05 GT acceleration problems

Smeaglly

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Alright so here's my delema, I replaced my stock engine with a 09 engine and ever since I've swapped it my car lags, I'll even go full throttle and the car acts like it is trying to catch up then it will randomly kick in and it'll act fine, so I've put a new fuel filter and and fuel pump, very recent oil change since engine swap, car is fully stock except exhaust

I've also cleaned throttle body thoroughly and swapped out a newer TB, cleaned motion plates, and put a new tune to see if it does anything which all of these had no affect and still idled and drove rough
 
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07gts197

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How does it act when revving in while stopped?

2 things come to mind with this; Maf, even though you already cleaned it, when you unplug it that is how the throttle will react. And loose spark plugs is the other. When I replaced the plugs I initially snugged them and it ran like crap. It would idle rough but would clear up at higher rpms, until I torqued them with a torque wrench. Then it was fine.
 

JeremyH

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Is it tuned? Same tb? As little things changened over the years so did pcm tune strategy maybe tune related. You mentioned motion plates do you have seperate plate style or the newer style built into the intake manifold. Maybe tune parameters are different on that as well.
 
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Smeaglly

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There is no tune and even when I did put a tune on it there was no change, it has the separate motion plates
 

Smeaglly

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So all of the things you guys have suggested I have done and there has been no change to the way the car behaves idling or accelerating the problem still persist
 

bujeezus

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2 things I didn't see mentioned was changing the fuel filter and checking the alternator. I know a shitty alternator will do weird things to these cars.
 

stkjock

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Alright so here's my delema, I replaced my stock engine with a 09 engine and ever since I've swapped it my car lags, I'll even go full throttle and the car acts like it is trying to catch up then it will randomly kick in and it'll act fine, so I've put a new fuel filter and and fuel pump, very recent oil change since engine swap, car is fully stock except exhaust

I've also cleaned throttle body thoroughly and swapped out a newer TB, cleaned motion plates, and put a new tune to see if it does anything which all of these had no affect and still idled and drove rough

/\ RIF :poke:

2 things I didn't see mentioned was changing the fuel filter and checking the alternator. I know a shitty alternator will do weird things to these cars.

the alternator is a great suggestion
 

Smeaglly

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I got a new alternator when I did the engine swap sorry I didn't mention that

Yes the cats are stock, if they were clogged how would I go about cleaning them?
 
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stkjock

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You'd replace them or delete them.
 

Smeaglly

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I replaced the cats technically yesterday and the problem is still there
 

Smeaglly

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Whatever the problem is going on me and my dad are completely stumped because we've both done just about everything we can think of and even some outta the box idea checks, but it's even weirder that there's check engine light turning on or even flashing, and codes haven't shown in a while but those went away after all the checks we've done too but yet the car still acts funny idling and accelerating
 

JeremyH

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Check for vac leaks yet? Maybe a wiring issue? Im trying to think of all the things that get touched when swapping a motor. Does it feel like the car just dies or stumbles, ie looses spark or injector pulse? Check all the engine grounds and harness connections?
 

stkjock

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check the wiring harness around the transmission, I've seen threads on swaps that the harness gets pinched in that area when reinstalling the trans/motor
 

rocky61201

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check the wiring harness around the transmission, I've seen threads on swaps that the harness gets pinched in that area when reinstalling the trans/motor

What he said. I pinched my transmission harness that leads to the O2's and transmission which shorted everything out and blew fuse 47 in the fuse box. O2's, cam position sensors, EVAP system, and a couple other things all share the same circuit. Short the circuit and the fuse blows. Yea I pinched it between the bellhousing and engine block when putting trans back in. Pulled trans again and repaired my wiring harness but still had the problem with the check engine light and sluggish performance.

Weird thing is I would get the check engine light but my SCT tuner wouldn't pull the codes but it would clear the check engine light and then the light would come right back immediately upon the next startup. Plugged in my buddies more expensive MAC tools code reader and got all the codes for all of the sensors on the circuit. Figured out on this forum that fuse 47 is blown when getting all of those codes at the same time. Fuse 47 is under the hood btw.
 
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deebo05

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engine light flash when your symptoms appear? if so its a misfire.

did you use the 09 coil packs? not sure what year car you have.

have you logged fuel trims to see if its a fueling issue?
 

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