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Discussion Starter #1
Hello,

I own 2003 saab 9-3 2.0t Linear.
The problem is that sometimes it cranks but does not start and has a smell of fuel.
Waiting for few minutes and trying few more times it starts and works well.
I think this could be related to the faulty CPS, but there is another problem that sometimes it quickly starts but works with missfire. If I stop the engine and restart it works fine.
These two problems mostly happen when the car is cooled a bit after the long enough trip to warm up the engine.

With the OBDII scanner mostly I see only O2 sensors codes, just last time when it started with the missfire I got P0638 and P0204 codes in addition. I have cleared them and they did not come back after the next start.

Could you please tell me what could be the reason of these two problems?

One more thing is that when the engine starts with missfire, disconnecting the MAF sensor does not have any effect. I do not think that the MAF is bad sine mostly engine works well.
So I do not understand why the MAF does not have any effect when the engine starts with missfire...
 

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2008 Saab 9-3 Aero FWD 6MT
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Start with the easiest. If you know the CPS is faulty, then replace it. Next would be coils and plugs, your car won't read sensor data until it's in closed loop.
 

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Agreed with MadRomeo. Replace CPS and then spark plugs (use only NGK spark plugs) and coils (use only original coils).
NeoBros sells Saab spares in reasonable price.
 

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Discussion Starter #4
Thanks guys,
CPS is just my guess, but anyway I will replace it. Also I will change the spark plugs.
These are relatively cheap to do, while changing the coils is not cheap thing.
I hope it's not a coil problem.

MadRomeo, could you please explain a bit what does it mean the car is in closed loop?
 

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When it doesnt start and it its only cranking does the tach moves ?
Were those the only codes in the ECU the 638 and 204 or u had others .
If only 204 and not 201,202,203 as well, then i would test injector circuit , if the there are other injectors codes then bad ECU
 

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Thanks guys,
CPS is just my guess, but anyway I will replace it. Also I will change the spark plugs.
These are relatively cheap to do, while changing the coils is not cheap thing.
I hope it's not a coil problem.

MadRomeo, could you please explain a bit what does it mean the car is in closed loop?
Modern fuel injected vehicles have two operating modes. One is open loop, which occurs during warm-up, the car runs on a different fuel map and doesn't take values from O2 sensors. Coolant temp, MAF, etc. adjust it. Then there's closed loop, which occurs above a certain coolant temp, in which the car uses all the information from the sensors to adjust its performance.

EDIT: Now includes proper punctuation thanks to Hus_sho.
 

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Discussion Starter #7
When it doesnt start and it its only cranking does the tach moves ?
Were those the only codes in the ECU the 638 and 204 or u had others .
If only 204 and not 201,202,203 as well, then i would test injector circuit , if the there are other injectors codes then bad ECU
yeah, good question about tach... I do not remember, did not pay attention on it.
If it does not move then clearly CPS is bad, right?
Anyway, I already have new CPS and I am going to replace it in next days. I hope this will fix no start issue.

Regarding the codes, I had only 638 and 204 + O2 sensor code (I do not remeber exact number). Since I do not have 201,202,203 as well, I hope the ECU is not bad.
However, it could be that only one FET inside ECU that controls 4th injector is bad...

I am wondering if a bad spark plug or coil could cause throwing the P0204 code.
 

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Discussion Starter #8
Modern fuel injected vehicles have two operating modes. One is open loop, which occurs during warm-up, the car runs on a different fuel map and doesn't take values from O2 sensors, coolant temp, MAF to adjust it. Then there's closed loop, which occurs above a certain coolant temp, in which the car uses all the information from sensors to adjust its performance.
Thanks a lot for the explanation,
so the car was in open loop when misfiring since it did not use information from the MAF.
It's weird since after restarting it runs well and is in closed loop since it uses the MAF information (engine dies if the MAF is disconnected).

So, no misfire in closed loop, while if there is a misfire then the car is in open loop...
 

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If u have 204 then bad injector/circuit or ECU .. and if the injector is stuck open then that explains a no start and fuel smell. I dont suggest replacing the cps unless u have no tach during cranking, replacing the cps comes with its challenges if u have any rust
 

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Thanks a lot for the explanation,
so the car was in open loop when misfiring since it did not use information from the MAF.
It's weird since after restarting it runs well and is in closed loop since it uses the MAF information (engine dies if the MAF is disconnected).

So, no misfire in closed loop, while if there is a misfire then the car is in open loop...
You are on the right track with your thinking. Keep going.
Now you have an idea of the problem, one that can be corrected by sensor inputs... Take the next logical step.
 

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Guys to clarify:
Closed loop: car uses oxygen sensors to judge wether it is running lean/rich and correct for the condition .
Open loop: car doesn't use oxygen sensor values (either because of a fault in the O2 sensors, or the sensors are considered not hot enough to be used yet, or other systems fault that affect closed loop control) what car uses in the open loop are fuel values stored during previous normal adaptations or zero adjustment if those adaptations were cleared .

Car uses MAF all the times, except during crank to start below 500rpm , and if there is a MAF fault
 

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Discussion Starter #12
Guys to clarify:
Closed loop: car uses oxygen sensors to judge wether it is running lean/rich and correct for the condition .
Open loop: car doesn't use oxygen sensor values (either because of a fault in the O2 sensors, or the sensors are considered not hot enough to be used yet, or other systems fault that affect closed loop control) what car uses in the open loop are fuel values stored during previous normal adaptations or zero adjustment if those adaptations were cleared .

Car uses MAF all the times, except during crank to start below 500rpm , and if there is a MAF fault
If a car uses MAF at all time (except during cranking), then I do not understand why disconnecting the MAF does not have any affect while running engine with misfire...
If the MAF is bad, then how engine can work well after restarting? and why I do not have relevant OBD code?
That's weird...

Thank you guys for posting here.
 

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The MAF is compared to a database inside the ECU, the ECU knows what to expect from MAF, .. and if u disconnect MAF the ECU will run on these figures, so if ur MAF is good, then these figures will match the MAF figures and thus there will be no change to the way the car running.
Even if the car runs different with MAF disconnected, that does not conclude the MAF is bad .
 

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The second part of ur question i didnt understand .. why u dont have codes for what exactly ?
 

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Discussion Starter #16
The MAF is compared to a database inside the ECU, the ECU knows what to expect from MAF, .. and if u disconnect MAF the ECU will run on these figures, so if ur MAF is good, then these figures will match the MAF figures and thus there will be no change to the way the car running.
Even if the car runs different with MAF disconnected, that does not conclude the MAF is bad .
sorry, I did not get... if the MAF is good, and engine runs well, then disconnecting it should have a significant effect, right?
and even if engine runs with misfire, disconnection/connecting a good MAF should have an effect, right?
 

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All the time .. the car might DRIVE crappy for a maximum of 60 seconds with a faulty MAF after 60 seconds the ECU will trigger a fault for the MAF and it will quit using its value.
So if u drive the car for more than 60 seconds and fault was triggered, then MAF ok.

Focus on ur issue, u have a P0204, chase that and forget the MAF now
 

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Discussion Starter #20
All the time .. the car might DRIVE crappy for a maximum of 60 seconds with a faulty MAF after 60 seconds the ECU will trigger a fault for the MAF and it will quit using its value.
So if u drive the car for more than 60 seconds and fault was triggered, then MAF ok.

Focus on ur issue, u have a P0204, chase that and forget the MAF now
Ok, thanks a lot, I'll forget the MAF
 
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