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Having issues after motor swap

Tiny
XKMACX86
  • MEMBER
  • 2004 CHEVROLET COLORADO
The truck: stock 04 Colorado z71 2wd
Stock motor: l52 3.5l 5 cyl 143 k miles

The replacement: stock 08 llr 3.7 5cyl 13k miles (per seller)

Using 04 pcm flashed 07 stock tune with custom tune to adjust for maf scaling.

The rundown: using 04 pcm and harness, all 04 sensors, 04 fuel rail, 08 injectors, 08 injector harness, 04 ported throttle body, 07 exhaust reluctor/actuator.

What we know: stock 07 will drop in to an 04 and run on the 04 tune and sensors.
04 and 07 exhaust reluctor are 5x. 08 is 4x. 08 lacks an intake cam sensor. One was we added one to the head in the proper location.
mechanically this motor resembles an 07 perfectly.
Compression is over 155psi, all timing marks line up correctly at tdc, coils check good, all sensors have proper resistance, only obd2code is p0300 random misfire (also pending)

The symptoms: truck will fire and run but will misfire constantly. Rpm will hover around 600+ which is normal idle rpm. Metallic sound coming from valve cover thought to be the timing chain. Tensioner is set and functioning, exhaust reluctor positioned correctly.
Mechanically and electronically this motor should be perfect.

What else can I check or is there something I have missed?
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Sunday, May 6th, 2012 AT 10:51 PM

12 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
Fuel pressure. If it's low then it will give a misfire as well as a vacuum leak
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Sunday, May 6th, 2012 AT 10:57 PM
Tiny
DJCL
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Check engine vacuum @ idle this will tell us about its breathing ability.
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Sunday, May 6th, 2012 AT 11:01 PM
Tiny
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Fuel is over 55psi while running. Crankcase vacuum is good. I dint have a gauge but there is substantial vacuum at idle.
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Friday, May 11th, 2012 AT 5:00 AM
Tiny
HMAC300
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You may have to chagne the exasut reluctor to aone tha tis compatible with the 04. That may be your problem. On vacuum can you tell the difference between 12" and 20"? Nope not without a guage.
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Friday, May 11th, 2012 AT 1:51 PM
Tiny
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Exhaust reluctor is 5x. Stock 07 tune is 5x
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Friday, May 11th, 2012 AT 2:20 PM
Tiny
HMAC300
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Yes but you are putting a 08 motor with 4x technology into 5x that may be your problem. It should only be the cam fazer
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Friday, May 11th, 2012 AT 6:02 PM
Tiny
XKMACX86
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  • 6 POSTS
You are correct except the fact wherei started I installed a 2007 reluctor/actuator which reads a 5x. Intake can is the same for all years in question
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Friday, May 11th, 2012 AT 7:10 PM
Tiny
HMAC300
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Ok one other thing are the cams the same between 07 and 08? If you had to add a cam sensor was there a slot to let the sensor read it? What was used to replace the cam sensor so that the motor will run right. I'm not real good on the electronic parts after 06
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Friday, May 11th, 2012 AT 7:14 PM
Tiny
XKMACX86
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07 intake cam sensor, set to the correct location and depth. 07 and 08 cams are the same.
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Friday, May 11th, 2012 AT 8:01 PM
Tiny
HMAC300
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Don't know what else to tell you. Now i'd be grasping at straws as well, maybe check motor mounts for tightness as that can sometimes give you a false reading.
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Friday, May 11th, 2012 AT 10:24 PM
Tiny
HMAC300
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Ok this has been buggin g me and I just looked up the wiring schematic and the 08 engine DOES show a camshaft sensor. They are in the front of the engine. It also shows a camshaft actuator solenoid. I'm sending a pic of where the cam sensors are supposed to be located. This may be your problem with the rough running as you only have 1 sensor and need 2 or the one sensor may need to be moved to the normal 08 position to get correct timing. I am only going by the charts and schematics that I am reading but I think you'll see what i'm talking about.
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Saturday, May 12th, 2012 AT 1:55 AM
Tiny
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I added a 07 intake cam sensor. The motor physically and electronically is now 07
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Saturday, May 12th, 2012 AT 2:54 AM

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