Brief history:

- No start problem traced to bad ECU. No check engine light illuminated.
- Replaced with ECU from '88 900S. Restored all functionality, except that A/C compressor would no longer click on (perhaps coincidental, perhaps the shop that diagnosed my bad ECU broke something else in the process?). Also "shift-up" light no longer functions w/ '88 ECU (matches wiring diagrams).
- Replaced with '90 turbo (Bosch # .. 580) ECU in hopes of restoring A/C function. No start once again.
- Re-install '88 ECU. Function restored, still no A/C or shift-up light.
- Remove '88 ECU. Car sits for a month parked, without any ECU, battery disconnected.
- Replaced with used '89 900S ECU (original part # ... 564). This ECU is known to function properly on another car. Car starts, and idles, but rough. CHECK ENGINE LIGHT on SOLID, and SHIFT-UP LIGHT FLASHING. Any sudden attempt to increase revs will stall engine. Slow, gradual pressure on the gas pedal will increase revs, but engine shakes uncomfortably. A/C, by the way, still won't click on.

In a previous post, someone suggested checking the AMM. I removed it, dusted it off, inspected it, and reinstalled it. Everything looked absolutely fine. I have no reason to believe it failed just sitting there for a month. I checked the vaccuum lines. They all look ok as well.

Has anyone ever seen this solid check engine light with flashing shift up light? It seems way too indicative of some sort of code not to be one, yet I can't find it in Bentley. Does anyone have factory manuals they could check for me? Could all the ECU swapping somehow have confused it?

The car is parked at my grandparents' house about an hour away. I'm going back to check on it, and hopefully fix it this weekend. So I've got a couple days to try to figure it out. If anyone has suggestions, I'd really appreciate it.

Cheers,

'Roo
'89 900S, 107k

posted by 12.13.238...

• '89 900S Mysterious ECU issues & fault code, Mr. Science, Tue, 20 Aug 2002 16:46:20 <-- Viewing This Message
  • connections to check..., JimBlake , Wed, 21 Aug 2002 08:16:09
    • AMM pin 1 is ground, pin 5 is +12v n/m, JimBlake , Thu, 22 Aug 2002 07:26:23
    • oops..., JimBlake , Wed, 21 Aug 2002 08:20:49
  • Re: '89 900S Mysterious ECU issues & fault code, Dan , Tue, 20 Aug 2002 20:56:49
  • Re: '89 900S AMM wiring or maybe bad AMM??, JohnK, Tue, 20 Aug 2002 18:58:43
    • Did not mention in post..., Mr. Science, Tue, 20 Aug 2002 20:47:03
  • Flashing shift light..., bazil burns, Tue, 20 Aug 2002 17:55:50
    • Interesting clue..., Mr. Science, Tue, 20 Aug 2002 18:14:34
      • No idea, but for some reason..., bazil burns, Tue, 20 Aug 2002 20:29:47
        • hmm.... relays..., Mr. Science, Tue, 20 Aug 2002 20:49:28
  • Re: '89 900S Mysterious ECU issues & fault code, Alex Bucell, Tue, 20 Aug 2002 17:11:04

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