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1981 8v c900 sedan, 1990 2.0 9k carlsson, 1992 21 c900 sedan
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Discussion Starter · #1 ·
Fitted replacement O2 sensor and a new TPS after recent diagnosis showed both to be out of spec when I was trying to diagnose rough running. I used genuine parts to replace both items.

Engine now starts but stalls out. I tried manual jumpering fuel pump (it runs) but same behaviour. No fault codes other than 12231 (no rpm).

Connected old TPS back in place of new one and same thing. Checked all vacuum hoses etc. just in case I forgot anything. Any suggestions?

Car was running albeit not great before doing the diag and replacement of O2 sensor and TPS. Was using it as daily driver.

Just tried starting with throttle pushed a bit and motor still stalls out both with fuel pump running off ECU control and manually as well. Still no additional fault codes being logged. Motor starts and I rev it to about 1500 to 2000 with throttle before it shags out.

I suspected an AMM issue but wasn't getting any AMM-specific fault codes previously. Is it possible that the new replacement (oldstock genuine Saab Bosch one) 02 sensor is bad?

Thanks if you can suggest something. I touched no electricals apart from the O2 sensor and TPS connections.
 

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I'd lean towards the O2 sensor being flaky if you've eliminated the TPS, but it's behaving like a bad AMM....so hard to tell. Have you made any progress?
 

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1981 8v c900 sedan, 1990 2.0 9k carlsson, 1992 21 c900 sedan
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1,028 Posts
Discussion Starter · #3 ·
I've verified the new TPS is bang on in spec. I've also verified the cold (ignition on motor not running) output of both the replaced and new identical O2 sensors to be the same (just under 0.6v) and the pre-heat circuit resistance is correct (4 ohms). Because of work and being ill I have not made more progress yet. I have not set up to test the CPS but if that is bad I have another Saabits kit for it here, and a full original CPS assembly untouched. I don't have a spare AMM, but I am considering other things too. CPS test is the next thing though.
 

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1981 8v c900 sedan, 1990 2.0 9k carlsson, 1992 21 c900 sedan
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1,028 Posts
Discussion Starter · #4 ·
Latest update - A few days ago I verified the CPS is working correctly with my meter connected at the EZK box as I manually turned the motor over.

I've pulled the knee bolster and swapped around the two relays at the ECU and also today I have replaced the fuel filter (as I wanted to do that anyway). I've manually run the fuel pump until I could hear the pressure regulator working (to indicate all air had been pushed out of the fuel feed to the motor).

When I changed the filter I initially has a leak at the seals on the filter inlet side (pressurised pump output side) and fixed that up so there are no fuel leaks.

Triple-checked there are no vacuum hoses disconnected around the engine.

Tried to start - it starts, tacho shows it's revving up to about 1100 as it fires, then the revs just drop away and the motor stalls once the revs fall to about 500.

ECU records no faults other than 12231 (no rpm).

Repeated same thing with fuel pump manually jumpered and get same result. Got the same result with the 02 sensor signal wire disconnected.

If I push the throttle as I start the motor it fires, goes up to the higher rev, and still stalls.

I'm going to get a spare AMM since without one I can't rule that out. I'm not keen to pull the fuel pump but will do that if swapping the AMM isn't the answer. I don't know if I'd find any new oldstock -019 AMM's and don't know of any place (here in Australia) than can test/service/repair them.

I'm leaving the knee bolster out just in case I'll need to do electrical testing around the ECU.

Is it possible, by some remote chance, that the ECU itself has a fault, based on the symptoms?

I haven't pulled the fuel pump out but that'll be another place to check.

Where are there vacuum connections off the intake manifold? FPR has one. One goes to the vacuum tank. One goes to the valve thing on top of the charcoal cannister.
 
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