Power dip at 4K rpms. Sticky vanos?

[4dri4n]

Hi everyone!

I have an m50 e34 525i. However I thought about posting in this forum because I have more engines in common with this section and is more likely that someone else shares or has experienced the same problem I have.

The thing is that I can clearly notice a dip in power around 4K rpms. The car has some kind of bipolar nature. It seems it gets used to some kind of driving. When I drive at low rpms and relaxed driving, it seems it performs better at low rpms and so. When you want to go mad with the car and push it to go up in the rpms range, it seems kind of lazy. Like if it is not used to go in that rpm range. If you keep enough pushing it and driving agressive it seems it becomes better and it clrearly performs better in the upper part of the rpm range. But, and this is a big important "but", if you want to drive it again relaxed and so, it seems like it has lost some torque and it takes a while driving it relaxed and smooth so it performs ok again in that lower rpm range again.
It's weird isnt it?

Well, I replaced a lot of stuff. I replaced all of the vacuum hoses, rubber boot, coils, sparks, knock sensors (both of them were scrap and car performed like BS), cam sensor, crank sensor, TPS, MAF and more stuff I cant remember. Water pump, thermostat, coolant hoses, emmm... fuel filter, fuel pressure regulator... well nearly everything. And it was awesome because it performs now much much better than when I bought it last year.
I also replaced vanos seals and so and it was a great upgrade aswell.
But the thing is that I cant get rid of that bipolar nature. I think that maybe it has to do with the vanos system itself. Well maybe the power source that controls it. It seems like if it was sticked every time it commutes. Like if there was some kind of lag. It should open/close at 4k rpms. However when I floor it at 2K rpms or so, then the car pulls like a lot, then at 4K it seems it takes a break, and then at 5.5k it rushes again until 6500 or so. I think it should pull strongly at 4k and give its maximum peak of torque around 5K but it clearly doesnt.

So I would like to hear some sugestions from you and what you think of it. Diagnosis says everything is correct. No faults or anything.

I would like to know aswell how the vanos is powered. I mean of course the DME must give some signal so the solenoid actuates. But there must be some kind of amplifier device wich sends the power signal to the vanos. Like maybe some relay, or maybe its the DME itself I dont know! How can I check/test this system? Maybe if there is some sort of device I could directly replace I would do it like immediately I dont know. Maybe my DME is broken... maybe last owner installed some BS ebay eprom with BS mapping... I dont know... there are so many things that can go wrong... well at least now I have like a lot of things I know for sure are OK.
What is left to replace that could influence somehow in the performance of the car are: intake air temp sensor, water temp sensor and fuel pump. Those 3 things are left to replace. But I dont really think they are responsible of that kind bipolar nature and the dip at 4K rpms... I am pretty sure it is a vanos thing...

[snow663]

Same problem i got just at a different rpm. Vanos is on under load <3k rpm off above 3k Flying525 seems to think i have a bad DME ive tried everything but, so ive got one coming in the mail.


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[4dri4n]

Well then I would like to have some feedback once you replace that DME!

One thing I forgot to mention is that the car seems to pull much better at low rpms when it is not fully warmed. I mean, when I start it and move arround enough so the temperature climb until nearly 12 o'clock, but tye engine bay and all sensors and intake manifold are not heated yet.

I believe I have seen somewhere that the ECU has some kind of cooling aswell isnt it? Like some fan for cooling or so... maybe its time to check whats in the box...

[FiberFast]

I would go like this.
1. Replace Vanos solenoid
2. Replace Vanos
3. Start looking at DME
The Dme's don't usually shit on you.

[snow663]

Well then I would like to have some feedback once you replace that DME!

One thing I forgot to mention is that the car seems to pull much better at low rpms when it is not fully warmed. I mean, when I start it and move arround enough so the temperature climb until nearly 12 o'clock, but tye engine bay and all sensors and intake manifold are not heated yet.

I believe I have seen somewhere that the ECU has some kind of cooling aswell isnt it? Like some fan for cooling or so... maybe its time to check whats in the box...

I too experience a difference with ambient temperature change. Also engine temperature, when warm My hesitation is around 5k and on. And right around 1700 it seems to die for a split second before taking off. Ive damn near built a new motor with no improvement besides fixing leaks. And replacing all the old original sensors with new ones. Fuel is good and spark is good. Compression checks out. My hesitation changes as the motor warms up from bearable to impractical to drive. Im pretty much at my wits end.
I also noticed that under certain conditions if i hold the throttle steady on flat ground my MPG gauge moves back and forth in alignment with a slight surge i get in power.

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[samy01]

if i hold the throttle steady on flat ground my MPG gauge moves back and forth in alignment with a slight surge i get in power.

i'm not sure about it, but as far as i'm concerned the MPG gauge is pretty much directly related to the injectors injection time

did you replace MAF or 02 sensors ? are they good ?

[snow663]

i'm not sure about it, but as far as i'm concerned the MPG gauge is pretty much directly related to the injectors injection time

did you replace MAF or 02 sensors ? are they good ?

Its got new exhaust gaskets and o2 and ive tried subbing a MAF i got from chris off this forum the MAF offered a slight improvement until the computer relearned the problem. It always "learns" the same problem no matter what i try.


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[samy01]

so you pretty much replaced everything ? on other cars i've seen stuff like this (well not exactly the same but similar) and it turned out the ECU was mentally retarded. personally i'd test another one to be sure it's good.

[snow663]

so you pretty much replaced everything ? on other cars i've seen stuff like this (well not exactly the same but similar) and it turned out the ECU was mentally retarded. personally i'd test another one to be sure it's good.

I have replaced everything with the exception of the IACV which is spotless and the DME which has spotty exterior corrosion but internally is clean as a whistle. So the DME may have been exposed to some form of corrosive vapor.

P.S. i have a dme in the mail so we shall see


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[samy01]

most of the time you don't see if the dme is bad. well i never opened the bad one actually. if you could get one easily to test it then i'd do that.

i don't have much experience with the e36 diagnostic software stuff, but on other cars you can hook up the computer to the car and while driving see most of the stuff that's going on with the sensors and all. i did that once with my e36, you could see all the sensors and exactly see what they're doing. wouldn't that help?

[snow663]

most of the time you don't see if the dme is bad. well i never opened the bad one actually. if you could get one easily to test it then i'd do that.

i don't have much experience with the e36 diagnostic software stuff, but on other cars you can hook up the computer to the car and while driving see most of the stuff that's going on with the sensors and all. i did that once with my e36, you could see all the sensors and exactly see what they're doing. wouldn't that help?

Yeah but mines obd1 so theres some hardware and software requirements i believe i have everything except the interface cable. Which runs about 80$ but that leaves me stuck to an old dell desktop pc.


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[FiberFast]

So you have a new vanos solenoid?
I want to know if that new DME worked out for you.

[4dri4n]

I am really interrested aswell in seeing if that new DME worked for you.

I'm back right now for a quick spin with the car. When the weather is cold it pulls quite well. I mean, I could be satisfied with the level of performance I have when it is cold as it is today. It really pulled well. I miss some torque down low at 1.5K ~ 2K rpms but I can deal with it.
But when it gets real warm during the day... it just doesnt pull always the same! Sometiles it pulls grat, sometimes it seems it doesnt... sometimes it is completely gutless... sometimes I can climb some hills at around 80 kmh in 5th gear and then floor it at 2.3K rpms and it surges pretty damn quick! Sometimes it doesnt. Not even in 4th gear.
I must say that despite all of that, the car improved like a ton! It was nothing compared to what it is now. Now I can drive it. I have this kind of bipolar nature, but even so when it is bad, it is much better than it was when I bought it 1 year ago. Vanos seals and knock sensors were what improved the most.
I bought some interface and ediabas software and so but I was unable to conect with my laptop. But I was able to do so with some diagnostics tool. At first I thought it may be broken. The fact that I disconect whatever sensor I choose and the check engine light does not come on may be a sign of a bad DME. I mean it could be the lambda sensor, MAF or even once that I forgot to reconect the TPS and the car drove like nothing happened... no light came on... it could be the light bulb itself I dont know...

Well any feedback, any coment experience will be a help!

Thaanks for posting!

[snow663]

So you have a new vanos solenoid?
I want to know if that new DME worked out for you.

I actually went through redoing the timing and followed the test procedure for testing the vanos travel with compressed air. It all checks out. I can activate it with battery voltage and its crisp and on time every time. I am getting power to the vanos from the DME too.


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[snow663]

I am really interrested aswell in seeing if that new DME worked for you.

I'm back right now for a quick spin with the car. When the weather is cold it pulls quite well. I mean, I could be satisfied with the level of performance I have when it is cold as it is today. It really pulled well. I miss some torque down low at 1.5K ~ 2K rpms but I can deal with it.
But when it gets real warm during the day... it just doesnt pull always the same! Sometiles it pulls grat, sometimes it seems it doesnt... sometimes it is completely gutless... sometimes I can climb some hills at around 80 kmh in 5th gear and then floor it at 2.3K rpms and it surges pretty damn quick! Sometimes it doesnt. Not even in 4th gear.
I must say that despite all of that, the car improved like a ton! It was nothing compared to what it is now. Now I can drive it. I have this kind of bipolar nature, but even so when it is bad, it is much better than it was when I bought it 1 year ago. Vanos seals and knock sensors were what improved the most.
I bought some interface and ediabas software and so but I was unable to conect with my laptop. But I was able to do so with some diagnostics tool. At first I thought it may be broken. The fact that I disconect whatever sensor I choose and the check engine light does not come on may be a sign of a bad DME. I mean it could be the lambda sensor, MAF or even once that I forgot to reconect the TPS and the car drove like nothing happened... no light came on... it could be the light bulb itself I dont know...

Well any feedback, any coment experience will be a help!

Thaanks for posting!

Its really hard to describe my problem to a T because it is always different every time i drive it. The only constant is the fact that it hesitates when hot. When cold its somewhat bearable.


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[snow663]

So i have replaced my DME and that was one of my problems but i still have some hesitation at high rpm and a power dip at 2000rpm when taking off.
I did some disconnect testing and i got some results im not really sure of but i think my upper end power loss has to do with the vanos and my power dip at low rpm comes from the IACV can anybody here verify my results?
Unplugging the vanos cost me a lot of power al the way up the rev range and i noticed after a high rev the vanos would rattle and rpms would hang at 5500 for 2-3 seconds before slowly coming down. But my top end hesitation blended in with the whole rpm range.
Unplugging the IACV caused my engine to idle at 1000 rpms, after 30 seconds or so idling it would dip, then rev a few times and then idle at 1000 again. Reconnecting it only caused it to rev to 2500 again and again requiring a DME reset to get my idle back.


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[4dri4n]

I think it is strange that the vanos fails. In theory, if you unplug the vanos what you should get is not torque down low until you hit 4K rpms or so.
That is why it is strange you say just the opposite of what everyone says...
Have you thought about fuel pressure regulator or maybe fuel pump or so!? I dont know I guess you already did...
Did you replace the relays aswell!?
I am starting to think thay my problem may have to do with 2 things... on one side maybe the fuel pump is in its last days... on the other maybe some stuff with tye DME. When the car is still a little bit cold, after a few minutes runing with it just when the temp needle reaches the 12 mark but you can still feel the car is not really warmed up yet, the car just pulls smooth and it surges quite well. I could live with it quite satisfied with the performance of it in the situation I described. Once it gets fully warmed and the weather is hot, it just feels sluggish.

A member from the spanish bmw forum described the same sort of thing with his 325i m50. He went for a dyno run and the results were like follow:

2rp9obn.jpg

The red line is the actual dyno test. The green line I draw it myself, and is what you would expect it was. I sometimes feel that dip just in there. I guess sometimes I dont feel it but is there aswell.
Anyone know what could be causing it!?

[snow663]

Im pretty sure i have sticky exhaust valves and a lazy IACV
If i hold a piece of paper up to the tailpipe it flaps back and forth and when it misses it sucks the paper in.


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[Eric93se]

Stop hijacking his thread! WTF


4dri4n, I don't think there is anything wrong with your Vanos. But the three things you did not check can be the cause of the poor performance, check fuel pressure, air temp sensor, and coolant temp sensor.

[4dri4n]

I think I finally found the issue. Went to replace the fuel pump these evening with a unit I had from a 520i e34. It cost 10 €. Now I know why it was so cheap. It's dead.
The fact is that when I disconected the clamps holding the hoses, one of them was loose. It was weird but I though, well maybe this one is coming back from the fuel rail. But it wasn't, It happened to be the pressure line. I noticed once I fitted back again the original pump. There are two arrows pointing the direction of fluid. And the one coming out of the tank was a bit humid, a sign that a small amount (maybe small maybe big amount) was leaking out of there.
I should replace all fuel lines. They are 23 years now think it's time to do so. Maybe I should buy a brand new fuel pump aswell.
Anyways, the car is still not at 100%. I think there is more room for improvement. Those two sensor remaining to replace are not expensive. IAT and coolant temp sensor. Will replace aswell.
I think that right now the car may take a bit time to improve as it seems as the adaptativity function is doing its stuff. It seems logical, as if it hadn't the proper amount of pressure until now, maybe it tried to correct the fuel deficit by increasing the time the injectors were open. I don't know.
The thing is that I'm back right now for a quick spin and it clearly performs different. It doesnt have the torque it had, but almost. But top end is clearly better. That's why I guess the adaptativity function is doing its things...

Don't know...

Thanks all! I will report results in a few weeks or so!

- - - Updated - - -

Stop hijacking his thread! WTF


4dri4n, I don't think there is anything wrong with your Vanos. But the three things you did not check can be the cause of the poor performance, check fuel pressure, air temp sensor, and coolant temp sensor.

Yeah, I will replace them for sure.

Thanks all!

[Eric93se]

You've replaced a lot of parts, you can clear engine adaptations. Remove the negative from the battery and touch the positive for 30 seconds.