Lately, when I "stomp on it" - I'm hearing a rattling, like detonation from the rear. This only occurs when I'm going along, downshift and tromp it, I will hear the "pellets in a can" sound that makes my teeth grit.

When I shift to the next gear, under heavy load...it rattles again.

I have NEVER had this happen before!! I do have a performance chip installed, but I've gone almost a year with that and SEVERAL DE weekends/races.

I have yet to see if I register a fault, but I guess that's the next step.

I plan on removing my alternator sometime this week to see if one of the knock sensors have come loose...will check the connectors at the "tree" as well.

My other plan is to go pump 5gal. or so of 110 octane into my tank, and after a few miles of driving around, seeing if it still does it - as it's possible I wasn't paying attention and put a tankload of 87 (normally use 93 octane) in there??

My point is, even if the knock sensors are out of commission, etc. the car shouldn't knock on a regular basis...ESPECIALLY IN COLD WEATHER!!

Other than that, I'm lost for ideas and will get a fault code readout at the local P-Car independent, I guess it would be relieving to see that a sensor has failed and just requires replacement.

Has anybody else had this occur?? It's got me miffed as hell.

 

My first guess was wrong octane gas or a bad batch of 93.
Maybe you should add a spark plug check in the checklist above

 

Yeah, that's another reasonable issue to look at.

...just thought maybe my dist. belt broke too?? That wouldn't cause detonation though, except for maybe one cylinder firing off because the secondary rotor stopped on it?

I want my MOMMY!

 

Hey Jeff,

For some reason, the pinging issue shows up much more often on the 993 board, and isn't all that uncommon. There used to be some great threads on the topic, but I'm not sure if they're still accessible, post-latest server upgrade.

I'm with you, it seems like the knock sensors should prevent audible pinging. But, considering how common pinging is on the 993 board--and that these cars have been checked out and seem to be mechanically okay--the knock sensors aren't perfect. Though, I suppose you'll still want to check out your knock sensors.

You might be getting carbon build-up in your heads. Perhaps a bottle or two of Techron (though I wouldn't hold my breath)? Change brands of gas? Or, your state may be changing the mixture/additives in its gas (seasonal). Mixing in some 100 octane racing gas ought to kill the ping--common (though pricey) fix on the 993 board. Other owners have just come to live with occasional, full-throttle, under-load, mid-RPM pinging.

If you can't find any good threads in the 993 archives, I do have one printed out that I can scan and send on to you.

 

Oh, one more thought. Most of the pinging 993s seem to be on the west coast, in states where only 91 octane is available (though a few stations sell unleaded racing gas). I don't recall if I read of cars pinging on 93 octane? People mixing in race gas with their 91 octane usually shoot for 93 octane, as I recall.

e.g.:

(4 gal/20)*100 + (16 gal/20)*91 = 92.8 octane

 

I'm thinking more and more that I got a tank of bad gas or picked the wrong grade...I was flustered the other day because a gift card for Amoco that I got for Christmas wasn't working right and I may have picked the wrong grade - that would be a first though - that I know of!

The "occasional full throttle ping" may be the "DETRIMENTAL EMPTY WALLET DOH!!" after an event next weekend if I don't get this resolved.

My point about the knock sensors is this: Even if one or both have gone South for the Winter, the cool Winter days and below normal engine temps should yield a scenario where the sensors wouldn't have to come into play anyway. At a track event, down South, mid-Summer...now you may have something to be concerned about.

My 964 has always spun like a top, and the percentage that the DME retards your timing if it reads pinging from the sensors is considerable...would be noticed at the seat of the pants for sure. My car is running AWESOME here lately with the cooler days, etc. and the sensors should pickup the pinging BEFORE my EARS do.

I dunno, but I'm confident I'll figure it out here soon.

 

Dear Jeff,
If you have a knock sensor problem they should be detected as failed by the DME and your timing retarded by 6 degrees. With this amount of knocking the timing should actually be retarded by 9 degrees and then the system shuts off and you go back to 6.
If you have never had the problem before then I would not suspect a failed knock sensor unless you can feel a reduction in performance.
Both sensors would have to be off their bridges to remain serviceable but not detecting any knock.
Obviously you do not have the Check engine light because a failed knock sensor should turn the light on.
I wonder if your chip has failed. The only way to prove this is to stick in the original and see if the problem is still there.
However I would totally agree that first the quality and the octane of the fuel you just used are checked.
Ciao,
Adrian
964C4

 

Jeff,

When my dist belt broke, it caused pinging when I step on it.

I would also suggest a bottle or 2 of techron and high quality gas to see if the problem persist if your dist belt is OK.

---
anthony

 

Yeah, I do my dizzy check about once a month...haven't done one in at least a month - so that is in order this evening. First I will stop by the local station that sells 110octane and put about 5gal. in there, go home, do the check, then take it for a "spirited" drive to see if I still have pinging.

Adrian, that is the first thing I considered, the chip...forgot to mention that was one of my suspects. I have the original and will certainly change it out if it is still acting up.

STILL, the knock sensors should eliminate pinging, especially to the point where it's audible for as much as I can hear it...it's quite obvious.

 

That's because 993 used Toyota manufacturing techniques

Maybe the DME operating system crashed and you should reboot (reset) it. Did you upgrade to Windows?

Sorry, it's quite late now at the office for me and I'm a little light headed from too much work!

 

apologies to Rob if he reads this ....guess I should be more supportive as a stockholder......but the stock price really needs a kick in the butt especially since I haven't had that blue screen thingy for ages, so they must have finally got it right!!

Apologies for side tracking Jeff.......I'm going home now

 

How about starting your diagnosis by going back to the stock chip? That's the most
logical and most expedient versus "throwing darts" at the problem. Pinging is the
most common problem with performance chips. Furthermore, you really never know
what's been done to achieve the so-called performance gain and how it's going to
affect the engine long term.

Good Luck
Loren
'88 3.2

 

why dont pull your secondary dist. cap off and see if you can turn the rotor..if you can you know the belt is broken..

 

Not an issue Dennis and i totally agree - My repaire Kiddy is a little south of 1K shares so it needs to get up there before i truck the car off to Va for Rehab. (up $0.46 so far today )

Anyway - Jeff
My car did this for ages here on the west coast (started in montana actually) i finally had to purchase a non-motorsports chip (weltmister) to go with the crap gas here.
I would definitly put some 100 Octane in it and see if that fixes it - if not your on the right track (do the chip last)

 

Awrighty guys...reread what I've input so far.

I check my dizzy belt often, usually about once a month...but admit I haven't in a month or so...that is first on my list after putting some 110 in my belly.

I agree the chip could very well be the culprit...but WHY NOW??? ...after almost a year of operating like a champ, several races, DE weekends, etc.

IF it were the chip, WHY aren't the knock sensors kicking in?? I should NOT be able to hear detonation this much as the computer would catch it faster than my ear could...at least in theory.

I will likely try the chip thing last, given these hectic past two weeks, I may have screwed up at the pump, although I doubted.

I always like to find a hardcore failure of a part, etc. to be satisfied that I've found the culprit...I hate this software crap!! Haha. If I were to find a broken dizzy belt, cool! If I changed the chip and all was good - BORING!

I'm just sitting here at work stewing over the matter, that's all...just wondered if there was something I was missing in my diagnosis - and just in plain DENIAL regarding the possibility that it could be my highly coveted chip!

Thanks for the suggestions thus far...keep 'em coming if we come up with something new. I was thinking the car was upset because I haven't Zymol'd it for a few months.