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Discussion Starter #1
My 4.8 auto with 212,000kms 2012 is lacking power, consuming fuel, and heating up. On cold start it is rough for a 5-10 seconds then idles around 800. Whilst cruising at 120km/h there is slight hesitation, almost a misfire. No codes from ECM or TCM. Longterm A/F ratio is 106-110 on both banks.

Stall test reveled stall at 1600rpm which is below 1900-2200 for these trannies, but tranny oil is not burnt, or dirty, but changed about 15000kms ago.

Car has had new fuel pump put in, new filter too about 5000kms ago, maybe less as preventive maintenance, don't want to be caught with a dead pump in the middle of nowhere.

I have had to recently change the alternator, which was already replaced with a remanufactured unit, but that lasted 20,000kms only to brand new nissan unit, AC compressor and condensor and front expansion valve replaced, as the compressor died, but that is not relative to the lack of power in the engine.

The lack of power is noticed when moving away from a stop, and reaching the desired speed is slower than usual, or when going up a very steep hill, and engine heats up, but I do live in Dubai and it is very hot now, 40C normally everyday.

Also when at highway speeds, putting foot flat to the floor, the engine revs up with very little acceleration, drops a gear and then some acceleration.

Timing is set at 5 degrees advance, as per factory manual. Engine head has been polished about 90,000kms ago with new valve seats, but it ran fine after the build. Replaced MAF and O2 sensors at the same time and had injectors cleaned on a machine.

Took it to a multi-brand garage, and they could not find any fault in the tranny, and dont want to open the tranny as they can't pinpoint the misfire, which they want to solve before looking for any other issue.

Any ideas, or what is a common failure on the 4.8 engine at 200,000kms.
 

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Discussion Starter #3
Check the cat
Hi we changed the CAT out with a hollow pipe, that I had when I bought the car, I had installed a cat from a scrapyard. Took a test drive, on first start, it ran rough, and the engine is running slightly rough at idle. Took a test drive with the Garages test driver, and he noted that from a stop the engine is able to move the car when you let off the brake pedal, before it wasn't and need a little throttle. But still the power is still not the same, the cat may have just freed up some power for lower speed. The engine is still running rough, and consumes fuel. We are now suspecting coil packs, and the plugs will be examined.

I do remember when the head was rebuilt, that the car ran similar when I picked it up, and the garage took 3 attempts to set the timing right. It ran well for another 90,000kms, and through some rough terrain too, carrying a load, and at times towing a trailer of 500-750kgs, also I did a trip climbing some mountains in January 2020 over some steep gradient on tracks, and the car ran great, but the weather was ideal max 25C, it is now 32C by 7:30am and reaches 40's by 11am.
 

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Discussion Starter #4
Okay so the lack of power and misfire is solved. It was due to incorrect timing being set by me. This is the 2nd time this has happened, the Nissan Data Scan, both desktop and android are showing inaccurate readings on the timing. I like to set my timing as per factory, which is 5 Degrees positive, and use the android and this time confirmed with the windows desktop software to 5 degrees. The garage used their diagnositcs, and it was retarded to -15 degrees, and they set too 5 degrees positive all good now. So this is to all those out there that there maybe an issue with Nissan Data scan. I have even just changed my laptop running Windows 10, so could not be a hardware or operating system issue and I confirmed with the android app, which is the same phone.
 
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