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Discussion Starter #1
I bought my 95 STS car with 102K on it and I'm not sure if the plugs and wires has been changed before my car still runs strong but my gas mileage has dropped to like 12-14 mpg and i have a black spot coming from the exhaust on the left side of my bumper. Does these sound like possible symptoms of weak plugs?

Also I was wondering how to change the plugs in the back? I cant even see them.
 

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1994 CADILLAC DEVILLE CONCOURS, 350ZR
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To Access The Back Plug You Must Remove The Coil Pack. Remener To Number The Plug Wire, Make It Easier When Pluggin Them Back. I Believe There Are 4 Bolt That You Hafta Remove. Its Easy Like Butter. And Also Use Anti Seize Or Whatever Its Called
 

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White Diamond '03 DHS (with DTS floor shift)
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Sounds like your running rich. Check the FPR. It sounds more suspect than the pplugs and/or wires.
 

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94CaddyConcours said:
To Access The Back Plug You Must Remove The Coil Pack. Remener To Number The Plug Wire, Make It Easier When Pluggin Them Back. I Believe There Are 4 Bolt That You Hafta Remove. Its Easy Like Butter. And Also Use Anti Seize Or Whatever Its Called
Sorry, but DO NOT USE ANY ANTI-SEIZE ON THE PLUGS. That can wind up causing some nasty problems. There's enough oil on the threads most of the time that it shouldn't be a problem. It might take some force to crack them loose, but you don't have to do it again for about 100k miles anyway, so just put them in with nothing on the threads and forget about it.

At 100k miles, you're due for plugs AND wires. On a 94, you need AC-Delco 41-950 plugs and AC-Delco wire set 628Q. You'll pay a few bucks more for them, but the engine was designed and tested with those parts and I think most people here will highly recommend them over anything else. You'll be glad when it's all done.

As for your exhaust sooty smoke, it could be lots of things. Have you checked for codes yet? Is your Service Engine Soon light on? Look at the first thread in this forum "Got codes?" and do what it says. Let us know what the codes are and somebody will be able to help you. My guess is leaking FPR, bad TPS or EGR, dirty injectors, weak fuel pump, or more than one bad O2 sensor. Have any starting problems?
 

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1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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They might appear to be in good condition and an ohm-test might even check out. But with 100k of engine heat on the wires insulation it is time to change the wires.
 

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Discussion Starter #7
My car is'nt throwing any codes at all but i due have a little trouble starting the car sometimes.It always starts but the engine turns over 3 or 4 times be for it kicks on.
 

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To check your wires you can mist a mild salt water solution on them, run the engine in a low light environment and look for a light show. If you see arcing, the wires are leaking. You should remove the beauty cover to see the complete wire harness.
 

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mcf1000x2003 said:
My car is'nt throwing any codes at all but i due have a little trouble starting the car sometimes.It always starts but the engine turns over 3 or 4 times be for it kicks on.
It sounds like you should definitely change the plugs and wires, but you should also check the FPR as Ranger mentioned above. Hot restart problems can frequently be traced back to a leaking FPR.
 

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1989 Sedan DeVille is now just a fond memory ....
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The only time you need any sort of anti-seize compound is when you have dissimilar metals i.e. aluminum heads and ferrous (iron content, standard) plugs. Electrolysis causes the aluminum to react with the steel resulting in fusion.

In situations where seizing is an issue I have always used a small amount of molybdenum grease on my plug threads and have not had any trouble at all.

PS. If you do not use anti-seize compound on your plugs in aluminum heads you risk the hassle and cost of replacing the heads at worst or removing them and heli-coiling new plug threads into them at best. ALWAYS use anti-seize compound with aluminum heads but only use enough to lightly coat the plug threads.
 

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Discussion Starter #11
I had a shop look at it and they said my plugs and wire appear like they was changes because the wires had some kinda tape indicating it is'nt factory installed wires.But then again i have heard some B.S from the mechanics in this area
 

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mcf1000x2003 said:
I had a shop look at it and they said my plugs and wire appear like they was changes because the wires had some kinda tape indicating it is'nt factory installed wires.But then again i have heard some B.S from the mechanics in this area
The plugs for your car are AC-Delco 41-950s and the wires are AC-Delco 628Q. If that's not what's on the car, I would change them out with these specific parts. Then you know for sure that you have what the engine was designed for and tested with. Anything else and you're doing the testing. If the plugs/wires are original, they're due to be changed. If they have been changed, they may have been changed with inferior components and you have no idea what kind of performance you are going to get with those. If you find that there are Bosch Platinum plugs in there, get those pieces of $#!T out of there ASAP.
 

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Kev said:
PS. If you do not use anti-seize compound on your plugs in aluminum heads you risk the hassle and cost of replacing the heads at worst or removing them and heli-coiling new plug threads into them at best. ALWAYS use anti-seize compound with aluminum heads but only use enough to lightly coat the plug threads.
I whole-heartedly agree. You don't know the feeling of going in for a "routine tune up", and then realizing the horror of a spark plug not coming or, or worse, just spinning. I had the former on an aluminum head 3.1L. I decided to just leave it alone vs risk the head.

Anyways, our old resident engineer recommended against it, but I think it's necessary, as long as you are careful not to get the antiseize on the inside of the spark plug, or on the porcelain. Also using it, you can't go by the recommended torque ratings anymore. I just go by feel anyways, but be careful.
 

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Dumb question here;

My engine is the 4.5 which I believe has aluminum block and cast iron heads right? Thus, I don't need anti-seize compound on my plugs. I don't know much about the N* though, are the N* heads aluminum or cast iron?
 

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1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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EcSTSatic said:
To check your wires you can mist a mild salt water solution on them, run the engine in a low light environment and look for a light show. If you see arcing, the wires are leaking. You should remove the beauty cover to see the complete wire harness.
I also take a screwdriver, attach a piece of wire to it and a good ground, then run it along next to the wires to see if it will arc to the metal tool. If it does, time for new wires...
 

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1994 CADILLAC DEVILLE CONCOURS, 350ZR
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davesdeville said:
I also take a screwdriver, attach a piece of wire to it and a good ground, then run it along next to the wires to see if it will arc to the metal tool. If it does, time for new wires...
Before i changed my wires on my Benz I see arc on the wire. I didnt really care I still grab the wire with my bare hand and it didnt shock that bad. But the best way is use a ohm meter or check the wire while the car run with no outside light.
BTW Dont try the bare hand thing.:tisk:
BILLSONG
 

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1995 ETC, 75 Deville, Cad500 powered 73 Apollo, 94 Mark VIII
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Well the screwdriver trick I use in conjunction with the mist during low ambient light conditions. I just got a wire with gator clips on one end and soldered the other to an old screwdriver.

I've never shocked myself on the N* but I have what's supposed to be a 50000v coil in my 75 Deville and that hurts pretty bad. Not as bad as 220vac like when I worked for an electrician...
 
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