I've got a 67 C10 Chevy truck with a TPI swap performed by a P.O.

It's an 87-88 5.0 TPI

I got a OTC 2000 scanner off ebay. It has an OTC GM 1981-88 cartridge and a Domestic Pathfinder 79-92 GM, Ford, Chrysler cartridge.

I've traced the ALDL wiring for ports B,E,M to the ECM Connector and did a continuity test on them. They're good.

I tested voltage at the ports. I get a solid 5 volts on B, and voltage bouncing around between 2 and 5 on E and M.

I tried both cartridges as both 87 and 88. But all I get is "NO DATA".

OTC book says to check the fuse to the ECM. I'm looking for it.

The truck seems to run fine. Any ideas?

Thanks

 

the only thing i can think of right now is make sure that port A in the ALDL has a good ground & then see if you can flash the check engine light.

 

Port A does have a good ground. But the CEL that is wired into the harness doesn't flash when I do the jumper thing.

And I haven't found a diagram showing me how to check the CEL wiring. That's the main reason I decided to just buy a scanner.

I checked the power and grounds of the ECM connectors. All good.

 

"But the CEL that is wired into the harness doesn't flash"
that may be the problem why you can't get communications.
some of the older ECMs need a working check engine light.

i don't remember when GM stopped using a lamp driver module to control the check engine light for certain, i want to say either 85 or 86.
if your system does not use a lamp driver module, then one side of the engine
light is wired to power & the other side goes to the ECM.

 

At the bottom of this link are wiring diagrams for that ECM:

http://www.diy-efi.org/gmecm/ecm_info/1227165/

RBob.

 

Thanks. Great site. I'll add that to my favorites for sure. I'm still not sure how to wire it though. Do I supply 12 volts to one side and the other side goes to the A5 ECM pin? Does the ECM provide a gound?

I'm a little confused because the Chevy Thunder site shows the A5 pinout having 0 volts 'key on' and 13.9v engine running

ECM Pinouts

[img]ftp://ftp.diy-efi.org/pub/gmecm/manuals/1227165/86-165v8tpi-5.jpg[/img]

Thanks,

 

the ECM does supply the ground to turn the light on, so when the engine light is on there will be little to no voltage on the ECM side of the light.

 

I disconnected the batter NEG. Unplugged the ECM and wired up the CEL to the A5 connector. Reconnected the ECM, connect battery, Key on and started getting code 12. And this is happening without the ALDL A-B ports being jumped.

I take her for a drive. CEL is flashing randomly. Turn her off and then key on, I get codes 12, 14 and 42. Again,I am getting codes without jumping the ALDL A-B ports.

I checked the Wire from the B port to the A9 ECM pin. It's not grounding out anywhere.

How can I be in diagnostic mode and be getting codes without the A-B terminals being jumped?

 

Guess I'll be checking the the CTS tomorrow. If the wiring and sensor are good, my book says I need a new ECM.

I'm thinking this is may be the problem and I'm probably just running in back-up mode.

 

I guess I just needed to drive it more after resetting the ECM. She doesn't throw codes without the jumper anymore.