Philes’ Forum – Summer 2019

by NJ BMW CCA

By Vic Lucariello, Sr.

Hello Bimmerphiles! Before we get to the sputtering saga, I need to correct an error I made in my last column, which addressed M3/S14 cooling-system flushing. I transposed Photos 3 and 4, and a vast multitude of you emailed to excoriate me for the error, which I apologize for. Heck, Editor Faber even docked my pay!

For years, Joanne and I had an 86 325e 4-door which we dearly loved. Texas car bought from the original owner. It carried us on several round trips to Colorado, a trip to Boston, and another to South Carolina. All without missing a beat and while returning 30 miles per gallon on the highway. So, when it began “hiccupping” when hitting significant bumps, I was surprised. The hiccup devolved to a “sputtering”, and then to an occasional temporary no- crank situation when hot.

During the symptoms’ devolution, I checked out the electrical system numerous times, doing voltage-drop testing of the power supply and grounds. Due to the intermittent nature of the symptoms, they were never present when I did my testing, and as you might expect, I never found anything remotely problematic. The symptoms, including the hiccup and sputter, seemed electrical in nature, yet the battery and alternator tested good, and my voltage-drop testing never revealed the source of the problem. I had previously encountered batteries that tested good yet caused strange electrical symptoms, so I switched batteries with my M3. While changing batteries, I cleaned the battery posts and terminals, and removed and cleaned the engine-ground- strap connections and the battery-ground-strap connection in the luggage compartment. These connections are the first things to check in electrical troubleshooting. The problem persisted. As the symptoms began to appear more frequently, I even disconnected the alternator and drove the car, but the problem remained. In some cases, a failing alternator can cause strange electrical problems such as I was encountering. By the way, the newer the car model, the more likely this is.

Finally – and luckily – as I was pulling into my Mom’s driveway, the beloved old E30 sputtered, then quit. There seemed to be no electrical power in the car. “Ah-Hah”, I cried! With the car dead it should be easy to find the problem! Alas, by the time I broke out some test meters, which by now I was carrying with me, the car started fine and ran normally. WTF?

It was finally time to break out the BMW ETM, or Electrical Troubleshooting Manual, which has schematics for every electrical circuit on the car. The schematic shows a separate feed from the battery to the engine-control computer [DME in BMW-speak], but all other power other than the starter motor’s travels on a single wire from an underhood junction with the battery cable to the underhood fuse box.

HMMM…..

After disconnecting the battery in the luggage compartment, I first checked the fuse-box-power-supply [FBPS] wire’s connection at the underhood junction with the battery cable. The connection seemed clean and tight, but I disconnected it and cleaned it with a fine Scotch-Brite pad. Finding the other end of the FBPS wire is not so easy, so rather than major surgery, I tried the following.

To gain access to the FBPS connection to the fuse box, you would really need to disassemble it, but there is a little trick that sometimes suffices. First, remove relays K3, K4, K7 and K8. The relay identifications are indicated on the fuse-box cover. Doing this is greatly facilitated with a relay-pulling pliers. See Photo #1. An internet search for “Bosch Relay Pliers” will reveal several sources for this handy tool, which you shouldn’t work on BMWs without.

Once the relays are removed, Photo #2 shows the top end of the FBPS connection with a 4-mm hex bit installed in it.

Note that the hex bit is a ¼-inch drive! You don’t want to use anything larger for this. Trust me. You can also use a 4 -mm “Allen Wrench”. I tried both the hex bit and the Allen, and the hex bit is preferable. See if you can tighten the FBPS connection a bit. If not, loosen it slightly and then retighten. Repeat a couple times.

After I tried this on our beloved E30, I was not sure I had accomplished anything, so I connected a couple digital multimeters, one with max-min-record capability, to two wires in the under-dash harness that I felt would be good to monitor when the symptom recurred. One was the power supply to the ignition switch, fed by the FBPS wire, by the way. The other was the ignition switch “RUN” output. I thought this would capture an intermittent ignition-switch problem, which would be consistent with the symptoms.

Well, as you might expect, now that I was poised to capture the problem, it never recurred! So I have to conclude that my manipulation of the FBPS connection was the “Fix.” It’s probably a good idea to check your E30s FBPS connection whether it needs it or not. I know I checked my M3’s!

That’s all for now, bimmerphiles. See you next time.

Anyone wishing to contribute to Philes’ Forum can contact me at vic.sr@njbmwcca.org. I’m interested in comments, tech tips, repair /maintenance questions, repair horror stories, emissions inspection sagas, product evaluations, etc.

© 2019; V.M. Lucariello, P.E.