View Full Version : m50b25 random no start for an hour
Happened twice, months apart.
About 6 months after I got the e34, and on the very first hot day I felt it hard to start, like nothing happening for a sec after turning the key. It was strange but I drove it anyway ~5km, parked it at a shop and then it wouldn't start at all. Rang around and all too busy, walked around the commercial business district looking for auto electricians and all too busy to drive out to the car as well. So after a long walk back and playing around with relays or whatever it started fine.
I drove it home and retested it for days, every time it started fine. So eventually I forgot about it. Anyone experienced anything like it? I mean I've got to suspect anything from key switch to aftermarket immobiliser, auto trans switch, relays to the solenoid on the starter motor itself.
Today (not a hot day), about 2 months later I start the car normally and make a few stops and starts (fuel station, brothers house, moving my car from the driveway to let his wife out, and the start to get home again). None of these times it hesitated to start like it did the last time the issue happened. All fine, then after I'm home for ~30min I go to start the car again. Full dash and lights, display etc etc, but no attempt by the solenoid to operate or the motor to crank.
But here's the problem, again after 1 hr it starts working fine!
This time because I was home when it happened I got a multimeter on it, but being by myself I could only just touch the solenoid loosely and have the probe sit there, same for earth. When turning the key there was a brief period of volts at the solenoid, but only 7-9v. But something there rules out immobilizer and auto switch. Now it could be the key switch? relay or solenoid I think
The only clue I have is the first time it was a very hot day. Second time not so hot but a lot of starts in a short period. starter/solenoid dying or something not flowing enough juice to it when hot?
E: Battery and connections is fine, of course it is because it's starting fine again right now. Battery bought 7 months ago and I have to remove it all the time (old e34, it's in the engine bay and nearly always in the way when I'm working on the car so most cables have been replaced as well and I've become very very familiar with all the part of the electrical system, all tight, no corrosion, good connections, full 12v etc)
Also no low voltage faults from the system. I know from experience if volts are low when trying to crank you get all sorts of unrelated fault codes, like trans program error. This hasn't happened when it 1) fails to start, or more importantly, 2) when it starts cranking and starting OK again. You would think if the start itself is stuffed it would draw more current than usual, maybe cause the battery to struggle and maybe trigger something like that.
ross1
01-07-2018, 08:15 AM
If you are confident your reading at the solenoid was correct then start by also taking a reading at the ign switch. If same or similar and 12v going in then your switch would seem at fault.
Intermittent electrical faults, gotta love them.
If I had to throw parts at this it would be a switch, after checking the wiring between sw. and starter.
Also worth mentioning is the ignition lock, there is a link between the key cylinder and the switch on the opposite side of the column. Those sometimes weaken and eventually break over time. An intermittent non engagement of the starter is an early warning sign. With that though it usually feels funny when turning the key, sometimes an almost imperceptible pause between turning the key fully and starter engagement.
Hope this helps
Also worth mentioning is the ignition lock, there is a link between the key cylinder and the switch on the opposite side of the column. Those sometimes weaken and eventually break over time. An intermittent non engagement of the starter is an early warning sign. With that though it usually feels funny when turning the key, sometimes an almost imperceptible pause between turning the key fully and starter engagement.
Hope this helps
Thanks.
Definitely sounds like this. First time it happened months ago when leaving the house I had to hold the key on 'start' for a few sec for anything to happen.
I would normally suspect the starter or solenoid but 2 months working fine since the last issue seems weird if it was that. I really do think it's key switch or something like that due to no other faults I can find.
I've just been looking at realoem and wow, I had no idea they're were set up like that, key barrel on the opposite side of the column to the actual switch. I can't make out this lock/link you mention though. Is it a part of the housing?
Hoping it's a separate part or a component part of the key lock assembly or the switch assembly, and not part of the housing.
E: If it's part of the housing I might have to try pull one off a wrecking car if it's possible to remove undamaged.
whiskychaser
01-07-2018, 10:16 AM
What you may have is a dry joint in the starter relay. When the car warms up, contact is lost. Cools down again and the contact is made. To test the starter, you could just jumper the main terminals with a screw driver. To test the line from the starter relay, run a temporary wire to the solenoid. If neither work, move the wire to the permanent 'live' side of the relay. What I am suggesting is similar to what Ross is saying but I am just starting at the dirty end :)
Oh, and don't forget the infamous fusible link
ross1
01-07-2018, 10:37 AM
Given the correlation with temperature I'd lean towards an electrical fault first. I mention the lock issue because it is fairly common.
The lock housing is a PITA job. getting one at a wrecker would mean a wrecker having the key too as you'll need it get the old lock out.
There are aftermarket sellers of the link alone, which is not sold separately by the Germans, the whole shebang is around $150 US last I checked, probably way more down under.
Again, rule out the electrics first.
- - - Updated - - -
What you may have is a dry joint in the starter relay. When the car warms up, contact is lost. Cools down again and the contact is made. To test the starter, you could just jumper the main terminals with a screw driver. To test the line from the starter relay, run a temporary wire to the solenoid. If neither work, move the wire to the permanent 'live' side of the relay. What I am suggesting is similar to what Ross is saying but I am just starting at the dirty end :)
Oh, and don't forget the infamous fusible link
Good thought, his symptoms reek of a bad solder joint.
Could be. I'm going to try jump it next time it happens. Hopefully by then I'll have some ins. high current wire (pretty tight between the intake man. and the brake booster otherwise). I'm going to try find some and keep it in the car in case it happens again while I'm still troubleshooting.
The intermittent nature of the fault is annoying though. First time it happens is Nov, and since then as I've not had the fault despite some high mileage and stop start driving on hotter days than today. I'll take some cable - and a phone with auto elecs on speed dial - in the future until I can do more tests. Hopefully if it' s going to fail it does it at home again.
Yeah that fusible link. What kind of PO did you think I bought from? Of course someone that does repairs with drywall screws is going to have coathanger wire in there. There was also a staple or something across the headlight fuses when I bought it because that makes both headlights work even when there's dry solder joints in the headlight control module.
I'm slowly fixing all these because good paint and no dents made me buy this one.
What you may have is a dry joint in the starter relay.
Are you talking about the relay in the fusebox? If you are ,the first thing I do is swap it with an identical one next to it and it has never helped.
Also, when remembering my first experience of this happening, it was the first start of the day, so everything cold. First turn of the key - nothing. Second turn of the key nothing - for a second (I've already started to release the key because nothing has happened for a sec but it just starts to turn while I was releasing the key so would have started). Third turn of the key - the usual very short delay and then it starts.
Heat would be a factor when it failed to start at all later on, but wouldn't have been a factor when it was strange to start during that morning
whiskychaser
01-07-2018, 01:25 PM
Yes. I meant the relay in the fuse box. 12v only represents a 40% charged battery and I'd suggest 7-9v on the solenoid wire is too low to throw it. Of course, if you only have 7-9v arriving at the starter relay, that is all you are going to get out of it. BTW, you might want to have a quick look at your engine ground to make sure it is intact and secure
BTW, you might want to have a quick look at your engine ground to make sure it is intact and secure
Will do. Do you know where it's supposed to be and what size cable it's supposed to be (no idea if the PO has done something dumb with it like moving it or fitting a tiny cable)
E: nevermind. I checked resistance from the battery -ve to the cyl head with a multimeter for got 0 ohms. Also while doing that I noticed a thick cable from the chassis ground bolt to the engine mount bolt, so that seems fine.
I've also got to sort out my relays as who knows what the PO did
https://i.imgur.com/uW2BaUl.png
#1 on my car is not some jumper plug, but a relay the same as the #2 starter relay - these are the two I switched as same pin outs and relay model #
Relays 1,2,4 are bosch 0332014456. Relay #3 is siemens v23134-k59-x108
When the car didn't start I have swapped #2 start relay with the identical relay from #1 or #4 which didn't help
I've got to track this down to work out if it's a power circuit or control circuit problem (to put into terms I can relate to).
Control circuit is: battery - fuse - key and switch - lock outs (imm. & auto switch) - relay coil - earth
Power circuit is: battery - relay switch - solenoid - earth
Giving it a bit of thought, if I could read some volts at the solenoid on the starter when turning the key it seems like a power circuit problem. But didn't hear a reassuring relay click when turning the key...
If it happens again I'll give power to the solenoid from the starter cable and if that works I can at least rule out the starter solenoid.
*Huge update*
I just took it for a short test drive and after stopping it would not start again.
I tried giving power directly to the solenoid and nothing happened so I resigned myself to it probably being a sticking solenoid or something bad internal to it as it fits the heat pattern.
While considering the tow home I remember reading that pin #11 under the diagnostic cap will turn the starter, so I tried that and it works (lucky I spent ages reading through threads yesterday!).
So 1) I must have not bridged the solenoid properly - hard to see and also fuel hose clamps cut up my hand
2) does that #11 pin go through all the cut out switches and relay? - if so they'e all good too I guess. Looking more like the key switch or something?
3) that #11 pin trick works with old m50s as well - 90/91, non vanos, battery in the engine bay
4) this intermittent nature, the heat on the first day and the multiple starts on the 2nd occurrence is really throwing me off - pointing towards starter/solenoid but I don't think it is them now for sure
I haven't fixed the problem, but I can defeat it! :D
Feeling boss, I thought I may as well stop at the second shop and do my errands, after that stop and it started normally by key then...
E: So the quest now is to find out the circuit for that #11 pin and find out what it bypasses (if anything). What ever it bypasses are likely culprits.
whiskychaser
01-08-2018, 04:55 AM
Pin 11 connects after the starter relay. So what you are doing is what I suggested in post 4 above - providing a live direct to the solenoid :) Now work backwards to the relay itself and see what is coming in/out of it.
Check out page 1240.0.01 of the wiring diagram
http://www.wedophones.com/BMWManualsLead.htm
Oh no, so #11 bypassed everything.
I'll be home tomorrow afternoon because my kid is visiting. Do you thing a 5 y/o boy will become bored of troubleshooting an e34 very quick? :ausw_6
If not I'll get him in the seat with the key to crank :smash
So my plan will be to pull the start relay and test for 12v across the coil terminals 85 and 86 when turning the key in order to test the control circuit
And also in another test to bridge 30 and 87 to test the power circuit wiring to and from the relay.
E: and to play with the loose relays putting 12v across the coils to check action and continuity across the contacts
Does that make sense?
whiskychaser
01-08-2018, 09:15 AM
Yes, bridge 30 and 87 and try it on the key. Manuals work like that anyway. If that works consistently, check that you are getting power up from the the gearshift lever switch to energise the relay when it is in P or N (relay pin 85 - 86 is just ground)
PS Having son around will be great fun. My late father always said he taught me all I knew about cars. TBF, I am great at holding a torch and passing spanners :)
Looks like I've been thinking about the relay in the wrong way. I thought it was a start relay, but it's more an anti start relay.
If it was a start relay then 30 would be hot straight from the battery, and the key switch would send power to 85 (coil) when turned.
But all this relay does is keep 30 open if the trans is not in 'p' or 'n' or some other anti start condition, so it's a just a lock out anti start relay. The key switch does all the work giving power through 30 and driving the solenoid.
Anyway, despite having some free time and an apprentice I couldn't replicate the fault. Started every time for the 20 odd times I tested it but with two hiccups.
The first hiccup was at one attempt to start there was a 1/2sec plus delay after turning the key. I really thought it would fail to start soon after that happening, but it started every time until I gave up.
Another I lost power to 85/relay coil and thought I was onto something, but it was the immobilizer kicking in and obvious to me that it was on. No hesitation after pressing the remote key and the immobilzer clearly went off, so I don't think it's that leaving me stranded on previous days. That tells me though the immobilizer is on the auto switch and coil circuit rather than the key switch and relay contact/ 30 circuit at least.
Just going to have to drive it as normal but always make sure I'm carrying some hook up wire to get me out of trouble and a multimeter to try diagnose.
I reckon though if the key switch has to do all the work to drive the solenoid because the relay only does lock out (not actual loaded solenoid current during start), it's probably that.
More confusion: Happened again and the relay was working, could hear it click when plugging in, and 12v was to to it. Removed the relay and checked input from key to terminal 30 when turning the key: 11.49V.
I should have shorted 30 - 87 but was in a rush and used diag conn. 11 again to get it going quickly and double check it's not the solenoid.
So it's either the relay , the wiring from the relay to solenoid, or the key switch not passing enough current...
But when it's working it works fine, can start/turn over all day. Found this out today because my fuel gauge is not working below 1/4 tank - it will read 0 -1/4 tank randomly but nothing in between. I only put 1/4 tank into it last weekend ($20) because the station/pump I went to only had 91 or 98, not 95. I didn't feel like paying the extra $10-20 for a full tank of 98 (again, again...). -95 is hard to find in some places so I often have this problem.
Anyway, today the car wouldn't start after a 1km drive to the shop. I turned it over about 20 times and it turned over every time.
I haven't driven much- not enough to use $20 fuel but so many stop , start and stop, moving the car around the corner or up the driveway to park in the sun, or short tips to test the key start means it used way more fuel than it should have, so 1/4 tank only lasted 70kms. Point is though the key start problem is so intermittent and it's driving me crazy and today caused a long walk with a fuel can I normally wouldn't have to do as I could trust km driven more reliably under 1/4 tank if I didn't have to do all these starts, stops and short trips I've been doing to try troubleshoot.
Once I fix this start problem I want to get a fuel gauge/sender that can read under 1/4 tank accurately :)
ross1
01-13-2018, 07:42 AM
A relay that clicks doesn't necessarily work. All this tells you is that the actuating coil is moving the contact points, not that the points are actually making proper contact.
A fuel gauge sender that was dead accurate would move to E at the same time your car stops, they are this way for a reason.
whiskychaser
01-13-2018, 08:27 AM
You could jumper the relay and leave it in. If it refuses to start then, you know it isn't the relay. Just remember it will then start in any gear. 11.4v at the battery would not be enough to start it. So your battery sounds fine. What are you using for the ground probe on the meter - strut top bolt or the engine? And is the relay/probe actually making proper contact with the terminals below?
What are you using for the ground probe on the meter - strut top bolt or the engine? Using something on the engine for earth, but just the probe resting or loosely wedged, nothing clamped or bolted
And is the relay/probe actually making proper contact with the terminals below? pretty sure it is. Today when it happened again I made sure I used male spades on my bridging wire to ensure a good connection and it seemed alright.
Happened again today (been fine since the 13th and while I don't drive the car every day, I often have to move it), and as usual it seems to not turn over at the worst time so only a quick testing is done.
It's definitely not the relay. This time I removed the relay and bridged 87 and 30 with some 2.5mm cable I had premade with long male spade connectors. Didn't turn over or even try to start or make any noises at the solenoid.
I don't think it's the wiring to the relay as I got 11.4v last time even when it failed to start (current is another issue, but the right things are happening you could say - enough to rule out g/b switch or immobiliser imo - but probably not key switch)
I don't think it's the solenoid, solenoid terminal (or final wiring run to it) as I can always get it going with #11 diag pin straight away
E:
Interestingly after trying bridging out the relay I resorted to using the diag plug # 11 pin power and with the relay coil removed the remote/trick start didn't work. Strange as I was under the impression pin 11 went straight to the starter solenoid or something but it definitely doesn't. It must use the control circuit or something because the relay had to be installed for it to start with diag #11 pin
So of note: in an auto if anything is wrong with the gearbox switch or anti start relay then the pin 11 trick isn't going to work. If that sounds wrong then it may be a clue in my car. If it ends up being correct then I also need to find everything in that circuit or can treat those components as "must be ok"
Anyway, I know from last time I had 11.4V from the key switch to term.87 on the relay. Next time I'll have a new cable made up to try putting 12v from the battery to term 30. But now I'm not sure if it will work without the anti-start relay installed after what happened with pin #11 not working without that relay fitted back in today.
E: Had problems starting it like I said, but I have taken it for long and short drives and done 4-5 more starts and working fine now. After 15min drive 2nd restart had a slight delay and I turned it off immediately to retest. That 3rd restart was instant so I drove it for 10 min and parked for 10min. 4th restart not instant but not as big a delay as start #2
whiskychaser
01-25-2018, 11:04 AM
Check out the diagrams on pages 7100.0.01-3 and 1240.0-01. They show that the black/yellow wire from the diagnostic connector pin 11 connects to the circuit after the starter relay at connector X20. X20 should be located to the right of the B+ terminal as viewed from the front of the car. The wire from the relay to the starter solenoid (via X20) should also be black and yellow. If the diagrams are correct, it doesn't make sense that you need the relay in. First thing I would check is that pin 11 of the diagnostic plug does in fact go to X20. FWIW, I think the pin on that is 18
Check out the diagrams on pages 7100.0.01-3 and 1240.0-01. They show that the black/yellow wire from the diagnostic connector pin 11 connects to the circuit after the starter relay at connector X20. X20 should be located to the right of the B+ terminal as viewed from the front of the car. The wire from the relay to the starter solenoid (via X20) should also be black and yellow. If the diagrams are correct, it doesn't make sense that you need the relay in. First thing I would check is that pin 11 of the diagnostic plug does in fact go to X20. FWIW, I think the pin on that is 18
Yeah, I didn't expect it so that's why I noted it as interesting for other people. Maybe something to do with my aftermarket alarm/immobilizer?
Anyway, happened again today (weather only 28C and car parked in garage). This time I put battery 12v+ to term 30 like I said I was going to do. Car started fine.
So it's either the key switch, or wiring to it, or the wiring from the key switch to the relay.
Tested 12V to relay pin like I have done before - 11.7v at the relay when turning the key. Tested volts under load (relay removed, jumper installed so I could use a MM probe) at term 30, volts go down to 8v and starter not operating.
So I think the key switch is just not passing enough current (11.7v unloaded, but not starting and nothing happening under load - 8v)
Remember at the very beginning in the first post I tested at the solenoid and only got 7 or 8v? At the time I thought maybe solenoid stuck and volts dropping due to that. But after so many tests I know now that it will start fine if I'm bypassing the key switch (using diag #11 pin and now 12v straight to term 30 relay output), so the key switch or wiring to/from it just can't flow the current and gets a volt drop down to 8v when the problem occurs.
Started 4 times today after the initial fail while taking test drives and running errands though.
shogun
01-27-2018, 04:36 AM
Reminds me of my wrenching buddies car some years ago , same symptoms, he changed a lot including ignition switch etc.
In the end it turned out that one fusible link had a difficult to see haircrack and depending on temperature sometimes there was contact and sometimes not.
From my website the description of the 2 fusible links based on E32 and probably the same for E32:
FUSIBLE LINKS A & B IN E32
X6400 is the power post inside the E box. It feeds only DME loads. Page 1361-01 for M30 and 1367-00 for M70. Fusible Link A is 50 Amps.
Page 0670-10 Fusible B is 80 Amps. It feeds all the Rear Power Box loads
whiskychaser
01-28-2018, 04:08 AM
You are applying external power to the ignition switch side of the relay if you use pin 30. That is why you needed the relay in. You will get a voltage drop to about 9v when the engine is under load (cranking). But when yours fails, it doesn't even try. Apart from that, I can't fault your logic :)
I'd certainly have a look at the fusible links as Shogun suggest. If they are fine, maybe locate connector X33 and check what is arriving and leaving the switch at that point? I think you are looking for pins 1 (to switch) and 6 (from switch to starter relay) and X33 will be located somewhere behind the gong panel above your feet
You are applying external power to the ignition switch side of the relay if you use pin 30. That is why you needed the relay in. You will get a voltage drop to about 9v when the engine is under load (cranking). But when yours fails, it doesn't even try. Apart from that, I can't fault your logic :)
I'd certainly have a look at the fusible links as Shogun suggest. If they are fine, maybe locate connector X33 and check what is arriving and leaving the switch at that point? I think you are looking for pins 1 (to switch) and 6 (from switch to starter relay) and X33 will be located somewhere behind the gong panel above your feet
In a no start condition, with a jumper wire in to bypass relay, it won't start, (voltage drop under load), so problem is before the relay.
Also no fusible links. a) one has a wire installed by previous owner to replace the link. b) battery in engine bay so no rear power block distribution.
Will think about getting a proper fusible link if I go ahead and order ignition switch (currently thinking of just getting a push to start button rigged up - if there's a nice place to fit a nice switch. Haven't really looked too hard at this idea, just a fanciful thought if the ignition switch is a PITA or pricey to get delivered to aus. I really wanted to worry about brake replacement and upgrades rather than this, and the susp knock on the front right even though I've finished replacing nearly all the susp...)
whiskychaser
01-28-2018, 12:10 PM
I understand that when it will not start, jumpering the relay makes no difference. What I am saying is that when you are applying your external 12v to pin 30, that is before the relay. So that is why you need the relay in place for it to crank. In doing so, you are actually proving that the relay works and that the gearshift wiring isn't the issue :) A switch wired to connector X33 would be my choice and the panel above your feet is soft enough to be drilled easily.
BTW. If it does turn out to be the ignition switch and you need to remove the cowls, bear in mind that there are two screws at the top. I certainly could not see them let along remove them without removing the steering wheel.
Powered by vBulletin® Copyright © 2025 vBulletin Solutions, Inc. All rights reserved.