9-5 Aero poor fuel economy

[rpiereck]

I am getting crappy fuel mileage on this car. It has been on a steady decline recently, but now it's down to SUV mileage.

I am getting 15-17 mpg on a daily basis.

The car is a 2000 9-5 Aero Wagon with an automatic gearbox. Before the fuel mileage went to poop I was getting 24-26 mpg daily driving, which was a mix of urban and rural, with some highway thrown in. Used to be that if I drove at fast Autobahn speeds I'd get 18 mpg, now I am afraid of even trying.

Knowns: Idle is good. Oil change is due (I hope to do it no later than next Tuesday, I am short on free time). Transmission oil hasn't been changed in almost 50,000 km. Air filter is a few months old. Tires are properly inflated (Michelin Pilot Super Sport Z-rated 225/45-17).

Unknowns: Vacuum leaks? Spark plugs? Bad fuel? O2 sensor? Coolant temperature sensor?

Other possibles: My boost controller is starting to do the famous Saab honking sound when the boost starts, could this affect fuel mileage? A few days back I had a CEL and the engine warning sign illuminated. I was hoping to plug in my OBD reader and get the codes, but by the time I got home the code was cleared, CEL and engine light were off.

With fuel mileage this bad I might as well sell this car and but my a 9-7x Aero!

[Tom]

Funny about the codes. Even though the CEL went out the codes should still be in the memory. The plugs are easy to check. I got improved mileage when I changed the plugs after about 60,000 km even though they appeared to be in reasonable shape with a good gap.

[rpiereck]

YEah, plugs are cheap and easy to change. I can't imagine leaving them in there for as long as the manufacturer recommends (200,000 miles???)

[Burnsside42]

YEah, plugs are cheap and easy to change. I can't imagine leaving them in there for as long as the manufacturer recommends (200,000 miles???)

Saab actually says either 30K or 60K based on the plugs and your model 9-5 - 9-3 SS are 100K - but 60K is better.

Basics First -
Check all vac lines for condition - even a dry rotted line can cause issues (Replace as many as you can)
Replace any suspicious parts - like your By Pass Control Valve (Hooter Valve)
New correct Spark Plugs
New Fuel Filter
Clean Throttle Body
Clean Air Filter
Tire Pressure - 36 all (I tend to run 38 front and 36 rear)
Fresh Trans Fluid! A simple Drain and Fill Will improve performance.

Disconnect the battery for a few minutes and reconnect to perform Swedish Tune Up

Do you ever clear your SID when you get gas? It's a good habbit to do this every few tanks of gas - otherwise your SID MPG will be way off and it will effect your DTE value.

[rpiereck]

I clear the SID every fill up. As far as the ECU reset, I heard remove fuse #17 for ten minutes will do it, correct?

[Burnsside42]

FYI - in our late 2001 Auto Wagon - we averaged 18/19 daily on mixed driving. Highway it averaged anywhere from 24-27mpg

Our last 9-5 wagon was an 03' with the 5 speed auto - that was getting 19/20 daily and pushing near 30 highway at times. Otherwise 26-29mpg highway was common.

It's a wagon and it's automatic - not a whole lot in it's favor unless it's just cruising long distance without slowing.

[nordwulf]

Fuel mileage has been consistent between my 2005 9-5 Aero and 2004 9-5 Arc with the 2.3T engines. Looks like the B235E in the Arc is tuned for economy compared to the B235R in the Aero, even though they are basically the same engines.

2005 9-5 Aero - avg 25.6 mpg - best 30.5 mpg
2005 9-5 Aero - avg 26.6 mpg - best 30.9 mpg
2004 9-5 Arc - avg 28.7 mpg - best 36.9 mpg

This is all mixed town / highway and 55 mph roads. I don't spend any time in stop-and-go traffic. I have been recording all fill-ups for a few years now and it it's interesting to have these records and see if there are any changes in fuel economy.

[saab95er]

Due you ever see puffs of black smoke from tail? Have you did the infamous pan drop sump cleanup? Did you verify fuel pressure and pull vac line from regulator to see if diaphragm has ruptured? Puffs of black smoke can be leaky injectors, the piss instead of spray. Sump drop...clogged screen can increase fuel comsumption since motor has limited oil to cool cylinders. Vac line is obvious...fuel drips equal bad regulator. Hope this helps.

[saab95er]

Oh and by the way...CITY type driving is murder, especially if heavy footed. I creampuff at stop and go traffic and never push boost hard. I get 21 easy about town. Give it a shot. Also the black puffs can be caused by water logged filter for intake. Less air, with metered fuel and load causes black smoke.

[rpiereck]

Well, I have had a steady decrease of fuel mileage, and I knew that moving to an urban area would lower my gas mileage, but not like this. After my first month in the new home I averaged about 17-19 mpg (from 22-24 mpg before). Now like I said it's down to 15-17 mpg. Just more urban driving (and it's really not that much) shouldn't acciunt for such poor mileage. Next week I'll have more time to take an in depth look at the car, I hope to find some fix for this.