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Discussion Starter #1
My QX 56 has 158,300 miles.... it started losing power as I was taking it in to Grubbs Infiniti.. it started missing when I pressed the gas to speed up. I coasted into the service center. I was told it was my Catalytic converters... they wanted $6004 !! They said I had after market converters and they were put on wrong and clogged. I drove away... SLOWLY...LOL....I had 3 different diagnostic tests ran after that. Not one showed Catalytic converter. One said cylinder issues.. I had the plugs changed and one coil replaced. 4 of the plugs looked real dusty brown, the other side looked dark black. After replacing them it still ran bad. Now the mechanic thinks it is my timing chain.... I don't know what to do... I know iam fully frustrated !! Oh.. to top it off... I called Grubbs back.. they said when they saw the after market converters they ASSUMED that was the problem and they had to start somewhere !!! They also felt the need to take my JBL ear buds !! I have no idea what is wrong with my vehicle.... PLEASE HELP
 

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did you just buy the car or have you had it for a while? did you purchase it used or new?

did you have the timing chain recall done?

what codes did you pull up at the obd port?

things to check:

faulty cats
faulty o2 sensors
dirty MAF
high pressure petrol pump
faulty petrol
VVEL system (rare)

if the cats were installed incorrectly , they can suck in air , causing an air leak. this can cause the 02 sensors to burn out prematurely and also affect the cat's performance.

should replace ALL coil packs and ALL plugs - what oplugs did you purchase? NGK iridium are recommended.
 

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Discussion Starter #3
did you just buy the car or have you had it for a while? did you purchase it used or new?

did you have the timing chain recall done?

what codes did you pull up at the obd port?

things to check:

faulty cats
faulty o2 sensors
dirty MAF
high pressure petrol pump
faulty petrol
VVEL system (rare)

if the cats were installed incorrectly , they can suck in air , causing an air leak. this can cause the 02 sensors to burn out prematurely and also affect the cat's performance.

should replace ALL coil packs and ALL plugs - what oplugs did you purchase? NGK iridium are recommended.
The code that comes up is P0300... I bought it used with 104,000 miles... it currently has 158,300.. while on computer it showed cylonoid 5 needed to be replaced. It was replaced and used NKG plugs.. I forgot to mention it is burning oil like crazy. Had the regular oil change done a month prior. Could barely see any oil on dip stick when I got it home.. no oil leaks.. the dealership stated they did the timing chain in 2015 at 85,000 miles... I believe that was BEFORE the recall.
 

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5,881 Posts
  • Faulty spark plug (s)
  • Faulty ignition coil (s)
  • Clogged or faulty fuel injector (s)
  • Intake air leak
  • Fuel injectors harness is open or shorted
  • Fuel Injectors circuit poor electrical connection
  • Ignition coils harness is open or shorted
  • Ignition coils circuit poor electrical connection
  • Insufficient cylinders compression
  • Incorrect fuel pressure
burning oil could be PC valves or /and head cover gaskets. does the car have any maintenance records? did the previous owner(s) use dino oil or full synthetic? did you switch to dino oil to full synthetic or vice versa? doing this on a high mileage engine can cause oil leak issues.

do you have smoke at cold startup?

have you done a compression test?
 

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Discussion Starter #5
  • Faulty spark plug (s)
  • Faulty ignition coil (s)
  • Clogged or faulty fuel injector (s)
  • Intake air leak
  • Fuel injectors harness is open or shorted
  • Fuel Injectors circuit poor electrical connection
  • Ignition coils harness is open or shorted
  • Ignition coils circuit poor electrical connection
  • Insufficient cylinders compression
  • Incorrect fuel pressure
burning oil could be PC valves or /and head cover gaskets. does the car have any maintenance records? did the previous owner(s) use dino oil or full synthetic? did you switch to dino oil to full synthetic or vice versa? doing this on a high mileage engine can cause oil leak issues.

do you have smoke at cold startup?

have you done a compression test?
I do not know the type of oil used before I bought the car.. I use full synthetic. There are no oil leak signs.. no smoke upon a cold start... haven't done a compression test..
 
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