Diagnosis help...

[MaddMatt]

The patient is a 1992 E36 4door 5speed with ~150K miles. Just bought it a month ago.

The symptoms are lousy fuel mileage (~20-22mpg).

What's new: spark plugs (NGK), air filter, fresh oil change, fresh transmission fluid (Redline), fresh diff fluid (also Redline) and a new O2 sensor.

Before I did any of that, we got ~20mpg. After I changed all that, we're still getting in the 20ish mpg range. Am I crazy to think it should be getting 25-27ish? It's really no better than the F250 Powerstroke I had (19.5mpg every time). I certainly don't expect the 34-35 I get with my Civic, but 20?!!??

In addition, I seem to be getting an intermittent check engine light. Oddly, the light seems to come on when I turn the *headlights* on. It goes out 2-3 minutes later.


Thoughts?

[RED328is]

Dude, i do alot of city driving and I only get like 22-23mpg myself.

[flyfishvt]

Is it a check engine light or is it the OBC that is giving you an error message?

[M52 Nick]

Could have LSD..

[FauxFox]

i get 20 too =/

bmw's are fuel hungry in the city.

but on the highway they get great gas mileage for a 6 cyl.

[MaddMatt]

OBC = DOA. It was busted when we got the car. The "check engine" light is on. Occasionally.

20-22 might be OK around town, but this is mostly seeing highway use. Some stop-and-go, but I'd estimate 75% highway.

[TCarlisle]

Are you in an auto or manual tranny? If you are in an auto, your mileage sounds about right.

[ross1]

The CE light coming on with headlights could be low voltage. A failing voltage regulator? The computers act up under low voltage and perhaps this is effecting your engine management. Easy enough to check.

[BMWMPow3r]

Get the bently manual. it will show how to pull the codes yourself and it will show you what each mean. It will pay for itself.

these cars get best mileage around 60-80 mph. that is low for a manual. I can get up to 27-30mpg on the highway, and the motor has over 200k with bad compression in one cylinder.

You more than likely have some codes saved, and that will for sure lead you in the right direction, instead of just throwing money at the car for parts it doesn't need. diagnose it with the bently. Its really easy to pull the codes yourself.

Are you sure its the check engine light and not the check light, they are the same color you know....

[MaddMatt]

Q:

Are you in an auto or manual tranny?

A:
The patient is a 1992 E36 4door 5speed


Are you sure its the check engine light and not the check light,

Now that you mention it, I think it's the "check" light. WTF is that? I jsut assumed it was the "check engine" light.

Sounds like I need a Bently manual. Where can I get one of these?

[BMWMPow3r]

internet, google it. You may still have codes saved that can lead you in the right direction.

the check light is just for ecternal lighting bulb burned out, low coolant, etc..

[RED328is]

You can get a bentley manual here -->Bentley Manual<-- (http://rapidshare.com/files/220869644/BentleyBMW-E36ServiceManual.pdf) (Click it)

[MaddMatt]

OK, I'm back.

Since last time, I've fixed a gas leak on the return line. I've added a chip and an intake. Mileage is still a LOUSY 20mpg in combined hwy/city.

A new symptom has come up. There's a miss, most notable when it's cold.

MAF? Coilpack? Injector? All of the above?

This thing just flat out does not seem to have much in the way of hp right now. Somethign isn;t right. I have taken neither to the strip, but I'm positive my 08 Si will absolutely slaughter it (I do a bunch of motorsports stuff, so I have a decent feel for that).

[bimmerfeel]

I'd bet coil packs. miss when it's cold=moisture. your grounding out the spark..changed mine the day I bought it. she's getting 28.3 mpg @ 80mph. 26 combined around town, and its a slush-box that I row. most of the electrical is going to start acting up, sooner or later. have a few relays on hand. the rubber is going to start checking out one piece at a time. start changing it out now. make sure the DME doen't get flooded. use the search. wiring at the trunk will short out...fix it, use the search. the window slides will be breaking right about now. easy, cheap fix, but it usually screws up the door panel attachments. just be ready for that. OBC can generally be resurrected(at least to some degree) see search. the weird acceleration feeling (almost like its stepping up) is because you have no knock sensors; DME slightly retards the timing under most HARD acceleration. this year also has no VANOS.

[MaddMatt]

I would LOVE to get anywhere close to 28mpg. I just filled it up and calculated 20.8 in combined city/hwy. That seems quite low for a 2.5L engine with a manual.

92s only have the 1 O2 sensor just before the cat, right?

What's your favorite place to get coilpacks? A few people are selling them on ebay for ~$150/set of 6. Seems reasonable.