We interrupt the re-capitation of Otto for this important message: I didn’t get far enough this week with the reassembly of Otto’s head to eke out a full column. Well, that’s not true: At this point in my journalist career, I could pound out 5,000 words about lint. But it seems silly to split the topic of head-assembly into two columns, when with another 45 minutes in the garage I could cover it in one and be done with it.
Instead, I used that 45 minutes to diagnose and repair the secondary air on my E39.
The 2003 E39 530i Sport that I bought cheaply during the dead of winter had been marooned for two months in one of my storage spaces out in Fitchburg. I’d driven it there back in April to retrieve the ’72 2002tii to take it on the Nor’East 02ers’ spring drive, but I found that the tii had an alternator issue, so I took the Euro 635CSi instead. That kicked off a chain of events resulting in my driving the Sixer to Sharkfest.
A few weeks later, I returned the Shark to Fitchburg, did a field repair of the tii’s alternator wiring, brought the tii home for a brief sort-out, and then drove it to the Vintage (you’ll read about both Sharkfest and the Vintage in upcoming Roundel magazine articles). Meanwhile, the E39 just sat in the garage in Fitchburg—which was ironic, since I pay good money for the Fitchburg spaces, and of all my cars, the E39 is behind only the Suburban on the list of the cars that don’t require pampered indoor protection.
In the meantime, I had the Z3 here at the house and was daily-driving it. There are few things as fine as having a convertible in springtime, so the absence of the E39 wasn’t exactly hardship. However, the E39 still wore the Massachusetts rejection sticker from when it had failed state inspection several months back.
The Check Engine Light (CEL) was lit when I bought the car. I’d hooked up an OBD-II code reader and pulled the codes. They were P0491 and P0492, indicative of the secondary air system not working. I cleared the codes and tried to sneak it through inspection before the CEL re-lit, but of course it failed anyway, because the secondary-air monitor showed up as “not ready.”
A rejection sticker gives you 90 days to fix the problem. After that, you risk getting stopped with an expired sticker, which is a moving violation that adds surcharge points to your insurance. I’d reached the end of my 90 days over a month ago. I had some driving I needed to do, for which the E39 was a more comfortable candidate than the Z3, so I had to get the inspection issue resolved. I drove the Z3 out to Fitchburg and swapped it with the E39.
Pumping “secondary air” into the exhaust is a technique that dates back to the 1960s, but since the adoption of OBD-II in 1996, most cars have secondary-air injection to help burn off hydrocarbons when the engine is cold. The system consists of a secondary-air pump (SAP), a check valve that enables and disables the air path into the exhaust manifold, a vacuum-control switch that turns the vacuum to the check valve on and off, a relay for the switch, and vacuum lines. Google “troubleshoot BMW secondary air” and you’ll find any number of good primers, troubleshooting guides, and videos.
The SAP is a big round cylinder nearly the size of a gallon of paint. On my Z3 and my M coupe, it is located up high on the right side of the engine compartment. The pumps on both cars are very audible as they run for about a minute after a cold start, then shut off.
On the E39, I wasn’t hearing the pump run at all, so I assumed that the problem was a dead pump. This is fairly common. I hopped on eBay and found that used pumps can be had for as little as $75 shipped, with a Monty Python-like “I’m not dead” guarantee. I nearly ordered one, as I was going out of town for a week and wanted it on my doorstep when I got home.
But then I hesitated.
In my first book, I talk a lot about a dynamic that pops up again and again that I refer to as the Rhythm of Repair: Do you methodically trouble-shoot a problem, find the root cause, and then order what you need, or do you roll the dice that a common solution you read about online (e.g., “I replaced the pump and the code went away”) will fix your problem without your having to do the legwork necessary to determine the root cause? It’s especially tempting to do this if performing a detailed diagnosis requires taking the car down; why lay it up and take it apart twice if the all-wise Internet tells you that the problem is nearly always the Gonkulator? (Or, for you Doctor Who fans, “It’s synaptic adhesion.” “No, it’s the chronostat.”)
However, reading the usual forums, I saw many posts that didn’t coalesce around the SAP. People reported bad pumps, yes—but also blown fuses, stuck check valves, bad relays, or simply rotted-out vacuum lines. A common troubleshooting technique is to simply wire the pump directly to the battery and see if it blows air. If it doesn’t, the pump is dead and must be replaced.
Unfortunately, on my car, the pump is not high on the right side of the engine like the pumps in my Z3 and M coupe; it’s up under the right front fender. So the car has to be jacked up and the fender liner has to be pulled out. So I didn’t order the secondary air pump; instead of jumping to a conclusion, I decided that I’d actually troubleshoot what was wrong.
Right call.
When I got back from my out-of-town trip, I walked through the troubleshooting procedure for the secondary air pump on the Bavarian Autosport blog (there are many, but this one is clear and complete). In order to test whether the pump is working, you need to verify that air is blowing out of it when the car is started cold. This means removing the hose that goes from the pump to the check valve. This hose is a plastic snap-lock hose just like the ones on the crankcase-ventilation valve (CVV), and unfortunately, just like the CVV hose, when I tried to remove it, the hose immediately snapped in two. But at least with it broken in half, the air flow out of it was immediately obvious.
So the pump was absolutely fine. I simply wasn’t hearing it run because it’s stuffed up under the front fender—also, for a car with 175,000 miles, it was surprisingly quiet. I ordered a replacement for the broken hose ($25), and in the meantime, I spliced it together by jamming a short section of brake-booster hose inside the broken halves and taping it up.
Following the Bavauto troubleshooting guide, I examined the check valve next. When I put a hand-suction pump (the kind I used to use to bleed brakes) on the check valve, the valve opened, so it appeared to be fine.
The next item was to examine the source of vacuum to the check valve. Uh-oh: When I started the engine cold, there wasn’t any vacuum—this wasn’t right! It likely meant trouble-shooting the vacuum switch, which appeared to be hidden up under the intake manifold. Yuck. Chasing problems in the myriad of little plastic objects tucked beneath the left side of the intake manifold is one of my least-favorite aspects of working on post-OBD-II BMWs.
But then I recalled a number of posts from folks saying that their secondary-air problems stemmed from deteriorated rubber vacuum lines. The check valve is connected via a small rubber line to a hard plastic line that runs around the back of the head. This in turn is connected to the vacuum switch. The check valve’s rubber line is plainly visible on the right side of the engine. When I inspected it, it crumbled in my hand. I replaced it.
.jpg)
The rubber line at the other end of the hard plastic line—the one that connects to the vacuum switch—is very difficult to see unless you pull the cover off the top of the engine, which is trivially held on by two 10-mm bolts. But even with the cover off, if you don’t know what you’re looking at—which I didn’t—it’s difficult to tell the SAP vacuum line from other black lines and mini-harnesses that run in the same location.
Of course, I was doing this at night in my driveway.
I have one of the $100 smoke-generating leak-testing machines sold on eBay, essentially a paint can with a heater and a compressed air-intake. You add medical-grade mineral oil, connect the heater to 12 volts, plug in a source of compressed air, and the unit outputs low-pressure smoke to a rubber hose that can be plugged into a vacuum line. When I plugged it into the rubber line connecting to the check valve, I didn’t even need to wait for the heater to begin generating smoke; I could hear air hissing out the back of the head. It only took a minute to find that the section of rubber line connecting the hard plastic line on the back of the head to the vacuum switch under the intake manifold had deteriorated so badly that it was completely severed!
Initially, I thought that I could splice the severed rubber line by clipping a one-inch section off the front part of the hard plastic line and using it as a stent—one is honor-bound to try questionable repairs like this when one writes under the name The Hack Mechanic—but, like the front rubber line, this line was so badly deteriorated that it crumbled when I tried to push the plastic stent into it.
I needed to replace it—but the end that connected to the vacuum switch was difficult to reach.
It was challenging to get my hands back there behind the head, but I managed to pull the deteriorated ends of the old rubber line from the hard plastic line and the vacuum switch under the intake manifold while losing only a minimum amount of skin, and replace the section of deteriorated rubber line with a new one. The photo below shows one piece of the original deteriorated hose (white arrow). Below it is the new hose I replaced it with, already connected to the vacuum switch beneath the intake manifold.
.jpg)
Then I cleared the codes, drove the car twenty miles, and verified that that the secondary-air monitor showed up as “ready” and that no new codes had been thrown. I had the E39 inspected—and approved—the next morning.
I was incredibly lucky that I got out of this so cheaply. I actually could’ve done it all for free; it was the act of verifying that the SAP was working that broke the $25 plastic hose. When the new hose arrives, I’ll install it the next time I’m in the neighborhood (the E39 could stand to have the valve-cover gasket replaced, as there is a minor oil leak on the right side of the engine).
I have to say that there is something incredibly restful about driving a car whose Check Engine light has finally been extinguished. And whose rejection sticker isn’t risking hundreds of dollars of insurance surcharges.
(Next week, back to re-capitating Otto. Or lint.)—Rob Siegel
Rob’s book Memoirs of a Hack Mechanic is available through Bentley Publishers, Amazon, and Bavarian Autosport—or you can get a personally inscribed copy through Rob’s website: www.robsiegel.com. His new book, The Hack Mechanic Guide to European Automotive Electrical Systems, can be pre-ordered from Bentley Publishers. Use the coupon code “BMWCCAELECTRIC” for 30% off list.
