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Jerry Newton
Jerry Newton, Cadillac Technician
Category: Cadillac
Satisfied Customers: 4508
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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I have a 1993 Cadillac Sedan DeVille with 4.9 liter engine

Resolved Question:

I have a 1993 Cadillac Sedan DeVille with 4.9 liter engine and FWD.

I would like to tune the engine for best performance with add on parts but stay within specs for the engine.

I think many of the aftermarket performance parts are probably junk, so I hope to get some good advice here.

I have read that the 4.9 engine is de-tuned for emissions reasons. Example are at:

Do these things really work? Is there a less expensive way to achieve the same thing. Would you use different parts, possibly more expensive? Do they conflict? That is, if one of the parts IS installed, should one of the other parts NOT be installed.

What spark plugs would you use? What about spark plug wires, voltage regulators and spark voltage boosters?

Please provide internet links for any parts that you recommend.

Submitted: 7 years ago.
Category: Cadillac
Expert:  Jerry Newton replied 7 years ago.
The 4.9 doesn't have a lot available with regard to aftermarket parts. That is, you won't find cams and headers and intakes for this. It's a unique engine, and by 1993, they actually had them working pretty well, although still leaking oil and coolant. They do make decent power. My advice is to stay away from all of the hype of aftermarket devices, and stick to basics. This isn't a performance engine, but it is a smooth runner when dialed in. Set the timing according to the book at exactly 10 degrees BTDC, any playing with timing will result in serious decreases in performance. The minimum air rate and TPS settings are very finicky on this car, find a factory service manual and read up on some TSB's about this, and set it accordingly. Injectors were problematic in different parts of the country, depending on the type of fuel available, you need to run an ohmmeter across each one and discard any that don't fall with 14-18 ohms. Electrical grounds are critical to performance as well, I can't over-emphasize this point. Use nothing except AC Delco plugs in this engine. Unfortunately, once you've got it dialed in, and you're getting your full 240 horsepower or whatever it was rated at, that's as good as it's going to get. The weak link in this powertrain is the transaxle, if you start getting too crazy with the horsepower, it's not going to stay together. Remember that the car was designed to be putted around on Sundays by Gramma, not drag raced.
Customer: replied 7 years ago.

I am/was not thinking about radical changes that would turn the car into a hot rod. That is, NO cams turbo/supercharges etc. I am grandpa (67 years old) and simply want a tip top daily driver.


My main desire is to correct any de-tuning that may exist to reduce emissions. The things I see on the internet seem to be parts that claim to alter the computers operation.


Is the engine de-tuned for emissions? If so, are there any parts available that will re-tune the engine for better performance?



Expert:  Jerry Newton replied 7 years ago.
I wouldn't say that the engine is de-tuned for emissions. They run very well as they are, when they're running correctly. Any attempt to override the computer programming, in my estimation, would put you at risk for engine damage, because this engine is already prone to detonation and whatnot. It sort of runs on the ragged edge as it is. Cadillac did away with it in 95, because it wouldn't adhere to OBD2 standards in place for the 96 model year.

Does it run pretty well right now?
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