[Ralph]

The other day I was out, parked, came back, started the car and it ran rough for a little while and the "service engine soon" light stayed on! I shut it off, started it again, and it was back to normal and has been good ever since. The only thing that I can think of might be the spark plugs because for a while my dad ran low octane in it and maybe detonation damaged them a little? I don't suspect anything else because it has 25,200 miles on it only. (1991 4.9) I do notice a little shake at idle until it is fully warmed up. But then if it is the plugs, wouldn't it always run rough until I change them, or could fouling be the culprit? Any ideas? Are Bosch platinum 1's ok in these engines? I don't want anything too fancy in the way of plugs because Iridium's are 20 dollars for a pair here! And Bosch 4's are 15 dollars for a pair, too expensive. I do want a longer lasting plug because of the awkward location of them on these sideways engines.

 

[Night Wolf]

I dunno what plugs you have, but in '92 the DeVille got standered platinum tipped spark plugs with a 100,000-mile replacement interval.

Why would your father run low ocane gas in it? the engine requires premium......did it run ok though?

The 4.9 always is rough at idel and stuff, I don't think it is really anything to worry about, scan the ECM for codes and see if anything comes up.

 

[2dfx]

Ralph you could also try NGK G-Power plugs, They're only 7.99/pair at Crappy Tire and I tend to view them as a decent replacement to the Bosch Platinums. Your rough idle could possibly be fouling - but do as NW says and run the diagnostic and see what codes come up.

 

[Ralph]

I dunno what plugs you have, but in '92 the DeVille got standered platinum tipped spark plugs with a 100,000-mile replacement interval.

Why would your father run low ocane gas in it? the engine requires premium......did it run ok though?

The 4.9 always is rough at idel and stuff, I don't think it is really anything to worry about, scan the ECM for codes and see if anything comes up.

I already checked my plug code, and they were not platinum for 1991, unfortunately! My dad ran lower octane for a couple of years because he didn't think it would do anything bad. Plus, we were paying about 87 cents a litre for gas on average in the last couple of years, but I certainly am not defending what he did. Personally I would not buy a 54,000 dollar car and not use the recommended fuel in it. I am a little upset that he did run the crap gas, it knocked a little around 40 mph, but as soon as I put premium in, it ran great. I have used nothing but premium, and will never go to a lower octane. There obviously is a good reason for GM to recommend the good gas.

I don't have the little computer to read the codes, but I will have to go to the dealership with my own plugs to get them changed (difficult in this car), and at the same time get the code read. I have noticed that when the Caddy dealership advertizes for tune-ups, it says "Cadillacs and vans extra." The only reason I can put on this is because these cars are a bitch to work with!

 

[Ralph]

Ralph you could also try NGK G-Power plugs, They're only 7.99/pair at Crappy Tire and I tend to view them as a decent replacement to the Bosch Platinums. Your rough idle could possibly be fouling - but do as NW says and run the diagnostic and see what codes come up.

I actually went to Crappy Tire tonite to check out the prices on plugs. What I really want are the Iridium, but I'm not paying 80 dollars plus 13% sales tax!! I did see the NGK G-Power plugs but cannot remember the price. (Are they platinum?) 7.99 a pair is pretty good, the same price as the Bosch 1's. I might wait until they are on sale again (like 2 weeks ago) to get the NGK, as I have heard they are standard equiptment on a lot of new cars.

 

[brougham]

You don't need a scanner to read the codes, you can get them right off the dash of the car. Turn the key on and then hold down the off and warmer buttons on the climate control panel until all the lights on it come on. I think on the FWDs the codes start popping up in the digital display for the fuel guage and gas milage. You can probably find another post here that has more detail about this.

The one time I tried a scanner on a Cadillac it was a 1988 Sedan DeVille and it didn't work anyway.

 

[Night Wolf]

yeah, no scanner, just have the car on and hold OFF and WARMER, then in the fuel data center, it'll display 8.8.8 then whatever coeds are in the ECM then .7.0.....then you can do some truly crazy stuff with the OBD.....

....there is a tach, digital speedo that goes up to 255mph built in, sensors in every single part of the engine you could think of that give you info, then you can put the tranny in override mode and shift up by hitting warmer and shift down by hitting cooler.....can you say Tap Shift? lol, I was driving around and playing with that for a bit, it was fun, but sometimes it wasn't fast to respond and would hold a gear too long, so I just went back to normal.....

I'd say get the factory service manaul, you'll be thankful you did.

 

[Ralph]

You don't need a scanner to read the codes, you can get them right off the dash of the car. Turn the key on and then hold down the off and warmer buttons on the climate control panel until all the lights on it come on. I think on the FWDs the codes start popping up in the digital display for the fuel guage and gas milage. You can probably find another post here that has more detail about this.

The one time I tried a scanner on a Cadillac it was a 1988 Sedan DeVille and it didn't work anyway.

Maybe I'll try that, interesting. I remember something about this on another thread about 6 months ago, and I tried it and nothing happened. My luck, I will probably short something out in the process!

OK, why do they make those little computers for cars if you can read the codes on the dash? I take it then only expensive luxury cars can do it.

 

[Ralph]

yeah, no scanner, just have the car on and hold OFF and WARMER, then in the fuel data center, it'll display 8.8.8 then whatever coeds are in the ECM then .7.0.....then you can do some truly crazy stuff with the OBD.....

....there is a tach, digital speedo that goes up to 255mph built in, sensors in every single part of the engine you could think of that give you info, then you can put the tranny in override mode and shift up by hitting warmer and shift down by hitting cooler.....can you say Tap Shift? lol, I was driving around and playing with that for a bit, it was fun, but sometimes it wasn't fast to respond and would hold a gear too long, so I just went back to normal.....

I'd say get the factory service manaul, you'll be thankful you did.

I'm not bold enough to play around with it like you described, it's hard to believe you can do all those things with the computer. I wonder what you can do with a new Cad with a more sophisticated system?

 

[brougham]

OK, why do they make those little computers for cars if you can read the codes on the dash? I take it then only expensive luxury cars can do it.

Because a lot of cars don't have digital displays to read out the stuff and especially back then a lot of makes didn't do things as overcomplicated as Cadillac did. On a lot of cars you can make them flash the codes out on the service light.

 

[Night Wolf]

I'm not bold enough to play around with it like you described, it's hard to believe you can do all those things with the computer. I wonder what you can do with a new Cad with a more sophisticated system?

Actually, IIRC all new cars from 1996 have OBD II which is alot more difficult to mess around with then OBD I

man this stuff is great though...... it is real neat to check out, and very, very helpful in doing stuff, an example, I can advance or retard the timing just by pressing warmer or cooler etc......

 

[Ralph]

Actually, IIRC all new cars from 1996 have OBD II which is alot more difficult to mess around with then OBD I

man this stuff is great though...... it is real neat to check out, and very, very helpful in doing stuff, an example, I can advance or retard the timing just by pressing warmer or cooler etc......

That's amazing! Are you pulling my leg?! GM would know they are losing money at their service dept. then if people could make those kinds of adjustments. I have never heard of the timing adjustment with the climate controls. I have seen in Hot Rod magazines that you can buy the little dial, mount it on the dash, etc, and adjust the cars timing for a race.

 

[Night Wolf]

I kid you not....... just get the factory service manual, some of the best $50 I ever spent....

....I can shut any of the 8 injectors down at a time to test if they are working and how well (only when parked though) there are sensors to test rpm, voltage, coolect temp, manifold pressure, vaccume, a 2nd fuel sensor that displays in a decmial how much fuel is in the tank, but one that is right int he open (for testing purposes) and moves around alot with the fuel sloshing around and stuff, sensors that tell you the temp in the car, exhasut temp, how much the butteryfly valve is open, which cooling fans are working and how well etc.....

....the timing thing is just 1 of who knows how much...... I didn't want to mess with more settings until I read up on them, but you can control all the voltages going to everything and all that, basically you have complete control over the engine all the time....

....2 things I were neat, and play around with often is first the digital speedo......my analog one stops at 85, I was like damn, now if I ever decide to go for a joy ride, I will not know how fast I am going, not true, just go in diagnostic mode, and turn it on digital speedo, and it tells you your speed, in numbers, up to 255

Also the tach, it is rpm/10 so like 250 means 2500 etc.... my car idels around 600-630rpm, under WOT, the 1-2 shift is at 45mph (I know, sucks) and one time wind out to 5250rpm, usually she shifts at 4900 though.....just neat to play around with....

....this stuff was actually put in the car to make it far more easy for the service guy at the dealer to fix the car, becuase unless you have the manual, you wouldn't know what does what, and most buyers of the car woudln't care to do any of this.

It is real cool though for gear heads to check out and play with

 

[Ralph]

OK, I believe you. Sounds cool. They put this stuff in these cars, makes me wonder why they charge extra to fix 'em then! Technology is supposed to make life easier, when all along, I think it just costs us more to fix.

 

[Ralph]

I don't know why the dealer wants to charge me 39.95 to retrieve codes if I can on the dash?? Anyway I bought the Bosch Platinums on sale, I'll install them next week and let you know how it goes. There are two in the back on the pass. side that look impossible!

 

[Ralph]

OK, I got the new plugs in, along with scraped knuckles. :crying2: The front ones were easy, and I was worried at first they would be seized, but they were good. The two that were stubborn were on the pass side along the firewall! I took off the strut brace, and had to flex up the heater hoses in the way to get 'em, and I'm glad they are done now. I was also worried that the L shaped electrodes would be a little banged up due to the fact that my dad used the crappy fuel for a few years, and there was some detionation, but they were just a little worn. It does not run any smoother, it is about the same.