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Discussion Starter #1
I'm more of a T5 and older guy, but my friend recently acquired a 2001 Saab 9-5 with a T7 turbo B235 engine, and it was inexpensive because it had a weird issue where too high of a load caused the engine to stall. As soon as the boost gauge on the dashboard goes out of green, the engine completely cuts out, no power, and you have to turn the engine over again. Sometimes it also has trouble starting, sometimes when it's warm but not always. Idle is always smooth as can be.

I immediately suspected CPS and/or DIC but we've tried three different CPS that have good resistance (~500 ohms) and like five DICs, Chinese and SEM. I dropped the intercooler to check for leaks anywhere in the system before the throttle body, everything is sealed up tight. Also checked the vacuum hoses after the throttle body, had to replace one for the boost solenoid valve, no change in symptoms. I've tried two MAFs, live data from OBD2 shows they are probably working correctly and unplugging the MAF doesn't prevent it from stalling under load/boost. Throttle body is not in limp mode (I checked the cog), O2 sensor oscillates normally and fuel trims are near 0%. Turbo has no play and rotates freely, you can hear the induction noise when you rev the engine in neutral. When he bought it, it had NGK iridiums but I replaced them with BCPR7ES-11, gapped to 1.0mm.

The various codes I've gotten so far:
P0172 (the reason I suspected a boost leak)
P0340 (first time I checked the codes, with the original CPS)
P0336 (second time I checked the codes)
P1300

I feel like I must be missing something, I'm not too keen on T7 type Saabs and I hope somebody can clue us in!
 

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Discussion Starter #2
To reiterate, this car will drive around perfectly fine as long as you stay out of boost. No misfires until you get the engine load up to the point where it asks for boost. I got the flashing check engine light once or twice while doing this, but typically it just shuts off completely. I tried another used BPC, double-checked that the BPC hoses were going to the correct nipples on the turbo and intake, ensured the cobra pipe itself was clamped securely, tested the boost diverter/bypass valve, no problems there either.
 

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Have you checked that bypass valve is intact?
Have you double checked that boost hose is firmly attached to throttle body?
 

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Have you double checked that boost hose is firmly attached to throttle body?
This!

it's odd but sometimes if that thing is not clamped down tight it'll pop up when the car goes into boost causing a loss of charge air, T7 goes nuts, car goes back to idle which is pulling a vacuum and the hose sits back down on the TB and all is good.
 

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Discussion Starter #5
Have you checked that bypass valve is intact?
Have you double checked that boost hose is firmly attached to throttle body?
Yes to both, I checked that the bypass valve can hold vacuum and I also substituted a spare working part. The boost hose had a pinched o-ring at the throttle body but I replaced that and it is clamped tightly.
it's odd but sometimes if that thing is not clamped down tight it'll pop up when the car goes into boost causing a loss of charge air, T7 goes nuts, car goes back to idle which is pulling a vacuum and the hose sits back down on the TB and all is good.
Unfortunately this car is not going back to idle, it stalls out completely, no power to the engine after you first get the needle out of green, even if you are flooring it. Really puzzling because it's pretty much not like other symptoms I've read about on these forums.
 

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just to exclude electrical problems:
1.
ground connection at thermostat housing
2.
ground connection battery to chassis, one to gearbox, another one to chassis behind front light/battery holder on driver side
3.
battery connection

other hoses
4.
short hose between intake manifold and fuel pressure regulator
5.
fuel pressure regulator (if you have access to used spare part) or testing of fuel pressure (engine in idle, hose disconnected, fuel pressure should be 3 bar, measured at big Schrader valve)
6.
hose at the back of throttle body to EVAP valve ( short rubber piece might have a crack, inspect well)
 

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Discussion Starter #7
just to exclude electrical problems:
1.
ground connection at thermostat housing
2.
ground connection battery to chassis, one to gearbox, another one to chassis behind front light/battery holder on driver side
3.
battery connection
Will do, I've done a simple visual on two of these grounds but I'll pull them all and check for corrosion next chance I get.

other hoses
4.
short hose between intake manifold and fuel pressure regulator
5.
fuel pressure regulator (if you have access to used spare part) or testing of fuel pressure (engine in idle, hose disconnected, fuel pressure should be 3 bar, measured at big Schrader valve)
6.
hose at the back of throttle body to EVAP valve ( short rubber piece might have a crack, inspect well)
The EVAP hoses are all good, have not tested the FPR yet although the hose appears intact. Thanks!
 

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could you check short term fuel trim with obd scanner during mild acceleration up to boost level if it continously increases (until it hits the 25% limit)?
 

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Discussion Starter #9
could you check short term fuel trim with obd scanner during mild acceleration up to boost level if it continously increases (until it hits the 25% limit)?
I took a look at live data the other day, I was surprised to see both the fuel trims staying near 0%. I might need to drive it around more because the battery has been disconnected a couple times.
 

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What exactly are both fuel trims?
short term should get active after 30-90s, long term requires some driving to change. With battery disconnected long term should be 0, while short term is active after mentioned time period.
We just want to find out if engine gets too much fuel or air when boost level increases. If short term remains at around 0 and all of a sudden engine stalls it might another failure than leakage. Short term remains active up to approx. 75% load and should compensate for medium leakages.
 

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As you have already tried to run the engine without maf sensor it should exclude most of possible leakages.
I suspect something with fuel supply. Or electrical fault.
Usually you have constant 3 bar pressure difference by fuel pressure regulator. When it is not working correctly this pressure difference will decrease with higher boost level resulting in leaner mixture.
As the engine is running smooth in (critical) idle conditions I do not expect wrong valve timing. Or why should it only become effective with higher boost level?
 

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It wouldn't have anything to do with Boost per se but rather as the timing needs to be adv/retarded with the increased load what it expects to see isn't there and therefore it just conks out.. easy check. Pull valve cover and turn crank.
An engine can seem to run fine and idle perfect with the timing off a few degrees. Once the fuel and air requirements are advanced or retarded- thats when the issues present themselves.
If the fuel pressure hasn't been checked it'd be a good idea to do so. This is when a tech 2 comes in very handy.
 

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How do you check fuel pressure with tech2?
Valve timing is fixed on this engine, there is no advance and retard in valve timing nor in air/fuel requirement.
Only ignition timing can be advanced and retarded.
 

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Does it feel like the turbo gauge is accurate and you can't get on boost at all, or does it seem like it's lying and the car is pulling pretty hard at the top of the green?

Have you checked that the wastegate valve is working properly, and it's hooked up correclty? The engine should have a different reaction (Check Engine light and cut back to base boost), but I think it's worth looking at.
 

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Discussion Starter #16
Hi everyone, sorry for the delay, I haven't been able to get back to the car but my friend ran OBD2 live data and livestreamed it for me so I was able to see some very useful information.
The Short Term Fuel Trim trends negative until it hits -25% and then the Long Term Fuel Trim very slowly drops to -25% over about 10 to 20 minutes of normal, out-of-boost driving. It stays there the rest of the drive. That explains the P0172 code.

The MAP seems to be reading normally, correlating with MAF as long as the car is on and snapping back to 100 kPa as soon as it goes into boost and stalls out. It can only spend about a second in boost and the engine just turns off instantly. He also noticed that the hard starting issue was greatly reduced when the Fuel Pressure Regulator was disconnected, a second newer FPR was installed with no changes (hard starting as soon as the vacuum hose was reconnected). The idle is still very smooth with no misfires whatsoever but it still can't go into boost either way. I don't think a significant amount of fuel is coming through the FPR but I haven't looked at it myself.

I am convinced the turbo gauge is accurate, I've driven many Saabs and this one definitely isn't getting any power from boost. The wastegate feels pretty good, the BPC has all the hoses hooked up correctly (and it's been swapped, the original one had a damaged plug but was working). I've played with the throttle body and the motor seems good, it attempts to save itself from stalling out but it simply has no engine power after the engine air pressure goes above 0 psi or 100 kPa.
 

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Discussion Starter #17
What exactly are both fuel trims?
The STFT goes as negative as possible (-25%) and then the LTFT follows, slowly.

If all the (good) suggestions check out it will be a good idea to pull the valve cover and check timing.
Will do, it's not super difficult and at least can rule something out with any additional expenses.
 

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Do you think you might have a fuel delivery problem? Maybe the fuel pump is not delivering enough flow to keep up once the boost comes on? Or a filter is clogged and is causing a low flow rate out of the pump?

What happens to the fuel pressure when you go into boost?
 

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Discussion Starter #19
Do you think you might have a fuel delivery problem? Maybe the fuel pump is not delivering enough flow to keep up once the boost comes on? Or a filter is clogged and is causing a low flow rate out of the pump?

What happens to the fuel pressure when you go into boost?
Well I have a fuel pressure kit, I can bring that down the next time I go look at the car to see, but it does get a rich code so I'm pretty sure the engine is attempting to reduce the amount of fuel getting to the engine.
 

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Yes, the engine is running with too much fuel and therefore tries to reduce it by adaption.
Has battery been disconnected after other fuel pressure regulator has been installed to reset adaption values?

there was another thread were there was suspicion that vacuum could/might pull fuel over EVAP tube. It would make sense in that way that in vacuum conditions you get much more fuel, adapt to -25..-50% and as soon as you enter boost area there is no more addtional fuel, but adaption still reduces fuel by 25...50%, which is too much, engine goes lean and stalls.
If long term adaption also applies during start (I am not 100% sure about that) better starting behavior with disconnected tube is also explainable: usually you would have 3 bar differential pressure, but with disconnected tube you will have 3.5....3,8 bar, resulting in square root (3,5/3) or square root (3,8/3) 8...12% more fuel which partyl compensates -25% long term adaption.

Proposal for further tests:
1. check fuel pressure (although they might be ok). engine running, tube disconnected, should read 3bar.
1b. check for residual pressure. engine stopped, turn ignition on, fuel pressure should jump to 3 bar, turn ignition off, fuel pressure should very slowly drop to minimum 2.2 bar within 20 minutes, if everything is ok it remains nearly constant within an hour. this could rule out dripping injectors.

2. disconnect EVAP, put a short rubber fuel tube on the throttle connector, plug the open end with a screw, fix the screw with clamp. Take care that the lose EVAP line does not interfere with the belt. disconnect battery for 60s to reset adaptions values. check driving again.

3.
check oscillating front O2 sensor again. In first post it was ok, but fuel trim were both?? around 0, later on both fuel trims -25, O2 sensor still oscillating or flat at 0,7..0,8V. (Although I do not see a direct connection between working and defect O2 sensor and boost/vacuum conditions). (Just in case: do not use any contact spray on the O2 sensor connector, it will destroy the sensor).
 
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