diagnosing a check engine light on an early 87 325is

[wakeboardr42393]

I have an 87 (2/87 to be exact) 325is. The "check engine" lamp came on today while driving home from work. What can cause this check engine light to come on? the stomp test does not seem to work on my car. how to i diagnose this? where do I start?


I drive it kind of hard sometimes. the light came on when i rev-matched before i downshifted (prior to acceleration). the rest of the way home i took it easy on the car because i'm not sure if it's safe to drive with the light on. The engine runs no different then it did before. It runs fine, has power, idles how it did before, etc.

I just did a thermostat replacement yesterday. My temperature gauge is a bit flickery. If i smack on the dash above the gauge, it jumps around slightly. After I did the thermostat replacement, the gauge seems to read hotter then it was before the replacement. since the replacement, it stays at about 3/4, and sometimes it starts jumping around a little. sometimes it stays in the beginning of the red zone, or somewhere between the middle and red zone, flickering a bit in and out of the red. if i smack the dash, it usually flicks to a cooler reading, but not all the time.

so I assume it's not actually overheating, but i could be wrong.

any info, suggestions, comments, etc? :) where do I start?

[wakeboardr42393]

holy crap- i just popped the hood to try to bleed the system and i found my coolant reservoir empty and coolant sprayed where the a/c condenser is. oh man. also i started it again after re-filling acoolant. the CEL is gone. could my thermostat be faulty?? I got it from a BMW dealer!

[mr.vang]

Buy my 173 DME and you can do the stomp test

[wakeboardr42393]

lol. no thanks.

i think i got the overheating problem under control. idk what was causing it honestly. but i did a bunch of things and now it seems to be cooling at least ok. the top hose is still much hotter than the bottom hose. but i'm not sure if that whole feeling the hoses thing is 100% straightforward. or even is real evidence of anything.

I disconnected the battery and did some messing around then re-installed. after driving around kind of hard again, the check engine light came back on ( was off after battery was disconnected and for about 20 mins of driving. ) but the engine did not seem to overheat as it did before.

any ideas what this check engine light could be? i don't even know what triggers this thing on these cars.

[wakeboardr42393]

Overheating problem fixed.

Well, the check engine light is intermittent at this point. it seems to come on at or near WOT. It then stays on for maybe a day or so before shutting off again. The thing is, It's not consistent. sometimes it does not come on at all when at or near WOT.

could the o2 sensor cause this? or TPS?

The o2 sensor looks very old and the body is splitting. but i read somewhere that the E30 does not use o2 sensor at WOT anyways?

I am going to buy a new o2 sensor just because it seems like it needs a new one. it could be the original from what i can tell.

could insufficient fuel pressure cause this CEL as well?

[jalopi]

does it run fine at WOT? all you've said is that the cel comes on when you do it.

[jlevie]

If the CEL is coming on when the throttle is more than 60% open (when the WOT switch in the TPS turns on), the O2 sensor won't be a cause. When at WOT the DME ignores O2 sensor data. Since the CEL has been on, there will be stored codes in the DME as to the cause. But with a 153 DME you have to use a BMW diag system to retrieve them.

Personally, I'd replace the 153 with a 173 (or later) partly to get better idle control and partly to avoid having to use a diag system to retrieve any fault codes.

[wakeboardr42393]

the engine runs completely fine at all throttle positions and engine speeds.

So with my DME, i will have to go to a dealer or specialty shop to retrieve codes? are there any scan tools i can buy for home for under a few hundred?

is the DME swap as simple as unplug the old, plug in the new?

[jlevie]

I don't know of any easily obtained inexpensive diag tools that will work on this DME. A dealer or a well equipped BMW indie are about the only choices.

[bmwstudent]

Yes the dme is as simple as unplug and plug