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99 STS engine and transmission into a 94 Eldorado


jlinde

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I know a guy here in Sweden who has got the information - from GM people that a 99 PCM can be reprogrammed

to fit a 94. I suppose that the connector near the brake booster is the point where the engine and transmission

electric connects to the instrument. So far I do not know if it can be directly connected there and that the

ABS and cruise etc are compatible (maybe those have to be connected separately). I know this type of conversion

can be made if the 94 intake is used instead of the 99 if retaining the original 94 PCM (but this specific

94 is the Y-win engine but I suppose a Prom for a 295 hp engine can be used) The idea with this conversion

is to put a nice low mileage 99 engine and trans into this 94 without getting into drivability problems.

I have no info about how a 99 transmission (electrically) fits into the 94 - can it be some problems with

for instance the TCC or VCC?

I am the guy that will do the installation but I will not start with it before knowing it is possible.

/Jan L

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well just to throw a few things out there.

1994 is OBD 1 and 1999 is OBD 2. very different. may work for you but cannot say for sure.

Before you think about changing the engine, find out if it has been timeserted, and I recommend doing a block test as it seems 1999 was most common for HG failure.

Transmissions were different also I do believe.

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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The transmissions were both the 4T80E but you do need to make sure that the axle ratio is matched to the PCM or you will get an intractable P0730.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I thought the 99 STS transmission is 3.71 ratio but I have no manuals for that and if it is I think it is

possible to put it together with a 99 block (which will be timeserted)and intake things from a 94 and

the PCM from a 94 with the PROM for the 9-vin . I know that the 99 heads have to be drilled and notched for

the EGR to become like the 94 heads. The PROM change is just something that I think is right -to change it from

a Y-vin to a 9-vin because of the camshafts. But as I said before I have no clue that the 99 transmission

can be handled by the 94 PCM. That mentioned above is one method of installing the 99 engine and trans into

the 94. (The current engine and trans does not work as they should.)

The other method of installing -which I really doubt- is to install the complete 99 engine and trans setup

together with its PCM -reprogrammed -well I wrote that before and I am just hoping to find out from somebody

if it is possible or not. The sources here in Sweden mean that GM (USA) said that it just to reprogram the

99 PCM. This is the most easy way as the intake does not need to be changed and the transmission is then

controlled by the 99 PCM as original.

/Jan L

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This swap can not be done too many issues with the computer from what I understand, I would be shocked if it can be done

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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The 94 engine had the EGR passages in the head vs. the exterior pipes so you would have to use the heads from the 94 engine on the 99 block along with the magnesium intake and phenolic spacer plates. Other than that, as long as the mounting points are the same and the PCM and wiring from the 94 are used, it may work.

Out of curiousity, why are you thinking about doing this swap? Bad head gaskets on the 94? If so, why not repair the 94's block???

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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The friend bought the nice looking 94 Eldo very cheap but with a wrong engine and transmission installed that do not work as they should and then he also got a partly wrecked 99 STS (80000 miles) very cheap and then he got convinced that this swap can be done.

I am nearly sure of that the 99 heads can be drilled: 2 half inch holes and 8 notches with a grinder

to get them to function like the 93-94 heads EGR-wise. The reason for using the 99 heads is that those are in

good shape.

Personally I have no idea how the different computers in those cars talk to each other -maybe the 99

interfaces the same way as the old 94 PCM with the other computers (IPC)- the 99 maybe just has more

values. This is just guessing.

/Jan L.

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I think that jlinde says that he understands the machining operations to allow the internal EGR to work on post-1994 heads and is comfortable with that. The thing that I believe is wrong is that someone says to reprogram a 1999 PCM. The OBD I PCMs had EPROMs that could be changed and programmed as aftermarket items but none of the OBD II Cadillacs (model year 1995 and later) can be reprogrammed like the OBD I Cadillacs. You are better off staying with the OBD I PCM.

The 3.71 gear ratio is used with 4T80E transmissions used with the VIN "9" engines, the 300 hp L37 motor that Cadillac uses with the STS, ETC, and DTS. I believe that the VIN "Y" engines, the 275 hp LD8 motor comes with a 3.11 final drive ratio in the 4T80E. The differential can be changed with not too much trouble after pulling the right half-shaft but it probably is easier just to get the right transmission. The final drive ratio is part of the programming for the VIN "9" engine and if the PCM doesn't match the ratio you will get a persistent P0730.

As to whether the 4T80E from a 1999 car is compatible with the 1994 wiring harness, I can't say, but I would expect that the worst problem would be a different connector because the transmission is the same internally.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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