eta burning oil and poor mileage

[sega01]

Hey everyone!

I have an '87 325-2 (base model eta coupe, but built in 1986 so I believe it has two fuel pumps) that's been treating me well for the most part. It idles stable, pulls really well, and feels great on the throttle.

However, I've been getting 23MPG at the very most even with mostly highway driving, I sometimes smell fuel (no idea how or why), the engine isn't perfectly smooth and will have an odd shake about every 3 seconds (barely affects driving, though, and it burns about a quart of oil ever 600 miles (mine you, I am using 0w-30 German Castrol).

It has 149k+ miles since it came with a bad odometer, as most do. I've driven it for about 7 of those, mostly on the highway.

Every since I've had it and could test, it's given me 19-23MPG no matter what conditions. The tires are good and pumped up. I've messed with different octane fuels from different stations. I've deleted/bypassed the ICV. The sparkplugs look fine (though maybe a bit whitish, I believe). I replaced the thermostat from a 75C to a 80C model recently. It's still a little slow heating up (6 minutes of driving, so maybe not) but always stays a touch over the before the mark before the middle (so I think that the thermostat to the dash is bad). I also don't have the MAP sensor in (but I live around 1k feet, so it's no big deal). I've also ran Seafoam through the crankcase, fuel tank, and intake manifold.

Any ideas of what things might be causing the problems? I haven't yet done a valve job as for all documentation says, the timing belt is 112k+ miles old and I'm worried that maybe it's slipped a tooth which would affect the valve settings and I'd need to redo them after the timing belt. I'll do the timing belt/water pump soon with a friend, but it shouldn't directly affect my mileage unless the timing is off.

Oh, I've also deleted the power steering and cut the belt to it and the A/C since I have a replacement A/C belt. Should be no strain on the engine there.

Let me know what you think.

Thanks so much,
Teran

[jlevie]

Whoa, 112k on the timing belt? Park the car until it is replaced as it could break at any moment.

There are a lot of possibilities for reduced mileage. The place to start given the mileage on the car, is to replace the O2 sensor as an aged sensor (useful life is not more than 100k) falsely reports a lean mixture. That causes the DME to increase fuel trim. Have a smoke test run on the intake to look for intake leaks as those will also bias fuel trim toward rich. Run the fuel system tests in the Bentley, check the cold start valve for leaking, and make sure that the time-temperature switch is good. Then replace the plugs, distributor rotor, cap, and ignition wires as misfire will reduce mileage. Also adjust the valves. If the engine has been running rich, or more importantly if the exhaust has been hydrocarbon rich for a good while, there is a reasonable chance of partial melting and plugging of the catalytic converter, which will adversely affect mileage.

An engine that is running rich will burn more oil, though there could be other problems that are causing excessive oil consumption. Compression (wet & dry) and leak down tests will tell a lot.