2000 XJ8 tapping noise after new plugs
#1
09-20-2009, 11:31 AM
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2000 XJ8 tapping noise after new plugs
Hello...thank you for any ideas...
On my first Jag...gosh what a beautiful car. It is a 2000 XJ8 VDP, 136,000 pristine condition. I took it to a mechanic to change a right rear hub and bearings...that went great. Then I had them check the spark plugs...they were old and oil was getting past the gaskets...so, bought new plugs (they gapped them at around .43 I believe)...that is what some site told them, changed out the header gaskets, changed oil, new air filter, and I drove off. The car sounded awesome...finally no road noise from the bad hub and bearings. I drove the car about 10 minutes and it starting making a tapping sound...does not increase in volume with revs, but does match the revs...it will not go away...it is there when the car starts, and does not dissapear when it gets warm. The mechanic says...drive it and see if it goes away...RED ALERT!! Mechanic is not very helpful...
Anyway...I need ideas on how to solve this or what might be the issue. I have thought it might be a coil went bad after they replaced the plugs, I was even thinking that they gapped them wrong and it is not getting the right kind of spark, and of course I have thought the worst...maybe something terrbile happened to my engine...
The car runs great other than the noise...no loss of power at all.
THANK YOU for any help!
On my first Jag...gosh what a beautiful car. It is a 2000 XJ8 VDP, 136,000 pristine condition. I took it to a mechanic to change a right rear hub and bearings...that went great. Then I had them check the spark plugs...they were old and oil was getting past the gaskets...so, bought new plugs (they gapped them at around .43 I believe)...that is what some site told them, changed out the header gaskets, changed oil, new air filter, and I drove off. The car sounded awesome...finally no road noise from the bad hub and bearings. I drove the car about 10 minutes and it starting making a tapping sound...does not increase in volume with revs, but does match the revs...it will not go away...it is there when the car starts, and does not dissapear when it gets warm. The mechanic says...drive it and see if it goes away...RED ALERT!! Mechanic is not very helpful...
Anyway...I need ideas on how to solve this or what might be the issue. I have thought it might be a coil went bad after they replaced the plugs, I was even thinking that they gapped them wrong and it is not getting the right kind of spark, and of course I have thought the worst...maybe something terrbile happened to my engine...
The car runs great other than the noise...no loss of power at all.
THANK YOU for any help!
#2
09-20-2009, 11:52 AM
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Morrison, the first check I would do is to get your hands on an infrared thermometer. Drive the car for a few miles (get it up to temp) and then open the hood with the motor still running. THen using the thermometer, check the outlet of each cylinder on the exhaust manifold. All of the temps should be very close to each other. If you have one cylinder that is running cooler than the others, that is your misfiring cylinder, which could cause the tapping that you are seeing. Also, do a quick check of the exhaust manifold for any signs of cracks. If a header is cracked, it can cause the tapping you are seeing too. You can also use a piece of hose or a cardboard tube to run along the header to listen for any gases escaping. Finally, get your hands on a piece of steel rod or a technician stethoscope and put it next to each cylinder. What you are listening for is the tapping that you are hearing and then trying to isolate it down to the cylinder that sounds the loudest. At that point, you can start checking the plug for a bad plug, the coil for any problems, etc.
As for the actual cause of the problem, it is hard to say what it is as it can be a lot of things. Based on the work you had done, I would be leaning towards a bad coil or bad plug. But, I am simply guessing. Hope this helps.
As for the actual cause of the problem, it is hard to say what it is as it can be a lot of things. Based on the work you had done, I would be leaning towards a bad coil or bad plug. But, I am simply guessing. Hope this helps.
#4
09-20-2009, 05:45 PM
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Thank you
Great feedback. The work was done at Firestone. I just dropped the car off at another Firestone here in Houston that actually fixes other Firestone repair shop mistakes...they have the best technicians according to the shop manager. They will be taking a look at it in the morning.
I did think about the noise always being there, but ruled that out because you can here it at idle without the previous hub issue. So it is definitely a new noise.
I am so happy I found this forum. When I talk to the head mechanic tomorrow I will ask him about isolating a bad plug or coil and checking for a header leak.
Great advice...and thank you so much. I guess the best news is that the guy at the new Firestone location seemed very confident it was something they could address. The last Firestone scared me when they said "just go drive it and see if the noise goes away"...never a good sign I would think.
I did think about the noise always being there, but ruled that out because you can here it at idle without the previous hub issue. So it is definitely a new noise.
I am so happy I found this forum. When I talk to the head mechanic tomorrow I will ask him about isolating a bad plug or coil and checking for a header leak.
Great advice...and thank you so much. I guess the best news is that the guy at the new Firestone location seemed very confident it was something they could address. The last Firestone scared me when they said "just go drive it and see if the noise goes away"...never a good sign I would think.
#5
09-20-2009, 06:56 PM
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