We have tended to run 91 octane since acquiring this 960 in September. Went down to the lowest recommended, 87, on a couple of occasions, including this week. Pinging is noticeable when heading up hill with a load. I burned down to 2/3 of a tank, topped with 91 and added two bottles of octane booster, which based on product claims would have boosted 3 points on a full tank. Given the approx 66/33 percent blend of beginning fuel octanes, that should have hit 90 overall in theory. Still pinging, but less. So the question is, what sort of problem exists? Carbon build-up effectively increasing the compression ratio? I just added some Marvel Mystery Oil (to fuel) as they claim some decarbonizing benefits, but not much has gone through yet. Is there any way I can retard the timing a bit to cease the pre-detonation?

Second issue: the car has lost power with my daughter driving, now on three occasions. It has occurred during a steady state cruise of 45-65 mph. Each time it shakes and shudders, and speed is reduced to maybe 25 mph. Typically, she pulled over at that point. It was smooth at idle for those periods, but shook under load and produced little power. She got the sense that feeding "normal" throttle would make it die, so she was very slow in application. A couple of times it just cleared up and ran fine after a few minutes. Yesterday she limped to the house, and I jumped in right away for a test drive. Ran great, aside from afore-mentioned pre-detonation (I added the boosters and Mystery Oil and 91 octane fuel during said test drive). I should also mention that I changed the fuel filter between episodes # 2 and 3. The filter looked very old and the support bracket appeared to have never been unfastened. I judged it would be possible to change without dropping the bracket, so it's possible it was original. However, the fuel I poured out looked fine - not water or visible contaminants. I still suspect a fuel delivery problem, but I don't know where to begin. She's afraid to drive the car, but she really loves the 960 overall (I have no reason to believe it's a ploy to drive other cars in our fleet). Plus her mom witnessed the behavior twice. However, neither of them are great at describing mechanical maladies. I love driving it, so I have no problem swapping, but the damn thing won't display its ugly head for me. I hate intermittent problems!

I'd appreciate thoughts on both issues.

 

I have been able to duplicate the power interruption a few times with me driving ... no common thread at all. The odd thing is that one cycle of the key clears it up instantly, at least until the next time. When it happens, the car shakes, feels like it's running on 3 cylinders maybe, can't go more than 25 mph or so. Feeding in more throttle doesn't really do much, as in half throttle equals about 25 mph, and flooring it yields no increase, nor does it make things worse. I've revved it up in neutral while afflicted, it's very rough but I've taken it to 3000 rpm or so. Another observation is that vacuum pressure must be very low ... when it's running like crap, the brake booster is doing nothing. It takes hard pedal to stop. Ideas? Thanks!

 

Is the check engine light on? Base on your symptoms you can possibly have bad coils or a bad power stage. If you remove the engine cover to get access to the coils, you can remove the coil cable to see which one is affected. If the engine shakes worse when you remove a cable that coil is good, if it doesnt that one is bad. You can also swith between coils to be more certain that it is the coil.