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Cars have come a long way in the last 20 or so years. Things like OBD (On Board Diagnostics) make repairs easier to diagnose as most codes will point you in the direction of the problem immediately. There are exceptions to this of course as some problems are more complicated than others but for the most part I find that stored OBD codes usually point me to the right spot for a diagnosis and more times than not the fix is easy. However, there is a downside to relying solely on the OBD system for determining issues with your car. I re-learned that lesson this past week.

If I were to describe my car's performance with one word, I'd call it "Lazy."

My 2000 BMW 528i has had a lot of parts replaced over the last few years. In many ways it’s almost like a new car except for the worn interior and a few exterior blemishes. This is to be expected on a 14 year old car with 136,000 miles. Recently, I’ve been noticing that power delivery has been lacking. This was particularly evident in the low end of the rev range especially when accelerating from stop lights. I also felt a severe lack of power at the top end as well.

My BMW 528i

There are several things that can cause any engine to run poorly. For an engine to run it requires fuel, air, and an ignition source. When talking about power issues I normally tell people to inspect their ignition system assuming that the fuel system has been inspected or addressed. More modern cars that have a direct ignition coil setup can often be overlooked due to how reliable they are in comparison to older style distributor setups. Typically, a failed ignition coil is easy to diagnose because you will receive a CEL (check engine light) or SES (service engine soon) light. Scanning your vehicle will show that a specific cylinder has seen misfires. One of the easiest ways to determine if the ignition coil is a problem is to switch the ignition coil from the dead cylinder to a good cylinder. The misfire should follow the coil. You can replace the ignition coil independently of the others and the problem is solved.

What happens when the issue isn't enough to trigger a CEL?

This scenario is great as long as you have a clear misfire or a clear problem which has triggered an OBD fault. What happens when performance is down but the issue is not enough to trigger a CEL or OBD code? Well, this is what I have been dealing with for a few weeks. The issue that I was experiencing could be felt in what I refer to as the butt dyno. My BMW’s engine just wasn’t running as strong as it had been and I wasn’t being given any clear cut reasons as to why. At this point I already had an idea as to what the problem could be and I assumed the issue to be related to my high mileage ignition coils. As ignition coils get older they may not fail 100% but they can wear out providing a weaker spark. A weak spark is not going to be enough to set off a CEL or SES all the time.

Coil Packs

I solved my performance issue by replacing the oldest part of my ignition system, which were the BMW ignition coils in this case. Believe it or not but 5/6 of the ignition coils on my 2000 BMW 528i were original (I had replaced the spark plug boots in the past) and had about 136,000 miles of service on them. This is pretty much unheard of for any ignition coils to last this long. Usually, I see ignition coils on stock engines lasting around 80K miles give or take. I let mine go for so long because they hadn’t been an issue until recently. My engine now delivers the power that I am used to and it seems to be running more efficient as my fuel mileage has improved slightly as well.

The moral of this story is simple. Sometimes you can’t solely rely on error codes from your OBD equipped car to tell you what’s wrong. To some degree you need to use your instincts and some common sense to find the root of the problem. In my case I already had a good idea as to what the problem was. I’m not a fan of throwing parts at a problem without having a good idea as to what the problem is in advance. Troubleshooting will sometimes be required but taking a moment to think about the problem can cut down on the amount of time required to trouble shoot the problem. If you’re lucky no troubleshooting will be required at all.

Ever have a phantom issue that OBD couldn't see?

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Written by :
Gareth Foley

Gareth is the BMW Make Level Marketer for FCP Euro and has been with the company since 2012. Gareth's BMW obsession started with a hand me down E39 528i when he was 17. From this car he learned how to do his own repair work while also learning more about BMW. When Gareth was at CCSU studying Marketing he had the opportunity to go to SEMA with the college car club. This is where he developed his love of the automotive industry. Since joining FCP in 2012 Gareth has sought out to develop one of the broadest and most accurate BMW replacement parts catalog. he can be reached at gareth1@fcpeuro.com


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