the end of the VSS? Is the VSS located on the end of the right side of the transmission?

 

[GJarrett]

Ok, to clarify: I pulled my VSS, not my ABS, and I did it with the tech standing right beside me under the lift at the service bay. Obivously depending on the model, engine, diffy ratio, 2wd or 4wd, year, and etc those things went in different places.

Nordic-Al, you don't need a "minimum $200" extra stuff done, just the $75 reprogram. That's all I had done except it cost me $96 + misc for a little over $100.

Gerald

 

[Robert]

Originally posted by GJarrett
Ok, to clarify: I pulled my VSS, not my ABS, and I did it with the tech standing right beside me under the lift at the service bay. Obivously depending on the model, engine, diffy ratio, 2wd or 4wd, year, and etc those things went in different places.

Nordic-Al, you don't need a "minimum $200" extra stuff done, just the $75 reprogram. That's all I had done except it cost me $96 + misc for a little over $100.

Gerald

I just found out some more information regarding where the VSS might be located. On a Ford Ranger board, I saw a post stating that beginning in 1995, Ford uses the rear ABS sensor as the VSS which would have no gear. So it is entirely likely that GJarrett's '99 EB's VSS is located on his rear differential. My '97 is located on my transfer case. My Haynes manual goes up to '98 and makes no mention of it being on the rear diff. So at least according to Haynes, the '98 should be on the transmission or transfer case but I couldn't convincingly say that is true. So the only things that are certain are that on a '99 it is on the rear diff. but I don't know which transmission/engine you have, on a '97 5-speed Auto it is on the transmission/transfer case, and on a '98 4-speed Auto who knows?