Engine Knocking under boost
 

After replacing my turbo to a K27, under around .7+ bar, I get engine knock. Few questions:

1) I first thought it was some thing loose I forgot to tighten. Sounding like rattling. I continued to run full boost for a few times. Could I have harmed the engine?

2) It did not knock with the K26. Does it make sense that the K27 would cause this?

3) How can I get rid of the knock?

4) Can I still drive the car safely but being careful not to boost?


Other background that may help: New plugs, dizzy, by-pass valve gasket, new air pump filter.

Thank you.

Timing?

First, I don't think you had K26 before. K26 is small turbocharger used in Porsche 944, Audi 200 Quattro. Early 930 were factory-equipped with KKK 3DLZ, not K26.

Second, make sure you don't have exhaust or vacuum leak. Sometimes it sounds like knock. Yes, you can damage your engine (it's mostly fractured compression rings) if you run it knocking, but it's impossible to say for sure how long you have to runt it that way to damage it.

3DLZ and K27 are roughly similar...K27 is somewhat more effective. So even if K27 is pumping more air into your engine, it's shouldn't ping at 0.7 bar if 3DLZ didn't at 1 bar.

I suggest to check for leaks...exhaust leaks can be checked by applying long rubber-hose to header flanges when car is hoisted on car-lift and motor is running. Also, check everything else that could be bumped during the swap - sticky pre-ignition mechanism, clogged fuel filter etc.

Also, it would be a good idea to get it on dyno and check Air/Fuel ratio, or use LM-1.

Chances are it is something to do with the timing. Have you verified it 100%, including the vacuum signal to it?

I am guessing you are running lean. The K27 puts more air in your motor and the CIS can't keep up. Did you set the timing to factory specs. If so back the timing off a little. Or get the air/fuel mixture measured on a dyno. Then you can make sure you aren't running lean

Thanks for the tips. I'll research on this board how to check/adj the timing or af mixture (unless someone's got a direct link to it).

I'm hoping it's an exhaust leak. The K27 didn't mate well with my Monty exhaust. I couldn't get one of the nuts on cause of the angle of the exhaust pipe. So I left it free hoping that the three other nuts would do it's job.

I doubt it. He said car is pinging at stock boost level (0.7 bar) and 930 CIS can keep up to 1 bar of boost w/o pinging even with 3DLZ. 3DLZ is less effective to boot so it heats up air a lot when pumping 1 bar so it would be even more knock-prone than K27.

Have you verified your boost? The K27 puts out a LOT of boost potentially and this could cause it.

A lean condition could cause it.

Too much advance could cause it.

Bad gas could cause it.

If all he did was change the Turbo out...then the above is a good start...put the fourth bolt/nut on.

He mentions a new dizzy so all bets are off...

An exhaust leak won't cause this problem. An intake leak might, depending on it's location. Verify there are no loose or pinched vacuum lines. Also, you mention a 1 bar spring in your mods. How have you verified the actual boost?

I tried to test the wastegate using compressed air. I was told the spring I have is a 1 bar spring, but I can only manage about .8 or so (stock). BTW, other than the compressed air test, are there any designations on the spring to indicate what is is? I can't seem to find anything.

If there is an intake leak, would this prevent me from getting a full 1 bar boost and at the same time cause a lean condition?

I'll try to do more troubleshooting. Everyone's input has been very enlightening. I love the knowledge of this board.

Porschett,

Have you considered that it might be a broken head stud?

That would cause a rattle under boost and possibly some damage to the head or cylinder.

And you did recheck the timing?

Just a thought.

Tinker

I did nothing on the timing. I figured a straight turbo swap does not necessitate a timing modification. I'll have to research on how to do this.

Can I continue to drive the car in this state (being careful not to apply any boost)?

You might want to try:

1. Check or retard the timing
2. Reinstall the original turbo
3. Run higher octane gas or premix with some race gas
4. Reduce your boost level
5. Check the mixture to make sure it's not too lean. Use an LM-1 unit:

http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_exhaus_pg11.htm#item44

-Wayne

One more thought - knocking will indeed destroy your engine if left unchecked. It's the single-most worst thing that can happen to the Turbo motors, and will indeed cause some serious damage, particularly if the car is running lean...

-Wayne

Thanks Wayne.

I'll try the following in order of least complexity:

Run higher octane gas or premix with some race gas
Check or retard the timing
Check the mixture to make sure it's not too lean.
Reduce your boost level
Reinstall the original turbo

Ah yes..I see. But an exhaust leak hear through the internet can be anything.

Why a new dizzy too?

No offense, but if your problems started with the changes, then target each of the changes. Start checking all the changes you made...eliminate to small stuff first.

The way I see it, the changes I made can only help (new plugs, dizzy, air pump filter, by-pass gasket). It should not make it worse. Maybe by making it better, I have to adjust things like a/f, timming, etc?

BTW, I changed those items above cause it was time for a 'tune up' and I had the 'While you have it apart, do this" mentality. Plus, it's a great way for me to really get to know the engine. 8)

I'm not breaking down the merit of fixing or renewing parts, but knowing what changes you made should be provide a good path to successful troubleshooting. Good luck.

Hi Guys,

I think I found the problem...the retard vaccum line (black?) is half crimped, limiting vaccum. So at full boost, it's not getting enough retard hence causing my knocking...does this sound correct? Advance (red line?) off boost, retard (black line?) on boost?