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.   ;)

I just did a search for TSB;s pertaining to your concern and came up with a spark knock related to the rear knock sensor.
Due to it's location it is easy to fill cavity with water from hood seal causing the sensor to not work correctly and or set a code P0332.
I have ran across this on Trucks but not in your application.Although it does list your application as a candidate for this condition.I would view a scanner and look at the knock sensor Pids along with computer advance and determine if this is indeed a spark knock you are hearing(piston slap).
All I got.
Post up some more info and people will give you more direction.
Ronnie.

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...

---

Another log...

The "rattle" occurred just about where the vertical line cursor is.

I'll post more info as I progress...

---

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,

Carl Grotti wrote on Mar 17^th, 2008 at 8:20pm:

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,

Hi Carl,

I'm using a scantool called "EFI Live" which consists of a hardware module (smaller than a cigarette packet) and software (which produced the graphs you see above);

the module can record in black box mode, or with a PC/laptop it does "live" mode;

If you want the website link, please let me know.

I'm an electrical engineer, but I used to work in my Dad's transmission shop (family business) a long time ago.

Thanks
Joe

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.

---

Questions:
- is top engine cleaner one of the fixes for knock...?
- if so, what is the correct way to apply TEC...?

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

Quote:

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)...?

Yes.


Quote:

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

I don't know, but it sure can make an engine Ping.  For example it is common for some Chrysler V8 engines to begin to leak under the intake and ingest oil.  Often times not enough to really make it smoke or show other evidence.  Unmanageable engine ping is one of the clear symptoms though.

I can see by your nice graphs that the knock retard is kicking in.


Quote:

what is the correct way to apply TEC...?

Sounds like you have already considered carbon knock.  This can make some really bad sounds and is often related to engine speed and load.

I have used the TEC many times with excellent results.  I pour it in while keeping RPM just high enough to prevent stall and, when I get the the bottom of the can, pour the rest in quickly enough to snuff the engine but not so fast as to hydro lock it  :o

Then let set overnight or all day.  Then take it out somewhere where you can blow it out with out getting a ticket for obliterating the traffic visibility for miles  ;D

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:

I pour it in while keeping RPM just high enough to prevent stall and, when I get the the bottom of the can, pour the rest in quickly enough to snuff the engine but not so fast as to hydro lock it.

Ok, thanks.


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

...Then take it out somewhere where you can blow it out with out getting a ticket for obliterating the traffic visibility for miles  ;D

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

Thanks, appreciate your comments,
Joe
;)

Quote:

...Then take it out somewhere where you can blow it out with out getting a ticket for obliterating the traffic visibility for miles

How does a shop or dealer service dept. do this...?  8-)

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

Dave,

Thanks, I'll look into Run_Rite.

Ve tool as in "virtual ve tool", no I have not used that;
I have used their flash/edit tool (which is GM specific) on another PCM.

Thanks,
Joe

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.

Sleuth,
I heard that water trick only worked with leaded gasoline , due to the chemical make up of the carbon.

I havent personally checked to see if this was true though.

Qwix

Wilf used the water blast treatment awhile back on a vehicle and it sandblasted the combustion chambers pretty good from what I remember.
I know antifreeze and water will sand blast a combustion chamber. ;)


Ronnie.

The MAF is in front of the TB... would I spray(mist) water directly into the MAF...?
I don't want to wet the MAF elements, I don't know if they would be harmed.

I could remove the MAF (it seems to run without the MAF) and spray water into the TB like that.

So, I would set the spray bottle to fine mist, and spray water in as I open the throttle wide (same as yo would on a carburettor)...?

Oh... that only works for leaded gasoline...?  I can try it and see.

Thanks.

Ok, I applied Seafoam...

I slowly poured it into a funnel I connected to the PCV vacuum port at the front of the intake manifold (motor was stumbling as I poured)... then when about 1/4 bottle remained I quickly poured it in... but the motor would not stall (it bogged down real low... maybe 200-300 rpm, but kept spinning and recovered)... is this ok...?  

Now I'll let it sit for 6+ hours or till the morning... then it will be fun.   ;D ;D

BTW: Being a DIY and being in a residential area means I have to watch what I do to respect the neighbours (noise late at nite, smoke, etc...).

Yup, so now you wait till morning and "drive it like you stole it" out of your neighborhood onto a bypass. The chemical has probaly soaked down into your oil rings(gonna clean them out) so when  do this type of treatment I always level my speed off(once all the smoking is done) and drive between , say 40mph to 60 on a gentle increase, then back down to 40, gently for several miles to seat the rings back in There is a chemical called "Chemflow" that works well for getting the sludge out of piston rings, have used it many times for stuck oil rings in Chevy`s without pulling the engine down--using the procedure mentioned by Tom. As for carbon, the best way I have found is to use a chemical(like run0rite etc..) and administer it into the intake system as a mist loading the engine down slowly, then tapping the rpm to 2-3 k a few times, letting it load back up and continue till you use all the chemical--when she starts to load up and miss--rap it up a few k-letting it load back up a bit--then continue. Clear your codes and adapts. I have never seen the runrite  hurt an o2 sensor or Catalizer. "Tune-up in a Can" brings back the part throttle response that seems to get lost with carbon buildup around the valves and piston tops. Never seen a customer balk at the bill when administered correctly either.Sometimes , depending on the engine etc, I move the connection around to make sure I get the cleaner throughout the entire engine, the pvc hose sometimes will not allow you to get good cleaning on the front of the engine
Dave

"Drive it like you stole it"...  ;D

It smoked pretty good, huge cloud of dark grey smoke on the freeway...   :D

Most of the ping seems to be gone, there is still some left... and it is preceeded by the "rattle" noise; should I give it another dose...?

I'll record some more logs.

Thanks.

Does it do it when it is COLD? Is it overheating? No water on the MAF.err.Sure if your neighbors can stand it, Guess you`ll have to say it "Mosquito Control" this time? Might want to take a look at the timing chain for wear perhaps? Dunno...at wits end. Perhaps some more and diffrent patterns to Look at, I`m sure someone will pipe up when they see something. Wonder what the Cam-Crank relationship is at when it does the deed?

Dave

Dave,

Does it when warmed up 192F-199F;
Does not overheat;
MAF is clean/dry;
Ok, I'll check timing chain.
Ok, I'll capture CMP/CKP waveforms on a scope, I'll have to figure out how to do this while driving.

Thanks,
Joe

This just a guess based on description and not being able to hear the noise in person. Have you checked the Bendix drive on the starter? They can get weak and the gear will move when the vehicle is accelerated and hit the ring gear.

Twelch,

I'll check the starter when I check the flex plate.

Thanks,
Joe

Starter and flexplate are both good.

Hey Joe,
Do you by chance have a slightly larger cam in this vehicle? If all your components are good and it is a tuning thing, perhaps a play with(dref) the IAT input and perhaps a MAP sensor input voltage --even the MAF -TPS may help resolve this issue, just remember that if you play with these it effects the whole range of operation. I have had to do this with "camed up" engines....It`s  tricky for sure cause you have to make the confuser think everything is still ok...
If it is unmodified, you will find your problem with what has been mentioned most likely.
Dave

wrote on Mar 31^st, 2008 at 2:29pm:

Hey Joe, Do you by chance have a slightly larger cam in this vehicle? If all your components are good and it is a tuning thing, perhaps a play with(dref) the IAT input and perhaps a MAP sensor input voltage --even the MAF -TPS may help resolve this issue, just remember that if you play with these it effects the whole range of operation. I have had to do this with "camed up" engines....It`s  tricky for sure cause you have to make the confuser think everything is still ok... If it is unmodified, you will find your problem with what has been mentioned most likely. Dave

Dave,

Good thought, shows you're thinking...  ;)

My car is stock, and has always knocked (the dealer technicians couldn't solve it)... I have been monitoring AFR (via exhaust lambda) and it is not lean... I also been monitoring ignition advance, and it looks normal (does not seem to advance excessively).

I have been following up on the suggestions as time permits (I have a wife and a job), and I do appreciate everyone's suggestions, thanks to all.

Next step is to take care of oil thru PCV and potential knock sensor problem (according to TSB).

I am trying to hook up a scope to record while driving...

Good thought tho... I'll do some research into IAT/MAP/MAF effects.

Thanks,
Joe

Hey Joe,
Re-vamping that PVC, say thru a water jug(you would have to make) could also help keep your engine cleaner--like the decarb you did-by taking the opposite side of the engine hose--the one that goes into the air cleaner, install a adjustable pressure relief valve in this hose and adjust to, say 4-6 inches of vacuum on the crankcase--need to plumb a vacuum gauge to set, will give you some mileage also.
Drawback: ?? gets messy in the container,(needs maintenance) but keeps the crude out of your engine

Dave

wrote on Apr 1^st, 2008 at 5:03am:

Hey Joe, Re-vamping that PVC, say thru a water jug(you would have to make) could also help keep your engine cleaner--like the decarb you did-by taking the opposite side of the engine hose--the one that goes into the air cleaner, install a adjustable pressure relief valve in this hose and adjust to, say 4-6 inches of vacuum on the crankcase--need to plumb a vacuum gauge to set, will give you some mileage also. Drawback: ?? gets messy in the container,(needs maintenance) but keeps the crude out of your engine Dave

Dave,

I'm going to do something like that, a oil-catch container inline with the hose feeding the PCV valve...

I'm also thinking to fit the later model valley cover that has integral crankcase vapor collector... GM changed from valve cover to valley cover crankcase vapor collection because of oil ingestion... this will also give me the opportunity to inspect/replace the knock sensors, since all of this requires pulling the intake manifold (which on a late Firebird is tucked under the cowl...   :o )

About the pressure relief valve in the fresh air hose from the air cleaner to the crankcase: are you saying to allow the crankcase to build 4-6 psi of vacuum before the relief valve opens...?  i.e. so the crankcase is always under vacuum and never at atmospheric pressure...?  Am I understanding correctly...?
Hmmm.... I'll try that, thanks.   8-)

Yup, but it could hurt you somewhat if you dont have good tight valve guides w/ seals etc....Race cars do , but we are getting off the subject somewhat.. Next time you check your oil, sniff the dipstick, does it smell like fuel? That is a good sign you have an engine management problem...If so you are diluting your fuel curve and you will see excessive emission on a gas analyzer, disconnect the pcv and retest..now its time to find out why... Not to mention what that gas mixture is doing to your rod bearing and internal components.

Can spark plug gap influence knock...?

There's a GM TSB 03-06-04-060A saying to use iridium plugs gapped at 0.040" (instead of platiunum ones gapped at 0.060").

Does anyone know why the change...?

Don`t know the answer to your question.You could have lean pockets that are not getting burned when this is happening.  If you were to check timing advance when it is happening-cruise speed, then massage your IAT signal(making it hotter retards timing) by adding some resistance to the circuit-cruise speed.You could index your plugs, modify them to where the flame front is being thrown to where you want it in each cylinder. I find this hard to do with plat-iridium plugs, you can index them but it is impossible to make them better because of the design. An old race trick is to grind the ground electrode-strap to an angle-marking the plug for correct indexing, another way to drilling the electrode and ground strap, but it is time consuming, works great.
http://www.siliconchip.com.au/cms/A_108762/article.html
Here is a link to something you may find interesting
Dave

Dave, thanks, I'll read that link.

Any progress? Been smokin` the neighborhhod up? Anything?

8-)

wrote on Apr 25^th, 2008 at 2:40pm:

Any progress? Been smokin` the neighborhhod up? Anything? 8-)

Hi Dave,

Thanks for asking...

I applied TEC one time only, and it was a big improvement, altho on a hot day in slow traffic it will knock slightly.

I still need to check my plugs again, and to check my knock sensors (under the intake manifold which is tucked under the cowl-overhang; I'm waiting for a manifold gasket set; the cooling system does not pass thru the manifold, so I am thankful)...

And my Mrs makes sure to keep me busy with other things... ;D

The 'rattle' seems to have moved from low range (1500 rpm) to mid range (2500 rpm)... it happens as you increase throttle thru low range, and it then stops as you keep increasing throttle to mid range.... I could be looking in the wrong place, but it does seem to me to be engine related... it's annoying, and I'm wondering what it is...

I have been under the car with a rubber hammer, I found this:
- the stock catback is sliding back from the Y pipe... I tightened the stock band clamp using a large breaker bar, but it is still sliding back... the Y pipe OD must have crimped, I'll expand it back out with a pipe stretcher tool;
- the O2 sensors (four) have a ring (for breathing fresh air I assume) which rattles and vibrates, but the sound it makes is very low;
- I need new motor/trans mounts, they're not broken but they're worn/soft/stretchy;
- the whole exhaust system has a very light rattle, but it doesn't seem to come from the cats;

I have been logging with the scantool every day and studying the logs; I'm logging pids like cylinder airmass to see if there's an abrupt change that may cause timing or AFR to change.

I have a Fluke color scopemeter (which I use for electronics) which I'm trying to connect up to the various sensors to take a recording when the rattle happens, but it's not so simple to figure out how to probe without puncturing wires (I'm a bit apprehensive about that) and how to run the test leads from engine bay to driver's seat;
I'm not too happy with the Fluke, it's not easy to use and the recording/playback user interface isn't very good.
I'm just about to buy a Pico Quad from AutoNerdz...  ;)

Cheers,
Joe
:)