B6 S4 no power in the higher rev range

[Walter0187]

Hi everyone

I bought a B6 S4 last year. It's a florida car and i got it with a non running engine. I used to own B5 S4s back in the days but have never had a B6 and was not aware they were using timing chains. I got the car for a winter project and love to work on cars and wanted to fix this. So i did a compression test and found no compression on driver side cylinders. (cylinder 5-8 i think). So i pulled the engine, pulled it apart, sure enough, all valves on cylinder 5 to 8 are bent. cylinder 1-4 were fine. there were several cracked chain guides, but the one that caused the engine to destroy itself was the one between the two cams on the driver side head. The guide broke and the chain was running on the metal piston for a while until it started jumping teeth and bending valves. The mechanical cam adjusters both had very little wear and look fine, so i didn't replace those and same with the electric cam actuators. I tested them by applying 12v to them and they work fine. I replaced everything else, guides and tensioners. Put everything back together, start the car up and drove it a little bit. It ran fine but at first was throwing codes for timing. I can't remember the exact code now. By the way, i bought all the timing tools for this car and used them, crank lock pin, cam lock bracket, and the Setting tool for the hall signal sender. So when it threw the code i figuered there was something wrong with my timing and was able to get the mechanical adjusters out without pulling the engine this time and realized i didn't tighten the five bolts on the mechanical adjuster enough and they came loose, so the unit was not sealed anymore. So i put everything back together again, set the timing again. Took it for a spin, and the car just does not pull. I can get it to highway speed quiet easily, but the car just doesn't pull much past 4k to 5k revs.

So i did a compression test again, i have compression on all cylinders, i have to say though, compression is slightly higher on the new head on all cylinders. about 150 on all cylinders on new head, 135 on all cylinder on the passenger side head. So that is a difference of about 10% and as far as i know 10% is still ok. i assumed that is because the new head had about 70k on it while my moter has about 138k. I reused the cams from the damaged head (not sure why i did that or if it matter). I was 100% sure my timing was right. So i tried a bunch of things. The car has an aftermarket cone type airfilter, I tried driving around without hood, to make sure the motor gets enough air, tried driving without air filter, tried driving with MAF sensor unplugged, drained the tank put new premium fuel in there, i discovered the flap inside the intake manifold was stuck, so i fixed that. But nothing changes. The car just doesn't pull in the higher rev range. And when i connect my vagcom, theres no engine codes what so ever (unless i unplug the MAF). I checked advanced measuring blocks, channel 92 to 94 i believe it is, and everything with the timing seems to be ok. both the lines, actual and specified follow each other pretty close.

So i'm at a loss here don't know what to do. I had a couple of days off of work last week and decided to pull the engine again to make sure my timing was all good and the mechanical adjuster and electric cam actuator work fine. So i pulled the motor, the timing is spot on. Everything lines up perfect, i can insert all the lock tools no problem. I still took the mechanical adjusters off and did the air test, and they release and lock just fine. I tried applying 12v to the electric cam actuators while blowing air through the holes and that all works fine. i cannot find anything wrong with it. Put everything together once more in record time (you get really fast doing this as ofter as i have now). take it for a spin, and still no power. My cousin just recently bought himself an s4 so i took his car to compare, and there's no comparison, his pulls strong. So i tried swapping his ecu into my car ( also had to swap cluster and key to defeat immo) and guess what, the car still doesn't pull. And vagcom shows no codes. So i checked a couple more things, i made sure my accelerator paddle works, it opens the throttle body valve 100%, I pulled my downpipes (thought maybe they were restricting exhaust air flow), take it for a spin without downpipes, (extremly loud) but still nothing.

I don't know what to do anymore. I have spend a ton of money and time in this car already and just can't get it going.
If anyone has any ideas or knows what else i can check, please tell me......

thanks

[badger.]

damn that sounds like a lot of work..I would think your best bet is do some logging while making the pulls and uploading for those much smarter than me with this platform to look at. I would imagine there is something in there that can pin point the cause.

My immediate thought was the knock sensor(s) as there have been a few threads on here where improperly torqued or over torqued or bad knock sensors can cause the car to be sluggish up at the higher rev ranges. Might be a quick fix, might not. I don't know if they alone can cause such a dramatic change or not.

[roboto_1337]

I could be completely wrong, so feel free to shoot this down, and I don't know if this would throw codes...

but is it possible that there's a pluggage in some of the injectors? or a problem with the fuel delivery system?

It may show up as running lean if there were problems I suppose... just a thought.

[Cinna696]

Wouldn't the car be in limp mode if you were just driving it around without downpipes? I would try swapping the exhausts since you have access to your friends car and testing it that way. I had a similar problem when I got a clogged cat with a piggie pipe purchase.

Have you tested the flapper actuator? Not just make sure it's unstuck - the power difference can be significant if it's not working properly.

What do your spark plugs look like? How are the coils?


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[Velox]

isnt 135 compression considered worn?would do a leadown test just to be sure

[roboto_1337]

could it be that the cam is positioned too far in advance? this would give you good low end torque and hp but rob you at the high end if it doesn't retard enough when the adjustors kick in...

just spitballin'

[Dolphin S4]

You said you still have one cylinder head that wasn't replaced? Replace it.

I had a vr6 with the same issues.

I had the valves just touch the Pistons and everything looked fine (no bent valves from what I could see).

Did a compression test that read out fine across all cylinders.

Car would pull ok but past
5k it would just run out of air almost and die off.

Put a good head on it and the power was restored.

Even though you're getting good compression and no codes it wouldn't hurt if you could swap a good head on on the side you haven't replaced

[AudiElite]

Sounds like the valve springs are weak. I know someone with one now and at high revs it has zero power and flashing check engine light with misfire codes. He compared the old valve springs to a new set and it was a pretty big difference. His still had great compression and drove fine. If you never drove it in the higher rpm range you would never know. Maybe check the other head and send it to be tested.