Horrible fuel economy after tuneup

SteveT · Post by **SteveT** » 27 Jul 2004, 13:55

I just gave my recently purchased '98 S70 GLT w/ 84000 miles a tuneup (plugs, cap, rotor, fuel filter) and I am still getting terrible fuel economy (about 10-12 MPG city, not really driving fast). However there are no other problems with the way the car is running; performance seems OK, no rough idle, engine fires up instantly, and no service engine lights or any others lighting up. The only thing that I can tell might be wrong (other than the crappy mileage) is that the exhaust seems to have a strong gasoline odor (it's not the gas tank because I don't smell it when the engine isn't running) indicating, I guess, that something is causing a rich mixture. Does anyone know what would be doing this, how to remedy it, and how bad for my engine, catalytic converter or whatever running it in this condition is? Thanks. Steve

kinetic · Post by **kinetic** » 31 Jul 2004, 13:04

96 850

I have a very similar issue- my plugs indicate a rich burn despite the TB and IAAC being cleaned, new cap&rotor, plugs, new MAF and new MAF. I only smell gas for a bit after its been run hot for awhile. and the engine doesn't turn over when its hot. Any ideas?

Post by **matthew1** » 31 Jul 2004, 14:22

You both should check for codes. The car can set codes without tripping a warning light.

SteveT · Post by **SteveT** » 31 Jul 2004, 19:34

After doing a little research I thought that my problem was most likely a vacuum leak (I haven't had the codes read since I had no CLE) and set about checking the rubber vacuum elbows. I started by removing the battery and tray and looking at the vacuum pump. I didn't notice any damaged lines, however I notice that there was a larger fitting on the pump which had one smaller line connected to it which was wide open...I looked around for a loose hose, none to be found and then for a plug, again none to be found. Does anybody know if this is by design...if this part of the vacuum pump is supposed to be open like this? Next I went to the elbow on the right side of the intake manifold (looking from the front). While trying to remove the elbow I broke the plastic hose inside the foam insulation :banghead: . Looking inside the engine I saw the end that had been broken under the space between the first and second pipes (from the left) of the intake manifold. How difficult is it to remove the intake manifold on this engine? Am I risking serious engine damage by running the car with this vacuum line disconnected? Any help that anyone can provide would be greatly appreciated.

potroast · Post by **potroast** » 31 Jul 2004, 22:50

FWIW, I also have an open connection on my pump. However I can't really confirm that it's not supposed to be there. I was experiencing 16mpg (horrible) and with some tweaking now have it up to 20mpg even with my now more-agressive driving. However, I'm still not happy, and am looking at what can be done to get it around 25mpg with the type of driving I do (agressive).

Kinda sad that my truck gets better mileage... That's not right!

If your exhaust smells rich, then I'd look at that... What octane gasoline are you running? For an N/A engine, you should be on 87. Running 91 is going to send unburnt fuel into the exhaust. Also, I would have your O2 sensor checked out. That could also cause a rich mixture.

Guest · Post by **Guest** » 01 Aug 2004, 09:18

I've run the car with both 87 and 91 and the rich smell was there in both cases.

potroast · Post by **potroast** » 01 Aug 2004, 13:52

possibly a fault O2 sensor, then.