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Discussion Starter #1
Hi,

So i need to more reseach in to this are. This is a therotical question as i am not sure it is possible. What i want to know is, can coil packs drain enough power out of the battery and thus alternator and limit a output on the battery to say 13.7v to make it look like the alternator is failing to reach proper voltage power?

My reasoning for this is pretty simple, brand new alternator, belts and all bolts installed. started the car, alternator charges at 14.35v right out the box. Drove it around, did 20miles to see how its performing come back home stop, see its charging at 13.7v. When you go under the hood the engine sounds like its chugging (like a tractor) and the engine moves slowly too (vibrationally and physically). It sounds really rough on idle (no stalling or misfires that i can feel or hear), Through searching online it basically comes down to catalyst convertor (passed emissions self test this morning), fuel filter or delivery (filter changed 4months ago) spark plugs (changed 5months ago) or coil packs. interestingly this only started 2 days ago when i replaced the alternator (the chugging)

Is it possible to test coil packs or do you replace them and see what happens?

Many thanks Alex
 

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2006 MG ZR +120 (HQM) 2004 MG ZR 105 (IAB)
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As it started when you fitted the new alternator, it would suggest that it is either the alternator at fault, or that there is a wiring/connector fault related to the alternator swap - perhaps a connector not contacting fully, or damaged wiring. I would start by carefully checking all the wiring related to the alternator and battery, including the battery earth lead connections to the bonnet landing panel and n/s inner wing. Also check the security of the connections to the starter motor.

Was the alternator a brand new manufactured one or one of the new/remanufactured/refurbished ones as some of these latter ones do sometimes have issues either from the start, or within a short time of fitting depending on how well the refurbishment has been done.

I would not have thought that the coil packs would cause a reduction in the charging voltage from the alternator. A faulty coil pack may well cause a misfire on the two cylinders it serves. Do you have an OBD code reader? as any stored fault codes may give further pointers.
 

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Discussion Starter #3
thanks for the reply,

i will check connections as suggested and go over everything. i have done this 2 months ago when i was told to check grounds etc before declaring the alternator to be at fault and since then i have change the starter ground cable, starter bolt, battery terminal ground, new ground bolt for the battery on the slam panel (nothing was faulty, just thought i change them as i live near a cheap diy store selling single bolts for like 40p etc). the only thing not changed in the alternator set up is the positive cable, top through bolt and the electrical connector to the alternator. I believe it was a remanufactured alternator.

is there any known reasons specific to the 25 that would make it chug that have no been covered in the generally reasons for a chugging engine? I presume a over tighten or under tighten belt would not cause this.

No check engine light and no dtc or pending dtc through the obd 2 scanner.

Alex
 
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