92 318i sedan - hissing while engine off for more than 24 hours

Hello all, New member here...

After owning a purple (Techno Violet I believe) 1997 M3 sedan many years ago, when I saw a 92 318i in need of ALOT of work, I decided to buy it as a winter car/daily, so I can put my Lincoln away.

After replacing the clutch, some body panels, and other odds and ends, Im having a major issue.

I drove the car last night, maybe about 60-70 miles total with no issues (other than a intermittent belt squeal from the alternator, which Im assuming is due to the bent mounting bracket.
I parked it in the driveway, and have not driven it since.

So fast forward to tonight... I went out for a few hours with my wife, and came home to a hissing/pumping/leaking type sound from the BMW. Upon further inspection, I noticed it was coming from under the intake manifold/injector rail area - also, I'm pretty sure I can hear the fuel pump running. When I unhooked the battery it went away. But after hooking the battery back up, the sound came back. I tried cycling the key - but that did nothing. The only way I've gotten it to stay off with the battery hooked up is pulling the fuel pump fuse.

I dont smell any gas, but I'm still afraid to start the car...

Anyone here have any ideas? Only thing I can think of is that the fuel pump relay is stuck closed, but the sound is much louder (and in the wrong spot - it sounds like the injectors are going too) for it to be *just* the pump, in my opinion.

I plan on removing one of the spark plugs tomorrow to see if the cylinders are flooded with gas or not.

Thanks, and sorry for the long winded post.

Welcome to the fest!

I'm surprised the battery was still up after all that time.

Good idea on pulling a plug to see if it's flooded. If it is, pull the other three, let it sit with the plugs out for a day. Then check your oil level. If it appears too high, or smells strongly of gasoline, the crankcase is probably flooded with fuel. You'll have to drain and refill with fresh oil, and it wouldn't be a bad idea to change the filter, too.

How to stop the pump from running....may be the fuel relay stuck. Pretty unusual but possible.

thats what im thinking (relay stuck) but why would the injectors be going too? are they tied into the fuel pump circuit in any way?

No, but if one were leaking, it would be getting full pressure since the fuel pressure regulator would be without vacuum and would react as though that were a wide open throttle condition, putting full pressure in the fuel rail.

The hissing may be something else entirely, too. First time I've heard of this malady.

the car does have 204,000 miles on it... so the relay being bad wouldn't surprise me.

Will update tomorrow

Pulled a plug this morning, and no gas in the cylinder. Tried to start it, and it started right up.

I checked the wiring going to the fuel pump relay socket, and one wire has melted/damaged insulation, and I can see bare wire.

Time to find a wiring diagram.

Sounds like you probably found the culprit. At any rate, here is an E36 electrical troubleshooting guide (downloads as a PDF) which you may find helpful.

E36 BMW Electrical Guide

Did she run hot?

I had a similar experience with a client's E36.

Loud hissing from right under the center of the intake manifold.
It didnt exhibit any other symptoms.

.. unfortunately.. it was a failing head gasket in this instance.

I think the blown head gasket idea is nullified because he can get the hissing to go away and return by disconnecting the battery and removing the fuel pump fuse.

understood..

Just speaking from experience.


Oh yeah... and lil' german gremlins.

Nope. And hissing sound is only when engine is off.

Also, it was making noise more than 24 hours after being last driven. Even made noise when I connected battery today.

Going to replace a chunk of the bad wire and see if that fixes it

Well.. Im glad its NOT the head gasket.

Originally Posted by 92_318i

When I unhooked the battery it went away. But after hooking the battery back up, the sound came back.

Originally Posted by 92_318i

Even made noise when I connected battery today.

Well if the hissing continued even after you disconnected the battery, you may have a blown head gasket. Whether or not disconnecting the battery and/or fuse makes the hissing go away makes all the difference in the world in terms of diagnosis.

Just to help narrow it down, you could try fully discharging the electrical system after disconnecting the battery by turning on the headlights. If the hissing continues after the battery has been disconnected and the electrical system has been discharged, there is no way it could be related to your fuel pump, since it would need electricity to pressurize the system. That's not to say that you shouldn't still fix your melted wires - absolutely do that.

That last statement was meant more as a "it's still doing it, so that rules out anything depressurizing.

It goes away completely when either the battery is disconnected, or the fuel pump fuse is pulled.

Pulling the fuel pump relat makes no difference.

Worse case scenario, I throw a switch on the pump fuse and switch off when I turn the car off.

To add some more info, the hissing I'm hear is deffinately the fuel circulating thru the rail, FPR, and back thru the return line. No leaks whatsoever.

Pump just won't turn off. I can actually feel the circulation on the regulator if I touch it

Will check the wiring guide when I get home later - OSU-Michigan game on now!

looks like the green/violet wire that controls the pump is shorted to ground to something... checking into it further in a little bit.

ok so I am updating this thread, in case anyone has a similar problem...

Apparently, when I bolted the trans back to the motor at 3am a few weeks ago (after replacing the clutch), I inadvertently caught the O2 sensor wire stuck between the engine & trans.

As I drove the car over the past few weeks, I'm guessing the insulation on those wires melted, shorted out, and caused all of my electrical issues.

the Heated O2 Sensor relay is tied to the fuel pump relay, and 2 wires coming off of the relay socket for the HO2S relay are melted/exposed, and one wire off of the fuel pump relay socket is melted/exposed (the one that goes to the HO2S relay).

Thank god I have a BSEE, otherwise I would be going nuts right now.

Time to cut/splice new wire for the O2 sensor, and start looking for the section of harness that comes out of the splice box and goes to the relay sockets.

Fun times. Glad you're on the road to recovery, hopefully.

Thanks. All is well now. Just have to Pick up bushings for that lower alternator mount