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Discussion Starter · #1 ·
I'm still trying to figure out why my car guzzles almost as much as the Porsche, and blackens the exhaust tip in no time. I assume it's running rich, so I'm trying to understand what might cause this.

I'm not getting any Check Engine or other fault messages.

A new coolant temp sensor was installed not too long ago. We switched the spark plugs to copper type with no change.

1.0Can the intake temp sensor, or the O2 sensors cause a rich running condition?

2. Or could it be that a cylinder doesn't fire properly or skips intermittently, leaving unburnt fuel go through the exhaust system?

3. Somebody told me the MAF has to be installed a certain way - anybody have a picture of the correct installation? (I am skeptical this could be a cause, since I read that a faulty MAF causes a lean condition.)

4. What else could it be?
 

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Maybe it would be worthwhile to have the camshafts timing checked.If that is off even a small amount it can make a big difference in running and efficiency. Also you could have the timing chain tensioner checked to make sure it isn't too extended and is functioning correctly.
If you find that the chain has stretched excessively, then you should have oil pressure checked.
 

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I'm still trying to figure out why my car guzzles almost as much as the Porsche, and blackens the exhaust tip in no time. I assume it's running rich, so I'm trying to understand what might cause this.

I'm not getting any Check Engine or other fault messages.

A new coolant temp sensor was installed not too long ago. We switched the spark plugs to copper type with no change.

1.0Can the intake temp sensor, or the O2 sensors cause a rich running condition? Absolutely! The engine runs richer when cold, lets not forget the thermostat.

2. Or could it be that a cylinder doesn't fire properly or skips intermittently, leaving unburnt fuel go through the exhaust system?
Erraticness in ignition will hit the MPG hard. and , there should be a resulting CEL and code.

3. Somebody told me the MAF has to be installed a certain way - anybody have a picture of the correct installation? (I am skeptical this could be a cause, since I read that a faulty MAF causes a lean condition.)

4. What else could it be?
Wish I knew..;oops:
Another thing to check is the exhaust, when clogged, things suffer.
Start time should be 2 to 4 seconds
Cold to warm time should be 2 to 4 minutes:cheesy:
Check your ECU.
 

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Discussion Starter · #4 · (Edited)
Maybe it would be worthwhile to have the camshafts timing checked.If that is off even a small amount it can make a big difference in running and efficiency. Also you could have the timing chain tensioner checked to make sure it isn't too extended and is functioning correctly.
If you find that the chain has stretched excessively, then you should have oil pressure checked.
I just recently had the main and rod bearings replaced. I would think that they had to open the front of the engine and check that things are set-up properly - no?


Thermostat had been replaced with the corresponding temp sensor shortly before I got the car.

Another thing to check is the exhaust, when clogged, things suffer.
How do I check this? The car has been mainly used for short distances in the past. 48k miles in 10 years.

(Edit for clarification: by the previous owner, not me! I drive mixed 60% hiway/freeway, the rest in suburban traffic. It had no trouble passing the smog test in December.)

Start time should be 2 to 4 seconds
Cold to warm time should be 2 to 4 minutes:cheesy:
That sounds about right.

Check your ECU.
How do you check this?
 

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The car has been mainly used for short distances in the past. 48k miles in 10 years.
You probobly just answered your question.... The short trips do not allow the engine to properly warm and get into closed loop. My wife has a short jaunt to work (~1.5 miles). She was complaining shortly after she started driving the vert because I was averaging 26mpg in my 900s and 22-24 in my stg3 (at the time) 9-3 with mixed driving. She was getting a wopping 14mpg. We switched for a week and my 9-3 dropped to about 16mpg and the vert was in the 20's. She started making a longer loop on mornings she had some time and mileage actually went up to around 19......... Her lead foot doesn't help either:cheesy:.
 

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Discussion Starter · #6 ·
You probobly just answered your question.... The short trips do not allow the engine to properly warm and get into closed loop. My wife has a short jaunt to work (~1.5 miles). She was complaining shortly after she started driving the vert because I was averaging 26mpg in my 900s and 22-24 in my stg3 (at the time) 9-3 with mixed driving. She was getting a wopping 14mpg. We switched for a week and my 9-3 dropped to about 16mpg and the vert was in the 20's. She started making a longer loop on mornings she had some time and mileage actually went up to around 19......... Her lead foot doesn't help either:cheesy:.
I no longer use it as the previous owner. I drive about 60% freeway and get 21 mpg, plus the tail pipe turns black within a day.

Short of an Italian tune-up (which can't legally done in the US because of the speed limits), what causes the engine to run rich even when warm and not at full throttle?
 

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Sorry, I didn't read close enough...
By coolant temp sensor I assume you are speaking to the EFI coolant sensor under the intake runner on the back side of the head? If not, replace that one. Next would be o2's which could on their way out but not to the point of throwing a code yet... Fuel pressure regulator? How do the plugs read? You can always get an o2 bung welded in for a wideband hook up and get a dyno done with data logging through the obd2. That will at least let you know where your fuel maps are.
Others can correct me, but Saab's seem to run rich fuel maps. My tips have always been black on them. Even before my tunes I was in the low 12's AFR. With my previous tune and current on the b234r I'm around 11.5:1 when warm and hard running. I still average low 20's with mixed and 30's on the highway.
 

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Bypass valve

I dont know if 9-3's have these, but 900's have a bypass valve that blows air into the manifold upstream of one of the oxygen sensors for cold starting, and if it doesnt close after the engine warms up, the engine runs EXTREMELY rich, to the point that fuel mileage goes down about 5mpg. The car will also blow about 5x the legal level of NOX.
 

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I dont know if 9-3's have these, but 900's have a bypass valve that blows air into the manifold upstream of one of the oxygen sensors for cold starting, and if it doesnt close after the engine warms up, the engine runs EXTREMELY rich, to the point that fuel mileage goes down about 5mpg. The car will also blow about 5x the legal level of NOX.
Where is this valve located? I'm very familiar with the 4 cylinder engines and I don't know what this valve is.

John
 

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I had forgotten that this engine did have a lubrication problem in its history. That is a possible cause for a stretched timing chain. I don't think you can assume that the repair persons checked for a stretched chain when they replaced the bearings. I suggest you ask them. Anyhow, I think checking the chain tensioner isn't difficult or expensive if you have it done for you, and this will tell you if the chain is stretched.
Whether or not the chain is stretched, I suggest checking valve timing.
 

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I am not sure...my mechanic had to replace it as the car wouldn't pass smog - not even close on the NOX...the part cost $65. I will ask him tomorrow and let you know. It is part of the cold starting system though, if that helps.
 

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I am not sure...my mechanic had to replace it as the car wouldn't pass smog - not even close on the NOX...the part cost $65. I will ask him tomorrow and let you know. It is part of the cold starting system though, if that helps.
No, it doesn't help. The only "cold starting system" that I am aware of is that it feeds more fuel through the injectors when it's cold. It's the fuel injected equivalent of a choke on a carburetor. This is a four cylinder, turbocharged Saab we're talking about, right?

Another thing that sounds strange is that excessive NOX is usually caused by lean running since NOX is formed by high combustion temperatures. Running rich causes low combustion temps.

There is a bypass valve that circulates compressed air from the turbo back to the turbo's intake when the throttle slams shut. However, this does not change the fuel mixture and is used during normal operation.

John
 

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You drive 60% freeway which means that you drive 40% stop and go and you get 21 mpg. If you do the math, that really isn't all that bad.
 

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The simplest thing that can cause the engine to run rich some of the time, and lean at other times is a dried out and/or broken vacuum line between the throttle body and the fuel pressure regulator.

For everything to work right, the FPR pressure has to follow the manifold pressure. Or, put another way, the fuel pressure has to hold at a steady level above the pressure in the manifold.

When running on vacuum in the intake, the vacuum line to the FPR lowers the absolute fuel pressure, when running on boost, it raises it.

That vacuum line is largely hidden by other things, and also exposed to a lot of heat. On some cars, it ends up looking like this:



What you see here, is the side of the hose which faced down, toward the engine, and is cracked along a length of a couple inches. Not visible unless you move the hose around or disconnect and pull it out).

When that line breaks, the engine will run rich when there is vacuum in the intake, and lean when on boost. The ecu can compensate for this partly, with the help of a good front O2 sensor, but at some point the leak gets too bigm and the engine starts running rich or lean, depending on the conditions.
 

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Discussion Starter · #16 ·
Thanks, guys! Keep the ideas coming, but please describe where to look for these items in the engine compartment. I'm not that familiar with the 9-3, yet.

You drive 60% freeway which means that you drive 40% stop and go and you get 21 mpg. If you do the math, that really isn't all that bad.
I'm not sure how your math works. Here is mine:

The 2001 brochure lists the HOT with automatic as 21/28 mpg.

If I do 40% at 21, and 60% at 28, then I should be around 25.2 mpg. This is close to the 24 mpg other owners said they were getting with similar cars.
 

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It's not my math, it's what you posted and 21 isn't all that bad, but it's not great and I don't have an auto. The manual means nothing as your car is used, and do a google search as to how they come up with these numbers. My viggen gets around 22 but it's modified. How do the plugs look and what kind are you using; How old is the MAF and have you cleaned it; have you checked each and every vacuum hose; what about the air/fuel filter, etc??
Why were the rod bearings changed, sludge, if so then maybe all the sludge isn't gone? Does your mechanic have a tech 2, if so have him hook it up, drive the car and look at fuel trims, etc.
I also drive a porsche, and your car gets much better gas milage than my porsche does.:confused:
The FPR is located on the right hand side of the fuel rail when looking from the front. It is on the end and under the fuel rail and has a very small vacuum hose coming off of it which attaches to the TB. As PMI stated, if this is off or cracked then mixture will be way off.
Do you have a cel or have had one?
Good luck
 

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Discussion Starter · #18 ·
It's not my math, it's what you posted and 21 isn't all that bad, but it's not great and I don't have an auto. The manual means nothing as your car is used, and do a google search as to how they come up with these numbers. My viggen gets around 22 but it's modified.
For the record: In 2001, Viggen was rated 20/31 mpg vs. 21/28 for my model.

How do the plugs look and what kind are you using;
Plugs are brand new copper types, as recommended by the guys on saabnet. They replaced the platinum ones, which also looked perfect. No difference between the two in how the engine feels or drinks.

How old is the MAF and have you cleaned it;
No, nothing done to the MAF, yet. I left it alone because I read that when it falis, the engine goes lean - the opposite of what I believe my engine does.

Someone also told me to check the direction of the arrow on the MAF, but I can't recall which direction the arrow should point.

have you checked each and every vacuum hose; what about the air/fuel filter, etc??
Air filter was just replaced before I got the car; how do I determine, if a fuel fiter is good?

Car has 51k miles on it now.

Why were the rod bearings changed, sludge, if so then maybe all the sludge isn't gone?
#4 bearing was worn unevenly (one sided). There was not much sludge, but a few random metal shavings in the oil pan.

Does your mechanic have a tech 2, if so have him hook it up, drive the car and look at fuel trims, etc.
The mechanic I'm normally using doesn't have the tech 2. I have not talked to him about fuel consumption, yet. I could try somewhere else.

I also drive a porsche, and your car gets much better gas milage than my porsche does.:confused:
What kind is yours? Any engine mods?

The FPR is located on the right hand side of the fuel rail when looking from the front. It is on the end and under the fuel rail and has a very small vacuum hose coming off of it which attaches to the TB. As PMI stated, if this is off or cracked then mixture will be way off.
That's the kind of information I'm looking for! This gives me something specific to look at and rule out. And your description will help me locate it easily. Thanks!

Do you have a cel or have had one?
No. Never seen a CEL since I own the car.
 

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The FPR is located on the right hand side of the fuel rail when looking from the front. It is on the end and under the fuel rail and has a very small vacuum hose coming off of it which attaches to the TB. As PMI stated, if this is off or cracked then mixture will be way off....


Should look something like this, not identical, b/c this pic is taken on the NG900, not 9-3. Pic is taken standing at the left front wheel, looking at the side of the engine.
 

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CEL light should be on

This is an emissions issue, and the malfunction causing it should be monitored. It could be your CEL is not working. Take it somewhere and have a code reader plugged in. You can also buy your own. Then take it from there.
 
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