As of lately I noticed she is not running that great, when I'm crusing along at about 45-50 mph, and I put my foot in it she stumbles a little and then takes off. Also I have been getting crappy gas milage ~14-16 MPG....and last time she had a tune up was about 30k ago. I figure its time for a tune up.

Hey all I need some help here with tuning up the 4.5. I want to change the spark plugs/wires, dist. cap, pcv valve, breather filter, air filter, and fuel fuel filter as well as set the timing (by the way, how is the timming set on the 4.5?). Now what is the trick to removing the rear plugs on the 4.5? Are there any special tool I need, technique, etc. Also how do I clean the fuel injectors? Am I forgeting anything, I changed the coolant (I used bars leak) along with the tranny fluid 1 month ago. I have no codes in the sytem except for E39. Any help/advice is appreciated guys, thanks in advance.

I tuned up my 88 Deville 4.5 last year. I assume the 89 Deville is similar. The back plugs were an absolute pain in the butt. For the two back plugs closest to the passenger side, I jacked up the car, took off the front passenger tire (for more manuevering room), and removed them from underneath. I think I had to use a u-joint and an extension, but I'm not sure (my memory fails me sometimes). You may be able to get the socket and wrench right up to them. The other back two I couldn't see and had to lean over the drivers side fender and do those by "feel". There is very little clearance between the firewall and the engine and I scraped up my arms pretty good and woke up the neighbors with a few choice cuss words. You may be able to get to all of the back ones from the top, but in my situation the back plugs were locked in there pretty tight and I couldn't get the leverage I needed from the top. I am assuming it's probably due to past mechanics not wanting to go through the trouble of changing them when doing a tune up (not the first time I have encountered this, which is why I do my own tune ups now). They looked as if they hadn't been replaced for a long (and I mean LONG!!) time. The front ones were pretty easy. I had to remove a bracket on the power steering pump to get to two of them. The old school way says to change plugs every 10,000 miles, but if you can afford more expensive high mileage plugs, you may be able to skip changing the back ones every other tune up, or at least extend your plug change intervals if you are particular about changing ALL of them at every tune up. I also made sure to put a light coating of high temp grease on the threads so that the plugs would be easier to remove next time around. I do want to be honest with you, I am not a professional mechanic with a garage full of Snap-on tools. I'm just a regular guy with a few tools and a floor jack. There may be an easier way to remove the back plugs that I'm not familiar with. Best of luck, and try not to wake up the neighbors like I did. :histeric:

As of lately I noticed she is not running that great, when I'm crusing along at about 45-50 mph, and I put my foot in it she stumbles a little and then takes off. Also I have been getting crappy gas milage ~14-16 MPG....and last time she had a tune up was about 30k ago. I figure its time for a tune up.

Hey all I need some help here with tuning up the 4.5. I want to change the spark plugs/wires, dist. cap, pcv valve, breather filter, air filter, and fuel fuel filter as well as set the timing (by the way, how is the timming set on the 4.5?). Now what is the trick to removing the rear plugs on the 4.5? Are there any special tool I need, technique, etc. Also how do I clean the fuel injectors? Am I forgeting anything, I changed the coolant (I used bars leak) along with the tranny fluid 1 month ago. I have no codes in the sytem except for E39. Any help/advice is appreciated guys, thanks in advance.

I am also a 'shade tree mechanic' and tuned my '89 Sedan DeVille just a few months ago. I did't need any special tools, just a good set of sockets with a few assorted extensions and universal joints, some ingenuity and a lot of patience. I was able to get all of the plugs out from the top of the engine. Mine had 75,000+ original miles and still had the original plugs! I came away with a few scrapes and bruises but it was worth it.
I am not familiar with the error codes, so can't help you there. I tried unsuccessfuly to clean my inectors with a professional system that I had aquired and just ended up using a fuel addative in the gas tank.
The results were dramatic for me. The car went from sluggish and guttless to a respectable accelerator. The mileage I have gotten on the highway ranges from 22 mpg to 25 mpg.
Hope this has been helpful to you. Good luck.
Kev

Kev, just wanted to ask you what brand of additive did you use for your injectors? Mine are fine, but I just thought I might throw an additive in my tank once in awhile for preventative maintenance.

I have the 1990 Eldorado and I use the STP fuel treatment and my Caddy gets 30 MPG and I average between 17 and 19 MPG in town. I have the 4.5 V8 with port fuel injection. I use the fuel treatment when my Caddy feels a little sluggish. I have 120,000 miles on her and she runs better than new!

Now what is the trick to removing the rear plugs on the 4.5? Are there any special tool I need, technique, etc.

I did my '93 Eldo from the top, using a variety of universals, wobblers and extensions. Kind of a bear to do the rears this way, but doable. One post on this subject indicated that the poster had good luck getting at the rear bank from underneath.

Thanks for all of the feedback guys, I just wanted to know if I was going to get in over my head or if the job just need some time to get done, I have a good assortment of tools and will have to dig up the u-joint extentions, but thanks again. As far a fuel system treatment I'd reccomend Lucast that stuff actually does something.

Let us know how it goes.

That's excellent gas mileage Radman. I average about 20 mpg city and highway combined. I was really surprised when I first bought my car at the good mpg and power combination the 4.5 has. Years ago, it used to be if you got 20+ mpg, you were driving a 90 HP 4 cylinder Datsun that was about the size of the hood of a Caddy!

I hope to get similar gas milage, I'll let you guys know how it goes, I'll probablly tackle this project next week (low on $$$ right now).

Kev, just wanted to ask you what brand of additive did you use for your injectors? Mine are fine, but I just thought I might throw an additive in my tank once in awhile for preventative maintenance.
I have a Wynn's injector cleaning system and when I tried to clean the TBI I think I used too much pressure and the car wouldn't run on the cleaner as it's suposed to. So I de-pressurized the can of cleaner and dumped it into the tank. So, long story longer, I used a can of Wynn's X-Tend Power Tune Injector System Cleaner (WHEW! that was a mouth full!) I'm going to give the system annother try with a lower pressure stting and if that doesn't work, I'm going to try the Lucas stuff that others have suggested.

I wish my Cadi would get me 30 mpg, with 19 to 20 around town, but I suspect the TBI is not quite up to the challenge. Multiport fuel injection is the bomb. That and dual exhaust are the two things I wish my gal had. I can always go twice pipes but the multiport is gonna be a heartbreak for me.
Cheers!
Kev
:thumbsup:

I have an 88 and I'm only getting an average of 13.3 mpg. I just got it last month and so far all I've done is change the oil and the front rotors and calipers. I want to give it a tune-up can someone give me a list (in order of importance) of what i can do to help my gas mileage.

I have an 88 and I'm only getting an average of 13.3 mpg. I just got it last month and so far all I've done is change the oil and the front rotors and calipers. I want to give it a tune-up can someone give me a list (in order of importance) of what i can do to help my gas mileage.

Do you have any idea of what has been done and when?

If there are no detectable misses or hesitations, changing out parts is unlikely to do much for mileage. You could wait until dark and spray a water mist from a bottle onto the plug wires and look for arcing. You could also inspect the inside of the distributor cap and the rotor for carbon tracks, cracks, and general condition.

How much of your travel is local driving? 13.3 isn't all that bad if it is mostly all stop and go. Mine doesn't do much better. What about your driving habits? Driving like Granny Maude isn't exciting but it does save gas.

Not mileage related but if you don't know when the coolant was changed you might want to be on the safe side, drain the rad and refill with 50/50 coolant/distilled water and add 6 of the Bars Leaks pellets or 2 tubes of the Bars Leaks gold seal powder.
FWIW
YMMV
DFB

I changed my distributor cap and rotor ($20) and picked up about 2 MPG and the car is noticably quicker. I plan on changing the plugs too, that'll probably help as well.

The most common things to degrade the fuel milage are:
Rear plugs not changed last tune-up.
Malfunctioning EGR (Exhaust Gas Recirculation system) fix for this is in the forum
Leaking FPR (Fuel Pressure Regulator) the check for this in the forum
Clogged/bad catalytic converter. If it rattles, it is shot.

BTW... most FWD transverse engine cars I have worked on have a front engine mount dead center of the compartment. I just take the bolt out, and rock the (cold) engine forward. That changes the angle and gives you the necessary extra inch + needed to get to those rear plugs.