No signal from ECM

[Alaskabuick]

I tried hooking my Scan master up today in a car I just acquired. I cannot get it to work correctly, it lights up for a second then goes blank. It works just fine in my Turbo T. I also noticed that the audible knock sensor stopped working when you 1st turn the key on? It used to make a noise every time I turned the key to the on position.

Is their somewhere I could check a connection that may be loose?

This car is new to me and just now going thru it for the 1st time.

Thanks,

Dennis

 

[RmvBfrFlght]

Check the fusible link at the battery. Small orange wire on the + terminal. That supplies power to the ECM.

Also check the ECM fuse in the fuse block.

RemoveBeforeFlight

 

[Alaskabuick]

The car seems to run fine, but not signal from ECM for scanmaster.

 

[davelostmissing]

Chase it back to A8 on the ECM
http://www.vortexbuicks-etc.com/ecmwiring.htm

 

[Alaskabuick]

Chase it back to A8 on the ECM
http://www.vortexbuicks-etc.com/ecmwiring.htm

Ok, I chased it back. I tested it with a 12v test light? Probably no right was since I see it is low voltage, like 4v?. I even spliced in my scan master wire at the ECM and will not feed data?

Hummm....

thoughts?

thanks,

Dennis

 

[davelostmissing]

The test light is not suitable for this. SM connected to ECM directly was a good test. Sounds like the ECM is bad, swap them?

 

[RmvBfrFlght]

Ok, I chased it back. I tested it with a 12v test light? Probably no right was since I see it is low voltage, like 4v?. I even spliced in my scan master wire at the ECM and will not feed data?

Hummm....

thoughts?

thanks,

Dennis

If it is a steady 4 V then likely the ECM is bad. With a DVM on the DC scale it should be around 2.5 volts. The output is 0 & 5 volts, with it switching between the two. This is why a DVM should show about half that at 2.5 V.

In the C3 series of ECMs there is usually a small transistor that drives the ALDL output. It likely gave up the ghost. May be able to replace it (use a PN2222), or get another ECM and keep this one as a spare.

RemoveBeforeFlight

 

[TurboBob]

ALDL comes out a quad-driver on these ECM's. Its the middle one on the bottom board.

Fixable, but probably easier to swap the ECM. Note that these chips don't usually die, but are "murdered". So check the solenoids and wiring for the other channels that share that chip:

Specifically the Fan Relay and TCC.

Bob

 

[Alaskabuick]

If it is a steady 4 V then likely the ECM is bad. With a DVM on the DC scale it should be around 2.5 volts. The output is 0 & 5 volts, with it switching between the two. This is why a DVM should show about half that at 2.5 V.

In the C3 series of ECMs there is usually a small transistor that drives the ALDL output. It likely gave up the ghost. May be able to replace it (use a PN2222), or get another ECM and keep this one as a spare.

RemoveBeforeFlight

Sorry, I did not explain the 4v very well. What I meant is I see on chart for the ECM that it is supposed to have around 4v. Should of been more clear.

 

[Alaskabuick]

Swapped ECM from another car and problem fixed. Now I need to find a new ECM, where can I get one? Or can I have it fixed?
Are there any other Buicks that share the same ECM?

Thanks guys for the help..

Dennis

 

[TurboBob]

Not sure you have any junkyards near you, but the ECM is reasonably common in the late 80's front wheel drive 6 cylinders (3.0L and 3.8L, not "3800")

Parts stores can get re-man'd ones.

Yours is fixable, but that is probably more expensive than getting another.

Bob