jonfkaminsky

For the last couple tank-fulls of fuel, I have been noticing some engine noise when in a high gear and accelerating from a lower speeds. Once in the power band the noise goes away. It is sort of a light rattle that I have heard in other vehicles under similar conditions: accelerating in a high gear for a couple seconds until the engine gets into the power band), OR shifting too early at too low of an RPM.

Anyway, I added a can of octane boost to my next tankful and the sounds seemed to go away after 10 minutes of running around. Otherwise performance seems normal, although I am currently hypersensitive to every little noise or puff of smoke.

So my question would be, if this is pinging, what could suddenly be the cause? I always fill up at the same station (92 RON+MON/2)..perhaps a crappy load of fuel in their tanks...

I'd appreciate any ideas or thoughts.

Thanks
Jon

Bill Wagner

From your description it sounds like pinging.

Have you checked your distributor belt? Pinging or dead silence are the typical symptoms (although in some cases it's severe pinging and backfiring). If the belt busted, it could explain why it started suddenly.

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jonfkaminsky

Bill-
Can I check by alternating pulling the center wire on each distributer cap and seeing if I can start? If I can start with either pulled, belts should be okay, right?

Jon

Gary C2

Jon,
Disconnect the harness going to the primary coil. If the car doesn't start, then it's most likely your distributor belt. If it isn't the belt then it's something in your secondary ignition circuit...coil, rotor, wiring.

Gary

jonfkaminsky

Gary can you confirm which one is primary? What do you mean harness? All the spark wires from the cap? or just the central wire?
Jon

Emanuele Ferry23

If it's a knocking problem you should hear a diesel-like metallic sound. I think 92 RON is a bit too low for the 964. My european-spec '90 C4 has a sticker on fuel lid which reads "use only 95 RON fuel". Maybe knock control of the Motronic has always been patching the problem by working "at the limit" and now you've fetched slightly worse fuel which doesn't allow correction any further. You may try a 98 or even 99RON fuel (In Europe we've got Shell V-power which is fully compatible with Catalytic converter).

Hope this may help

jonfkaminsky

Emanuele-
We rate fuel a bit differently here in the states. We use (RON+MON)/2. So 92 octane in the US is NOT the same as 92 RON. I can't provide the exact conversion because it depends on both RON and MON values and each supplier's formulations is different. Suffice to say that while both tests use the same test engine to determine the values, the MON test specifies a higher test RPM and inlet air temp. RON is usually the higher number by 5-10 points. MON is usually thought to affect the engine's ability resist knock at high speed, part throttle, and performance. RON usually is taken as the index to low to medium speed knock and engine run-on (dieseling).

The only thing that matters in the end is the observed road octane number (RdON).

A typical 89 (RON+MON)/2 value corresponds for example, to say...95 RON and 85 MON.

Bill Wagner

Jon:

If you disconnect the primary distributor and the car won't start then you've confirmed the secondary is malfunctioning. You don't need to disconnect the secondary distributor because that's the one you're trying to test. You can tell the secondary and primary by looking at the base of the distributor. The primary distributor is driven mechanically off the engine, so it looks like it's lined up with the engine connection, but the secondary will be offset and look like it's dangling in space.

The best way to check is to pull the distributor cap off. If the secondary belt has not snapped but is in the process of failing the belt may have skipped a tooth or two. In this case the DME will likely be able to still adjust the timing enough to allow the car to start with only the secondary connected. If you have the manuals, there is a picture of the relationship of one distributor wiper to another in section 03, page 8. The diagram is actually a timing diagram showing how they should line up at TDC, but it does show the relationship clearly....they look like they're about 60 deg. out of phase with each other as far as appearance goes.

If you start pulling any wires remember to be sure to keep them well out of the way of the fan.

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jonfkaminsky

Thanks, Bill. I'll try this tomorrow or Tues and post results.

Thank you,
Jon

Jeff Curtis

Jon, most certainly double check your distributor belts by the methods mentioned...I use a timing light and put it on at least TWO different spark plug wires on the secondary dist. to verify everything is "A-Okay".

BUT, my best guess at the noise you're hearing is transmission rattle, indicative to the G-50 gearbox when "lugged" - meaning the high gear, low speed scenario you painted.

My car makes this noise and is quite noticeable...much worse after the Cup clutch/lightweight flywheel install...but it's not abnoxcious or anything.

By all means, do your distributor checks...and when verified okay, consider my suggestion...another way to check is at idle, you might get a slight rattle out of the gearbox - check it by parking the car next to a cinder block building and letting it idle, get out and listen as you walk around the car.

You may not experience the "rattle" that I do if you don't have a Cup Clutch/flywheel from what people say. Understand that was my first upgrade the second day I owned my C2, so I don't really know if it rattled at idle with the P.O.S. Freudenburgh "dual mass" flywheel it came with.

jonfkaminsky

Everything is A-Okay with the dist belts. Perhaps Jeff is right- transmission noise. Sure sounds ping-like to me. And the octane booster seemed to help. I can't tell anything anymore...I am so hypersensitive to every little thing!

scotsman60

Jon,


My 90 C2 also exhibits pinging when I'm in too high a gear at low revs.

I'm in California where the best we can get for gas is 91 (R+M)/2.

My problem doesn't occur all of the time but is most noticeable on very hot days or when I've been stuck in traffic and the engine temp is high. The higher ambient temperatures are consistent with pinging.

Can you correlate your symptoms to high ambient temps?

I believe that there is a switch on the side of the DME to account for the low octane rating - I haven't actually confirmed that myself.

I find that I can always avoid the pinging by being in the right gear but on the morning commute I get lazy about shifting.....

I considered octane boosters and even mixing in some Toluene to reduce pinging but decided to just avoid the problem by staying in lower gears for now.

Doug

scotsman60

Jon,


I thought about the O2 sensor as well but didn't do anything about it.....

I'm doing a 60k service in the next couple of weeks and I'll replace the O2 sensor then. I'll do the valve adjustment too (first time - a bit nervous) so if my pinging goes away I won't really know what cured it.....

Mine also started pinging without warning - I drove it for a year before I heard it and it still only comes intermittently.


Doug

mojorizing

Hi Jon,

You used the word "rattle" in your original post....Let me share a story that happened recently. Last week I partook of a one-day auto cross. On the first session, someone made a comment that my car was pinging...I wasn't too concerned...hell, I had just run over 2 DNF cones...so I was warming up and so was the car. After the next race, now a couple of the gearheads said I was pinging and my brother took me aside and told me it was very noticeable! We reviewed some video that was taken while I was on the track....the audio didn't pickup anything unusual. I couldn't hear it while driving. Revving the engine at stand still didn't reproduce the sound. But now I was concerned, and I stood out the rest of the day. I attributed the pinging to bad gas. A week later, I was warming up my car in my garage and I noticed the heat shield on the cat was rattling...my brother was present and he said that was the soung he heard on race day, only louder. The sound tapered off as the car warmed up...typical of a loose heat shield. I snugged up on the 10mm bolts holding the shield. Life is good. My story is that I believe it was the heat shield making the sound as the fastners loosened....at first noticeble from only outside of the car, till a week later they got really lose, from inside the car. That's my story and I'm sticking to it!
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ersh

Hi Jon,
For what it's worth, while at the PNWR dyno day I heard a 911SC 'pinging' or 'knocking' while at full throttle on the dyno. While the mechanics there said it was pre-detonation it sure didn't sound like a ping or knock but sounded more like a 'snap' or loud 'tick'.
I had always associated pre-detonation with that diesel sound but not so with this car.

Allan
'93RSA 3.8