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Discussion Starter #1
My 2006 3.5 with only 80,000 has a bad head. It's 8 months out of warranty and GM is not willing to help me out with it. It seems a 3.7 swap is going to be the cheapest fix. I've read through the threads and still have a couple questions for the forum.

1. Am I better off buying a used 2007 3.7 or should I find a reman long block?
2. 3.5 mani bolt up as is or do I need to port it to fit? Would the 3.7 manifold be a better choice?
3. I've read the fuel rail from the 3.5 needs to be used...which injectors (3.5 or 3.7)?
4. Does it matter if the used 3.7 comes from a 4x4 (my truck is four wheel drive)?
5. If I bought a long block, wouldn't I need to reuse the coils from the 3.5?

Thanks for the help.
 

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pssssssshhhhhhhhhhhhhhhhh
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For the ones I can answer,
2. Manifolds are interchangeable, I didn't notice a difference in mine from the 06 3.5 to a 07 3.7 mani

3. Injectors are the same

4. Oil pans might be different? I think they are


Sent from AutoGuide.com App
 

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Monkey Slut!
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1. Am I better off buying a used 2007 3.7 or should I find a reman long block?
2. 3.5 mani bolt up as is or do I need to port it to fit? Would the 3.7 manifold be a better choice?
3. I've read the fuel rail from the 3.5 needs to be used...which injectors (3.5 or 3.7)?
4. Does it matter if the used 3.7 comes from a 4x4 (my truck is four wheel drive)?
5. If I bought a long block, wouldn't I need to reuse the coils from the 3.5?

Thanks for the help.
1. Look at what your options are, finding a low milage 3.7 might be hard.
2. 3.5 bolts right up, you just have to port match it. It's really easy to do.
3. Injectors are the same, no need to switch them.
4. The 4x4 has a deeper pan, if your a 4x4 than your fine. I had to switch them because I'm lowered.
5. Coil packs are different from the 3.5 and 3.7. Not sure that answers your question.
 

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maniac mechanic
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My 2006 3.5 with only 80,000 has a bad head. It's 8 months out of warranty and GM is not willing to help me out with it. It seems a 3.7 swap is going to be the cheapest fix. I've read through the threads and still have a couple questions for the forum.

1. Am I better off buying a used 2007 3.7 or should I find a reman long block?
2. 3.5 mani bolt up as is or do I need to port it to fit? Would the 3.7 manifold be a better choice?
3. I've read the fuel rail from the 3.5 needs to be used...which injectors (3.5 or 3.7)?
4. Does it matter if the used 3.7 comes from a 4x4 (my truck is four wheel drive)?
5. If I bought a long block, wouldn't I need to reuse the coils from the 3.5?

Thanks for the help.
1. Reman is safer, but the head problems are less common on the 3.7L so I wouldn't rule out a used as long as the price is right.

2. 3.5L mani will bolt up but port matching is recommended

3. Since you have a 2006 with a returnless system you don't have to worry about getting the fuel rail.

4. the 4x4 and 2wd are the same only the transmission pans are different, so no issues there.

5.You cant use the 3.5L coils on the 3.7L head so you will need 3.7L coils

let us know if you have anymore questions
 

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Discussion Starter #7
1. Reman is safer, but the head problems are less common on the 3.7L so I wouldn't rule out a used as long as the price is right.

2. 3.5L mani will bolt up but port matching is recommended

3. Since you have a 2006 with a returnless system you don't have to worry about getting the fuel rail.

4. the 4x4 and 2wd are the same only the transmission pans are different, so no issues there.

5.You cant use the 3.5L coils on the 3.7L head so you will need 3.7L coils

let us know if you have anymore questions
Wait a tic...are you saying I don't need to swap the fuel rail? The 06 is the same? I hope so...this just got a bunch easier. So basically the egr block off plate needs swapped and I'm home free?
 

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maniac mechanic
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Yes sir. Just pop your hood and confirm that the fuel rail does not have a fuel pressure regulator attached and only one feed line going into it. They change the trucks to returnless at some point in 06 and yours should be but I saw one or two that didn't. Regardless you dont need to buy a new rail either way, just have to retain the factory one so don't throw it out with the old motor.

If yours looks like this you have the same as the 07's and nothing is needed


If it looks like this, you will have to keep this fuel rail and attach it to the 3.7L because the 3.7L will come with the one above which won't work on the return system. That round thing to the left is the fuel pressure regulator
 

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... That round thing to the left is the fuel pressure regulator

Not sure (mine is an '05 with the return-style system) but..

I believe that thing is a fuel pressure sensor.

As I understand the later return-less systems, the control circuit located in the rear under the chassis is the regulator.

The sensor mounted up front measures the pressure and returns a measurement signal to the control-unit.
The control-unit then varies the speed of the pump motor to increase the pressure (by running the motor faster) or decrease the (by running slower) to maintain fuel at the correct pressure.

I could be mistaken, but that's my understanding.
 

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Discussion Starter #10 (Edited)
Not sure (mine is an '05 with the return-style system) but..

I believe that thing is a fuel pressure sensor.

As I understand the later return-less systems, the control circuit located in the rear under the chassis is the regulator.

The sensor mounted up front measures the pressure and returns a measurement signal to the control-unit.
The control-unit then varies the speed of the pump motor to increase the pressure (by running the motor faster) or decrease the (by running slower) to maintain fuel at the correct pressure.

I could be mistaken, but that's my understanding.
Either way...just looked and mine doesn't have it, I am good to go with the rail on a 2007 3.7. Can't thank you guys enough for the help.
 

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Monkey Slut!
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1. Reman is safer, but the head problems are less common on the 3.7L so I wouldn't rule out a used as long as the price is right.

2. 3.5L mani will bolt up but port matching is recommended

3. Since you have a 2006 with a returnless system you don't have to worry about getting the fuel rail.

4. the 4x4 and 2wd are the same only the transmission pans are different, so no issues there.

5.You cant use the 3.5L coils on the 3.7L head so you will need 3.7L coils

let us know if you have anymore questions
The 4x4 pans are deeper, I had to change mine. My motor came out of a Z71 and couldn't use the pan or pick up tube for the oil pump.
 

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I have a rebuilt 3.7 with a 2wd pan for sale in the classifieds. Been bored .02 over. The head has around 40k on it. It will be shipped complete besides the timing set.
 

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Discussion Starter #14
I have a rebuilt 3.7 with a 2wd pan for sale in the classifieds. Been bored .02 over. The head has around 40k on it. It will be shipped complete besides the timing set.
I saw that motor in the classifieds. Sounds interesting, but I'm really looking for something I can get in hand and have it in ASAP. Swapping the motor is within my realm but dual overhead cams and timing sets are not. Appreciate the offer sir.
 

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Discussion Starter #15
Another question for you folks. What will I need to do differently since mine is a 4x4? Can't seem to find a 3.7 swap write-up on a 4wd truck around here....
 

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[MTS] Who is this guy?
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Another question for you folks. What will I need to do differently since mine is a 4x4? Can't seem to find a 3.7 swap write-up on a 4wd truck around here....
I'd imagine nothing aside from swapping your 4x4 pan onto the 3.7 if it is not out of a 4x4 originally. But I could be wrong.
 

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Discussion Starter #17
I figured the pan would need swapped if the new engine came from a 2wd...I'm asking more about dealing with the transfer case while removing the motor. I'm planning on keeping the transmission in the truck and pulling just the motor, seems easier on a 4wd truck. I could be wrong.
 

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Monkey Slut!
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Shouldn't be any problems just swapping the motor and leaving the transmission in the truck. Those top bolts are a bitch to get to though, there is a water line that goes across the top of the tranny make sure you get that one.
 
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