Car: 2001 Firebird Trans Am (5.7L V8, 4L60E, 3.23 axle).

Symptom:
Lightly opening the throttle at 1000-1500 RPM in 3rd gear you will hear a "rattle" just prior to onset of spark knock; and then when coasting with zero throttle under the same conditions the rattle can also be heard; otherwise if throttle is opened a larger amount, the rattle/knock don't occur.

the "rattle" sound is distinct from the sound spark knock makes, and is coming from the engine, and not from chassis;
under no load (rev up in neutral while car is moving at same speed or stationary) the rattle/knock cannot be heard;

MAF sensor is clean, air cleaner filter is new, no air leaks, long term fuel trims are +/- 1%, MAP/TPS show sensible values, plugs/wires are new, plugs look normal and not fouled, ECT is from 192F-199F, running 91 unleaded (CA), octane boost and/or mixing in 100 unleaded makes no difference, fuel filter changed every 15K miles, fuel rail pressure normal 58 psi, car came with no EGR.

TCC is in applied state when rattle/knock occurs (factory programmed).

I have noticed some oil in the PCV plumbing and a light amount of oil on engine side of the throttle plate.

Questions:
- what is the "rattle"...? It seems related to spark knock, but could it be something else (flex plate, valvetrain, pistons)...?
- the car has always knocked since new, I have never been able to correct this, what else can I look at...?

Thanks, I enjoy reading this site.   

Ronnie,

Thanks for the reply.

I checked the operation of my knock sensors, the audible knock seems to correlate with KR seen my the logs...
the only knock pid that the PCM reports seems to be KR (knock retard degrees)... see attached.

[oops... I forgot to position the cursor]

Ok, I'll pull the manifold off and check the knock sensors for water/corrosion [I have a new set of knock sensors].

The only DTC I get is P0420 (bank 1 cat efficiency), and I'm going to diagnose this soon
(it happened when I put new O2 sensors [only because I had them] prior to a smog test;
I'll swap left/right after-cat sensors and see if it's the left cat or the O2 sensor)...
you can see HO2S12 V is reacting too soon in the attached pic.

I do hear piston slap at cold idle, but it does go away once warmed up or under any load.

I'll post more info...

Hi Joe,

I really like that graphing you're using. If you don't mind, what scanner/graphing program are you using?

By the way, you seem more like a technician rather than a non-technician.

Thanks,

I have another log from my commute home today...

The "rattle" was clearly heard right where the cursor is in the attached pic and is immediately followed by audible knock.

I'll post more as I progress... 

Thanks for viewing.

Another question: if oil is being drawn thru the PCV plumbing into the intake manifold, could this be a direct cause of knock
(other than the indirect cause which would be the resulting carbon deposits in combustion chambers)...?

Does oil ingestion lower the effective octane number of the fuel/air charge...?


Carl,
I'm not a technician in my daytime job, so I posted in this section of the forum;
I do like reading the technician's section, there's some very good insights there. 

Thanks,
Joe

Hi Tom,

Ok, I'll have to "revise" the PCV plumbing... PCV is picked off from rear of both valve covers (Firebird style)... I'll swap to the valley cover PCV pick off (Corvette style).

Tom Roberts wrote on Mar 18^th, 2008 at 10:52am:

Ok, thanks.

Tom Roberts wrote on Mar 18^th, 2008 at 10:52am:

I live in So. Cal. so I'll probably have to do it at night somewhere remote, this is going to be fun... 

Thanks, appreciate your comments,
Joe

Hey joe,
Usually they use a tool made by several tool companies that mist the chemical into the intake system--look for a company called Run-Rite, I have had good success with there product-Intake cleaner. One can also use water..its an old trick..back in the day.

http://www.efilive.com/

Here is a link to the soft Joe is using.

Have you played with there "ve tool"  Joe? I like the way they graph it and show fill blocks, very interesting and similar to a tool called Escan, automotive test solutions.Have you found it to be accurate.
Dave

Progress so far (...I have a day time job and a wife...):

I now have a few cans of "Seafoam" and a can of GM TEC... will do this Fri/Sat.

I'll be removing the intake manifold to check the knock sensors (I read the TSB pointed out by Ronnie, thanks Ronnie)... I have new sensors so I'll replace them, and while I'm there I'll replace the valley cover with the later MY valley cover which has integral PCV plumbing... this should eliminate oil ingestion thru the PCV plumbing.

Thanks, I'll post up as I progress.