Questions and Answers

BMW Knocking Around Q. Vincent, I came across your web site while trying to understand, and seeking a solution to, a knocking problem in my BMW E39. My car's specs are: 10/1997 BMW E39 523i (Euro-spec) M52 single VANOS, 6-cylinder/4-valve, 2,494cc Automatic Transmission DME: Siemens Petrol type: Shell 98 (or higher) Current mileage: 61,500 KM Predominant type of driving: Urban Problem: Knocking under load

The car was purchased in late 1997. In 1998, I had the original EPROM replaced by one written by Superchips. Up until about 2 months ago, the engine ran fine. Then the rattle started. First, imperceptibly. Now, noticeably, even within the cabin. The local agent hooked up all manner of diagnostic hardware to the car but could find nothing amiss.

The agent reported that the VANOS was stripped and timing advanced (!). I subsequently brought the car to another shop specializing in BMWs. I explained the problem to them and the action taken by the local agent in detail. Having ruled out hardware problem, they surmised it was probably the EPROM. They downloaded the Superchips programme and sent that to Hiop, a specialist German BMW tuner. Hiop, among other things, re-writes EPROMs.

The new EPROM (which Hiop said was closer to, or, stock) was returned and downloaded into the car. The problem still persists. Barring a strip to inspect the engine, octane booster and gas and oil treatment (decarbonizing type) were added to my petrol tank just today. As an added precaution, I tanked up using Shell's new V*Power petrol, a higher-than-98 premium petrol.

With the new EPROM, new petrol, new additives, the car pulls noticeably smoother and quieter - the knocking remains but less loud. Please note that a visual inspection of the sparks have not been conducted.

After all this, I received a call from my mechanic who said that Hiop inspected some of the code of the Superchip EPROM and found the fuel/air mixture to be richer-than-normal for the low-end rev-band. Hiop is continuing to inspect Superchip's code as and when time permits.

My question is this: is there anything that can be done to eradicate the knock? What is causing the knock? Is there a direct relationship between the Superchip EPROM and the knock? Will the knock go away?

I truly appreciate your insight and advice in this matter.

Warmest regards,
Roy

A. I don't know how much I can help you Roy, you've gone beyond what BMW intended for that car. I can tell you what's causing the knocking (Detonation is the technical term) but, other than returning the car to BMW specs, I don't know what to tell you to get rid of it.

Detonation, or pinging as it's more commonly referred to, results when the fuel mixture is prematurely ignited in the combustion chamber. This will result in severe engine damage over time. Damage such as burnt valves, melted spark plugs and, in some cases, it will burn a hole right through the top of the piston.

The pinging is, mostly, due to ignition timing. That is controlled by the PCM, which gets it's specifications from the Erasable Programmable Read Only Memory (EPROM). There are two knock sensors that detect this pinging and sends that data to the PCM which retards the timing to eliminate it. In this case the PCM can not adjust the timing enough to get rid of it.

The only thing I can suggest to reduce the pinging is to install a colder plug. This might lower combustion chamber temperatures enough to eliminate the pinging but I wouldn't bet the ranch on it.

Additional Information provided courtesy of ALLDATA