heres a link to what it says for a 51, http://www.mifbody.com/DTCs/DTC%2051.jpg

also heres links to the rest of em. LS1TECH - View Single Post - OBD1 DTC Codes & Troubleshooting

if 51 keeps coming up i would say pick up a tested ecm, run between 120 and 200 bucks. make sure you get the right one for your trans, make note of any numbers on the ecm.

 

Yes, I did disconnect the battery before removing the ECM. Will disconnecting the battery alone reset the ECM and clear the error codes?

 

you can insure a ecm reset by touching the battery cables together (pos and neg) for a couple minutes, while they are "not" connected to the battery of course. make sure to unhook any aftermarket stereo equipment or electronics

 

Yes, I did disconnect the battery before removing the ECM. Is disconnecting the battery sufficient to reset the ECM and clear the error codes? Or are there additional steps necessary to clear the error codes?

 

it should reset,,, if you question if it did you can insure a ecm reset by touching the battery cables together (pos and neg) for a couple minutes, while they are "not" connected to the battery of course. make sure to unhook any aftermarket stereo equipment or electronics, this also resets any sensors memory.
__________________

 

Woops! didn't realize the thread became a 2 pager. Sorry for the duplicate post.

 

My car did this for a while and it didn't throw codes. I changed the spark plugs and that fixed it.

 

Good info given here from Craby.
My suggestions are:
1. Change fuel filter, it has been sitting for a long time.
2. Run a can of injector cleaner at the next tank fill.
3. As said, disconnecting power to the ECM resets it - drive the car for it to relearn.

My '88 Dually OBD1 sputters, surges, anything with an S, until I drive it to operating temp and give it WOT. The more its driven, the better it runs.

When ECM is put into diagnostic mode, first DTC should be 12 - ECM is communicating and good. You can short OBD 1 connector pins A to B and count the CEL flashes for DTC's, ie, flash, space, flash, flash, space, space, 12, 12, then the rest of the DTC's given by flashes.

And yes, a spark plug change, new air filter, make a world of difference.