Random no Start

[dragon850]

Recently developed random no start issue, happens cold or hot pretty much randomly. Cranks coughs does not start.
Things checked:
Swapped in different dmes, no change.
Checked fuel pressure at both rails, holds perfect pressure during no start. Pumps are getting 13v at idle.
Checked fusible links, the drivers side battery link on the negative cable is not there, the pass side link on hot cable looks in top shape.

When no start condition happens dmes throw code "100 Fault unknown output" error on both banks.

[dragon850]

Any input?

What ever it is it's affecting both bank at the same time, so not isolated to a single bank.

[koenig d]

Double check hidden fuse
low voltage from 1 battery can cause strange problems.

what device have you got for checking fuel pressure?

[dragon850]

Double check hidden fuse
low voltage from 1 battery can cause strange problems.

what device have you got for checking fuel pressure?

Which hidden fuse are you referring to? I have 1 fusible link on the pass side positive battery cable that looks good. Is there another fuse I don't know about?
Measured fuel pressure inline with fuel pressure gauge, both pumps prime and pressurize during non start as well as hold perfect pressure during the car running.

[koenig d]

image.jpgThere are 2 both in the boot/ trunk.
One of them powers the DWA just a guess no power to DWA and the alarm will stop the car from running

[dragon850]

<img src="https://www.bimmerforums.com/forum/attachment.php?attachmentid=607150"/>There are 2 both in the boot/ trunk.
One of them powers the DWA just a guess no power to DWA and the alarm will stop the car from running

I inspected 1 it was good (pass battery + terminal), the other one is eliminated on my car.

[dragon850]

After doing some reading I am starting to realize I looked in a wrong place for the second fuse (the one in the shrink tube), seems like both fuses are on the passenger side battery positive cables...
Will look again today.

[dragon850]

OK, so found BOTH fusible links, they are on Pass side red battery cables, one in the black box another in heat shrink wrap. Both are 80A fuses.
They looked OK, but the one in heat shrink was covered in battery acid oxidation so I will replace both for good measure.
Tested both crank sensors, both tested OK at 530ohms.
Started the car, it started perfectly fine...but like I said it's random.

[ChrisFuture8]

Hmmm. Something is not making good contact. You moved stuff and it started again. Trace back to the parts you've touched next time it doesn't start one component at a time...?
Have you run an Ohm meter across the fusible link with crud on it to check for resistance? Just thinking out loud.

[shogun]

Have you run an Ohm meter across the fusible link with crud on it to check for resistance? Just thinking out loud.

Also thinking out loud, do it, in many cases the cracks cannot be seen in the fusible link, as they are under the rivets.
One of my wrenching buddies had this problem years back, 850 was running perfect, then all of the sudden it did not start, then started again, and so on.
He installed many things new, even a new ignition switch, in the end it turned out, that he had only checked 1 fusible link and the other one had small cracks , difficult to see, and sometimes (maybe based on temperature) it still worked and sometimes not.

[dragon850]

I have ordered 2 aftermarket ANL type fuses with enclosures and will be replacing both for good measure. Will drill out the rivets off the OEM fuse. I was surprised that when I cut off the heat shrink wrap alot of oxidation powder fell out, it was all around the fuse and rivets. Will update this thread with the result.

[BMSman]

What is the normal procedure for replacing these fuses? Un-solder them and solder in new ones?

I would have expected problems cranking (starting) the engine if this fuse was bad but there was no mention of this.

I wonder if anyone has a diagram showing all the ground points on the car. After 25yrs or so it might be a good idea to clean and re-tighten all of these... something I'd like to do on my car.

[shogun]

I drill the rivets out and remove the old fusable link, for new one use bolt + nut and that will do. On the E32 one of the 2 fuses is anyway bolted on.
pics on my website http://twrite.org/shogunnew/data/electrical.html
there on the E32 fusible link A is 50A and feeds only DME loads for the e-box in engine bay, the fusible link B is 80A and feeds the rear power box under rear seat.


showing all the ground points on the car>>>>>see ETK, all are shown

[Hyper]

...ground points...

Could happen that way.
As an example, just yesterday I resolved a random no-crank (*) problem on another type vehicle.
Ground strap, engine to chassis, not bolted down tight following a wrench session.
Strap provides a high capacity return path for the starter, but also the alternator.
Note that the engine might zero-ohm to the chassis via other paths, but these won't support big amps.
Otherwise, it would drive perfectly.


* OP said random no-start

[dragon850]

Recieved 2 ANL style 80amp fuse boxes, replaced just one that use to be in black box so far, I drilled out the other fuse that use to hide under the shrink wrap but the anl box was clearly to big, so will go with something smaller. Progress so far:

Sent from my SM-G925T using Tapatalk

[ChrisFuture8]

Yes, they are big and heavy duty. I use them fuses for my stereo power setup (2).

[bruinbro]

This happened to me and it was a hairline crack in the fusible link that you had to use a magnifying glass to see.

[8eights]

The fuse in the shrink rap is usually the issue, Why not just test with bridge clips to see if the issue has gone? Have yet to see that fuse blown because of a short, only cracks from age/vibration, Did the same post with a replacement audio fuse holder some 10 years ago.

[dragon850]

OK, both fuses replaced with ANL style 80amp fuses and enclosures, overkill I know, but won't have to worry about this ever again.



Sent from my SM-G925T using Tapatalk

[dragon850]

Car starts every time so far, however it's still not perfect, once in a while starts lumpy on one bank then smooths out. I suspect maybe it's another issue.

[XAlt]

Car starts every time so far, however it's still not perfect, once in a while starts lumpy on one bank then smooths out. I suspect maybe it's another issue.

That's a vacuum leak if I've ever seen one

[dragon850]

That's a vacuum leak if I've ever seen one

Well funny you say that, just tested with smoke machine, 0 leaks.
Also it starts lumpy on 1 bank about 1 out of 5 starts.

Sent from my SM-G925T using Tapatalk

[XAlt]

Well funny you say that, just tested with smoke machine, 0 leaks.
Also it starts lumpy on 1 bank about 1 out of 5 starts.

Sent from my SM-G925T using Tapatalk

I guess it calls for unplugging one MAF connector and finding out which bank is the culprit.

Such a useful feature

[dragon850]

Yeah, I know which bank it is... but to figure out what is causing this random stumble on start up thats another story...

Sent from my SM-G925T using Tapatalk

[cartoonz]

Have you tried bypassing the fuel pumps with a pressurized external tank? I read somewhere how that's how the really smart people do it...lol