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3400 Engine Swap

Chapter 4: Prepping the new motor - Part 1

So the junkyard just dropped off your bright shiny (ok, most likely old, grungy) 3400 in your driveway. I suppose you want to know what do do with that
beastly hunk of iron and aluminum now, don't you? Read on to find out what needs to be done to the motor before it is ready to power your J-Body.

Strip off all the unnecessary garbage

Your motor probably came with a bunch of junk you don't need.

  • Wiring Harness. If your engine came with the wiring, it is of no use to you. I stripped mine off & tore all the wires out to have on hand for other projects.
    Some of the connectors may come in handy, and if the wiring between the CPS and ignition module is there, you can use that.
  • Engine Mounts. Depending on what your motor came out of, it may have a varying array of motor mounts on it. These are of no use
    as you will be reusing all of your stock mounts. Get that extra metal out of the way.
  • Alternator Bracket. You'll be re-using yours, so get this off of there, along with any pulleys or tensioners that may be attached.
  • Idler Pulleys. Remove any extra pulleys, as you probably don't need them, or will need to relocate one later if you don't have A/C.
  • Cam position sensor. This sensor located under the power steering pump area, going into the block is not used. Don't remove it though, or
    you'll have a hole to plug. Just snip the wires off flush.
  • Crank Pulley Sensor. Behind the crank pulley you will have a sensor with a pigtail hanging off of it. You don't need this, so get rid of it along with the bracket the sensor is attached to.
  • Power steering lines. If your motor came with a pump & lines, you'll need to use different lines, so remove the lines that came with the pump.
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Clean that beast up

The amount of effort you want to put into engine cleanup is entirely up to you. A little paint here & there goes a long way to making it look real nice in your engine bay.

I'd recommend pulling off the plenum (you will need to to deal with the injectors & harness anyway) & front valve cover and giving them a shot of paint at least. Polishing up the 3400 lettering will really set it off.

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LIM Replacement

If your motor is pre 2003, I'd highly recommend replacing the Lower Intake Manifold gasket now. It will be much easier to do with the engine out of the car
and will be good insurance since these are know to leak even at low mileages (mine went around 15k miles). I will add a separate how-to on LIM replacement in the future,
but this is a pretty simple procedure with the engine out of the car.

Fuel Injectors and/or harness

Decision time. Do you want to run your stock injectors from your 2.8/3.1, or use the injectors that came with the motor?

Options comparison

  • Stock Injectors
    • Advantages
      • Less initial work. Just swap in the injectors, use your old harness & go
      • You know your injectors work. Sometimes the injectors get clogged when sitting in the junkyard, so your new engine might have injectors that require cleaning
      • No computer modifications needed
    • DisAdvantages
      • You will be pushing the limits of flow in the injectors, running the risk of leaning the engine out at higher RPM's
  • 3400 Multec2 Injectors
    • Advantages
      • These injectors were designed for the motor with enough flow to keep it running happily to redline
      • Newer injectors that are probably better balanced than your old injectors
      • No need to swap injectors or remove them from the rail
      • These injectors provide enough flow to even a decently modified N/A motor
    • DisAdvantages
      • You will need to modify your injector harness to plug into these injectors by cutting the connectors off the 3400 harness & soldering them on to your stock harness
      • You will need to have a custom computer chip burned, or the car will run obscenely rich
      • Injectors could be clogged, requiring cleaning

Personally, I would recommend going with the Multec2 3400 injectors & purchasing the computer chip. You will make more power & be much happier with the end result

Modify your harness

Like I said, to use the new injectors, you will need to modify your injector harness.

  1. Remove the injector harnesses from both of your motors, paying attention to the routing. You will end up routing the harness more similar to the 2.8/3.1 routing than
    the 3400 routing.
  2. Remove all the loom & tape from both harnesses.
  3. Cut & splice the connectors. For wiring the 3400 injector plugs onto the stock harness, one bank of the stock harness has a pink and blue wire, the other bank has a pink and green wire. The 3400 connectors all have a pink wire and a random colored wire. Match up the pink wires when making the new connections. The random colored wire from the 3400 plug goes to eaither the green or blue, depending on which bank you’re on. All the plugs are the same, so it doesn’t matter which plug you use where.
  4. It is advised to use heat shrink and solder all your connections. Alternatively, you could pop the wires out from the 3400 and stock connectors, and insert the wires into the plugs with the pins instead. I'm not sure if the 3.1 and 3400 harnesses use the same size pins or not, or if you'd need to install new pins.
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Belt Routing

Your 3400 will come with a variety of idler pulleys on it. What it has exactly depends on the year and model it came out of. In most cases
you'll need to remove all these pulleys. Depending on whether the pulley in the tensioner is ribbed or not, you'll need to swap your old tensioner over. Just make sure the
tensioner pulley is NOT ribbed.

If you're running AC, then you don't need to worry about any other idler pulleys. If you don't have AC, you'll need to make sure you have a ribbed idler pulley
unstalled in the boss under the waterpump. Some earlier 3400's have a different front cover that does not have this boss. You can see the boss in the pictures below. I'm
running AC, so I didn't need to install an idler.

If you are running AC, you'll need to make sure your front mount bracket is made to allow the AC to bolt up.

The length of your belt will is affected by many variables, so it is best to measure. I have AC and an underdrive pulley, and was able to use the stock size belt from the 3.1 with AC.

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Chapter 5: Prepping the new motor - Part 2 »
Page Last Modified: 06/19/2018 4:15 pm

3400 Swap Navigation

  1. Introduction / Why should I swap?
  2. What parts am I going to need & what will this cost me?
  3. Removing the old engine
  4. Prepping the new motor - Part 1
  5. Prepping the new motor - Part 2
  6. Installing the new motor (Coming Soon)
  7. Tuning your new motor (Coming Soon)
  8. Troubleshooting your swap (Coming Soon)
  9. Frequently Asked Questions (Coming Soon)
3400 Swap Home
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