Randomly Dying.. Not Clue

[Midnight Sun]

A little background. I went on vacation over the weekend, I drove over 120miles to the airport on Friday and it ran perfectly. I parked it for 4 days, and it started fine last night and ran perfectly for about 80 miles.

Then, all of the sudden the tach drops to zero. I immediatly think "oh fuck, timing belt/head gasket/something horrible" Thankfully, I was right next to an offramp, so I get off. Completely shut it down and look around. No coolant, no horrible mechanical noises. Hey, it even starts right up again.

Odd part, I never lost any electrical, radio played, heater blew hot, power steering was fine, power brakes were good. It was just the engine that died.

So I keep driving, about 5 minutes go by, it does it again. Same procedure, this time I turn it off for a few minutes before restarting. I drive it again about 7 more miles to a rest stop. I let it sit for a good 15 minutes, thinking that it wont restart this time. I try to let the engine rest, because I dont have a clue.

Starts right up and cruises up to 75mph no problem. At this point it is 1:45am and I just wanna get home. I figure fuck it, I have another m20 that I can swap in, so lets just get home and go to bed. It dies again. I start feeling unsafe so I throw on the flashers, and bog it in 5th and only go 55. Ran fine.

I get home, and cant rev it out, it the exhaust makes a sort of pulsing noise, I am assuming it is starved for gas. I just cannot figure it out. I can bog it out from 1st and second just fine, but the instant i get it under load it cuts out horribly and almost dies.

This morning, starts perfectly, idles great, ran well to class, started after class. I putted threw town. Tapping red line, running through the gears.

I am totally lost.


I am thinking major ECU issue, or a fuel issue.

[RobertK]

If the problem seems like it's fuel related and tends to get worse after the car warms up then try checking the O2 sensor first.

[DarkWing6]

O2 sensr wouldn't cause it to die completely though, would it?

I had a somewhat similar problem and it turned out to be the main wiring harness for the engine. There was a bunch of corosion in the main connector below the throttle body. It is a somewhat common area to see corrostion, so I would check there too.

[James Crivellone]

O2 sensr wouldn't cause it to die completely though, would it?

I had a somewhat similar problem and it turned out to be the main wiring harness for the engine. There was a bunch of corosion in the main connector below the throttle body. It is a somewhat common area to see corrostion, so I would check there too.

only 88+ cars had that connection ;)

[RobertK]

O2 sensr wouldn't cause it to die completely though, would it?

I had a somewhat similar problem and it turned out to be the main wiring harness for the engine. There was a bunch of corosion in the main connector below the throttle body. It is a somewhat common area to see corrostion, so I would check there too.

If it's causing it to run to lean or rich it could bog or kill the engine.

[Mike325]

I have driven with no o2 and the engine ran kinda crappy, but did not want to die once.

But on my sister's civic, when the o2 was bad, it would not idle and it ran crappy most of the time. Do you have a check engine light?

[jlevie]

The tach dropping to zero suggests that the DME is freezing. That could be an indication or a bad DME, but is more commonly caused by a lack of power to the DME (low system voltage or a failing main relay/fuse).

[Midnight Sun]

The tach dropping to zero suggests that the DME is freezing. That could be an indication or a bad DME, but is more commonly caused by a lack of power to the DME (low system voltage or a failing main relay/fuse).

That is what I was told by a BMW tech. I am really hoping that is the case because I cant afford/dont feel like doing a bunch more work.

He also mentioned that relay's on Bimmer's have an odd tendency to go out sporadically instead of at once.

So, how do I tell if a relay is bad? Where is the best place to buy one?

[Midnight Sun]

Since the manual is useless... Which relay am I looking for

K?

[BDSax]

my car has a problem like that. but it will shut down then back on within a second. i changed the O2, all the fuel and ignition stuff and its still going on, so i gave up and decided to put a m50 in.

[Midnight Sun]

Since the manual is useless... Which relay am I looking for

K?

[stein]anyone... anyone[/stein]

[xLibelle]

if you have an electrical problem, like a soft supply, the first thing to go is the engine. check your battery and alt first. its easy since someone else does it for free. you can also hook a jump from another running car to test when you see problems while reving.

next is fuel supply. you can get a fuel pressure kit or build one for cheaper. there are lots of details on this and the usual fuel pressure at different rpms.... none of which i have with me to present to you now.

hmmm, the other thing is a vacuum leak. i cant imagine it give you this much trouble, but its worth checking. spray something like throttle body cleaner on the intake housings after the AFM up to the TB

[jhower08]

do you have an extra ecu? if so drive your car around untill it dies like this and keeps dying. then when it shuts off one of the times plug the other ecu in and see if it fixes it. this happens to me periodically and when it does i just quick reach in the glove box and plug the other ecu in and it runs fine. (yes i could just leave the other ecu in but id rather have the one with the chip in it and i dont feel like swapping the chip bc im doing a complete engine swap in a week or two)

[rcko]

mine turned out to be ECU... I am doing what jhover08 is doing also...

In the mean time I am looking for another DME since the "good"one thats starts reliably has a bad idle control circuit.

Used DMEs go from $60 - $150. no guarantess as to their condition tho. My first has a bad idle circuit control but at least the car runs and starts reliably. It replacement idles fine but has this intermitent non start.

Ck the relay first tho.

[euroe30]

i had the same problem. i replaced all of the fuel components (relay, pump, filter, lines,and some ignition parts too: cap, rotor, plugs wires and so on.... it was my air flow meter. good luck