Help with Check Engine light

[wcdeane]

We are a family of eight… a his and hers kind of thing. And everyone in the family loves my ’91 SE, but no one is allowed to drive it without my knowledge and permission. Problem is…I have reason to believe from past events and clues left behind that not everyone has abided by this rule. For this reason I now disable the car every time I travel. I do this by pulling the 10 amp fuse to the ECU.

Last night upon returning from a 3-day trip I replaced the fuse and started her up. I instantly got a “Check Engine” light. So, I hooked up my lap top and ran “FreeScan”, only to find “no fault codes reported”. The car starts a little hard, and seems to idle correctly, but has quite a bit of stumble at various points of acceleration. I didn’t run a report, because it was getting late, but I plan to do so tonight.

But before I do so I was wondering if anyone might have a clue as to what this could be. I am aware of the need to break in the chip (with a bit of mild driving) after the ECU is disconnected. I did this repeatedly with no positive result…the “Check Engine” light and stumble persists. All the vitals (fluid levels, oil pressure and the like) seem to be OK. And one more thing...the light seems to come on steady and will periodically flash a few times. I have not detected a pattern to the flashing as yet.


Any WAG (wild ass guess) is welcome at this point…and note that I have not ruled out tampering.

Walt…’91 SE

[swedishsurgeon]

Hello Walt,
When you pull the fuse to the ECU, your taking away the battery voltage the computer uses to keep stored values. When you reconnect it, the computer must "learn" all over again. If you would like to keep people from driving the car, pull the fuel pump fuse as the car will just crank over but will not start. The easiest solution to keep unwanted drivers out is to lock the doors and keep the key with you or put a sticker in the window that the car will "Blow-Up" if tampered with! After the second Bond movie, they might think twice!
About computers, please read my post on: Engine Check Light on - under deceleration

Cheers,
Robert

[wcdeane]

I was aware that the computer had to relearn a few things after it is disconnected. In fact, I have done this many, many times for one reason or another. However, on previous occasions I have never had such poor performance after the reconnection. It really ran lousy. I decided to drive it to work yesterday in spite of its sorry state, and by the end of the day it seemed to be running OK. So, all is well at this point.

Thanks for the tip on the fuel pump fuse. The evidence would indicate that this is a better choice.

Walt…’91 SE