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I have replaced all the spark plugs, coil packs and got a new valve cover and for some reason my car has skipping going on between 50 and 60 mph (that I can notice). I'm also getting very low fuel economy (24.8 mpg now and 33.4 before). Please can someone point me in the right direction on what to possible look for next. 136k miles with a recently replaced CVT transmission..
 

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Define "skipping"; is the engine bucking at higher speeds? Did your "skipping" start after you replaced plugs and coil packs. I can see replacing spark plugs as a regular periodic maintenance item but why replace all the coil packs. What brand of spark plugs did you install; the standard plugs are DENSO FXE20HE11C. If you installed some other aftermarket plugs, then that could be your "skipping" problem. Nissan engines often don't run too well with aftermarket plugs.

Generally one of the first things to do when trouble shooting a problem like yours is to perform an ECU code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores. As an alternative, most auto parts stores will perform the code readout for you free of charge. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction. If you have a copy of the FSM for your vehicle, the code readout procedure is described there along with a listing of codes. You can download a copy of the FSM from this web site: Owner's Manuals. The section EC.PDF is the one you need to read.
 

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Discussion Starter #3
Define "skipping"; is the engine bucking at higher speeds? Did your "skipping" start after you replaced plugs and coil packs. I can see replacing spark plugs as a regular periodic maintenance item but why replace all the coil packs. What brand of spark plugs did you install; the standard plugs are DENSO FXE20HE11C. If you installed some other aftermarket plugs, then that could be your "skipping" problem. Nissan engines often don't run too well with aftermarket plugs.
The coil packs had corrosion on the ends and we hooked a computer to it and drove it to see they were all miss firing at some point. The spark plugs are Bosch brand. And it doesn't do it at like 70 mph or higher...but like I will accelerate to about 55 and then I will slightly let off to maintain that speed and randomly it will jolt or buck as you mentioned. It's not as bad of a jerk when cruise is on..
 

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Sup Mod keeping the peace
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Since you have new coil packs, check for strong blue spark on each one; sometimes a new coil pack doesn't produce a good spark; especially aftermarket types. Many folks here on the forum have had bad experiences with using Bosch spark plugs; as soon as they switched to NGK or Denso OEM types, the problems went away. I myself have run into a similar problem with aftermarket types years back; been using NGK since then with no problems. Aftermarket spark plugs do OK with engines such as the older GM V8s, Chrysler V8s; but not so with Nissan.
 

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Discussion Starter #5
Since you have new coil packs, check for strong blue spark on each one; sometimes a new coil pack doesn't produce a good spark; especially aftermarket types. Many folks here on the forum have had bad experiences with using Bosch spark plugs; as soon as they switched to NGK or Denso OEM types, the problems went away. I myself have run into a similar problem with aftermarket types years back; been using NGK since then with no problems. Aftermarket spark plugs do OK with engines such as the older GM V8s, Chrysler V8s; but not so with Nissan.
I will look at the spark and then see about getting some NGK or Denso OEM plugs. I will post an update as soon as I can.
 
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