Which PCM??

[Caddilac-T]

Hi all,
I'm new to this site, and I'm new to Cadillac ownership, but I' not new to cars and mechanics on a whole. I've been doing my own wrenching for over 30 years. I'm looking forward to my 60th b'day next month. I have own dozens of cars before but never a Cadillac. Now, I love my latest girl, a 2001 SLS, that drives like a dream but now needs mechanical attention: here's some background, I, being the second owner, acquired the SLS from a negligent previous owner, for whatever reason developed a serious rod knock. So instead of trying to deal with this fact I had the opputunity to purchase a low mileage(45,000 mi.)2001 STS engine complete with pcm engine harness, etc. At the same time - I removed the heads and installed Norm's inserts, new head bolts, gaskets all around, and general clean-up on the STS engine. I will also use a better type front mount, if I can find one that is proven. My questions are; when I install the STS engine and pcm, will it interface directly with the SLS electronics and functions? any mods necessary? what effect will it have on the tranny shifts? But if I use the SLS pcm with the STS engine, would that be compatible with the operation of the engine parameters, fuel management? spark table? etc.
Caddilac-T

[Ranger]

You need to swap transmissions as well. They have a different final drive ratio.

There are two threads here on motor mounts. If not on this page, then probably only a page or two back.

[chp350]

If my understanding is correct the only difference between a y or 9 engine is the cams to give the extra hp...both engines you have are of the same year so why not just use your orginal sls heads and then no other parts swapping would be involved

[Caddilac-T]

Hi Ranger,
Thanks for your reply. However, I would like to keep the SLS tranny, and also the extra 25 or so horses the STS has. So in that light, would it be more avantangeous to use the original pcm on the car(SLS) or the pcm that came with the STS engine?
Caddilac-T

[Caddilac-T]

Originally Posted by chp350

If my understanding is correct the only difference between a y or 9 engine is the cams to give the extra hp...both engines you have are of the same year so why not just use your orginal sls heads and then no other parts swapping would be involved

I'm actually interested in keeping the STS engine in it's original power level, and yet just use the better suited pcm in this project. I also want to retain the final drive of the SLS(3.11). Any ideas?,suggestions??
Caddilac-T

[Ranger]

Originally Posted by Caddilac-T

Hi Ranger,
Thanks for your reply. However, I would like to keep the SLS tranny, and also the extra 25 or so horses the STS has. So in that light, would it be more avantangeous to use the original pcm on the car(SLS) or the pcm that came with the STS engine?
Caddilac-T

This has been discussed before and I don't think the two play well together. Remember, you are only getting those extra horses at 6500 RPM. I think the torque range is more important. Gotta believe that the engineers knew what they where doing.

[Mark C]

The STS PCM won't work with the rest of the controllers in your car. All the major controllers know the VIN of the car and will not talk to a controller containing another vehicles VIN. The PCM can not be reprogrammed with a new VIN, you need a new (never been in a car) PCM and then the dealer must program in the VIN and flash the unit for the rest of the info.

[ejguillot]

If you need the STS PCM reprogrammed to match the VIN of the rest of the car, AJ (ajxtcman) on this forum can do that. When he custom programmed a PCM for me, I bought a used PCM and sent that to him for reprogramming (so I could keep the stock one). Note that while AJ's reprogramming will make the PCM match up to the rest of the car, the PCM will throw a code until you have the crank sensor variance relearned. You'll either need access to a Tech 2, or pay someone to do it.

[Caddilac-T]

Originally Posted by ejguillot

If you need the STS PCM reprogrammed to match the VIN of the rest of the car, AJ (ajxtcman) on this forum can do that. When he custom programmed a PCM for me, I bought a used PCM and sent that to him for reprogramming (so I could keep the stock one). Note that while AJ's reprogramming will make the PCM match up to the rest of the car, the PCM will throw a code until you have the crank sensor variance relearned. You'll either need access to a Tech 2, or pay someone to do it.

That's the can-do attitude I'm looking for --Thanks , now after AJ vin matches for me, what kind of every day operational difference I should expect? a little better performance? gas mileage? better shifting? anything at all? Any other ideas for this swap??
Caddilac-T

[submariner409]

With a STS engine/SLS transmission/??? PCM you're looking at:

Less performance (mismatched torque curve for the final drive ratio), better gas mileage on the road (lower highway rpm), lower gas mileage in the city (greater throttle opening for equal acceleration - the final drive/torque thing again), probable strange shift points, and maybe a Pandora's Box of electronic problems. There's a lot of the entire car captured in the PCM - not just engine/transmission parameters. I believe that the only Northstar FWD PCM work currently being done by AJ is speed limiter removal - your PCM, a week, and $300 +/-.

"Any other ideas.........?" Convert to the STS drivetrain or stay with the SLS drivetrain. Mix & match in this breed of FWD cat is not the best way to go.

What is your current speed limiter setting ??? Driver's door sticker, tire rating. That also figures into PCM calibration, and is VIN-specific.
S = 112 mph, H = 130 mph, and W/Z = 150+ (depends on drag and wind conditions). I'll guess that an SLS is either S or H.

[Mark C]

You will get a transmission output shaft mismatch error, since its going to be looking for RPMs based on a 3.73:1 ratio transmission, while you have a 3.23:1 transmission installed. That may cause other issues, like the transmission starting in 2nd gear, etc. Your SLS PCM won't know you have a larger STS intake (or exhaust I forget which is different) camshaft in the car and you would be better off keeping the SLS PCM.

[Ranger]

Sub, I believe the SLS is S rated.

Mark, the STS trans is 3.11:1
It's the intake cam that is different.

I remember this being discussed a long time ago when the Guru was here and he advised against it for all the reasons you guys mention. I recall him saying you won't be happy with the outcome.

[submariner409]

Yep - STS is 3.71:1 and SLS is 3.11:1 final drive., therefore the rpm differences and highway gas mileage increase for the SLS.

[Caddilac-T]

Hi again,
Thanks to all who contributed to my questions about the pcm usage. This is a wonderful thing, this forum. You members gave me factual information I can count on. Because of the info presented -- I will retain the SLS pcm, and use the SLS heads on the STS shortblock, just to keep it within the stock parameters with no suprises!! Thanks again fellow members!
Caddilac-T

[submariner409]

...............when you get it on the road, c'mon back !! We'll give you some simple tricks to make it the best it can be.

Our bad: Welcome Aboard !!!!!