Well what do you think of this then.. (archive)

Hi,

Thanks for your response to my O2 question on the Roadfly bulletin board. You sound fairly on top of things so I thought I'd try running my headache by you in a little more detail.

I bought the car (84 528e) in the spring and gave it an air filter along with a few other things. For approximately the month of November my daughter had my car while I worked on hers. I mention this in case the colder weather might be having an effect. When she returned it, it had this fuel efficiency problem.

While I had the car, I got 32+ mpg on a routine 600 mile trip. Actual verification matched OBC average within a tenth. Routine trip around here (~60 miles) produced about 31+ mpg--also confirmed with actual. Once I drove purely to see what I could get; I got 36.2 mpg.

When my daughter first returned the car, I got 27. I also confirmed this with actual on the 600 mile trip. Enough confirmations--I feel now that I can pretty much rely on what the OBC gives me. And past couple of days it's been down to 23+.

Also new since the car came back is a racy idle (~1250) when the car is fully warmed up.

Now here's the thing that's got me freaked. It's not the cost of fuel. My plugs are all showing a white on the electrodes that reads very lean to me. Years ago I was a motorcycle mechanic. I never saw plugs with electrodes quite like these bosch platinums but I would be very alarmed if I pulled plugs on a bike this white! And yet, with plug electrodes this white, I expect to see a fairly opaque exhaust pipe end but this is not the case. (although it certainly is not pitch carbon) I haven't done a compression test yet but the car seems to run fairly strong and smooth and still has a nice abrupt, thump-down "compression" stop when it is turned off.

I checked the following per Bentley:

OK throttle switch

?: temp sensor sort of within range (changed the soldered in resistor to 270 ohm, was 500+ ohm) except when totally warmed up reading about 200 ohm but engine may be warmer that warm spec given at 176 degree F.

OK: temp switch

OK: O2 sensor but not with Bently test as conclusive

OK: cold start system

OK: fuel pressure

Poor: ICV reads above range and amps don't change when turning screw

?: The idle speed control unit had a wire pulled out and taped back. It was a wire from the temp sensor. I hooked it back, got the proper reading, but there was no change in idle. Also could not check terminal 3 (per Bentley) described as engine speed because I didn't have a LED and am not smart enough to improvise on that.

So what do you think? I would appreciate hearing anything you had to say.

Thanks, Walt

Follow Ups:

[ Follow Ups ] [ 5-series (E28) Message Board ] [ Msg. Board FAQ ]

Questions, comments, or problems, please visit the Roadfly help desk.