detonation at part throttle Turbo'd s52

[billyr3d]

Hello Neel, I was desperately searching the internet for answers when I cam across a discussion that you had with someone in regards to VANOS and it's effects to engine drivability. You sound very knowledgeable with ECU tuning and my fingers are crossed in hopes of you shedding some light on the situation

I have had a persistent detonation problem with my 1998 BMW M roadster equipped with a Technique Tuning stg 1 Turbo kit ever since I installed it. I am a professional technician that has 15years experience working with german cars and have tried just about everything to eliminate the problem.

The following is a write up that I posted on a forum in hopes of someone else having the same issue..

I completed the install of the TT stg1 kit on my 98' s52 about 2 weeks ago. During my first test drive, and going up a hill at part throttle is when I first heard, what we'll call 'engine detonation' until proven otherwise. The night was late and I was tired, so I tucked the car away and left it for the next day to start looking into and re-test driving, to find out exactly when and what was causing it. I’ve been chasing it ever since

Here’s what happens. Driving along at cruising speeds, rpm’s around 2000-3000 and then beginning my accent to ‘boostville’ with moderate load (part throttle) I hear a distinctive detonation noise coming from the engine that sounds worrisome. This turned into fear of blowing my engine when I took it to the dyno to see what numbers I was making. Standing next to the car under load was terrifying! The noise was so much more predominant with all the other sounds eliminated, ie wind, tires, etc. All that being said, the dyno results look great though, right? Click Here to view

I sent the ECU to the tuner, who then did his magic and verified that indeed I logged some occurrences of detonation and that the lambda adaptation was +10%. He suggested that a significant vacuum leak or faulty maf could be the culprit and quickly had one out to me the next day along with the adaptations of the ECU reset.

In the downtime, I installed an autometer vac/boost gauge. I removed and inspected the newly installed NGK BRK7E’s which all looked great. I then used a bore scope and checked every cylinder thoroughly finding only some normal carbon deposits.

Excited when I got the shipment, I installed the ECU and replacement Maf and took her out for a test drive. Detonation resumed Boost gauge reading a max 6.5 but averages 5psi. I have an 8.5 spring installed in the wastegate? So, what could it be? I got on the phone



and called the tuner for some much needed assistance. Always helpful, they had some fresh suggestions. I checked everything that I touched during the install, making sure all connection where tight and right. I performed an injector flush/combustion chamber servicing. I replaced the fuel filter



and tested the @ idle fuel pressure which was 45psi with 20in.hg being applied to the regulator. Road tested, detonation still present.

I drove around and emptied the tank of the 94 octane fuel and headed to the racing fuel depot. Pumping in the 110 Octane fuel I watched the numbers on the pump and saw nothing but dollar signs even though they weren’t displayed.

With fingers crossed, I drove around for 10 minutes before easing into the test. Third gear, moderate to heavy load, rattle rattle rattle.


My next plan is to test the fuel pressures during driving conditions. I couldn’t do this today as I didn’t have a long enough hose for windshield mounting. I’m also planning on picking up a wideband AFR gauge so that I can see if the noise and AFR’s are directly related. Unfortunately, I also have to get a second bung installed as the down pipe only has one that the factory o2 sensor resides in.

So, that's my story. I'm open to ideas. Thx for reading.

**UPDATE June 28 2009

Alright, well believe it or not, I'm still dealing with this detonation problem. I left off with wanting to test the fuel pressures while driving and install an AFR gauge.

I've done both. The fuel pressure under load is approximately 51psi - OK. I went through some BS with the AFR gauge but finally got it all straightened out. The gauge that was sent to me was defective right out of the box. as if I didn't have enough headaches already.

I've been watching the AFR gauge closely since I installed it last week and here's what I'm finding... When I first start the car, it kicks and shakes a short bit (15 sec) before getting it's footing and stabilizes around 14.7- all good.

I start driving - first gear, not going anywhere in a hurry, and she fights a bit to keep a cool stoich mixture but manages to do a half decent job. - this seems all most the same for all gears under the same circumstances.

Now, ease into the throttle (partial load, starting to make some small boost if any) and the numbers start really fighting - 15.7>16.0. 16:1 is the leanest my autometer gauge reads and pegs there for a second or so as long as I stay in the partial load range, all the while I'm hearing the detonation that I've been complaining about.

If I really get into her, WOT or decently into it I get 11:2 > 11.7:1 all good right?

I've read the tps readings from carsoft to ensure that the DME is in fact seeing the movement of the throttle in the partial ranges and it is.(0.76v@idle) I am gonna check to see what the temperature readings are tomorrow of the intake - maybe it's reading a consistant but in spec value? i do find that when the night is cooler the detonation seems to be better...

Today Neel, I went out again with the carsoft program and logged as much info as possible. I find all the specs to be within the normal ranges. The only values that I am unsure about are the camshaft position and the injection timing. I do not have any nominal values for referance.
What I did notice today, and this is where you come in, is that when my VANOS switches from LATE to EARLY is when the detonation seems to occur. Is it possible for the VANOS to be malfunctioning without setting faults or is it more likely that the retuned ECU is not correctly tuned? I do have the catalyics still installed and the tuner said that he was fully aware of this during his tune.

I'm really stuck here Neel, any input at all would be greatly appreciated. Looking forward to hearing from you.

[Neel]

Let's get to basics here:

Top reasons for detonation:

1. Too low octane.
2. Too much intake air temp.
3. Too much engine temp.
4. Too much timing.
5. Too lean mixture.

You've eliminated 1-3. And you KNOW 5 is happening. So there you go. This ain't rocket science.

Motors WILL detonate at part throttle/light load. And 6psi of boost at 2-3k is NOT trivial. I'm not surprised that you are detonating, and I'm not surprised that you can't fix it.

I think some better data logging equipment will confirm this. You should get something that will allow you to log boost, RPM, throttle position and lambda in a synchronous manner. If you see it go lean when boost comes up, your tuner needs to fix it.

This is why I don't care for stock ECU reflashing. Do you know what your timing is when its detonating? Does your tuner? Why don't you just add some accel fuel? How about some fuel with rate of change of MAP? You probably can't becuase the stock ECU won't let you.

Until you address these, you will not fix your det problems.

-Neel

[billyr3d]

Hey Neel, I understand that it is a timing issue having eliminated the other possibilities as indicated in the original post. My question is more so, why is the timing out? I'm curiuos about the VANOS operation before I send the ECU back for a retune. I can not adjust any of the parameters as it is a factory ECU as you made mention.As I indicated, the noise seeming is directly related with the operation of the VANOS. Am I infact getting the 12.5 degrees of cam advance and the ECU isn't compensating or vise versa? If I'm not getting the 12.5 degrees I would imagine that I am creating higher combustion temperatures and pressures that are causing the detonation. The engine does run hotter then I would like. Do you know the nominal values I should have on the camshaft position sensor and the ignition timing? WIth that info I will likey be able to pinpoint the problem.
Thx for your input Neel.

[Neel]

I understand that it is a timing issue having eliminated the other possibilities as indicated in the original post

Wait, am I missing something? In your previous post, you said:

Now, ease into the throttle (partial load, starting to make some small boost if any) and the numbers start really fighting - 15.7>16.0. 16:1 is the leanest my autometer gauge reads and pegs there for a second or so as long as I stay in the partial load range, all the while I'm hearing the detonation that I've been complaining about.

You have to FIX this before you do anything else. Its TOO lean at part throttle under boost. This about this for a second - 0psi boost is the same manifold pressure as you would see at WOT if it was NA. So you have MORE cylinder pressure at those light loads/part throttle than that engine (and the tune made for it) experienced at WOT. If it doesn't have similar or even more fuel, its gonna be too lean.

As I indicated, the noise seeming is directly related with the operation of the VANOS

I'm not even going down this path because I think that's the tail wagging the dog. The VANOS is designed to maximize cylinder filling across the rev range. I don't think temps are your issue. And higher pressures? That's what you want. You just need to get your fuel and spark right for those higher temps and pressures.

Regards,

Neel