BMW E34 520i intermittent running issue

[adam73bgt]

Hoping to get some advice from the BMW pro's on here on an occasional running issue on my 520i with the M50TU engine

I've had the car for just over a week and in that time I'd say its happened twice, last happened this morning.

Car was still warming up, I was accelerating with mid throttle in 3rd gear, up a slight hill at reasonable revs (probably around 2-2.5k rpm, not labouring the car), the car was pulling ok but then there was a jolt as it stopped pulling briefly before going back to being fine again. Then when I got to a junction a shortwhile later, the revs dropped as I put the clutch in to the point where the car nearly stalled

After this, the car warmed up fine and was fine all the way to work


I have noticed the car sometimes doesn't pull all that strongly below 3000rpm, but I've been struggling to work out whether thats just because its a small engine in a big car


The previous owner did have the crank sensor changed (not sure what brand) and had the ecu 'chipped' to help with low down power (now wondering if this was effectively just covering a different fault)


From having a look round the net, cam position sensor and/or VANOS seal change/rebuild seem to be the cures for sluggishness below 3k rpm but I don't know about the jolting


Any ideas?

Cheers

[andrewbaran]

Check everything on the intake side of the engine - vacuum leaks are often to fault on these engines. Common split is the ICV hose.

The crank and cam sensors are possibilities - the crank sensor can chafe on the front of the engine.

The VANOS seal is also a possibility too - could be sticking open or closed a bit and freeing up when the oil warms properly? VANOS is what killed my 525i The unit on the front of the cam cover was very tappety - definitely sounded like it had died. Circa 3k rpm is activation point for VANOS too.

[andrewbaran]

Oh, and if you have the ICV hoses etc off, pull the sensor off too and spray it through with intake cleaner. For a sensor that is meant to only control idle, it does do some weird stuff.

[adam73bgt]

Cheers I'll start by looking at the intake side of things then and work my way through the sensors after that

Looking around on the web, the advice seems to be to only use OEM cam/crank position sensors, is this entirely necessary? Or is it possible to get away with aftermarket sensors?.... (senses potential can of worms opening )

[andrewbaran]

I have some pattern ones on my E36. Most of that "buy BMW only" stuff seems to be on BMW specific forums, so my view is that it's just OCD people getting their knickers in a twist.

I got mine from "Ace Car Parts" on ebay - Looked up the part numbers on bmwfans.info and typed that into their ebay page.

[j4m35]

These engines don't have a lot to give below 3,000RPM even with VANOS. If it feels like it's gotten worse, and you have a rattling noise coming from the front of the engine on start-up, a VANOS problem is likely.

Regarding BMW or aftermarket for sensors- My approach would be to try to find out who makes the OEM BMW sensor (possibly Bosch or Siemens?) and google that to see if you can get the same part without the BMW box tax.

[adam73bgt]

Hmm the car was worse this morning, lurched a couple of times near where it did it before, then did it a few more times, was almost kangarooing along lol, then I went and put some fuel in as it was getting a bit low, the engine reached full temp and it was fine

[Iain]

The crank sensor for my 525i took some finding as there was a few different plugs but no reason to buy genuine. Febi stuff is pretty good from what I've used.

[gazzab1978]

the lambda sensor could also be a bit iffy, not sure about the bmw engine but on my old mx5 i had similar problems and a new lamda sensor cured it, although it was a much simpler engine.

[ettorebugatti]

Could it be the fuel filter?

Always tricky to solve intermittent errors.

[07lilredwagon]

how are the grounding wires on the car?...good strong grounding on the battery too?....wires may look fine, but check resistance.

I rebuilt my vanos valves as opposed to getting new ones and used carb cleaner to get a lot of old black oil sludge out of them...This was in an N52 motor though...

thermostat okay?

sorry, not much help....but you never know

JP

[ChasR]

Jan 27, 2016 9:51:44 GMT andrewbaran said:

I have some pattern ones on my E36. Most of that "buy BMW only" stuff seems to be on BMW specific forums, so my view is that it's just OCD people getting their knickers in a twist.

I got mine from "Ace Car Parts" on ebay - Looked up the part numbers on bmwfans.info and typed that into their ebay page.

That depends .

I have once or twice been caught out by pattern sensors and the hassle of returning them to a German Swedish and French firm after a 4 week wait of the unit being 'tested "/ . It's luck of the drawer really.

In my case it was down to a faulty ABS sensor in a wheel bearing unit (they'd void the warranty if I fitted in my old sensor). Another friend went through 3 sensors on his wife's Polo being going cosher to cure an intermittent fault.

That said I have used pattern sensors on a few occasions fine as a result of the price difference and been OK .

[adam73bgt]

Its been a while, so I'd better update on this

Thanks for all the suggestions everyone


So I checked the intake side of things and it seemed fine, the throttle body was clean and moved freely, and I gave the MAF a clean out with some contact cleaner

This didn't make a difference and it began running worse and worse to the point where it wouldn't start!

I found a fair bit of oil pooling in the rearmost spark plug hole so I cleaned that out and have bought a rocker cover gasket kit in preparation

This sorted the idle but it would still cut out under acceleration.

So I changed the Cam position sensor which seemed to sort it out and yesterday I drove to Liverpool and back quite happily

But then I go to start the car today and I get this



After it cut out in that video, I started it again, revved it a couple of times and it smoothed out and was fine again for a 30 odd mile round trip

Any ideas anyone? Can Idle control valves fail when cold but be fine when hot?

[ChasR]

When you say that it would cut out under acceleration do you mean stall or begin to misfire etc.?

If you haven't already done so I'd clean out the ICV . I'd also be tempted to check the resistance values on the temperature sensor.

[adam73bgt]

Feb 27, 2016 22:36:29 GMT ChasR said:

When you say that it would cut out under acceleration do you mean stall or begin to misfire etc.?

If you haven't already done so I'd clean out the ICV . I'd also be tempted to check the resistance values on the temperature sensor.

Yeah it used to have a couple of misses then as it got worse it would totally cut out

So before I fitted the new cam position sensor on Thursday, it cut out completely as I was accelerating and I managed to limp it back. But since I fitted it, it's not cut out on me while driving

Yeah I think an icv clean out makes sense, though I wasn't sure if it made sense for it to idle rubbish when a bit cold but be fine once warmed up. It's also not consistent, so when I started it again after that vid, it was still cold but idled fine while I waited for it to warm up