Cable Operated Speedometer?

[Specter]

I was having a discussion with my friend where we were talking about the operation of speedometer. Would it really matter if your speedometer is working through the conventional cable system rather then getting readings from the ecu? I am asking this in both terms, accuracy and performance. Does your vr4 speedometer operate on cable system or does it gets signal from the ecu? I am not sure how should it be as i recently swapped a 4g63t into my galant which previously had a carburetor engine. Please clear my confusion on this topic.

 

[grocery_getter]

Stock GVR4 have cable drive from the transmission directly to the back of the instrument panel. Later on mitsubishi have electrical signal that goes straight to ecu and then from ecu to instrument panel. Accuracy wise I have no idea. Its just nice when the ecu knows the vehicle speed because then a lot of other speed dependent control can be done using the vehicle speed signal gathered at the ecu.

 

[prove_it]

The ecu get the Vehicle Speed Signal(VSS) from the instrument cluster. The cable goes to the cluster then a sensor sends the info over to the ecu. On 2nd gen eclipse and talons mitsu switched to a sensor on the transmission which sends the signal to the ecu then to the cluster.

 

[Wizardawd]

And to be honest, most of the inaccuracies from the speedo system are from the tires. Think about how much the diameter changes from when they are new. Then you have the gear drive in the tranny itself which doesn't exactly fit ultra-tight, so there's some error there.

Wiz

 

[Specter]

Okay great replies so far, just the ones i was looking for. So for my setup, i need to find the exact location on the back of my cluster from where i can run a wire to the ecu, doing so will probably result in "something" better. That is what i get so far, though i do like to know what would be better?

 

[prove_it]

Quoting Specter:
I am not sure how should it be as i recently swapped a 4g63t into my galant which previously had a carburetor engine.



Wait, what? You did what? /ubbthreads/images/graemlins/uhh.gif

The speedo needle is driven by the cable in a normal galant I'm familiar with. I don't think I've ever seen a carburetor equipped galant. I would assume it's an older year so the speedo in that should be strickly cable driven and yes you'll need to run a wire from the cluster to the ecu, but the ecu doesn't really need this input to run correctly. Also if it is an older body style chances are that the factory cluster won't have a VSS anyway. So you would need to swap the cluster for one that has a VSS.

 

[JSchleim18]

He's overseas...they had a 1.8 carb'd motor IIRC in a 6th gen galant body.

 

[Specter]

^^ He is right, around here galants have a 1.6L-2.0L carburetor engine depending on the trim level. I swapped a 4g63t so imagine that, only 6g galant in my country with a 4g63t. Okay back to the topic, i swapped in a cluster from that of a vr4, it has that boost signal guage on the rpm side. So i guess i should be able to run a wire from it to the ecu.
But if it does not affect in any way how the ecu performs, then i do not want to do it, unless some one says otherwise.

 

The ECU only needs the tach signal so that it can flag a CEL if you have an ignition misfire. It will run fine with no tach signal at all, it just will never throw a CEL Code 44. The worst that can happen is that if your dash tach is incompatable with the tach signal your motor is putting out, the tach will act a little crazy.

 

[Specter]

^^ Great, thanks a lot!