S50B32 cutting out - Vanos solenoid diodes dead?

[OliSmith]

Hi all,

Issue is happening on an E36 M3 Evo for context - apologies, I know this is a Z car forum. I have uploaded this post onto m3cutters, but wanted to open up the chances of getting to the bottom of this issue. Hope this is OK.

I've had my car for 10 years now, and in all that time it's had an issue where under certain conditions, the engine cuts out. The issue only happens when it is a hot day, say about 25 C or warmer (engine temp plays no part in the issue though) and only when under heavy throttle/WOT. The RPM it happens at varies, but I'm pretty sure it always happens over 3k RPM. Over the years I've replaced a few bits chasing the issue - fuel pump, fuel pump relay, knock sensors, and probably more that I've forgotten about. I've also obviously done service items including fuel filter which was last done less than 12 months/1k miles ago. It's been plugged in many times through INPA, DIS, and iCarsoft CR Pro - no codes present for the issue whatsoever. I have been chasing this issue for quite some time although has been on the backburner as it only happens in hot weather. Steve at MrVanos has also looked into it for me when I took it there in 2014 for other work but was unable to find anything at the time.

I've narrowed the issue down to the fuel pump losing 12v power supply. I've verified this by cutting back the sheathing on the fuel pump power supply wires under the rear seats and soldered in two wires running to an LED which I can see from the drivers seat. When the fuel pump has power, the LED is illuminated and when the engine cuts out, the LED goes out. When the engine cuts out I don't lose electrics to anything other than the fuel pump. Lights, radio and all the other instruments still work normally - it just feels like I've hit a rev limiter or lifted off the throttle, but my foot is still firmly planted on the throttle. If I dip the clutch, the revs drop to 0 RPM. I then obviously need to coast the car to the side of the road safely (which can be pretty hairy depending on the situation!), switch off the ignition, wait 10 seconds (that seems to be the time that you need ignition off before the fuel pump will prime again before starting) and start the engine again. Car fires up like nothing happened and runs perfectly again. The car drives faultlessly the rest of the time, makes good power, idles smooth, no funny noises or anything untoward.

I watched the YouTube video from Evolve Automotive where Steve @ MrVanos, appears to talk about the Vanos on these engines:

Skip the video forward to 14 minutes and he starts to talk about the issues with solenoids, but specifically at 14:20 he talks about the diodes in the plugs which can go bad and cause issues, he even mentions that he's seen failed diodes 'trigger the fuel pump'. This led me to do a bit of research about what diodes do and how to test them. I understand that diodes are essentially like a one way valve and protect components from a reverse pulse. That means failed diodes in the vanos plugs can send a reverse pulse to the DME, hence leading to the strange electrical issues like Steve explains in the video above.

This video is very useful and talks about replacing the diodes and shows the wiring diagram of the plugs (1:45 onward) and a photo inside a plug after dismantling it (4:25 onwards).

I believe this video was created by @Pingu - any help you can provide would be greatly appreciated.

Yesterday I disconnected the plugs to both inlet and outlet vanos solenoid units and attempted to test the diodes (forward biased) in the connectors plugs by using a multimeter's diode testing mode - negative lead to the cathode (which is connected to the two outside pins of the plug) and positive lead to the anode (centre pin). I got a reading (voltage drop I believe) of 0.003 over all 4 diodes. I then switched to reverse bias, so negative to anode and positive to cathode and got the same readout of 0.003 across all 4 diodes. I presume these readings means all 4 diodes are shorting and therefore need replacing? Either that or I'm doing something wrong/my multimeter isn't functioning correctly. The multimeter does read 1 when the positive and negative aren't connected to anything and it reads 0.000 when I touch them together which implies the multimeter is working as it should. If the diodes were dead, it seems strange that the car runs normally in cooler temperatures - I believe temperature does affect the flow of electricity, but that's all a bit over my head. I'm by no means an expert when it comes to electronics, so apologies if any of that wasn't clear or I used incorrect terminology.

To summarise:

1. Given the results from testing the diodes, does it look like my diodes are dead (and potentially causing this issue) or could I be using my multimeter incorrectly and barking up the wrong tree?
2. Can I remove the solenoids on the car without removing the whole vanos units and if so, what's involved to dismantle and re-assemble - are there any good DIY guides? I assume I'll need to let out the pressure from the oil lines and bleed it when re-assembling.

 

[Pingu]

It is not necessary to remove the solenoids in order to test them, but you will need to de-solder one of the terminals from each solenoid. If you are happy to solder the wires back to the solenoids in situ, just leave the solenoids in place.

<edit>If you do it in situ, don't forget to disconnect the plugs that are behind Item 13.</edit>


Yes you can remove the solenoids with the VANOS in the car. In fact they are easier to remove as the weight of the engine and car is helping keep the VANOS from moving. You don't need to worry about pressuring the system. The system will be de-pressurised when you dismantle, but you will get some oil loss. You just need some rags to stop the oil going all over the front of the engine and the belts.

Remove Item 13...

Remove Items 10 and 16. Try not to damage gaskets 11 and 17. They are quite expensive, yet unnecessary. Some people just clean the surfaces and use Hylomar (or similar). This will mean the solenoids are pressed into the VANOS more tightly than if the gaskets are replaced.

With Item 10 removed, use great care to remove the solenoids (25). Some use screwdrivers to attempt to lever the solenoids out, but I recommend using a plumber's wrench to slightly twist each solenoid (by 15° or so, left and right). This will break the bond that will have formed between the seals (27 & 28) and the VANOS body. I was then able to use the wrench to extract each solenoid. Each pair of solenoids is connected to a plug that is easily disconnected.

Repeat when Item 16 has been removed, remove the solenoids (26).

The solenoids are all the same, but I don't think that anyone has been able to source the solenoids individually.

The difference between Items 25 and 26 is the length of the wire. Don't get them mixed up. It is possible to fit Item 25 in lieu of 26, but the wire for 26 is too short to reach 25.

Items 27 and 28 are NITRILE as standard, but are best replaced with VITON.

https://www.porterbility.co.uk/vanos_images/013_Solenoid_Circuit_Diagram.jpg

Unfortunately, my website isn't https, so I can't link images (just use the link) <edit>it is now https</edit>

To test the diodes, you will need to break and remake some joints. Set you multimeter to diode setting, test the multimeter by connecting the two probes together - you should get a buzz.

To test the upper solenoid, de-solder the green wire from the solenoid, connect the red probe of your multimeter to the green wire and the black probe to the black wire - multimeter should buzz. Reverse the probes so red probe is to black wire and black probe is to green wire - multimeter should not buzz.

To test the lower solenoid, de-solder the red wire from the solenoid, connect the red probe of your multimeter to the red wire and the black probe to the brown wire - multimeter should buzz. Reverse the probes so to red probe is to black wire and black probe is to green wire - multimeter should not buzz.

Basically, with the plug disconnected from the solenoid, it should buzz in one direction, but not the other. The wire colours may be different, but the theory is the same. You must disconnect one of the wires from the solenoid or the multimeter will buzz in both directions as the multimeter current will pass through the solenoid.

For info, the diode is a fly-back diode. When an solenoid is switched-off there is a spike voltage which flies back in the reverse direction. To stop this spike returning to the controller a fly-back diode allows the current to constantly flow through the solenoid until it decays to nothing.

 

[OliSmith]

That's fantastic @Pingu, thank you very much for the reply.

If I were to remove the solenoids from the car, does the VANOS need bleeding after re-fitting everything? I think you did answer this by saying "You don't need to worry about pressuring the system." but not sure if you meant not to worry about pressure when removing the solenoids?

I think there should be plenty of room to do it without removing the solenoids though, especially if I remove the rad fan and cowl which is easy enough.

Thanks again!

 

[Pingu]

That's fantastic @Pingu, thank you very much for the reply.

If I were to remove the solenoids from the car, does the VANOS need bleeding after re-fitting everything? I think you did answer this by saying "You don't need to worry about pressuring the system." but not sure if you meant not to worry about pressure when removing the solenoids?

I think there should be plenty of room to do it without removing the solenoids though, especially if I remove the rad fan and cowl which is easy enough.

Thanks again!

It's not necessary to pressurise the system. Let the car idle for about 30 seconds without revving it. The engine note will change when everything is pressurised. It should only take a few seconds, but 30 is plenty.

 

[OliSmith]

Quite belated, but finally got around to looking at this today as it's a nice hot day (which is when I get the cutting out issue) and I had some time to spare.

I whipped out the solenoids as I think I would have struggled to de-solder and then re-solder the wires with the solenoids in the VANOS housing. Thanks again for your very comprehensive and helpful instructions above @Pingu.

Firstly, my multimeter doesn't buzz on diode testing mode, it just displays the numbers (voltage drop I believe?). It's a fairly cheap B&Q Multimeter - model number MS8233A to be precise. '1.' is shown when the probes are connected into the multimeter but are not touching anything.

Testing the left/passenger side side solenoids (ie, item 25 on the parts diagram above) which I believe is the intake side, I get a reading of around '0.480' when testing with the red probe on the green wire, black probe on black wire. Multimeter displays '1.' when I reverse the probes. For the other solenoid with the red probe on the red wire, black probe on the brown wire, get around '0.480' and when reversing the probes I get '1.'. So inlet solenoid diodes seem good.

The right hand/driver side (item 26) which I believe is the exhaust side, again I get a reading of around '0.480' with red probe to green wire, black probe to black wire, and '1.' when I reverse the probes. Now when I test the other solenoid with red probe on red wire, black probe on brown wire I get '1.' and the same when I reverse the probes. That would imply we have a bad/open diode on the exhaust solenoid, right? Which given, as you mention it's a fly-back diode, could be sending a reverse pulse to my DME and causing the strange issue I'm having of the fuel pump losing power.

I'll need to order some diodes. You mention that it's a 'Sintered gladd avalanche diode' and you chose to use a BYW32. Presumably these would do the trick: https://www.ebay.co.uk/itm/312026586512

I'll also order some Viton seals for reinstalling the solenoids and some fibreglass resin to rebuild the plug as you did.

Thanks

 

[OliSmith]

Scratch that actually, I don't know whether my multimeter was playing up in the heat or I'm cracking up, but I've just tried again and I'm getting consistently in the region of 0.450 to 0.510 across the four solenoids when testing forward bias, and '1.' when testing reverse bias which means it looks like the diodes are fine

I guess I'm barking up the wrong tree. Perhaps I need to get the DME checked over.

EDIT: Scratch that again. I heated the plugs and solenoids up with a hair dryer, at first they were reading normally to indicate they were fine, but I went back to check them 5 minutes later and one of the solenoids, this time on the intake side, was giving me an open reading in forward bias. I've recorded a video to show this and me comparing it with the exhaust side which was giving a normal reading. See here:

View: https://youtu.be/8fo3enVfGoA


So perhaps they are defective after all, but only at a certain temperature range.

 

[Pingu]

This is the circuit that you are testing. The 0.5 ohm reading will be the resistance of the solenoid coil. You will need to desolder at least one of the connections on the little circuit board on each solenoid so that you can measure the resistances. It looks like you have done this on one (I saw a loose red wire).

I assume that your multimeter reads 0 if you connect the leads together and 1 if they are apart.

If it is this multimeter, one click further clockwise is the buzzer (I think).

Digital 0-600V Multimeter | DIY at B&Q

Digital 0-600V Multimeter - B&Q for all your home and garden supplies and advice on all the latest DIY trends

www.diy.com

Use the buzzer to do the test if possible.

• Test the inlet and exhaust solenoid pair seperately.
• Desolder either the black or green and either the red or brown. It doesn't matter if the colours on your solenoids are different, just desolder one wire from each solenoid.
• Test across the solder points on each solenoid. It should be 0.5ohms is both drections. It should buzz on the buzzer setting in both directions. This test confirms the solenoids are working.
• Test from centre pin on plug to the outer pin. It should pass current in one direction only. Your multimeter would read 0 (buzz) in one direction and 1 (no buzz) in the other. This test confirms the diodes are working. If the reading is 1 (no buzz) in both directions, the diode is blown.
• Test from the centre pin to the other outer pin. Again, it should pass current in one direction only.

Let us know how you get on.

 

[OliSmith]

Just to clarify, I have de-soldered the green/red wires on all four solenoids, leaving the black/brown wires attached. In my last post and the video, at first I was testing with the black probe to the brown wire and red probe to the red wire (which was de-soldered) on the inlet solenoids. I’m showing that I’m getting an open reading. I then switch to the exhaust solenoids, again with the red probe on the red wire (de-soldered) and the black probe on the brown wire to show that I’m getting a reading of 0.500 (basically confirming that my multimeter is working ok). I then switch back to the inlet side and show an open reading again with the red probe on the red wire, black probe on the brown wire. I then switch probes, so red probe on brown wire and black probe on red wire. Not really sure why I did that tbh, I guess just to illustrate that I definitely had the probes on the right wires initially.

I did also check continuity across the terminals on the solenoid circuits using the buzzer setting and that was all fine.

I’ll do your suggested tests across the pins and report back.

 

[OliSmith]

View: https://youtu.be/vleJ2yyfGuo


Apologies for the awful video quality, was a quick zero prep video.

It seems to me that at least two of the diodes are open, but only at certain temperatures.

 

[Pingu]

View: https://youtu.be/vleJ2yyfGuo


Apologies for the awful video quality, was a quick zero prep video.

It seems to me that at least two of the diodes are open, but only at certain temperatures.

Just a small point about posting on the forum. If you type @Pingu in your post, I will get a notification. You should have a red number by the bell at the top right, because I have quoted your post. If you don't do the notification thing, I may miss any future posts.

I agree that all your solenoids look to be good.

The first diode you tested looks like it is faulty. The second one tested exacly like I expected a good one to test.

The reason you are not getting a buzz when testing the diodes is that their resistance is 0.5 ohms and your buzzer is not getting enough ooomph to buzz. It's not a problem, as I can see the reading is infinity in both directions on the first test, and 0.5ohms in one direction and infinity on the second test. The diode test on the multimeter is the same test as the buzzer test, but without a buzzer. They are both continuity tests. The diode test gives a more accurate measurement of the resistance.

The third diode looks ok and the fourth looks to be duff.

It seems very coincidental that the resistance of the diode is the same as the resistance of the solenoid. I would make 100% sure that the disconnected wire is isolated. I'd be tempted to put some insulation tape on it just to be 100% sure.

 

[OliSmith]

Ah, sorry. Ok, thanks for all your help with this. I’ll share the results of my diode replacement once they arrive.

 

[OliSmith]

Bit of an update. I've been doing this over the few hours I've had spare over the last week and not quite finished yet - hoping to get them sealed and back on the car tomorrow.

Ground down the moulding around the diodes using a dremel. No idea how you managed to do it so cleanly @Pingu, you must have some precision dremelling skills!

I managed to nick the wires a bit and take some sheathing off, but given it's all going to be resealed in epoxy, it doesn't really matter. Soldered the new diodes in, tested with multimeter, all working as expected. Soldered the wires back onto the solenoids.

My rebuild differs slightly from yours Pingu, in that I've designed and 3D printed a new housing which I am going to fill with epoxy resin to encapsulate the circuit and also seal the housing together.

I've bought new Viton seals for the solenoids and I will give the solenoids a clean with brake cleaner before reinstall. Just a couple of things I'm not sure about though:

1. Both solenoid covers were missing the gaskets and there wasn't any sealant around the mating surface. The car ran perfectly and made good power prior to removing the solenoids (except for when I had the spontaneous cutting out under WOT issue which I'm fairly sure was caused by the diodes) and didn't leak any oil from the solenoids, so presumably I'd be OK just putting it back together as it was without any Hylomar?

2. There was orange silicone-like gasket/sealant material on the solenoids (see images below), looks like perhaps it was applied liberally around the circuit boards and had run down the body of the solenoid before setting. Is it safe to assume this was simply applied to support the solenoid circuit board? If so, it doesn't really seem to be doing much, so I'll dab a bit of epoxy between the circuit board and the solenoid body.

The solenoid seals were replaced by MrVanos in 2014, so he installed them like this without a gasket and presumably applied the orange sealant.

 

[Pingu]

@OliSmith

I like the 3d printed casing .

There is not any need for a gasket on the plate, as there is no oil in the void. The only purpose of the plates is to stop the solenoids being blown out of the VANOS body by the very high oil pressure. You just need to stop the circuit board from earthing, and a few drops of epoxy resin should be good enough.

You shouldn't need any sealant, the o-rings should be good enough. There is a possiblity that the body was damaged when the solenoids were removed in 2014 to install new seals, and the sealant is for that.

 

[OliSmith]

@Pingu

Thanks, was a fairly straightforward design and print, printed them in PETG which is chemical resistant (potentially making it more difficult to stick together, but the epoxy resin seems to have done the trick. I'd imagine the surface roughness will help)

Re the gaskets on the plate, that was my understanding too - I couldn't see any need to install one so I just put it back together dry. Couple of photos below showing the finished casing:

Since reinstalling, I started the car and let it idle for a while. As you had said, it was a little rough initially until the system pressurised, then all seemed well. I went for a quick drive up the road and initially all was fine, but as soon as I got the RPM a big higher (3k+ RPM) it developed a rough idle. Has to be something related to the VANOS I'd imagine as that's all I've disturbed and I never had this issue before. No fault codes either.

I started it this morning. Still had a rough idle, but I had an idea, what if a VANOS solenoid is sticking slightly (I did clean them with brake cleaner and coated them in fresh oil prior to reinstall, but still a possibility). So with the engine running, I lightly tapped around VANOS unit local to the solenoids and sure enough the rough idle cleared. I had a wheel alignment appointment this morning as I've recently finished installing a Bilstein B12 suspension kit, drove to the garage about 5 miles away in fairly slow moving traffic and the car drove fine, rough idle didn't come back.

After the alignment was done, I decided to get the revs up a bit and see if the rough idle comes back and unfortunately, it did. I've yet to see if tapping with a hammer will make it clear again, but it does seem that perhaps at least one solenoid is now sticking. I guess I need to take the solenoids out and give them another clean with brake cleaner?! Is there any way of dismantling the solenoids to more thoroughly clean them that you're aware of?

Edit to add: Just seen this (post number 6 specifically): Vanos operation question (bimmerforums.com). Will give this a try and report back.

 

[Pingu]

The only thing that I did with the solenoids was to "flash" them with 12 volts and I could hear them click. Don't leave them connected or you will burn them out.

You can clean them by leaving them immersed in electrical contact cleaner, then blowing them clean with compressed air. Immerse the nozzle in clean engine oil.

Make sure that you use the correct engine oil.

S50 and S54 use different engine oils.

I completely stripped my VANOS and the diaphragm springs when I did mine, so I eliminated all possible problems. It is unlikely, but you could have a blockage in one of the galleries in the VANOS. I would be very surprised of this were the case, but if someone has run the car on cheap oil, anything is possible.

Double check all the soldered connections on the circuit boards on the solenoids

 

[OliSmith]

Whipped the solenoids out again last night, sure enough the red wire on the exhaust solenoids was loose. Re-soldered and checked all the others, as well as cleaned all the solenoids more thoroughly. A couple definitely seemed a little gummed up and were opening with a much more audible 'click' after a few cycles of spraying with brake cleaner, activate with 12v on/off a few times and compressed air.

Put it all back together, took it for a short drive including some high RPM and all seems fine. Fingers crossed it's trouble free for the foreseeable. Shame the weather has cooled off now, so can't say for sure whether my original cutting out under WOT on a warm day issue is resolved. I'll post back in here once the weather picks up and I can say for sure - just in case anyone else is searching and comes across this thread, it's handy to have it closed out. It's forecast to be a nice sunny day this Friday...

Regardless though, thank you so much for all your help on this @Pingu, both through this forum and through your original YouTube videos. You're a credit to the community

 

[OliSmith]

Shame the weather has cooled off now, so can't say for sure whether my original cutting out under WOT on a warm day issue is resolved. I'll post back in here once the weather picks up and I can say for sure - just in case anyone else is searching and comes across this thread, it's handy to have it closed out. It's forecast to be a nice sunny day this Friday...

It got up to about 26 degrees on Friday. Took her for a spirited drive and all seemed well, so it seems this issue is solved!

 

[MattD]

I have the same issue on my s50b32, when the weather is warm and the engine ia running for few hours, the engine just cut off when I WOT, it seems i have a dead solenoid? fyi, i have replaced the solenoid on the exhaust side due to it popping out due to wear and tear of the seals it seems, i have changed the seals in the vanos solenoid and soldered the solenoid on the exhaust side, but i never replaced the cam side. currently my car runs well on cold temp but the idle is rough can still pulls but when its warm i could not WOT and have to wait the engine to cool off then the egine will start. Could I have a dead solenoid on the cam side..fyi my exhaust solenoid was burnt hence i changed them to a used ones and once reinstalling back the car then runs rough but can still pulls hard.. could it be my cam side solenoid is not functioning or dead when its hot? please help me

 

[OliSmith]

When you say that you have to wait for the engine to cool off, is it about 10 seconds? If so, it’s waiting for the fuel pump to prime again. For me, the faulty vanos solenoid diodes were causing the fuel pump to lose it’s power supply, hence the engine loses fuel and cuts out. If I flicked the ignition off and tried to start the engine again straight away, the fuel pump wouldn’t prime but if I waited 10 seconds or longer before trying to start you could hear the fuel pump prime when turning to ignition and the car would then start straight away.

Personally, I’d highly recommend taking both the exhaust and inlet solenoids off and testing/repairing them as described by Pingu above. Make sure you test them in a warm environment if your issue only happens on a warm day like it did for me. Are you in the UK? I could send you some 3D printed plug covers for the diodes, same as the ones that I made for mine if you cover the cost of postage.