Civic : 17.95 MPG ? SuperMID is way off ( I hope )

[Cd]

I just filled up my tank and did the calculations : 28.4 MPG.

This is for my automatic 1993 Honda Civic DX hunchback. Why so low ?....well the car has been sitting for the last six months with me replacing fuel pumps and such and priming the pump quite often to test it ( the problem turned out to be a bad ECU )

What bothers me is the reading on my SuperMID which was fairly accurate before +/- 5 MPG or less.

Without changing the parameters, it is now saying that my last trip of 15.63 Kilometers resulted in a consumption of 7.63 km/l and that my average speed was 4 Km/h ! Speed is WAY off !

If the distance parameter is correct, how could the speed parameter be so far off ?

The distance parameter seems correct compared to what my odometer reading says, but what could cause the other readings to be off ?

I know that the wiring to the injector wire is making good contact with the wire to the SuperMID, so i'm really puzzled.

I just replaced my VSS with a new part since the original one seemed to be faulty. The new one is now also acting strange and the needle is bouncing around.

Could any transmission damage cause strange symptoms like this ?
I have a habit of coasting with the car in Neutral and the engine revs really high when i slip back into gear if i am going less than 45 mph. ( engine on coasting )

[Cd]

Wow, 70 views

[GRU]

Do you do short drives with a cold engine?

[Cd]

Yes this was a short drive, but the engine warmed up quite quickly ( Texas heat )

What concerns me is that the parameters are so far off, yet the distance parameter is correct.

I hope nothing is wrong with my transmission.

Thanks for the reply.

[hawk2100n]

If I'm not mistaken, in this car the VSS is just an induction type sensor that counts the pulses on the final drive. Since your needle seems to be bouncing around then you must be getting an intermittent reading. I would trace back the wires and especially look at the connection at the sensor and then the connection at the MID. One or both could be causing a short.

Also if the computer is not getting a normal reading from the VSS it may affect the transmission. I am not sure if the transmission is electronically controlled but if it also relies on this reading to guess what gear to re-engage into from N then it would default to 1st or 2nd gear and cause the high revs. That is speculation but I think a very plausible scenario in your case.

The distance parameter in the MID might come from the speed and it interpolates between speed readings in the event of sensor failure but it doesn't have the same bit of code on the speed side. Depends on who coded it originally.