I have a 1992 Camaro and the speedometer is either not working at all or suddenly jumps between 50 to 80 regardless of speed. I replaced the VSS and the problem remained. The car was changed to tpi from tbi and the wiring was changed at that time. Speedometer has worked correctly since the change for years until now

Any ideas on what ccould be casuing this

Thanks

 

Does the ecm see the Vss signal by using a scanner to view?

 

I could be wrong since I'm not 100% of F-body speedo schemes during that era but it could have something to do with the 1228746 ECM using an optical VSS vs the 1227730 ECM using a magnetic. Pretty simple for someone with PROM tuning capabilities to flip a bit and make the 1227730 use the optical instead.

 

the 8746 has a flag for the Vss ? I thought that was a 730 thing. Should now use a buffer to correct the signal

 

Oops misread the post , from tbi to tpi sd or maf ?

 

From tbi to TPI SD, running an EBL.

When changed to TPI did some rewiring under the dash to make the speedometer work and had no issuies for several years until it suddenly stopped working

 

Datalog see if the ecm is seeing the Vss signal optical on pin c6 of the p4. If the p4 sees the speed signal the internal buffer in the ecm is bad or wiring from ecm to c207 or the speedometer itself. If it’s an issue with the ebl can use the wayback machine website to view self install jumper install. I’m assuming it’s wired from
a vss buffer and not directly to b9 and b10.

 

Hooked up my laptop to try datalog for the VSS and the tachometer and voltmeter were now not working along with the speedometer

Heads up display for the EBL reported MPH and RPM the whole time

I did the datalog through the heads up and did not see a column for VSS, where do I see this?

The datalog is attached

 

You ip gets a tach signal from the distributor, the ecm get the signal from the icm. The voltage is seen at the ecm off the fuel pump switch iirc. So not related to your dash signals .of wire from the ecm to ip is good might try a different cluster. Just curious is the ip fuse good ?
if the ecm doesn’t get a Vss signal you see malf 24 and no mph.

 

Replaced the fuse for the guages and it immediately blew

headlight buzzer also came on when I tried the headlights with the car on

 

Now to find the short

 

Here's the factory Schematic for the 91 Camaro GAGES FUSE:

** The circuit FEEDING the GAGES, TURN/BU, and ECM fuses is a heavy gauge PINK wire from the ignition on the column. That PINK wire circuit also feeds the SIR, INJ2, INJ1 fuse on 1 branch and the "F4" terminal on the C100 connector on another branch. ( PINK wire @ Coil, OR EST Distribution w/VIN '8') Figured that might be important if you can't find the short on the GAGES circuit "after" the fuse box.