Hey guys, need some of you g sedan experts help!

My 2003.5 g35 engine blew. So i purchased a 2004 56k engine. i took it to my local shop RR (racing results) They dropped the engine. after they did that they found that the cats were clogged so they gutted them in the mean time. Car was fine with new engine. then with the unclogged cats the engine in miss firing. ecu says random miss fires need help!!!

 

check plugs? im not sure what else to say....

umm how much did you pay for the engine and to have it swapped in im curious, mines making some weird sounds from time to time and im a bit scared

 

i changed the spark plugs allready same prob. i payed 1600 n 700 to swap

 

wait so it worked fine with clogged cats?

 

Check your Coil packs and see if there is oil in your spark plugs That can be a common and major problem. If the coil packs were bent or not taken care of when the engine was transfered that could be the cause too.

 

no it didnt work but it wasnt miss firing it was just no power n lazy

did a compression check= ok

check coil=ok

check all seals n gaskets= ok

checked spark plugs= ok

currently cleaning fuel injectors but problem still presists

 

So they gutted the cats.

The engines are the same aside from age correct?

Everything else is the same, aside from the gutted cats?

Right?

What's changed.

The cats are gutted.

The ecu is likely in limp mode due to the excessive air flow over the o2 sensors.

 

the only thin different is the yrs in the engine.

my cats were clogged, my cats are gutted now but i think its the cats or a hole in them when they were gutting them out. no miss fires b4 cats were gutted out!!! cats clear n now miss fires. but if i had test pipes wouldnt it b the same essessive air flow?

 

try using new cats

 

If the engine ran fine with no misfires after it was replaced and before the cats were gutted wouldn't the solution be to replace the cats with new ones?

What's interesting is that a plugged cat usually causes an engine to miss, stumble or run poorly but as you said your porblem started after they were gutted.

I'm no expert but I'll assume the lack of back pressure from the missing cats (or honeycomb in them) is throwing off the pre and post cat 02 sensor readings and as a result leading to the miss.

Also, there's a reason why your cats became plugged. The most common cause is an excessive fuel mixture (running too rich). The likely culprit is an exhausted o2 sensor(s). Cats also become plugged from an overheating condition. You don't state why your original engine failed? You've got me wondering now...

 

Piston #6 used to randomly misfire on my car, it was due to the coil pack being loose. Check the contacts on all six packs and make sure they're on securely.

 

the engine was replace due to bad or worn connecting rod aand bearrings. the engine was replaced it was running very poorly so the took the cat off n put it on a lift and ran the car. car was fine changing gears perfectly. gutted out the clogged cat and then the car missed fire. the tech at the shop told me its not the cats!!

 

hmm do they have some cats that they can try or try removing them you never know our cars ate weird like that, changing my engine oil fixed my rear axle click issue, go figure

 

I find it hard to believe that the cats have anything to do with the car misfiring.

 

i found it hard to believe my engine oil had anything to do with my rear axle but hey it fixed it