Going from a 4.0 to a 4.6
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Northstar Engines and System Technical Discussion Discussion, Going from a 4.0 to a 4.6 in Cadillac Engine Technical Discussion; I have a 1995 Oldsmobile Aurora with 156,000 miles. I like the car and was wondering if I could put ...
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    93greeneldo is offline Cadillac Owners Member
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    Going from a 4.0 to a 4.6

    I have a 1995 Oldsmobile Aurora with 156,000 miles. I like the car and was wondering if I could put a 4.6 Northstar in it so I could have a newer engine with less miles and more horsepower. Let me state now that I DO NOT want to sell this car and buy and STS with one already in it. I like THIS CAR and want to try and do something with this car. Since Mine is a 1995 it is OBD1 and the engine is controled by a seperate computer than the rest of the car. So, my first question is will the motor fit in there are bolt up to my original transmission? Second question, is the trasmission in the Aurora the same and the ones used in the STS's and the SLS's and if so would it bolt into the aurora? Would it be best if I could find a car the was wrecked in the rear and try and get the entire cradle to go into the aurora or would it be best just to stick with my transmission and the 4.6 Northstar? I know there will be electrical and wiring and computer issues but Those can be conquered with time and patience. One person on the forums talked about using a 4.6 block and rotating assembly with all the Oldsmobile pieces on it, is that a possibility. Is there any aftermarket performance chips available for a 1995 aurora to change values in. The only features I want to retain are my speedometer and Tachometer on the instrument cluster, I do not car if the fuel mileage computer does not function. Any hep or suggestions would be much appreciated by anyone. Thanks, Jeremy

    edit-sorry, typed 1993, meant 1995 aurora, sorry for any confusion

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  3. #2
    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Going from a 4.0 to a 4.6

    It's as close of a "drop in" swap as you're going to find. I wouldn't expect anything but minor issues. You might even be able to swap your 4.0 memcal for a 4.6 memcal from the 93-95 4.6 computers.

  4. #3
    chevelle is offline Cadillac Owners Enthusiast
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    Re: Going from a 4.0 to a 4.6

    A 93 Aurora....???....never heard of one of those. Are you sure it isn't a 95 or later...???

    Mechanically, the swap you are describing is dirt simple. Externally, the 4.0 and the 4.6 are exactly the same. The 4T80E transmission is the same in the Aurora or the Northstar Cadillacs aside from the final drive ratios in some cases. In any case, if you keep your trans it will bolt up perfectly.

    You want to find a 95 thru 99 Northstar 4.6 to make this work. If it is a 95 it will bolt right in and you can just put your Aurora engine cover onto it. If it is a 96-99 you will want to use your existing throttle body and such.

    The real problem here is that the 95 Aurora was a speed density fuel injection system. The PCM is calibrated for a 4.0 liter engine and putting a 4.6 liter engine into the car will make the fuel injection system run very lean. Unavoidable as speed density systems need to have the accurate displacment programmed into the PCM. The Cadillac PCMs for the 4.6 will not work in the Aurora. This is hard to get around. Impossible from most standpoints. You could use an adjustable fuel pressure regulator and bump the fuel pressure up a bit to compensate for the lean offset due to the displacement increase. It won't drive perfectly but it would be better than nothing. Since the 4.6 will be about a 15 percent increase in displacement it will make the fuel injection system about 15 percent lean. So...bump the fuel pressure up 15 percent. I think that system ran between 40 and 50 PSI so you would want to bump the pressure up to 46 or so at idle to get in the ballpark.

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    auroradude is offline Cadillac Owners Fanatic
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    Re: Going from a 4.0 to a 4.6

    heh heh heh, if my engine ever tosses a rod or head gaskets etc, byebye sweet sounding 4.0. Time for the pimp daddy 300hp engine. And I hold that with me forever, I will NEVER back down from that statement. No *****ing out like everyone else did. I agree with eldorado1, it cant be that hard and my mechanic already said he can do it. Just gotta have some spare change and about a month

    Ah, now that Chevelle has posted some interesting info...hmm. That seems tricky and $$$$ range to come up with a solution. Easily hours and thousands of dollars.

    Worst case scenario can always get a jasper 4.0 and have it built bulletproof, bulletproof trans, 50hp shot of nitrous.

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    93greeneldo is offline Cadillac Owners Member
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    Re: Going from a 4.0 to a 4.6

    Thanks for all the information but here are some more questions. First, will the motor mounts be the same for the 4.6 or will they be different from the 4.0? Second, since my car's engine is controlled by a seperate computer could I possibly just use a cadillac 4.6 pcm to run the engine or could I make a stand alone harness like they do in fieros and such? Third, since the engine will run lean is there any way to open up and change things in the aurora pcm to compensate for that either by reprogramming or by a new chip? Are any chips even made for this car? Also, in your guys opinion, should I keep my transmission or try and get a complete assembly with engine and transmission to put in the car. And finally, should I look for a 1995 Northstar as it will be the same year as my car and is still OBD1 so I will have a few options for computer programming.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Going from a 4.0 to a 4.6

    can you get a picture of your pcm?

  8. #7
    93greeneldo is offline Cadillac Owners Member
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    Re: Going from a 4.0 to a 4.6

    The computer for the engine is up under the dash so ill have to take a picture later but when I type in Engine computer into advance auto parts it comes with with a representative picture so it's not exact but I remember when I was trying to get it to pass emisions and I thought I had a bad computer I was looking and found one one e-bay and this picture looks similiar.

    Hope this helps, will get picture of actual unit as soon as I have free time, Thanks, jeremy

  9. #8
    parts68 is offline Cadillac Owners Fanatic
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    Re: Going from a 4.0 to a 4.6

    I dont agree that the 4.6 memcal wont work.
    Even so try the 4.0 memcal as the PCM is same on both.
    Look at the BLMs and see if it readjusts to around 140.
    These PCMs are very forgiving.
    Im ready to do some tuning on a couple of 95 Roras I have
    and have a 4.6 with spare heads also.The 95 is going to be the
    easiest swap ,just make sure you get a memcal for a VIn Code 9
    Caddy.If someone can supply me with a complete VIN for a 95 300
    HP STS I can get the memcal # for you. New from GM is only about $60.
    Or Im looking into piggyback chips and using old memcal for limp modes
    and supervision of various sensors.
    I have a friend whos deep into the reprogramming and has a chip burner
    but not sure how busy he is right now.
    Ive got a bad PCM but good memcal for 95 Rora autobahn,thinking of having the chip cloned so I can experiment with the piggyback.
    I have a 95 autobahn PCM right in front of me as Ive been playing with them.
    Service code is 16197429 BMRY.
    The last 4 letters is your eprom code.This is for the 3.71 axle ratio. I can use any spare PCMs and or memcals to sort this out if anyone has one.

  10. #9
    chevelle is offline Cadillac Owners Enthusiast
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    Re: Going from a 4.0 to a 4.6

    Quote Originally Posted by 93greeneldo
    Thanks for all the information but here are some more questions. First, will the motor mounts be the same for the 4.6 or will they be different from the 4.0? Second, since my car's engine is controlled by a seperate computer could I possibly just use a cadillac 4.6 pcm to run the engine or could I make a stand alone harness like they do in fieros and such? Third, since the engine will run lean is there any way to open up and change things in the aurora pcm to compensate for that either by reprogramming or by a new chip? Are any chips even made for this car? Also, in your guys opinion, should I keep my transmission or try and get a complete assembly with engine and transmission to put in the car. And finally, should I look for a 1995 Northstar as it will be the same year as my car and is still OBD1 so I will have a few options for computer programming.

    The engine mounting scheme for the Aurora is completely diffferent from the Cadillacs with the 4.6 Northstar but the 4.6 will bolt up to the Aurora engine mounts perfectly fine. Just leave all that as is.

    Keep your trans. The speedo and such are calibrated for the final drive ratio in your car which could be different with a different 4T80E from another application.

    The mechanical parts of the engine do not care whether the controller is an OBD2 (1996 and later) controller or not. The engine parts are the same as well as the sensors from 93-99. Your PCM will run the 4.6 fine from that standpoint. If you get a 4.6 from 93/94 it will have a different intake and intake hardware from your Aurora and will much more difficult to make work. If you get a 4.6 from 1996-99 then you will not want to use the mass air flow sensor from the 96-99 engine. Use your existing throttle body and intake hardware onto the 4.6. The throttle body is the same part so there is no difference in flow.

    The Block Learn values will shift and partially compensate for the leaness due to the increased displacement as parts68 suggests but it cannot nearly compensate for the difference required. Besides, that only encompasses operation in closed loop situations and will not affect the full throttle operation where it will still be lean.

    Actually, I believe the fuel pressure was increased on those systems for 1996 so simply using a 96 fuel pressure regulator on the 95 would raise the fuel pressure and give an across-the-board rich shift to the cal that would pretty much compensate. I've never done that specifically but it would be worth a try to get the calibration in the ballpark.

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    chevelle is offline Cadillac Owners Enthusiast
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    Re: Going from a 4.0 to a 4.6

    Quote Originally Posted by parts68
    I dont agree that the 4.6 memcal wont work.
    Even so try the 4.0 memcal as the PCM is same on both.
    e.

    Uh..have you ever tried it..??? LOL It will probably start and run the engine, yes, but it turn on a number of warning lights and set codes and the dash info will be screwed up to some extent. The PCM's are the same, yes, but the calibration chips are distinctly different in ways other than just the engine control due to the different communication schemes and architecture of the cars.

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    93greeneldo is offline Cadillac Owners Member
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    Re: Going from a 4.0 to a 4.6

    Ok, I understand the the computers will be different and the car will run lean. So should I try and get a 1995 4.6 complete with harness and computer and bolt that in and let it run the engine then. Or should I try and reprogram the 95 aurora computer to run the 4.6. I was trying to stay away from 1996 and newer stuff because of the change from OBD1 to OBD2 but if I do a complete change from the 4.0 engine and computer to the 4.6 engine and computer that problem is solved. How do the guys running northstars in their fieros get them to run. Are they just using the engine and computer from the cadillac and not worrying about the extra wire. Do 1995 northstars have a seperate computer that runs just the engine like my car or do they have a computer that runs the car and the body all in one.

  13. #12
    chevelle is offline Cadillac Owners Enthusiast
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    Re: Going from a 4.0 to a 4.6

    Quote Originally Posted by 93greeneldo
    Ok, I understand the the computers will be different and the car will run lean. So should I try and get a 1995 4.6 complete with harness and computer and bolt that in and let it run the engine then. Or should I try and reprogram the 95 aurora computer to run the 4.6. I was trying to stay away from 1996 and newer stuff because of the change from OBD1 to OBD2 but if I do a complete change from the 4.0 engine and computer to the 4.6 engine and computer that problem is solved. How do the guys running northstars in their fieros get them to run. Are they just using the engine and computer from the cadillac and not worrying about the extra wire. Do 1995 northstars have a seperate computer that runs just the engine like my car or do they have a computer that runs the car and the body all in one.
    The PCMs are exactly the same part number between a 95 Cadillac 4.6 Northstar car and the Aurora 4.0 car. The difference is in the internal calibration or the "chip". You don't need nor want the entire wiring harness and stuff. Just put the 4.6 engine in and use the aurora harness and PCM. You cannot easily get around the computer problem. Unless you can find someone who has hacked the PCM and can reprogram the "chip" changing the entire box or other ideas will accomplish very little. If you put the whole Cadillac harness and box in the car as a standalone system the dash and the rest of the car will not work and it would be an abortion.

    That is why mechanically it is a very simple swap but electronically is almost impossible to do it "right". The best you can hope for (unless you find the guy that has hacked the PCM and can reprogram it for you) is to jimmy the calibration in the 4.0 box for the 4.6 by raising the fuel pressure to offset the lean condition.

    The Fiero guys just get the engine to run with the Cadillac controller and don't hook up the check engine light and they don't have all the dash and car electronics that you do to worry about. They just want the engine to run. If that is all you want and can accept a blank dash then set up the Cadillac box in the car...LOL. Plus, most of the Fiero guys are not running the 4T80E transmission so they do not need the vehicle speed inputs to be correct and do not need the transmission control from the PCM. Many of the Fiero swaps actually use the more often hacked computer from the LT1 engine since they don't need the trans control that requires the correct Northstar PCM. The Fiero swap is more difficult mechanically but much much easier electronically since the Fiero had no electronics to interface with the PCM and those swaps are hot rods anyway so poorer driveability and lack of automatic trans control are not such and issue. Besides, with a 4.6 Northstar in a Fiero, even if it is only making 3/4 of the power it is supposed to it is still wickedly fast so they don't really notice that it doesn't run just perfect...LOL.

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    mtflight's Avatar
    mtflight is offline Cadillac Owners Connoisseur
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    Re: Going from a 4.0 to a 4.6

    Quote Originally Posted by chevelle
    The PCMs are exactly the same part number between a 95 Cadillac 4.6 Northstar car and the Aurora 4.0 car. The difference is in the internal calibration or the "chip". You don't need nor want the entire wiring harness and stuff. Just put the 4.6 engine in and use the aurora harness and PCM. You cannot easily get around the computer problem. Unless you can find someone who has hacked the PCM and can reprogram the "chip" changing the entire box or other ideas will accomplish very little. If you put the whole Cadillac harness and box in the car as a standalone system the dash and the rest of the car will not work and it would be an abortion.

    That is why mechanically it is a very simple swap but electronically is almost impossible to do it "right". The best you can hope for (unless you find the guy that has hacked the PCM and can reprogram it for you) is to jimmy the calibration in the 4.0 box for the 4.6 by raising the fuel pressure to offset the lean condition.

    The Fiero guys just get the engine to run with the Cadillac controller and don't hook up the check engine light and they don't have all the dash and car electronics that you do to worry about. They just want the engine to run. If that is all you want and can accept a blank dash then set up the Cadillac box in the car...LOL. Plus, most of the Fiero guys are not running the 4T80E transmission so they do not need the vehicle speed inputs to be correct and do not need the transmission control from the PCM. Many of the Fiero swaps actually use the more often hacked computer from the LT1 engine since they don't need the trans control that requires the correct Northstar PCM. The Fiero swap is more difficult mechanically but much much easier electronically since the Fiero had no electronics to interface with the PCM and those swaps are hot rods anyway so poorer driveability and lack of automatic trans control are not such and issue. Besides, with a 4.6 Northstar in a Fiero, even if it is only making 3/4 of the power it is supposed to it is still wickedly fast so they don't really notice that it doesn't run just perfect...LOL.
    Is the Fiero approach similar to what Chrfab does?

  15. #14
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    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Going from a 4.0 to a 4.6

    Maybe bigger injectors?

  16. #15
    93greeneldo is offline Cadillac Owners Member
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    Re: Going from a 4.0 to a 4.6

    I was going to ask about installing bigger injectors to offset the lean condition, is that a possibility. And you say to just put the 4.6 in and plug all the sensors back in. Are you saying that most if not all of the electronics from the 1995 aurora will fit a 1995 4.6. If so that makes my engine search much easier.

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