Need Help Speedometer and Odometer stopped working

[9cobrastang7]

After getting my car dyno tuned I drove it around for about 68 miles and my speedo and odo stopped working all at the same time. I'm assuming that is must mean that the OSS (since I have a T-56 there is no VSS) went bad since everything was working properly up until that point? Also, I'm pretty sure that my battery died and I jumped the car. In the past this caused the same result (with a different speedo), but everything started working again.

Here's my checklist that I have gone through

The power wire is getting the volts needed as I have my turbo timer hooked up to the same wire and it is working fine.

Horn/interior lights/everything works. I have not seen a blown fuse.

I have even hard wired the pink/orange to the gray speedcal wire and white to the grey/black wire

Things I'm wondering how to check: Can I tap into one of the speedcal wires to see if the OSS is sending a signal. If it is - its the speedcal that died and if not is the OSS that has failed.

Does anyone know what the replacement part # for the T-56 OSS is? The part # is see is like XR3R-7103H-AA and I cannot find it anywhere.

Thanks for any help you guys can provide!

 

[mwolson]

If you take out the Speedcal and run the OSS, you will see about 4X of your actual speed if the OSS is working. Then you can assume that the Speedcal is the problem.

It will be exactly 4X if you have a 3.27 axle ratio.

 

[006]

I *JUST* did this job on my buddy's 96 V6 yesterday.

Here is a write up that I used:

[ame=http://www.3.8mustang.com/forum/showthread.php?t=168525]DIY: Repair your broken Odometer & Tripometer - 3.8 Mustang Message Board[/ame]


The main drive gear you see in that photo is like $25.00 plus $4.00 shipping...sucks!

If the odometer and mileage both stop working, it's supposed to be that bad boy.

 

[mwolson]

006, the OP lost his speedo/odo, not just the odo.

This means he's probably lost his OSS or VSS signal.

 

[006]

006, the OP lost his speedo/odo, not just the odo.

This means he's probably lost his OSS or VSS signal.

Ahh! :rockon:

Got your info..I'll pass it on.

BTW, I just picked up an 03-04 cluster that I'm gonna take to my buddy at Ford and have it programmed for my pats and to match my mileage.

 

[mwolson]

Ahh! :rockon:

Got your info..I'll pass it on..

Thanks!

BTW, I just picked up an 03-04 cluster that I'm gonna take to my buddy at Ford and have it programmed for my pats and to match my mileage.

For what car?

 

[9cobrastang7]

If you take out the Speedcal and run the OSS, you will see about 4X of your actual speed if the OSS is working. Then you can assume that the Speedcal is the problem.

It will be exactly 4X if you have a 3.27 axle ratio.

I was thinking about doing this. Thank you for the information! You wouldn't happen to know the part # for a replacement OSS would you?

 

[mwolson]

Sorry, I don't. If you find it out, I'd be happy to post it on my VSS/OSS swap how-to page: VSS/OSS Swaps

 

[006]

Thanks!

For what car?

My 95 with the 99-01 Cobra swap.

Here is my current cluster:

 

[mwolson]

How tough was it to rewire the older car for the newer cluster?

(sorry to hijack the thread.)

 

[9cobrastang7]

I'm seriously starting to believe that they don't make a replacement. I did find the OSS replacement for automatic transmissions, but it is way too small for the t56 OSS hole. I've been searching for days and cannot find it on ford parts sites or on the Internet. So I'm hoping it's the speedcal and I can just get it replaced. Could juming the car cause the speedcal to fry since it's hooked to a constant 12v supply? But if this were the case my turbo timer would also be fried. Hmmm

 

[9cobrastang7]

Not a problem. I'm interested on how he did that also.

 

[mwolson]

I'm seriously starting to believe that they don't make a replacement. I did find the OSS replacement for automatic transmissions, but it is way too small for the t56 OSS hole. I've been searching for days and cannot find it on ford parts sites or on the Internet. So I'm hoping it's the speedcal and I can just get it replaced. Could juming the car cause the speedcal to fry since it's hooked to a constant 12v supply? But if this were the case my turbo timer would also be fried. Hmmm

Who knows what failure may have occurred. Could be anything.

The voltage in cars can be pretty messy. It isn't 12V when the car is running, then it is typically over 14V. Anything that has inductors in it can cause voltage spikes that can play havoc with electronics.

One big cause of electronics failures in cars occurs when the battery is disconnected from the circuit while the alternator is spinning. Due to the way the magnetics of the alternator works, the current flow can't change very fast. So if the battery is suddenly disconnected, all that current that was charging the battery has to go somewhere. It goes to the electronics, but, knowing Ohm's Law, all that current through a fixed resistance causes the voltage to spike really high. That is fatal for many electronic circuits.

If you have a main battery shut-off for your car due to track requirements, and if it just cuts off the battery and not the alternator too at the same time, then the tech inspection could cause any unprotected circuit to fail. If one circuit fails, then that circuit could actually protect the other circuits, so they all may not fail.

Jumping the car can produce voltage spikes, so yes that could have been the source of the problem.

Also, if the electronics for the car are well designed, then they will have an 18V Transient Voltage Suppressor (TVS, AKA Transorb) such as an On Semiconductor ICTE-018G across the power and ground wires. Circuits with one of these will not fail due to supply voltage spikes. For some reason most car electronics designers fail to put one of these devices in their circuits. I can't figure out why. I put them in everything I design. The volume price is 39 cents.

You can add them outside of the electronics you wire into your car, but they can be difficult to find. Digikey has a minimum order quantity of 1500 units and they don't keep them in stock. Grrr.

Hall effect sensors are pretty robust, so the good news is, it is probably not what failed, although they do sometimes fail.

Let us know what you find out.

 

[006]

How tough was it to rewire the older car for the newer cluster?

(sorry to hijack the thread.)

The entire car from front to back (including doors, taillights..everything) has 2001 Cobra wiring. :-D

 

[9cobrastang7]

Alright, I took off the speedcal and hooked up the wires as they would be from the factory and guess what? I was doing 90 down my street:banana: So the sensor works fine and now I'm guessing it is the speedcal. I called up Dallas Mustang and althought I never got to talk to anyone they're shipping me out a new unit. I checked all my wires again and everything is wired as it should be.
One thing that I did check was the power wire to the cig lighter and it read 11.76 and when the car was running 14.XX. Shouldn't this wire be a constant 12v? I also checked the battery just sitting there and it was also 11.76. Is my battery bad?

 

[mwolson]

11.76V with the engine not running and 14V+ while it is running is perfectly fine.

 

[9cobrastang7]

Alright, sounds good. Thank you for the confirmation. Guess the speedcal died somehow, oh well got a new one on the way.
On a side note... to keep this from happening in the future can I run come type of inline fuse so that this doesn't happen in the future?

 

[mwolson]

Electronics can fail for a lot of different reasons. While the power in your car is not the cleanest power in the world, most car electronics are designed to work over a range of voltages from 9-18V. So many Speedcals are out there working fine, that it seems Dallas Mustang did a pretty good job of designing it. You just found one of the few units that failed. So it probably wasn't your car that caused it to fail.

However, FYI there are two power supply related things that can kill car electronics faster than anything else. The first is someone accidentally hooking the battery up backwards and the second is having the battery become disconnected while the alternator is spinning.

Hooking the battery up backwards most often happens when someone makes a mistake while jumping the car. If, while your alternator is spinning, your battery cable is loose and vibrates off, or your battery cutoff switch just cuts off the battery and not the alternator, too, then you will get a high voltage glitch on your power lines.

Many circuit designers do not put protection against these two things into their circuits, but you can add them to the circuit. If you just put a 1N4001 to 1N4004 rectifier diode in the power circuit to the Speedcal, it will protect it from reversed polarity. Install it so the black bar is on the Speedcal side of the power circuit.

If you could find one, you could also put an 18V TVS (Transient Voltage Suppressor) or Transorb across the power and ground for the Speedcal. Unfortunately, I haven't been able to find a supplier of these components that have a minimum order quantity of less than 500 units. I keep looking...