Hello everyone,
I've been lurking in the shadows here and am a new poster so would first like to say thanks for the wealth of info you all share in this forum. I have a 2/90 build E34 M5 Dinan 3.9 Stroker with 145k miles here in the U.S. and it's been a fantastic DD for the last 11 Months. I am also experiencing pinging and have been down a few different paths as well. In summary, I believe as others have said, that poor fuel and lower available octane is a contributor to my issue. I live in Arizona so the high ambient temps don't help either.
Dinan built the stroker package with a complimenting tune. The previous owner stated he had the tune modified for California gas but his repair history also points to pinging. In fact at 90k he was serviced for pinging, at 99k a faulty ICV and fuel pressure regulator were replaced, then at 100k, poor compression on #4 cyl. Cause was pinging due to intake leak. Result, burned piston and a $20k rebuild. When i bought the vehicle i immediately had valves done, plugs, wires, cap/rotor, air filter, replaced all vacuum lines and balanced TBs. Recently, I've replaced coolant temp sensor, O2, checked TPS, and now rebuilt MAF. A few things i have not done include injector flow check/cleaning, Inlet temp sensor, recheck for new/undiscovered intake leaks, fuel pump and regulator and ignition coil.
I have four scenarios: (1) With the Dinan tune and the car as it sits as mentioned above i get pinging. (2) Blend a strong octane booster less pinging, (3) blend 100 octane race fuel with 91 Shell to yield at least 95 octane, I don't get any pinging and the car runs really strong. I've also gone 5 gal of straight 100 octane and results were even better. But, at $9/gal here in AZ, that's not a long-term solution. (4) swapped out the Dinan tune for a stock 3.6L chip running Shell 91 only and I also don't get any pinging in 110+ degree heat with AC running. My solution now will be scenario 4 until temps drop. I will also start snooping for intake leake. This being the cause of the earlier burned piston and the fact that I have similar symptoms scares me a bit. I also don't know if running the stock 3.6 chip in a 3.9 that needs more volume of everything is a good long term solution. I've had several people say that I may just have to live with it unless I want to keep blending fuels. Perhaps a new custom tune for our crappy gas is in order? I don't know.
Pinging for me is experienced under about 1/4 throttle load in 2nd and higher gears around 2,000 - 2,500 RPM. Above that I can go WOT but also get a very sharp metallic ping that is less than .5 sec in duration but at a much more dangerous 5,000 - 6,000 RPM range. With the lower RPM range, say a pull from 2k revs in 2nd gear, the ping will last until the revs build. The upper range is only very brief. I've adopted my driving style to avoid pinging at all cost.
Recently I started getting intermittent idle "spikes" where idle would stay at 2k RPMs after clutch engagement while decelerating. After a few seconds it would return to normal just under 1k revs. I didn't have any CELs or codes stored but figured ICV and/or MAF. As the MAF has not been touched since new, and ICV has been replaced within last 50k miles, I went the MAF route. I sent the unit to Kevin at Injection Labs in Colorado. Great resource and he stated most issues related to MAF begin when the unit is about 40 mv out of spec. I was 35 mv so not bad. I had it rebuilt anyway and installed yesterday along with my Dinan tune but as stated above, still pinging
Although this got me thinking about "what's next", I think I will stick with using my stock 3.6 chip with 91 pump grade Shell gas in the summer and will test the Dinan tune this winter when temps cool. Looking forward to hear how things go with the OP as well.
Aaron