Any ideas?
Thread Starter
Le Mans Master
Joined: May 2004
Posts: 5,866
Likes: 60
From: Hellinois
Finalist 2020 C4 of the Year - Modified
Any ideas?
I am getting a new tune for my car and the tuner just told me my datalog I sent him is showing no m.p.h. yet there are load changes etc. that tells him I was driving the car. The dash speedo works fine so can anyone shed any light on what may be causing this?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
From your forum name I assume the car is an '85 since you didn't tell us...
The speedometer signal goes from the VSS (Vehicle Speed Sensor) in the transmission to the instrument cluster. After some magic, it gets sent to the ECM. Apparently that last part has a glitch. It could be a bad connection inside a connector, broken wire or something similar.
The load value is calculated by the ECM. I don't remember the exact algorithm, but it is something like the ratio of TPS percentage to RPM. Airflow might be involved also. That means that when the ECM sees (for example) a high TPS percentage and a low RPM then it knows the engine is under a high load. It uses the load value to add more fuel if it is needed.
The speedometer signal goes from the VSS (Vehicle Speed Sensor) in the transmission to the instrument cluster. After some magic, it gets sent to the ECM. Apparently that last part has a glitch. It could be a bad connection inside a connector, broken wire or something similar.
The load value is calculated by the ECM. I don't remember the exact algorithm, but it is something like the ratio of TPS percentage to RPM. Airflow might be involved also. That means that when the ECM sees (for example) a high TPS percentage and a low RPM then it knows the engine is under a high load. It uses the load value to add more fuel if it is needed.
