Just back from a successful test drive of an hour or so, no problems. Took the whole distributor off last night and found that the connector on the + terminal of the coil was almost snapped off at the join to the wires. So replaced that and put the distributor back on, seems to be running great.

However I jumped the diagnostic connector again to be sure, and yes the check engine light does stay on with the key turned to 2. With the connector not jumped it stays on just 2 seconds as normal. Does this definitely mean the ECU is in backup mode? I tried pulling the fuse that you described, but there's only a 10A fuse under the hood for the ECU and a 20A in the driver's footwell. Is it not either of these? I wasn't able to locate the one you're referring to.

Thanks again
Carl

 

I gave you the wrong fuse position from 94 Manual. The 90 Accord manual I have shows fuse 24 (7.5A) at outside rear corner of underhood fuse box. You need your own shop manual from Online Manuals links in DIY section.

From 90 Accord manual "When the Check Engine warning light and the self diagnosis indicator are on, the backup system is in operation."

I think self diagnosis indicator is the red LED inside the ECU. It can be seen through a window in the ECU/TCU cover. You have to pull the carpet back on pax side to find the ECU/TCU cover beneath passenger foot area.

Hopefully you found the cause of missing.

good luck

 

Tried removing that fuse. Still getting the check engine light on with the connector jumped, but nothing on the LED on the ECU, and nothing without the connector jumped. So I think I'm in the clear, and the engine seems to be running fine.

Thanks again for all your help!