Engine Swap - Cadillac STS 4.6 1999, new engine 1998
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Cadillac Seville / Cadillac Eldorado Forum Discussion, Engine Swap - Cadillac STS 4.6 1999, new engine 1998 in Past Cadillac Vehicle Discussion; Hi All I am helping a guy that is swapping engines on a Cadillac STS 4.6. The old engine's threads ...
  1. #1
    turbolino is offline Cadillac Owners Member
    Automobile(s): Seville STS 1999
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    Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    Hi All

    I am helping a guy that is swapping engines on a Cadillac STS 4.6. The old engine's threads were unusable for inserting studs or coils, so he purchased an engine off ebay - made 1998, the old one was 1999. Now he swapped the engines and first noticed erratic fuel pump engagement when turning the keys for the first time - the pump was either not running at all, and when turning off the key it started to run (?!). Quite obviously the engine didnt start at all, plus he noticed some relays were getting really hot under the left passenger seat.

    Now I asked him if he only changed the engine core - his answer was yes, all sensors etc remained the same, except the oil pressure and temperature sensors.

    Now my question is - did anyone try to swap a 1999 and a 1998 engine and encountering any problems?

    Thanks

    Joe

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  3. #2
    N*Caddy's Avatar
    N*Caddy is offline Cadillac Owners Master
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    '97-'98-'99 engines are identical in every single aspect. He made some wiring errors.
    (Well for '97 the air filter and some other dressings (including harness) plus placement of the coil pack is slightly different if we are talking Seville, plus the lack of torque struts 98'+ plus the P/S pump slightly different, but these are things that can be swapped from the old engine). The actual engine is the same.

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    Better late than never: Did your friend realize that the old head bolt hole threads are completely drilled out and the new, clean holes tapped for the larger inserts ? .......... the new, larger diameter insert threads use new, clean block metal and the inside insert threads use the original size head bolts.............

    www.huhnsolutions.com

  5. #4
    turbolino is offline Cadillac Owners Member
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    Hi Submariner

    Yes he went for Jake's studs (pain to get them to Europe) - he first had to remove the old coils in that engine (surprisingly the engine was coiled with around 65000 miles on it)..hope he got this job OK, I didnt had a chance to check myself, but he said it was an OK job (he never did it before on the Northstar).
    What gives me headache is the issues with the "new" engine and its behavior - especially the fuel pump. I will get to check the wiring myself next week and see how it goes - I will certainly appreciate any hints..:-)

    Cheers

    Joe

  6. #5
    turbolino is offline Cadillac Owners Member
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    Quote Originally Posted by N*Caddy View Post
    '97-'98-'99 engines are identical in every single aspect. He made some wiring errors.
    Well I hope he didnt make any errors - the process is quite straightforward, but thanks for your info regarding the engine compatibility

    Joe

  7. #6
    turbolino is offline Cadillac Owners Member
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    ..I just came off the phone with the guy - on of the "G" points (G100, 101 or whatever) apparently was oxidized so the whole orchestra of electrical miracles didnt work as they should.
    Over the weekend oil change plus finetuning and test driving will conclude this chapter of the car :-)

    Thanks for your help

    Joe

  8. #7
    Submariner409's Avatar
    Submariner409 is offline If it won't run, slap in a big stereo
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    Glad you found the gremlin....... and you're not the first............ These cars use quite a few ground points, and many of them are 'bundled" into a single box with terminal ring which is bolted to a weld stud on the body metal. The individual connectors inside the box seem to oxidize and lose proper contact. Several members have resorted to physically removing the box and crimping individual ring terminals to each black ground wire.

  9. #8
    turbolino is offline Cadillac Owners Member
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    Re: Engine Swap - Cadillac STS 4.6 1999, new engine 1998

    thanks for the info. Yes, the car seems to have a few more gremlins like that...for one the fuel gauge shows erratic operation - goes from full to empty and intermediate without any warning. I guess this might be also due to a bad ground (havent used the search function for this yet) - perhaps it is also the sensor, which got some beating (there is an unfindable leak into the trunk, so this needs to be adressed as well), plus the LH power window (drivers side) went T/up, so we need to find a new mechanism (the steel wire got all entangled and is screwed up)...plus many more things
    But hey, so what, its a cadillac :-)

    Joe

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