[Help Please] Engine jerk after changing wires and plugs
Thread Starter
Senior Member
Joined: Apr 2005
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05 CLK55
[Help Please] Engine jerk after changing wires and plugs
Hi guys,
I recently noticed a problem with my car after switching from Stock wires and plugs to Magnecor wires and Denso plugs. The car would jerk when I am driving steadily at around 110-140 km/hr. This happens about every 20 mins when I make long hwy trips. It sounds like the car revs up for a split second with almost no observable change in rpm. It feels like the car suddenly jumps forward. I am sorry if my description don't make any sense to you, but I hope you get the idea. The Denso plugs that I was using were IK20. So after I noticed this problem, I went back to my tech and ask him to put on a set of NGK plugs, which were one heat-range colder than the stock ones; the problem remain unsolved. I really want to hear some of your opinions. My engine is stock. Could it be that I am using the wrong plugs? or Could the problem be caused by the Magnecor wires? I have read many posts regarding engine jerk, but none of them seem to address the kind of problem that I am experiencing. I have had the tech take apart the gear box and checked, the gear box is in perfect condition. In addition, my car has fairly low mileage, so I don't expect it to give me such a headache at this time. All inputs are welcomed and pleased. Thank you very much!
I recently noticed a problem with my car after switching from Stock wires and plugs to Magnecor wires and Denso plugs. The car would jerk when I am driving steadily at around 110-140 km/hr. This happens about every 20 mins when I make long hwy trips. It sounds like the car revs up for a split second with almost no observable change in rpm. It feels like the car suddenly jumps forward. I am sorry if my description don't make any sense to you, but I hope you get the idea. The Denso plugs that I was using were IK20. So after I noticed this problem, I went back to my tech and ask him to put on a set of NGK plugs, which were one heat-range colder than the stock ones; the problem remain unsolved. I really want to hear some of your opinions. My engine is stock. Could it be that I am using the wrong plugs? or Could the problem be caused by the Magnecor wires? I have read many posts regarding engine jerk, but none of them seem to address the kind of problem that I am experiencing. I have had the tech take apart the gear box and checked, the gear box is in perfect condition. In addition, my car has fairly low mileage, so I don't expect it to give me such a headache at this time. All inputs are welcomed and pleased. Thank you very much!
Last edited by D_Star; Oct 2, 2008 at 06:35 PM.
Super Moderator
Joined: Jul 2006
Posts: 3,365
Likes: 12
From: Orange County, CA
GMC - Miata - Trek - P-Car
Several here have experienced problems with their Magnecor wires. The original equipment wires, although pricey, have proven worthy even on members’ highly modified engines.
Since you’ve twice swapped in a fresh set of spark plugs, logic would likely dictate that they’re not the source of the problem. Mine has had Denso’s IK20s installed for <10k miles with nary a hiccup.
Because it’s intermittent, offering a proper diagnosis here is all that more challenging. I’d respectfully suggest retrieving stored ECU data via MB’s STAR-DAS equipment – perhaps from a competent independent technician. Doing so will provide tremendous insight on its operating parameters, even if the CEL was never illuminated.
Barring that, an inexpensive onboard/handheld scanner may help to determine the source of the problem when it’s occurring.
Since you’ve twice swapped in a fresh set of spark plugs, logic would likely dictate that they’re not the source of the problem. Mine has had Denso’s IK20s installed for <10k miles with nary a hiccup.
Because it’s intermittent, offering a proper diagnosis here is all that more challenging. I’d respectfully suggest retrieving stored ECU data via MB’s STAR-DAS equipment – perhaps from a competent independent technician. Doing so will provide tremendous insight on its operating parameters, even if the CEL was never illuminated.
Barring that, an inexpensive onboard/handheld scanner may help to determine the source of the problem when it’s occurring.
Former Vendor of MBWorld
Joined: Jan 2007
Posts: 3,193
Likes: 3
From: Glendale Arizona
C55,SL55,C63
Stupid question, are your plugs gapped right? dont know if that would cause it but. I would say ask this question in tech section but its hard to get an answer of there sometimes and you might find yourself waiting.
