: Going from a 4.0 to a 4.6



93greeneldo
04-03-06, 10:19 PM
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

eldorado1
04-03-06, 11:35 PM
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.

chevelle
04-03-06, 11:49 PM
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.

auroradude
04-03-06, 11:50 PM
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.

93greeneldo
04-04-06, 09:57 AM
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.

eldorado1
04-04-06, 10:16 AM
can you get a picture of your pcm?

93greeneldo
04-04-06, 11:08 AM
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.
http://www.partsamerica.com/product_images/img/a1c/rep-computer.jpg (javascript:popImage('/img/a1c/rep-computer.jpg', 'Cardone 778429');)
Hope this helps, will get picture of actual unit as soon as I have free time, Thanks, jeremy

parts68
04-04-06, 08:34 PM
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.

chevelle
04-05-06, 12:21 AM
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.

chevelle
04-05-06, 12:24 AM
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.

93greeneldo
04-05-06, 12:37 PM
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.

chevelle
04-05-06, 01:08 PM
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.

mtflight
04-05-06, 01:14 PM
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?

dkozloski
04-05-06, 01:15 PM
Maybe bigger injectors?

93greeneldo
04-05-06, 04:15 PM
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.

eldorado1
04-05-06, 07:18 PM
using bigger injectors is no different than turning up the fuel pressure. The difference is, you can turn the fuel pressure up for free. The security torx bit in the middle of the FPR is the adjustment screw. You can break out the security pin and it becomes a regular torx bit.

I didn't know the computers were programmed so different... but I guess it makes sense if they have different accessory computers to talk to, and different dash controls...

parts68
04-05-06, 07:46 PM
If anyone has the memcal from a 4.6 and 3.71 axle ratio I ll try it on one of my 95s. I hear what your saying about the FPR,been doing that for years on our GTP hot rod. I didnt realize that the "code" hadnt been broken on OBD1s. My friend that does this says he can use tunercat software and will clone my chip with 4.0 and 3.71 gears,then go from there.I have heard of alot of hot rod guys using later N* with 95 intakes so they can custom make a GM PCM work.
Also superchips does offer upgrades for the OBD1.

auroradude
04-05-06, 08:46 PM
Parts68, I would be very interested to see how this swap goes. You would be the one to pave the path for other's in this situation.

I guess not having all the electronics would suck (I love them..Oil pressure DIC readouts and batt voltage, trip computer etc) are all premium electronics. Pretty much defeats the purpose of having a Caddy or aurora luxury car if you just want the power and no electronics..LOL. This may be out of the world, but what about swapping in and custom fabricating the 1995 cadillac DIC into the aurora? Lots of $$$ probably if you cant do it yourself.


http://westersgarage.eidnet.org/ -- Supposedly these guys have hacked the PCM for the auroras. they wanted $350 for a "performance" PCM, with you sending back the core. Check that out.

parts68
04-05-06, 09:49 PM
I cant see paying $350 for an OBD1 chip.
I know that theres alot of others that have "cracked" it.
OBD1 is not as secure as OBD2. Using the 4.0 memcal
and remapping the fuel curve is most likely the way to go.
BTW I have contemplated the swap and have all the ingredients
but dont have the time or need for it right now,just willing to help with someone thats in that need .

93greeneldo
04-07-06, 11:27 AM
OK, so what I would need to get this swap to waok would be a 1995 300 horsepower 4.6 and a burned chip in my computer. It almost sounds too simple. So will the 1995 4.6 work with the wiring harness in my Aurora? If there is anything else I need let me know because I am going to start looking for the parts now. I did find a 1995 STS motor for $1300 but it would cost me about $400 to ship it too me. Anybody else know where I can find a motor. Oh yeah, I am not positive that my car has the autobahn package on it, you said you could tell me if I looked at the computer and gave you the last four digits, is there any other way to find out, thanks, jeremy

parts68
04-07-06, 05:53 PM
Post the VIN and ill find out.
As for needing a 95 motor thats only if you dont want to change the intake.
Otherwise you can use any 4.6 FWD up to but not including 2000.
The 300 HP would be the way to go but the torque on the 275 horse is about the same. I guess its all about bragging rights.
Im getting closer to finding the computer parts needed.

Intheknow
04-07-06, 06:36 PM
I had the same idea when I had an Aurora. I put 215,000 miles on my '95 Aurora and loved every minute of it. I sold it and bought an '01 STS and I have never regretted it. Sure the Aurora had styling panache that the STS lacks, but it is made up in performance and luxury. The hassle of fitting a 4.6 into the Aurora, to me, isn't worth it when you can get the STS all ready to go. The difference in performance is impressive too.

STS 310
04-07-06, 09:05 PM
I do believe that this project would be a first on the forum.

For some reason, and I dont want to be a stick in the mud, but I think I can remember something like this being shot down even with the OBD 1.

I thought the tranny was different?

auroradude
04-08-06, 01:07 AM
Yeah you probably put a ton of money into that 95 like i have, right?? The 95s are the biggest money pit cars i think ive ever seen.

parts68
04-08-06, 09:22 AM
Same tranny
alot of the problems with cars are the care previous owners did for them.

93greeneldo
04-08-06, 09:31 AM
Ok here is my VIN # 1G3GR62C1S4118519 Thanks for your help with that. And to answer some peoples questions of why I want to do this with this car is because of several resons. One, I know I could buy an STS with all the features for less money but I like the styling of the Aurora much better than the STS and it is far more aerodynamic than the STS and eventually when I buy another daily driver I would like to turn it into a track car, stripping it down and trying to make it run with Camaro's and Firebirds. Second, I like cars that are different that the normal cars. Another project of mine coming up is swapping a 200- Pontiac 3.8 supercharged engine and transmission in a 1991 pontiac bonneville. I like cars that look stock and are very fast. I already have a 1993 Trans-am that is fast and attention getting, I like cars that surprise people. And third, and possibly most important, I already have a 1998 Eldorado Sport Coupe so I don't see the point in having two cadillacs that are essentially the same car. Thanks to everyone that has been helping me with this. I hope that if this works we can use it to help other people with Aurora or other swaps in general. Jeremy

93greeneldo
04-08-06, 09:36 AM
And to Aurora dude, I have put a grand total of $500 dollars into my Aurora. That includes new coils, sparkplug wires and plugs, brakes and pads all around, a battery, front struts and a catalytic converter. Everything except the converter I did this car runs real good and has served me well. I bought it for $2000 in decent shape a year ago. $500 in a year isn't too bad to me. My 1998 Aurora I had was 100 times worse, I had over $3000 in problems crop up in that car in only 3 weeks of ownership. I sold it at a serious loss. This 1995 with double the miles has been far better to me. Next year it is getting a frtee paint job courtesy of the local college bodyshop so I want to do things to this car to make it different than everything else. Auroras can be reliable as long as you take care of them.

parts68
04-08-06, 11:50 PM
Can you look at your tire info and see what speed rating it is?
this will tell us what trans you have and I can find out what PCM
memcal you have with that.

93greeneldo
04-09-06, 12:39 AM
Ill look in the morning about the tire info. The tires are newer on the car but I don't know if when they were put on if they were correct replacements. What should be on a aurora with the autobahn package?

parts68
04-09-06, 10:19 AM
replacement tire are most likely not correct as v rated tires arent cheap.
look at the tire info tag on drivers door
should be for a "v" rated tire if autobahn

93greeneldo
04-09-06, 11:10 AM
Ya I just realized I should look at the sticker on the car instead of the tires, I'll look when I leave for work and post later.

93greeneldo
04-10-06, 03:01 PM
Well, the replacement tires arent V rated but the car is. On the door sticker it read P235 60R 16 V. Well, mine is an autobahn so thats good news for me and my idea. Any revelations on the computer front?

parts68
04-10-06, 08:39 PM
your PCM code should read BMRY.Chipset could be 3 choices depending on what revision it was.Speed limiter is set at 139 from factory. I hope you dont try it without V or Z rated tires.
You will have a 3.71 axle ratio.

93greeneldo
04-11-06, 09:47 AM
I thought that it meant the Auroras were ungoverned. Anyways, ya I wont be doing this conversion without the proper tires, I am just trying to gather information about the car and what I want to do so I can gather parts. Thanks

infin1ty
04-13-06, 10:21 PM
Look for the code "QQX" on the tag under the spare tire cover. If it has that code - it has the Autobahn package.

parts68
04-14-06, 09:31 AM
hummm I have 2 95s and a 96
95s dont have broadcast sheet on spare tire cover
96 does.
95s are in the trunk behind the trim cover on 1/4