NHTSA opens preliminary probe into more than 870,000 GM vehicles

[WalleyeMikeIII]

Case in point with a gen 5 6.2

Investigating Oil Composition, Direct Injection, & Low-Speed Knock

The discovery of low-speed knock events exclusive to direct injection led EFI University and Lake Speed, Jr. of Driven Racing Oil to examine the cause.

www.enginelabs.com

In general bore size , combustion chamber design, ignition timing , and afr are foundational drivers of pre-ignition because they determine the pace of the flame front.

Low engine speeds and low throttle positions are low VE which require higher ignition timing. The pace of the flame front is relatively slow.

A large and fast change in throttle position can trigger a pre ignition event… even with low dynamic compression. This is a rapid change from low ve to moderate or high ve with ignition timing still at a fairly advanced stage. The flame front is a bit too slow and ignition occurs in advance of it leading to pre ignition.

Modern engine controls have done a good job of managing these lspi events…. But it is always an issue that requires consideration for obvious reasons.

Throw in fuel dilution of the oil and you can get a situation like in the case above, where the system detects the lspi event but can’t do anything about it.

That article is some fascinating stuff; and is dated in 2017. I would expect the conclusions have been reached by now. And I would expect the Big 3 (and others) were and are aware of it. So...did they react? Would be interesting to see the actual conclusions of that research...I will search for a follow up article when I get time. Thanks for sharing.

 

[jfoj]

I think like anything there was a funding issue that impacted carry on testing.

Not condemning any of these guys for their knowlege and/or testing, BUT they really did not perform "Real World" testing and "Real World" data gathering.

These motors in daily use rarely ever see anything above 2500 RPM, there testing did not even start until above this RPM. They need to test, dyno and load the engines how the vehicles are driven on a daily basis to really get the real world info.

Driving my truck, the engine never gets over 1800 RPM on the highway unless I really need to pass and get around traffic. The engine typically runs around 1600 RPM for the majority of my highway drives and I have started to monitor the Calculated Engine Load % and I was SHOCKED at least with the 6.2l the engine tends to operate often between 50% and 90% calculated load without ever downshifting under most conditions. This in terms is literally "Low Speed" and High Loading conditions that need to be tested and replicated in the lab enviroment.

The other thing that needs to happen during this style of testing is to pre-contaminated the engine oil with fuel to simulate what happens in the real world. Baseline the engine with clean/fresh oil, then start to contaminate the engine oil with fuel and possibly water and then see what happens. There is enough data from oil sampling (Speed Diagnostics is Lake Speeds Oil Analysis Company) they know what the typical and higher range of fuel contamination actually is based on sampling. Then they probably need to push even further with fuel contamination because there are times where the fuel levels are probably higher before some of the fuel is actually "cooked" off.

 

[blanchard7684]

Driving my truck, the engine never gets over 1800 RPM on the highway unless I really need to pass and get around traffic. The engine typically runs around 1600 RPM for the majority of my highway drives and I have started to monitor the Calculated Engine Load % and I was SHOCKED at least with the 6.2l the engine tends to operate often between 50% and 90% calculated load without ever downshifting under most conditions. This in terms is literally "Low Speed" and High Loading conditions that need to be tested and replicated in the lab enviroment.

Damn. The 5.3 in my suburban can’t sniff that. 1600 rpm and up to 90% load is nuts.

 

[KMeloney]

Anyone have any sense for whether the 6.2 failures occur only at highway speeds? Most (if not all) of the stories I've read about have occurred on the highway, presumably at or over 65 mph. I haven't read about a failure occurring in town/in stop-and-go traffic.