'88 3.2L possible pinging under load

[Techno Duck]

I believe while accelerating under load, around 2500-3k rpm in 2nd or 3rd gear i am hearing light pinging from the engine. The car runs fantastic otherwise and i probably would say nothing were wrong if it weren't just for the faint noise i hear. It's entirely possible i am just hearing something else, perhaps a rattling or something but it does sound like pinging to me, like the very faint sound of a metal ball bearing in a metal coffee can. This happens even at part throttle going from 2500-5000 rpm, not just WOT.

Only have 91 octane available and its been noticeable after multiple fill ups so i doubt bad bas. Engine rebuilt about 8k miles ago (PO had this done). Brand new cap and rotor, spark plugs (NGK BPR6ES @ .027 gap), relatively new ignition wires. Valve adjustment just performed with no affect. Car has cat-bypass with M&K 1 in / out. Steve Wong chip tuned for exhaust; i have contacted him to verify if this chip is tuned for 91 octane. The PO who installed the chip was from NorCal so i assume it is for 91 octane. Still waiting to hear back from him regarding this.

I have verified the jumper on the DME harness (for CA and Japan delivered cars) is disconnected and also verified the position of the FQS is set at zero.

Injectors are likely original (162k miles) and will be replaced with rebuilts when i pull the intake to replace the fuel lines soon. Fuel filter is of unknown age but i don't believe its too old, regardless it will be replaced as well.

The old plugs looked a bit lean on 4 of the 6 cylinders but nothing i found alarming.

Any other ideas on what i can check? I unfortunately do not have a stock chip to put in for testing purposes. Some things i was thinking of trying for troubleshooting purposes

-Add octane booster to tank to try and bring 91 octane up to 93-94 octane and see if noise continues. Alternatively a place about 1 mile away has 100 octane at the pump i can fill up on.
-Set FQS to position 4 to retard the ignition
-Check throttle body opens 100% and check operation of the WOT switch
-Replace O2 sensor of unknown age; car gets great gas mileage so i am just doing this to establish a baseline on the wear and tear parts.

I was also wondering; if the pinging were caused by pre-ignition, would this show as a lean condition with an AFR gauge? I was planning on hooking up a temporary AFR gauge to verify that the idle CO adjustment and overall mixture is correct. Like i said with 160k+ miles i want to just make sure everything is dialed in right, who knows what the PO's did in this time. As someone who loves to mod cars i always like to know what the AFR is doing.

Any other things that could cause pinging? I am still learning the 911 3.2L but i do have some experience with Bosch Motronic having had a 944 for almost 10 years. I have a bunch of work i am going to do on the car over the coming months just to refresh things and verify operation..

-Replace fuel injectors, fuel lines, fuel filter
-Replace all vacuum lines and intake manifold gaskets
-Check condition of AFM wiper; car runs great but i believe is untouched with 162k miles
-Replace all breather hoses..etc associated with intake manifold removal

I am also on the hunt for a stock DME chip for an '88, as this car does need to pass smog every 2 years.

Appreciate any feed back on other things that i can check. Like i said its entirely possible i am hearing something else, i may bring the car to a local independent for a better trained ear than mine.

[911obgyn]

if you have the noise under load it may be pinging, if you can make it happen while sitting at those RPMs it may be a chain tensioner going bad. Bang around on your exhaust pipes and see if anything rattles.

[steve911T]

Yes, my suggestion also, check to make sure all bolts are tight on the exhaust system. I had a bad tensioner and it was noisy between 2k and 3k. It did not seem like a pinging noise but more of a rattle. Steve

[Techno Duck]

Thanks for the suggestions guys! I do not believe any exhaust bolts are loose as i replaced all of the exhaust gaskets between the header to crossover, test pipe, muffler recently and used all new hardware; i had a bunch of leaks present as it looked like the old gaskets were reused at some point. This noise has always been present faintly as far as i can remember also. The cylinder heads are also still perfectly clean around the exhaust ports so i don't think any of those flanges are leaking. The noise was present before and after i swapped out the mufflers also. I made sure the M&K muffler was well secured with the supplied t-bolt clamps, no budge or rattle at all when i gave it a few love taps with a closed fist. Ill give everything a few love taps with a light mallet to be sure though, maybe one of the heat exchanger heat shields is working loose.

I can rev the engine at idle freely without the subjective pinging sound appearing. Only appears under load.

[ischmitz]

If you have access to a stock chip install that and try again. It'll quickly tell you whether it's pinging or not. Or maybe someone close by has a stock DME you can try.

[Duc Hunter]

A lot of pinning is related to high temps too. Does engine temp have any effect? Also, are you sure it goes away under more load? Maybe try windows down where you are driving next to a curb/wall/fence? When mine was pinging that really helped me hear it.

[ClickClickBoom]

Try position 2 or 3.

DME Fuel quality

DME FQS (Fuel Quality Switch) settings for our 911's are as follows:

Switch Fuel Ignition
1 0 0 stock setting
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3deg
6 +3% -3deg
7 +6% -3deg
8 -3% -3deg

[Arne2]

Originally Posted by ClickClickBoom

Try position 2 or 3.

DME Fuel quality

DME FQS (Fuel Quality Switch) settings for our 911's are as follows:

Switch Fuel Ignition
1 0 0 stock setting
2 +3% 0
3 +6% 0
4 -3% 0
5 0 -3deg
6 +3% -3deg
7 +6% -3deg
8 -3% -3deg

Do these still work with an aftermarket chip?

[ClickClickBoom]

Originally Posted by Arne2

Do these still work with an aftermarket chip?

Mine seems to work with the Steve Wong chip.

[Techno Duck]

I am going to have to look around for a stock chip; unfortunately it is the only stock part i did not get when i bought the car . Ill need one anyhow eventually to run SMOG.

I am out of town a few weeks so ill check this stuff when i get back. Ill probably first try bumping up the octane. There are two boosters that are well regarded; Royal Purple brand says it will boost octane 3 points with 20 gallons which should give me around 94 octane. Torco Accelerator is another that depending how i mix it with the tank can boost anywhere from 4-10 points. For less than 20 bucks and being able to order from Amazon i figure this is easy to try.

Regarding the FQS settings, i figured setting #4 which is retarding the ignition 3 degrees would be the best to try followed by setting #5 which is retard 3 degrees plus +3% fuel. If i am getting pre-detonation, would it still happen regardless of how much extra fuel injected?

As far as conditions where it happens, ive noticed it happen accelerating maybe 3/4 throttle from 2500-5k rpm at night next to a concrete divider; ambient temp around 75-80 degrees and oil temp around 180-190. And also most recently accelerating up a medium grade at also a brisk pace from about the same RPM range; ambient temp was about 90-95 degrees, oil temp was showing around 200 degrees F.To clarify i can hear the subjective pinging start around 2700rpm then continue through about 4k rpm; it may continue after that but it might be getting drowned out by the exhaust which is on the loud side right now. Basically i think regardless of temp i can get the sound to replicate by just accelerating hard up through the RPM range.

Can anyone comment on how AFR would look if i were getting pre-detonation? Would it show any appreciable change?

[9112gun]

I had the same problem - started running pure gas (non-ethanol) and it went away. Our cars don't like modern gas. There is an app called puregas that will tell you where stations are that selling old school gas.

You pay a little more but worth it.

[spyerx]

We can't get pure gas in CA unless buying race fuel. All gas sold is 10% ethanol and max 91 oct.

Use Torco to try boosting the octane.

Regarding smog if you have your stock cat good chance it passes with wong chip.

[Techno Duck]

Forgot to follow up on this, problem solved! I put a can of Torco in and it made no change. Fast forward to about 3 weeks ago and i peaked under my car to verify sway bar size so i could order new rear bushings and i measured an 18mm rear bar which i found strange. Long story short, for some reason one of the PO's installed an 18mm rear sway bar, all of which do not have the 'hump' to clear the transmission mount on a G50 car. The rear sway was vibrating against the mount as the car warmed up. Put on a proper 21mm rear bar and problem solved!

[Cairo94507]

Wow. Thanks for the follow-up. Glad it was not engine related and easily solved too.

[Techno Duck]

Ive been slowly going through the car and thankfully have not found too many questionable things done by the PO. Just your typical horrible aftermarket stereo wiring and a really badly done manual switch for the oil cooler fan. All of which were easily rectified. The 18mm sway bar was interesting though.

Still planning on pulling the intake and addressing vacuum lines / hoses, injectors and fixing an oil leak from the triangle next week.