Well this is a strange one.... (is there anything else with this truck?? lol)

So I think i may have identified the issue with why the speedo/performance gets wierd....

On my tablet bluetooth adaptor it's reading ECU speed its anywhere from 30-60mph HIGHER than GPS and actual speed...


Interesting to note is the speed on the speedo is accurate ...... Somethin aint adding up here

Any thoughts? ideas on what to check on? ....

 

Bad VSS (vehicle speed sensor)
Unplug it, re-test your speed.

 

doesn't the VSS control the speedo as well?

 

+1 on the bad VSS...........
Discovery speed sender

 

You can rebuild it for less then $1 there is a thread on it I did mine it is simple

My speedo is 5 fast but computer is dead on with GPS, are we sure both read from vss and not one running off ABS wheel sensors?

 

Hmmmm.... possible i suppose ... they gotta be doing somethin different or my ECU is hosed readin that much more than whats real...

ABS is out and has been on mine for a bit. Before today the difference between ECU and vss was only 1-3mph, well since i been checking...

And today is the first day I've had an issue in a while


Ironically the p1179 dissapeared now

 

D1 gets from VSS, D2 averages the wheel sensors. VSS begins to fail, and eventually makes ECU think you are approaching takeoff velocity, and it will cut out injectors and spark. Cluster has another board inside that takes samples from the VSS to drive the speedo. I suspect that the data sampling or smoothing rate of the speedo board is different from the ECU, the ECU might sample fewer pulses and as such be subject to quite an impact of "jitter" of the signal. I think you can have a flakey VSS and the speedo not show it dramatically.

 

Vss it built cheap with plastis washers not bearings it is probly bad, plastic wears out causing too much shaft play then it starts to bounce around in its case hitting the sides

 

Yes I can confirm this.