Northstar Rich at Start-up?

My Uncle just picked up a "certifed pre-owned" '06 Caddy DTS with 18,000 miles. It has the standard 275 h.p. 4.6 liter Northstar V-8. He says the car emits "some black smoke on start-up". I am in CT, the car is in south PA...so I have not witnessed the smoke on start-up myself. Is this typical? Do Northstars run that rich at start-up?

Thanks for your insight,

Ray

Nope, something is going on if it's visibly black smoke. The dealership that sold it to him should be able to figure out what's going on and let him know if it's got a problem or if he's seeing things funny.

Bryce

have fun diagnosing with the 260+ sensors....

I troubleshot an ongoing no-start when warm issue with my N* powered aurora. started fine HOT, started fine Cold. just not warm.

what was it? found some obscure reference to a Coolant Temperature Sensor. $14.00 part. headache factor? Immense. some days I want to shoot the car. with a canon.

OBD-II Scanners will not read 80% of the special sensors GM built into that engine setup.

I will bet the CPO car has sat for a while on the lot. Likely the only times it moved was during across lot ventures. Fill up the tank with some LOWER octane fuel and some Valvoline Synpower FI cleaner and drive the snot out of it for a tank or two then reassess.

I have a 98 Eldo and even though there are some differences like COP and watercrossover redesign, slightly longer headbolts with a deeper thread, and a half case seal redesign the heads/cyls are the same design.

The prime culprit of your problem is excessive carbon buildup, since these are high reving DOHC engines that get driven by older folks (Devilles in particular) chances are you've got a ton of carbon buildup. There are two things to help, first some WOTs, second seafoam the engine, just be VERY careful and slow when you suck the seafoam into the PCV. There's a dealer reccomended spray you can spray into your TB while running but I found it was way easier to stall the engine going this route, I'd say go front PCV with a cup full of seafoam and just barely let it suck it in, let it sit an hour, go driving, change your oil and plugs afterward, and switch to synthetic. My Eldo sat for a year before I picked it up and the POs had been running dino through it, needless to say on the first 20 WOTs or so, I'd emit huge clouds of black smoke. Between WOTs and Seafoam, I cleaned it out...

And as Grtechguy pointed out these cars are probably the most annoying vehicles to DIY, period. Get a factory service manual if you plan on doing any other repairs yourself, you would not believe some of the godawful steps you have to take to remove/disassemble unrelated parts to get to the one you're after. About the only thing beautiful on these cars is the efficiency of packaging which from an Industrial Engineer's standpoint is a thing of beauty, but from a car-guys perspective is a royal PITA...

John Brown,

Why the 87 octane fuel with the Valvoline Synpower FI cleaner?

Thanks,

Ray

87 octane is "easier" to burn, allowing you to lean out the mix and ru a little closer to detonation making the combustion chamber hotter allowing it to burn off any carbon etc. The Synpower cleaner will help nibble down the carbon as well. Also regular unleaded tends to get changed over more in the tanks (more people buy it and the tanks get refilled more) allowing "fresher" fuel to be stored in the tank which may help you if this is actually a fuel problem vs a carbon issue.

Also his car may just be running NAWWSSS...

Thanks John. I'm pretty sure that my Uncle is not runnin' giggle gas in the Caddy.

All Northstars 2000+ run on 87 normally, burning 93 doesn't buy you anything, if you run it in pre-2000, which were 93 only it would automatically detect it and back off on the timing. My seafoam method stands, it works, you can alternativley add a can to a tank of gas and it'll help alot as well...