ok so hopefully someone can help me out since there was no said word of how this issue was fixed. i swapped motors as well (not just the block) we put a new air filter, plugs, wires, ignition module, battery, FPR, cleaned up the MAF sensor. at first the car ran so bad and sucked down a TON of gas and so we changed out the TPS unit and that helped with my fuel issue. the car runs ok when at idle, but seems that the longer she is run and the hotter she gets the worse she runs. i did NOT have ANY of these issues prior to the engine swap. my engine gave me no warning signs anything was wrong until something broke inside and she make loud knocking and practically killed over within a few miles of driving. (VERY loud knocking on the top part of engine wouldnt go above 25, starts but ran really rough while knocking very loud and when we went to pull it in the garage she wouldnt move but the engine did rev up.) i had my mechanic put it on his 4k$ scanner. when i started the car it read cyl 3 misfire. we drove it down the road and it changed to cyl 2. there was also low readings on the MAF sensor so he advised me to clean it which we did. he said to change the coil packs so we replaced one (5/2) coil pack because im running out of money to work on this car. my hubby took her for a run after all this and the check engine light started blinking when he romped on it and it gave him a code for cyl number 2 misfire. we decided to do compression test to find out that all cyl are good and have same compression. i took it for a run after we destroyed 4 wires in the process of the compression test. she seemed ok so i thought oh good maybe its just them wires are bad? until you give her more gas. i romped on it she lacks power and once she hits about 3500-4000 rmp it signals the check engine light to blink about 15-20 times and it will go away. so i called the hubby and told him to get the scanner ready for as soon as i pulled in the driveway. brought up code p0300. so within a lousy 750 miles on the new but used engine i have had fuel issues, no guts,and 3 different codes with a ton of new parts....this is me: is there someone else out there that can help me narrow down the issue? who has had experience with this code and what did you do that helped?

 

Heres something that is highly over looked when it comes to the po300 code..

As you may or maynot be aware of...

These cars are completely electronically controlled...

A lot of the time random misfires are due to a worn/bad faulty battery!
Just cause the battery starts the car...doesn't mean it isn't worn out!

I would either have the battery tested... OR ... Replace it Immediately!
You generally only get a good 3 yrs of operation out of them. But some get lucky and get 5 yrs out of one... So if yours is 3 years or older.. I would highly recommend replacing it!
Thus eliminateing this as the culprit. you just might find your car will once again return to a normal state of operation!

1 other thing to check that's pretty critical for random misfires is also Proper plug Gaps!.... Whats your gapped at?

One more point of interest....
Cleaning a MAF... doesn't always do the trick!
Generally, Its a good idea to replace it with a new one....
Always, Always, Always Use an OEM ACDelco MAF replacement...
any other brands are junk and will prove useless...
Our Monte Carlo's run best on only OEM GM parts!

1 other thing to remember...
Have you checked it for possible Vacuum leaks? Don't know how to test it?
Heres how,
Get a can of carbureator cleaner.... while the vehicle is idleing.. spray it around the vacuum lines, head etc.... If you find an area that the idle changes or stalls the motor..you found the vacuum leak! repair that area(Vac lines) and or head/intake and do the test again..once you found no more vac leaks... The problem should be resolved!


Hope this helps!
Once you get it straightened out...please inform us of what you had done to get it back up and running in tip top form!
Thanks!

 

my battery is brand new. it was one of the things listed as replaced. i know cleaning a MAF doesn't always do the trick (its worth a shot tho)...but what gets me is NONE of these symptoms were there until AFTER the new engine was put in. There is a high possibility its the wires or plugs. i have no idea what they are gaped at. they always come pregaped for the car and that's the way we put them in. im going to check the wires on my MAF sensor since my mechanic said they feel a little lose and the readings were just slightly low on it. but i just don't understand why that sensor would go the instant we changed the engine. i was going to have the dealership reprogram the computer...but i don't want to waste any more money. im about ready to sell the car. I wouldn't get enough out of it tho in the condition its in to get another decent one.

 

I would recommend...
getting the battery tested..... also take the time to check the plug gaps...Not all plugs are treated the same.... Especially with new plugs...
Always check/reset the plug gaps before you install them.

Its so easy to "Touch/Contaminate" a sensor... any grit grime,grease..even oil off your skin can also contaminate it. Depending how it was handled...etc

 

While disassembling a 2004 mc ss I found a plug wire that was burned through. Would have never seen it if not dealing with the uim/lim disease because it was stowed in the plug wire block behind the passenger side torsion mount.

 

after watching some videos for a few hours yesterday we are going to check for any vacuum leaks, swap out the map sensor and double check the wires on the MAF sensor. I am also going to check my catalytic converter. theres a possibility that during the swap something could have been jarred lose and clogged the pipe. i plan on replacing all the wires again simply because i was told they are a junk brand by 3 different ppl. If we still have our old battery i will swap it out, but i doubt anything is wrong with my brand new battery that is oversized for my car.lol if there is anything else that anyone can think of...always welcoming ideas!!