: 99 Deville misfire and fuel sensor

02-06-06, 08:45 PM
Hey guys, got an odd problem that I haven't experienced before. My 99 Deville, 65k miles, just had a full tune up with AC delco parts at 55k (due to poor quality gas fouled the plugs and killed 2 of the wires). [new plugs, wires, fuel filter, pvc filter, air filter]

Here's the issue... usually, I don't warm up my car at all, just wait 2 secs or whatever and drive off. Never been a problem for any caddy that I've driven for past 15 yrs. This week, in long island weather, starting up the car at 1000rpm and driving off, when I approach a stop light, the engine starts to rumble loudly, and it rumbles more as I quickly reach 0 mph. At the same time, the fuel gauge drops quickly from 8 gal down to 4 gal, then E with the bingo warning going off. It's like the gas/fluid gravitated to the front which gave a false reading. After 1 min or so, eventually the PCM registers a P300 code for misfire.

Here's the thing. Once the car warms up where it idles at 600-650 rpm, the rumble/misfire is gone, and so is the odd fuel sensor. The problem persists from 1000 RPM to 800rpm or so at idle. I've never had that fuel sensor thing happened ever in any of my caddies. Oh, and the gas I use is 93 octane Shell for the past 9 months since I've learned my lesson with crap cheap gas.

Anyone has an ideas?

02-06-06, 08:53 PM
So it starts, idles and runs ok til deceleration? Acceleration ok? Does this happen every time or is it intermitent?

02-07-06, 07:41 PM
Acceleration is fine until I decelerate. When the engine rumbles, acceleration isn't smooth, so that forces me to grandpa the pedal. The rumbling diminishes when the car is fully warmed up. Problem seems to start only on fast speeds of 50-60mph then moderate/rapid deceleration while the car isn't fully warmed up. It seems to be less of a problem when I know I'm approaching a red light and I shift to neutral while decelerating. This problem has been going on every single time from cold start for the past 3-5 days or so.

Tonight, I let the car warm up till 850rpm idle and drove off. No issues. The car had 3 gal of fuel left, filled it up with prestone water remover/fuel injector cleaner (maybe some crap/junk in gas tank -- worth a shot) and filled it with 17 gal of 93 shell. While leaving the gas station, I decelerated at the light going roughly 25-30mph at 40 yards away from station. No misfire/rumbling, but the fuel sensor problem was there. Instead of saying F, it said 18. Drove about half mile and it reverted back to F. Gonna see if fuel is an issue tomorrow.

Also, forgot to mention. I did an oil change during thx giving with Mobil 1 10w-30. Oil sensor says 66% life left, and I always keep the dip stick at half (0.5 qt from full). Perhaps it's time I should go with a lighter weight oil? Or stick with the known plan of warming up the car till 850rpm?

02-11-06, 08:29 AM
Sounds more like an electrical problem then fuel, though I am at a loss as to what it may be.