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power loss at high air temperatures/altitude

2349 Views 9 Replies 6 Participants Last post by  rawill
Hello All,

I'm having some issues w/ my '95 9000 Aero I thought I might ask the forum:

Whenever its very warm 100F+ or when I'm driving at high altitude (8500 ft+) I lose power intermittently when the engine is under load. The power loss is abrupt and will make my head snap forward and doesn't feel like its good for either the engine or tranny. It feels like the engine is momentarily getting 'stuck', but there's no sound, ticking, or pinging of any kind. Otherwise at high temp/high altitude the car drives fine, engine temp is OK, no CEL etc. This issue is will disappear when I descend to a lower altitude or when the air temp drops.

I'm also have a warm start issue (which I think is related) - on warm days the car will stall on start-up or nearly stall, causing the RPMs to oscillate between 1500 and 500/near stall - I can remedy the situation by revving the engine and attempting to hold it at 3000 for 60 sec, after which it settles down and is good to go.

Other details: I'm using 91 octane fuel, spark plugs are new as is the DI, coolant is new, recent oil change. Previous owner replaced the fuel filter 1 year ago, reman'd throttle body 2 years ago, and fuel pump two years ago. I've recently had a JZW stage 1 tune but the problem is more or less the same before and after.

Right now my thinking is that the culprit is the fuel pump, non-return values, or pump relay.

Does the relay have any known air temp sensitivity?- I've noticed the central locking module does. If the fuel pump is gradually on its way out why does the car do just fine at 5000 ft under heavy acceleration when I'm presumably I'm using tonnes of fuel and the pump has to work hard to keep the pressure up but it dies on a easy hill climb at 8500 ft? I know the ECU will alter the fuel maps and timing based on ambient temp and pressure - does anyone out there have any experience how this might affect a weak fuel pump?

Does the MAP sensor on the 9000 fail at higher altitudes? I had one go on my 9-3 but it was more of a 'sudden' event.

This week I'll be checking the fuel pressure etc. I'd like to get this problem solved... getting stranded on Pikes Peak, CO this weekend kinda sucked...

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Should be good to 10,000 ft according to SAAB.

Where are you?

Sounds like you're hitting the overboost cut out.
I'm in Boulder Colorado - roughly 5300 ft. Nice to hear there's fellow saab'ers in Calgary (I grew up there and can't remember seeing many 9000s).

When it happens I'm not sure that I'm close to max boost - just before it 'balks' I'm at the start of the yellow zone. My 9K will boost to the end of the red zone w/ the JZW tune. I don't have a calibrated boost gauge so I don't have any exact numbers .... another weekend :)
The only component of the Trionic system that is admittedly subject to skewed outputs (due to differences in atmospheric pressure) is the MAP.

But the deviation is slight and the ECU can compensate.

On the other hand a common symptom of a failing CPS seems to be intolerance to high temperatures. And, the ECU cannot compensate for a temporarily lost crank position signal - the engine just shuts down until the pulse is re-established.

You might try searching "CPS" - there have been several recent discussions on this issue.
You might consider checking for stored trouble codes.
Ditto on the last two. An erratic crank position signal will trigger several stored codes.

You might also consider cleaning your MAP sensor, although it might be better to replace it.
Sounds like you're hitting the overboost cut out.
That was my initial thought too.

Something blocked on inlet or similar, causing the combustion charge to heat up.
But that does not make sense if it is happening before you get to the red zone.
Thought I might finish the story on this thread.

Both issues are now resolved.

For the warm-start my problem seemed to be a fuel pressure regulator that wasn't behaving as it should. The FPR varies the fuel pressure as a function intake manifold pressure. My theory here is that once warm the FPR was not responding properly to idle vacuum in the manifold - but once I got on the throttle it would work properly enough so that engine wouldn't be fuel starved and stall. This condition would only persist for a minute or so and then everything was back to normal. I could probably test the FPR's response to manifold pressure but an accurate vacuum/pressure pump wasn't available. Sufficed to say with a new FPR my problem is fixed.

The high altitude/high temp bucking issue was solved by swapping my existing fuel pump which was previously replaced by the PO with a highflow Walbro 255 lph unit. Upon removing the pump, I found that the PO's mechanic had installed a unit that wasn't an OE part - likely some cheap knock-off ;oops:. This may also explain why the sending unit's fuel level sensor never fully worked and looks slightly different from various pictures of it on the internet. The non-OE pump was obviously having issues keeping up with fueling demand or was intermittently failing when the ambient temperature was high.

So far I've driven my 9K hard on 100F days at altitude and had no issues.

Hope this info helps someone out there

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Like wise, glad it is all good,

2 years to solve the issue, but all is well that ends well ;ol;
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