After CMDP speed gauge become crazy

[BFHvette]

his is the first time I write in the Forum
Please help me
I have 05+ Mustang 5spd mod Full Exhaust,JLT and Pulley.

303rwh.
The problem Comes when installing Charge Motion Plates from Steeda(Racing)

+SCT Mail Tune,when I push the fuel pedal To listen the exhaust the speed gauge rises with the car parked and use hand brakes?????????
Please help

 

[cekim]

his is the first time I write in the Forum
Please help me
I have 05+ Mustang 5spd mod Full Exhaust,JLT and Pulley.

303rwh.
The problem Comes when installing Charge Motion Plates from Steeda(Racing)

+SCT Mail Tune,when I push the fuel pedal To listen the exhaust the speed gauge rises with the car parked and use hand brakes?????????
Please help

Well, that's strange... Other than damage to wires/connectors during install, I doubt this has anything to do with the CDMPs or tune itself...

The speedo is computed off the tailshaft speed of the transmission. There is an electronic sensor at the rear of the transmission that measures the shaft speed which is then divided by the rear-end ratio and multiplied by revs/mile to compute speed...

So, I'd start by checking the wires there and at the rear of the engine where the CMCV connector used to hook up to the CMCV - presuming it is now left dangling? That point in the wire harness for the engine is not only where the CMCV connector breaks out, but also the O2 sensors and tailshaft speed sensor. I suspect something may have been damaged during install...

If there is no damage to the wires - you may have a lose ground, bad PCM or failing alternator...

 

[BFHvette]

Well, that's strange... Other than damage to wires/connectors during install, I doubt this has anything to do with the CDMPs or tune itself...

The speedo is computed off the tailshaft speed of the transmission. There is an electronic sensor at the rear of the transmission that measures the shaft speed which is then divided by the rear-end ratio and multiplied by revs/mile to compute speed...

So, I'd start by checking the wires there and at the rear of the engine where the CMCV connector used to hook up to the CMCV - presuming it is now left dangling? That point in the wire harness for the engine is not only where the CMCV connector breaks out, but also the O2 sensors and tailshaft speed sensor. I suspect something may have been damaged during install...

If there is no damage to the wires - you may have a lose ground, bad PCM or failing alternator...

Thanks for the quick response
Sorry i forgotten to tell you that I also changed Driveshaft

 

[cekim]

Thanks for the quick response
Sorry i forgotten to tell you that I also changed Driveshaft

Again, that would only matter if in the process you hit the output shaft speed sensor on the rear of the trans...

Out of curiosity, does the speedo "work" when you are driving or have you not tried?

 

[BFHvette]

Everything is working well except speed problem.
Previously the problem i noted a weakness in the front lights.

 

[cekim]

Everything is working well except speed problem.
Previously the problem i noted a weakness in the front lights.

So, when driving the speedo reads correct, but at idle in neutral, you can rev it and see it go up?

My first guess is that this and your lights are related and you have a bad ground somewhere...

Have you by any chance pulled the ground cable off the engine?

There are also ground wires just above the pass side headlight and another strap on the back of the engine (to the DS cylinder head)...

a speedo walking up as you spin the alternator really stinks of floating grund to me... Could be a bad sensor, or a cross coupling (short) that is pulling it up, but the headlights also being fishy is starting to add up...

In addition to going over all the cabling behind the intake to make sure nothing got pinched or hit a header - also check your neg battery terminal... These are not fun to debug unless you can an issue visually...

 

[dustindu4]

more importantly, does the mileage indicator go up when revving too?

 

[GIG4FUN]

so weird... I can not image more to suggest to you. Backtrack everything you did with a new set of eyes... (rested & clean state of mind).

 

[Clay]

more importantly, does the mileage indicator go up when revving too?

+1 lol, does the odometer move?

 

[BFHvette]

more importantly, does the mileage indicator go up when revving too?

No, not show any movement.
Only the speed moving moment for a little when push the pedal then return.