engine 4.5 or 4.9 help 1990
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, engine 4.5 or 4.9 help 1990 in Past Cadillac Vehicle Discussion; Hey Guys I am a newbie so please correct me or direct me if I am in wrong section. I ...
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    LuvTap is offline Cadillac Owners Member
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    engine 4.5 or 4.9 help 1990

    Hey Guys I am a newbie so please correct me or direct me if I am in wrong section. I have a question I am trying to help my brother-in-law with his 1990 cadilac deville his 4.5 engine is blown and he found a 4.9 engine (not sure of the year) at a very resonable price. My questions is could the 4.9 be used in the 1990 model to replace the 4.5 engine or are there too many complications,like motor mounts, electronics, inigtion etc. I am sure somone probably answered this years ago but I dont know where to look for the answer. Thanks in advance.

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    jayoldschool's Avatar
    jayoldschool is offline GM RWD V8 addict
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    Re: engine 4.5 or 4.9 help 1990

    Welcome! His car is FWD, so I'll move this over to the correct section for you.

  4. #3
    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    It's possible, but yes, other things would have to be changed as well. Unless you want to take the opportunity to upgrade, I'd just look for a 4.5. They're plentiful and cheap.

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    drewsdeville is offline Cadillac Owners Master
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    Re: engine 4.5 or 4.9 help 1990

    I wouldn't go that far... The '90 4.5 was a one year only engine, and last I looked 4-5 years ago, they were getting scarce. I can't imagine what it would take to find a good example of one now - 23 years after that one year production!

    You could actually PROBABLY make it work with little effort. Just about the entire engine is identical, with the exception of the rods, crank, and pistons. Block, heads, intake manifold, exhaust manifolds, and just about everything else that bolts to the exterior of the engine (except for the extra 3 #/hr injectors, A.I.R. pump and piping which could be swapped over or eliminated, and the missing detent cable provision on the throttle body that you'd have to swap over) is identical. The PCM hardware (motherboard, plugs, case) is also identical, though I'm not sure how the 4.9 would run on a 4.5 EPROM (the displacement is greater, but so is the injector flow rate, so that would make an interesting experiment). I wouldn't think you'd be able to run a 4.9 EPROM since it would expect the newer 4T60E trans there, but who knows...

    Of course, you should still do your homework, and if you attempt, still expect some hangups - just in case. For a better source for both the 4.X engines (and the N* for that matter), as well as GM PCM operation, check out Pennocks Fiero Forum.

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    MoistCabbage's Avatar
    MoistCabbage is offline Cadillac Owners 10000+ Posts
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    Only the injection system is one year only. The long block will swap from any 4.5z

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    drewsdeville is offline Cadillac Owners Master
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    Re: engine 4.5 or 4.9 help 1990

    The heads (valve size, combustion chamber shape/size, port shape/sizes), rods, and pistons are very different on the TBI engines relative to the PFI variants... I'm not sure you can even get a PFI intake manifold to seal on TBI heads, but if you could, I'm not sure how well it would work.

    The 4.5 PFI longblock is near identical to the 4.9, but very different from the earlier TBI 4.5

    The only options here will be with the PFI engines.

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    LuvTap is offline Cadillac Owners Member
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    Re: engine 4.5 or 4.9 help 1990

    Quote Originally Posted by jayoldschool View Post
    Welcome! His car is FWD, so I'll move this over to the correct section for you.
    THANKS much appreciated

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    VEGASELDO91 is offline Cadillac Owners Fanatic
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    Re: engine 4.5 or 4.9 help 1990

    Just curious; but how did the engine blow?

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    brougham is offline Cadillac Owners Master
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    Re: engine 4.5 or 4.9 help 1990

    I've seen the 90 4.5 in 1988/89 cars before and done as a normal engine swap so it should be easier to use a 4.5 then make a 4.9 work. I don't know if the computer is smart enough to automatically adjust for the displacement difference or if it would starve the bigger engine and cause other problems because it's strictly calibrated for the 4.5.

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