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Dr. Hamman
Dr. Hamman, Automotive Engineer
Category: Car
Satisfied Customers: 5821
Experience:  30 years experience, Repairing, building, & designing, automobiles.
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Check engine light on,says system too lean and engine misfire

Customer Question

Check engine light on,says system too lean and engine misfire comes up after diagnosing with an obd,its an 06 Range Rover Sports,what could be the solution
Submitted: 5 years ago.
Category: Car
Expert:  Dr. Hamman replied 5 years ago.

Hi, I will do my best to assist you. When you are finished please click on accept. I don't get paid unless you do. I don't know if you are a pro or a novice so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answer will be based on what you have posted. Feel free to add any additional info you feel is needed.

The first thing I would suspect is that one of the spark plugs may not be set to the proper gap. Also damage can occur to the high voltage system that attaches to the plug, when it is removed to change the plug. I will say this isn't real common, but it does happen.

I would also carefully check the wires and vacuum lines that may have been disturbed in the process of changing the plugs. It is possible that you have a vacuum leak that is causing the lean mixture. If you want to search for vacuum leaks then get a can of WD40 and spray all around the suspected areas. If you hit a vacuum leak then the engine will speed up for a second or two. This is the best way to find hard to locate vacuum leaks.

Odds are that a close visual inspection with a WD vacuum leak check will reveal the problem. If the problem still remains you will need to inspect the plug gap and the secondary ignition system for defects. Don't overlook any wiring you may have been around in the process of changing the plugs. Just a little tug, or pressure can cause problems. If you disconnected any electrical connections make sure they are clean and tight. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.
Customer: replied 5 years ago.
Am a novice in this and i also have the landRover LR3 with the same problem,it also says random misfire,system too lean,prime petrol on both cars so am not sure its just the spark plug wires,please expantiate more on this generic issues
Expert:  Dr. Hamman replied 5 years ago.
Hi, I will do my best to assist you. When you are finished please click on accept. I don't get paid unless you do. I don't know if you are a pro or a novice so we may have to fine tune the answer. I only know as much about your problem as you have told me in your post, so my answer will be based on what you have posted. Feel free to add any additional info you feel is needed.

The spark plug wires can cause a misfire but they will not cause a lean mixture. It is possible for the onboard diagnostic system to mistakenly perceive a misfire as a lean mixture. The onboard diagnostic systems can be wrong about a lean mixture warning. Also worn, or bad oxygen sensors can cause a false lean mixture warning, so can bad electrical connections to the oxygen sensors. This type of problem can be VERY hard to find without special tools and special training. Go over the things I suggested carefully, and see if you can spot a problem. Look carefully because it doesn't take much of a problem to cause issue like this. If you have any more questions I am here to help. Good luck, and Thanks for using Just Answer.


I hope this helps, 100% satisfaction is my goal. If the answer is not clear, please reply and I will assist you more. When you're satisfied, click on accept. I don't get paid unless you do. A bonus and positive feedback are always appreciated, good luck and Thanks.
Customer: replied 5 years ago.
So you feel it might be the o2 sensors if not the plug wires
Expert:  Dr. Hamman replied 5 years ago.
The O2 sensors can be involved. Normally if you have a misfire, and a lean mixture there are two different problems. This is not always the case. Don't overlook the spark plug gap, that causes lots of problems.

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