BMW 318ti, Just E36 Things – Breakdown and Cabin Filters

Ah damn, the reliable second car became slightly less than reliable.

To be fair, it was probably my own fault for leaving the car for a couple of weeks without driving it, outside, in all weather…

I needed to swing by the hardware store to grab some things, and had my choice of cars. Of course, I took the Tomcat for a spin (because after spending all that money, who wouldn’t?) and it performed flawlessly.

Upon returning home I realised I had forgotten the one thing I went there to buy

That could only mean one thing, I had to make another trip. Since it was a hot day, and the Tomcat lives outside now, the last trip was a hot one. This time, I chose to jump into the Compact instead.

It fired up straight away and settled immediately into its usual slightly rough idle. All seemed good. I set off down the road and within a few meters, it misfires. Just for a second, but it was there. It clears as quickly as it came on, and the car returned to driving normally. Pulling away from the next intersection I give it a boot full, and it is running like clockwork. Weird, maybe it just needs the plugs I bought a while back, fitted.

I get to the store, do my shopping and jump back in the car. I turn the key. The engine cranks, and cranks, and cranks.

I try a couple more times, you know, just in case it decides it wants to be nice. Nope, just cranks.

Occasionally I can get the engine to start, but it runs super rough and shuts off immediately. 1 in 20 tries, if I give it a boot full of throttle it will rev up, super rough and then stop dead.

Interestingly, the transmission warning light is on. I think nothing of this at the time though.

I pop the hood, wiggle some stuff, which makes no difference. I try unplugging the AFM, no change.

My wife is at the supermarket in the Honda, so I send her a text letting her know I appear to have broken down, and that I’m going to walk home and come back for the car later, once the store had closed.

Thankfully my wife was awesome enough to come find me on my walk home and gave me a lift.

Googling the fault came up with many many common issues; crank sensors, fuel pumps, etc etc. If it has it, it can break.

Later that evening, once the store had closed, we drove back and checked the car. Sure enough, on the first try, the engine started, and as long as I kept the revs up it would run, albeit rough.

After getting some heat into the engine, the roughness cleared and it would idle, so I wanted to try a lap around the carpark to see if it would make it home. It takes off in second gear, since the trans is in limp mode (warning light on) and proceeds to die on the other side of the carpark. Stopped dead mid turn, like the ignition had been cut.

It wouldn’t start again, just lots more cranking.

A (not so) quick phone call to the AA, and a technician was on the way. In the meantime, we did some window shopping, and my wife took a couple of photos of the car.

The BMW where it rolled to a stop, and the ever reliable Honda Fit lurking in the distance. The Compact is a decent looking little car; I quite like it. When it goes.

After about half an hour, the technician arrives in their tow truck. Sure enough, the car starts, misfires a couple of times and then idles like nothing happened. I give it a couple of laps of the carpark and it drives perfectly fine. I ask him to follow me home and we drive off in convoy.

The car acts perfectly on the drive home. Not so much as a stutter. I thank and wave off the towie.

I couldn’t be bothered with the car at the time, so it sat out on the street on the naughty step for the night.

The next day, after work, I pulled the car into the garage and had a look at what was going on. My leading theory based on the symptoms was a soggy DME (ECU).

It’s quite cool that with the removal of one 10mm bolt, you can set the bonnet into service mode, where the hinges kinda flip over and the bonnet opens vertical. The car is nose down in the photo, otherwise it would be straight up and down.

The DME is behind the battery, so that has to come out first. Once the battery is out, this cover is held in with those two round clips. You’re meant to pry the centers out and then remove them, but I just pulled the whole clip out by hand, in one go.

Removing this allows you access to the actual sealed cover, held in with a bunch of little screws

Once that cover is removed, it can be unhooked from the main loom. In this car, there are also a pair of relays attached to the inside of the cover. I left these attached and just set the cover aside.

The DME is sitting right on the bottom of the stack (with the trans controller above it). You can remove the DME connector by unclipping and lifting up on the silver locking tab, which will push one side of the connector away from the DME. Continue to gently rotate the connector, and remove the hook in the other end. This will allow you to grab the DME and just slide it forward and out of its bracket. It’s not held in with any screws, just friction. To actually remove the DME I had to turn it 90 degrees so it would slip past the fuse box.

The above images pinched from doing the same check on the M328i as I forgot to take any of the compact.

This left me with an empty space

Hmm, that black bracket looks damp. Oh damn, so does the underside of the DME. It’s soaked.

I removed all the screws in the bottom of the housing, bent back/broke off the tabs, and opened it up.

It was dry inside, but immediately I noticed the corrosion on the circuit board.

It wasn’t terrible, but there were a few patches of obvious corrosion. Thankfully no obvious damage to the traces or any components, but the water must’ve been shorting it out.

I gave both sides of the board a good scrub with contact cleaner and a toothbrush until I was confident the corrosion was cleared off. I then reassembled the DME ready to refit.

The water had to come from somewhere, so I needed to do some digging. E36 are known for blocking the cowl drains, but I could find very little information about these on the compact (as they have a different firewall/cowl set up to the other E36s).

These next steps are also, coincidentally, the steps to remove and replace the cabin filters.

I did this with the battery removed, and I’m not sure if you have the space with it installed or not.

The first step is to remove the little grate above the engine. This is the inlet for the fresh air. This plastic mesh has a series of (probably broken) clips along the top edge. Mine just pulled up, along with the rubber.

This will leave you with a metal tray, with a plastic insert.

To remove either, you need to remove the two screws in the tray, which hold the wiring loom to the bottom of it

The wiring loom can then be pulled forward off its clips.

There are now two screws on the firewall, one on either side, that need to be removed to free the tray

With them removed, the tray is just wedged into place. You can pull it forward and remove the plastic insert. This is a deflector to direct air and water to where it needs to be. It is held in place by the big tray, and by hooking over the metal edge at the top.

Now pull the tray completely out and marvel at the stupidly placed/designed cabin filters that have never been changed, and how disgusting they are. On this car, there are two curved panel filters, as opposed to some that had a pair of round filters, one either side of the blower motor.

Both of mine were PACKED solid with grime, and jet black. I don’t have spares on hand, so have removed them for the time being.

Now, if you look down into that cavity the blower motor is in you will see two rubber grommets on the front, down the bottom. One is in the RH corner, and the other is on the left but closer to the center. These are the two drains. Both of mine were 100% clear, and free flowing. Damn.

For further investigation, I removed the main cowling under the windscreen. On other E36s this covers the drains, but on this, it covers nothing but steel.

I marked the wiper placement, removed the caps over the nuts

And removed the wipers completely

Now the trim can come off. The LH side is held in with two plastic screws on the far left, and then a series of clips on the underside. The RH is just held with clips on the underside.

It was super manky under these

A real good cleaning, and I put it all back together again. No real obvious sources of water ingress, other than just so much dirt under the trims that maybe the water couldn’t drain away as it should’ve.

I feel like due to the design there is a perfect storm that can result in the DME getting drowned, no matter what. There is a drain in the front corner of the DME housing; just a small gap (red line) between the base and the dividing wall (black lines) that I guess is meant to allow any water that gets into the DME enclosure to drain next door and go out the cowl drains.

The problem is that if the car is leaning to the left, as it does when parked at the side of the road, any water would pool on the other side of the enclosure, where there is no drain. In theory, if it had rained hard overnight, with the car parked on the street, there could be water pooled there. Now, if you drove a very short distance (a couple of blocks) and then park nose up (as I did), there is the potential that water could run towards the back of the car and drown the DME, instead of running forward and down out the drain.

Without blocking the drain and potentially causing more issues, I can’t see any way to remedy it. It’s just a bad design. If the DME was raised up a couple of mm off the bottom, it would be fine.

It’s just something I will need to keep in mind. But if it happens again, at least I know what it is, and there is nothing actually wrong with the car, it’s just an E36 thing.