Electrical Problem

[kena]

Particularly during colder weather40'ish versus 60'sh my 914 won't run smooth when I turn on the headlights or the rear blower for heat. Also the engine RPM's drop about 500rpm when the load is placed on the electrical system. Headlights on..rpm's drop...headlights off..rpm's increase. The car bucks and hesitates as if the throttle position sensor is malfunctioning. It improves a bit as the temp reaches the 180 mark. I believe the TPS is malfunctioning due to the voltage drop when the lights or heater comes on. Do I have an alternator problem(I recently replaced the voltage regulator) or is it possibly something else like a bad ground strap? The alternator seems to be working ok. My lights stay steady at idle unless the idle goes below 600rpm then they dim and the radio will shut down temporarily until the idle speed increases. What should I be looking for?

[Joe Ricard]

I would first eliminate all the easy and cheap stuff. every brown wire ends up connected to the chasis somewhere. clean them all. yes I would also go after the transmission ground strap. along with the connectors to the altenator. If you really feel the need each of the connections in your fuse block (one at a time of course).
If that don't fix it them you at least can eliminate more of what it is not. keep us posted.

[philinjax]

Replace the voltage regulator again. If that doesn't cure the problem, it is likely that the alternator just isn't putting out the voltage it should.

If your battery voltage, measured at the battery terminals, at 1000 rpm is less than about 12.5 volts, either your regulator or alternator is defective.

Phil

[Dave at Pelican Parts]

http://www.pelicanparts.com/techarticles/914_alternator_troubleshoot/914_alternator_troubleshoot.htm

[ack_tm]

kena, I have the same problem as you. Funny, cuz we also have the same water condensation in the trunk problem too...

I've tried replacing the alternator, no luck. I've tried different voltage regulators, no luck. I've tried cleaning the ground points, no luck.

We are looking at the FI system as the culprit. Possibly the MPS or Auxiliary Air Regulator. Both had a vaccuum leak. However, I've replaced the MPS with a good one and that hasn't helped, so next I'll try replacing the AAR and see if that helps.

ACK!

[pbanders]

OK, guys, some of you have seen my psycho web site with all that info on D-Jetronic. Why did I do it? Because I had the same idle problem that's described here and I wanted to fix it!!!

Note: the stuff below assumes your engine is in good mechanical condition (good compression, intake vacuum, and valves adjusted) and that your ignition is correct (right timing and dwell, plug gap, all parts in good condition and vacuum cells that don't leak, right part numbers, etc.).

On my car (YOURS MAY BE DIFFERENT), the cause of the problem was a rich idle mixture. I had thought (mistakenly, from my days of owning carbs) that you adjusted the idle mixture to attain a maximum rpm for a specific setting of the bleed screw - WRONG. Set the idle to the factory spec of about 2 to 2.5 % CO (that's for my 2.0L, it's different for other engines) when fully warmed up, and adjust the bleed screw with minimal electrical load (no lights, etc.) for 1000 rpm. That's it. Now I can turn on the lights, heater blower, fresh air blower, etc, and I only get about a 150 rpm drop. Not as good as my M3, which has an idle stablizer (damn thing stays stuck at 650 rpm no matter WHAT), but a sight better than dropping below 500 rpm and boggling along.

The way you can tell if you've gone too lean is to park near the top of a gentle, long grade, and start the car when cold. As you go down hill, lift off the throttle completely. If you get any sounds of popping (very easy to hear), you're too lean, go clockwise a click on the ECU knob and try again. BTW, believe it or not, this method is recommended by the Elfrink FI guide and it works.

Don't go randomly changing ANY FI component without having shown it to be faulty. Use my web page to diagnose the parts first before chucking them.

Brad Anders

[kena]

Brad I was sceptical about your comment that this problem of driveability(bucking when lights or heater blower were on) was most likely related to D-Jet/lean/rich mixtures. After reading your post I reset my ECU to the factory mark and reset the idle to @1,000rpm. Voila...most of the problem disappeared. I also repositioned my K&N filter which had slipped off the air box flange..ie. no filtering and I pulled the hoses on the AAR valve to make sure it was functioning properly..it was. I haven't been able to drive the car on a moist/wet night to see if the problem still exists..but so far this seems to have eliminated most of the problem. I thought that particularly on damp evenings due to wear on the tracks of my Throttle Position Sensor this condition could cause excessive arcing that may have been causing the bucking. By setting the ECU to factory mark I can smell that is is idling much richer than before. I did notice some bucking when the motor is still not warmed up completely when both headlights and heater blower are turned on but it is not as severe as before. Seems to me the more I learn about these cars from all you people out there the more I realize I need an AirFlow meter.
Hey Bowlsby...someone should bring one if they have it to our next breakfast meeting. I'll keep everyone posted on whatever I next discover.

[pbanders]

Hey, glad to hear my suggestions had some positive effect. BTW, you're not looking for an "Air Flow" meter, you're looking for an "Air/fuel" meter, or more properly termed, a gas analyzer. A lot of people have had success using the O2 sensor approach, but by design, it has a different response than you would want to have for a meter transducer.

My take on the mixture/idle/lights thing is that it is a combination of feedback effects with the ECU (puzzle for you FI guys out there - what is the feedback loop in this system? don't forget, it has no O2 sensor? extra points if you can identify two loops), and power production at idle. Wrong mixture = lower idle HP = more RPM effect due to alternator drag.

It's not a voltage thing at the ECU. I've carefully monitored the line 16 and 24 voltage and there's no significant effect in switching on the lights.