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Mad_Max

95 E36 M50B25TU not starting

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I've got a 1995 E36 325i sedan with an M50B25TU. It was starting and running rough, wouldn't idle at all. If it stalled sometimes it would fire straight back up, however last time it stalled it didn't start until I'd walked away for ages.

So I got to yesterday and pulled the ICV to clean it, see it that helps the idle issue. Also replaced a few rotten vac lines and hoses while I was there. It started and ran, idle was still erratic but definitely better. Turned it off and it fired first time. I went out (in another car) for about an hour, came home to grab the sedan and it wouldn't start, it would just cough like it wanted to start but wouldn't catch.

I've swapped the crank angle sensor and double checked (visually) for any form of decent vacuum leaks, still no luck. I've got fuel at the rail, and I doubt it's a coil/plug issue as it has been running up until yesterday. Last night it would only crank over, this morning I tried and it coughed like it wanted to start but didn't catch. So i"m kind of stumped for ideas.

There is an aftermarket alarm there that, while the doors lock and unlock fine, the horn on it sounds like it's dying from pneumonia or something. 

I'm fresh out of ideas and things to check/try. I have a stack of parts so swapping parts doesn't worry me. I'm thinking it could be a relay failing (intermittently stopping either the DME or ignition system from working) or maybe the aftermarket alarm has packed up completely, I really don't want to be going through the wiring to remove it.

Anyone else got any ideas? Any other thoughts? This one has me stumped.

Edited by Mad_Max
Wrong year in description

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23 minutes ago, dirtydoogle said:

Got a spare cam angle sensor? 

Yeah probably do have a spare one here. I was always led to believe the crank angle sensor was the fallback, i.e. cam sensor fails and it'll still run, just not well. At least that's what my other sedan did when the cam angle sensor failed - it ran, but you could hear the injectors going (in batch mode so all firing at the same time).

Will try dig a cam angle sensor up and swap that over, see what happens - you may be right as this one will have a different setup (OBDI) than my other 328i (OBDII) so the cam sensor may have failed and it may be causing the problem.

Failing that I think I may remove the alarm and restore the wiring, to eliminate that being a problem.

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I've had no start and backfiring out the intake with cam sensor code present 

However will run with an error count as opposed to total failure 

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8 hours ago, dirtydoogle said:

I've had no start and backfiring out the intake with cam sensor code present 

However will run with an error count as opposed to total failure 

Yeah that's exactly what I was thinking, cam sensor won't cause a no start issue, just bad running conditions. I'm going to try a new cam angle sensor and swap the fuel pump - the more I think about it, the more I suspect fuel pressure is a problem given the fact it will cough but not catch.

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I may not have been clear enough sorry, the cam sensor can cause a no start situation. I had one recently and it would cough and not start with a dead cam sensor 

 

It's worth ruling out and only takes a few minutesto change if you have small hands 

Edited by dirtydoogle

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I would suspect the engine is flooded given by your description. 

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11 hours ago, dirtydoogle said:

I may not have been clear enough sorry, the cam sensor can cause a no start situation. I had one recently and it would cough and not start with a dead cam sensor 

Yeah fair call on that, managed to do the crank angle sensor without too much hassle so cam angle sensor shouldn't be too bad. Will give this a go and see what happens when I've got some spare time.

35 minutes ago, hotwire said:

I would suspect the engine is flooded given by your description. 

Interesting, any thoughts or ideas what would cause the engine to flood? If it was a carb engine I can fully understand flooding being an issue and would be most likely culprit, but I've never seen a FI car flooding unless someone has messed with the fuel maps? Not knocking your suggestion at all, I'm wondering what would cause it.

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These kinds of problems are always hard to diagnose on the internet.

i have found M50s not running right or at all is usually crank position sensor either failed or just grubby usually from oil leaking from every orifice on the engine. and if not that next best bet is the air flow meter. There are two pin configurations for them, and other engine sizes don't work.

Did you replace the O ring where the ICV tube connects to the manifold, and is that fitting clipped in correctly? they often break off when disturbed, so it isn't sealing right. Also check the intake boot thoroughly for cracks. check oil cap is on nice and snug and dipstick is in the tube correctly. Have you tried scanning the car?

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7 hours ago, _ethrty-Andy_ said:

These kinds of problems are always hard to diagnose on the internet.

i have found M50s not running right or at all is usually crank position sensor either failed or just grubby usually from oil leaking from every orifice on the engine. and if not that next best bet is the air flow meter. There are two pin configurations for them, and other engine sizes don't work.

Did you replace the O ring where the ICV tube connects to the manifold, and is that fitting clipped in correctly? they often break off when disturbed, so it isn't sealing right. Also check the intake boot thoroughly for cracks. check oil cap is on nice and snug and dipstick is in the tube correctly. Have you tried scanning the car?

Hi Andy, yes agree 100% it's very hard to diagnose with any main accuracy, seen many, many times where people give horribly wrong advice.

I suspected crank angle sensor first off, swapped that with no improvement. Will be trying the cam angle sensor as well when I get a break - probably some time in the next few days. Will also clean the trigger wheel, see if that makes any difference. Have checked the intake boots as well as every other hose I can find to see if there's any holes, splits, tears etc.

First thing i double checked was that everything to do with the ICV was reconnected properly, and it seems fine - the seal you mention seems to be nice and tight in the back of the manifold. I'm going to swap the AFM from the other M50B25 and see if that does anything. I replaced the oil cap as the original one had a shagged seal, so that's on tight, as is the dipstick.

I haven't tried scanning it as I've never had any luck scanning OBDI cars, can never seem to be able to read the DME..... Might have to see if I can borrow a scanner that works.

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On 23/12/2017 at 10:16 PM, Mad_Max said:

 

Interesting, any thoughts or ideas what would cause the engine to flood? If it was a carb engine I can fully understand flooding being an issue and would be most likely culprit, but I've never seen a FI car flooding unless someone has messed with the fuel maps? Not knocking your suggestion at all, I'm wondering what would cause it.

It is a total myth on only carb engines flooding.

I go out on "no start" AA calls to find a flooded engine frequently - probably once a week on average. All are fuel injected. All but every time can be traced back to the last time the engine was started. It has always been started then stopped, usually moving out of the garage to wash then moving back or moving the car to access another. Next day the car will not start. 

The engine is running on fuel enrichment for cold start/run - as with the old school choke, so more fuel/cold engine & the excess fuel sits there. If the engine next time does not start on first catch then the problem just compounds - giving your symptom.

It will not be the alarm/immobiliser, nor fuel if it has pressure in the rail.

Before you go replacing all parts on a whim, make sure you have good battery & crank the engine WOT & see if it will clear & start. Otherwise remove the plugs & see if they are wet.

Edited by hotwire
spelling!

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So it turns out that the bolt holding the cam angle sensor in position was loose. Tightened that up, checked everything, turned the key and it fired straight up, and has done every time since. So I suspect the cam angle sensor wasn't located correctly, causing the no start issue.

Now I just have to get the damn thing to idle correctly, but that's another story.

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