rpm/ecu problem

[JaBoT]

I'm having a problem where my ecu isn't reading the rpm's correctly. I have tried 2 different analog tachs which both say I’m idling around 1100 rpm when my ecu thinks I’m at 850. What actually sends the rpm signal to the ecu? and could this be the problem?

 

[JaBoT]

anyone?

 

[T-top87GN]

The ECM gets it's speed from the VSS. So yes that's why things are off.

 

[bruce]

Originally posted by Bandit
The ECM gets it's speed from the VSS. So yes that's why things are off.

See what reading that TE stuff does to you.
He's taking RPM and you reply with vehicle speed. LOL

Sounds like the cylinder select may be set wrong, and there are some aftermarket tachs also need reworked to be able to read the GN DIS.

 

[Tim Riecks 6]

The VSS gives the speed of the car (MPH) to the ECM. The RPM (tachometer) input comes from the ignition module pin D.

 

[JaBoT]

It's not the tach, i checked it by hooking up the rpm probe (the one that goes on a wire like a timing light) from a state inspection machine and the autometer tach is right.
I also figure it's the computer because acording to directscan my car is idling at 850 with 8 gms/sec maf. It should be at 5 gms/sec at 850rpm. That's also another indicator the ecu is seeing the wrong rpm.
Any other ideas would be great.

ANd just for the record my vss is working fine

 

[T-top87GN]

Doh!!! I replied to the wrong thread! Sorry guys