Car Trouble!!

[Big Rat]

Normally with a p0300 the first step at the shop is to go into your missfire history per indvidual cylinder.  This will show you an individual missfire count for cylinders 1-8.  What you will normally find is that you have a main culprit cylinder.  Eg. #2 has 16500 missfires while #3 and #4 have 250-500, but since you have missfires on 3 cylinders it will throw a p0300 (random missfire) rather then just a p0302 (missfire #2).  Start checking here first.  Now if your missfires are evenly distributed then you are looking at a mixture and/or timing issue.  The battery issue may have something to do with this, but would be unlikely unless system voltage was actually getting under 12v's while running.  If you have access to a good scan tool, the above should be your next step.

 
BigRat  

[Captain Virgil Hilts]

Have the battery and the charging system checked completely first. Then have the fuel pressure and volume checked next. After that, then look at the ignition system. Most often, if it does not set a code for a specific cylinder, it usually isn't a plug wire. The late GM cars usually drop one specific cylinder when the ignition system has a problem. Or two, if the problem is a coil rather than a wire or plug.

[CAP1]

My 1999 Deville (The Bop Mobile) recently started running rough.

I ran a couple of bottles of fairly expensive injector cleaner through the gas tank and the problem seemed to go away.

A few days ago when I fired it up, it started running rough again even more pronounced than before.

Code P0300 seems to be the culprit. (random misfires)

I pulled a plug and it had a white coating on it. (running lean)

I checked and replaced the somewhat clogged fuel filter.

Problem is still there.

Dead battery this morning also.

Any Ideas? The car has 78k on it.

(Image removed from quote.)

p0300 is a random misfire. that means that every cylinder is misfiring at one point or another.

99......you have the 4.9L or the 4.6L?
when you had the plug out, did you look at the gap, and the condition of the electrodes? if these are as little as .05 too largely gapped, they'll make a misfire.
 if you have bosch platinum in it, get them out. they suck. the center electrode wears down below the porcelain, and creates a misfire.
 
 if this is with coilpack, check the ignition wires. they'll cause the same sort of problem. look for a whitish mark on the wires....this is normally evidence of arcing.
 i've very rarely seen injector problems with cadis, but if you suspect this, go to a repair shop that uses a fuel injection cleaner called "motorvac".
you'll find that a thousand times better than anything you can pour into your gas tank. it shouldn't cost more than $150...more than likely less. while it's there, if your filter was pretty clogged, then have them check the fuel pressure, as a clogged fuel filter will trash a fuel pump fairly quickly. and on fuel systems......when you start it tomorrow, look underneath at the gas tank, and see if it looks like it's caving in on itself. older cadis used to have problems with the gas caps not venting properly, and would cause running problems.

 in all honesty, it sounds like you might wanna be in the ignition system first. especially if you haven't tuned her yet. there is no such thing as a 100k spark plug. not even in cadillacs. 

 on a seperate note.......i used to have that much hair..............

if you need anything else, post here, or feel free to pm me, and i'll do what i can to try and help ya out.

[CAP1]

Sound's like you got a fuel injector bad . Take a long screwdriver and hold it on each injector and to your ear and see if it makes a clicking sound .

sometimes you can have a perfectly normal sounding injector, but it still won't flow fuel.

[CAP1]

Have the battery and the charging system checked completely first. Then have the fuel pressure and volume checked next. After that, then look at the ignition system. Most often, if it does not set a code for a specific cylinder, it usually isn't a plug wire. The late GM cars usually drop one specific cylinder when the ignition system has a problem. Or two, if the problem is a coil rather than a wire or plug.

my experience on these engines has been plugs with a p0300. everyone falls for the 100k mile tune up line.

[1Boner]

Just got back from AutoZone.

New battery, they checked the old one , wouldn't hold a charge.

Car is still running rough.

Off to my mechanic buddies house to see what we can see! lol

Thanks for all the great answers guys!!! 

[Captain Virgil Hilts]

A white coating no longer necessarily indicates a lean condition. It can be caused by all sorts of deposits.

Did you check the gap and the condition of the center and ground electrodes?

The two plugs that tend to yield the best results in those cars are the original AC Delco plugs, and the RapidFire AC Delco plugs.

Cap is right, the plugs are past due unless they've already been changed. They never work as well as they should past about 60K at best. Besides, they tend to weld themselves into the heads. An expensive set of plugs is still far cheaper than pulling a head off to remove a broken plug and/or repair the threads.

The best luck we've had is with Taylor, Moroso, or MSD wires, after that, the original AC Delco wires. The AC Delco wires will go about 60K, the aftermarket wires mentioned above go about 80K or so. The parts house brands go about 40K at best.

[uptown]

Worn muffler bearings?

[Tigger29]

I'm gonna try that.

But wouldn't the plugs be all wet from incomplete combustion? (rich)

Theoretically, yes.. but most of these newer cars run as lean as they can without spark knocking (for fuel economy purposes) so the plugs tend to be white regardless.  The plug wires are allowing spark most of the time, but when put under a load they are intermittently arcing out.

Do this:  Pull the car into a garage (or outside at night).  Remove any plastic covers over the top of the engine.  Start the engine.  Spray down the plug wires with a spray bottle of water.  Watch the light show begin!

Likewise you can do the same with some carburetor cleaner, but you'll be spraying down the engine with a fire extinguisher shortly after!!!  haha

[1Boner]

Worn muffler bearings?

I bought 3 new "UsuckerU" muffler bearings at a fairly reasonable price (only $249.95 ea.)

The problem with these bearings is, they need to be packed with Blue Whale blubber.

Now as we all know, Blue Whales are on the endangered species list!!

Which makes it very expensive.

So, I sold the wifes car so I could buy an ounce of it.

Well, long story short, it didn't solve the problem.

However, I'm now having a rough time driving around town without a crowd of fat chicks chasing me down the street!!

Apparently its some sort of aphrodisiac!!

[fbWldcat]

 

[uptown]

  welcome to my world man 

[maddafinga]

My 1999 Deville (The Bop Mobile) recently started running rough.

I ran a couple of bottles of fairly expensive injector cleaner through the gas tank and the problem seemed to go away.

A few days ago when I fired it up, it started running rough again even more pronounced than before.

Code P0300 seems to be the culprit. (random misfires)

I pulled a plug and it had a white coating on it. (running lean)

I checked and replaced the somewhat clogged fuel filter.

Problem is still there.

Dead battery this morning also.

Any Ideas? The car has 78k on it.

(Image removed from quote.)

I don't know beans about working on cars.  Just wanted to say that I have that exact same car in the exact same color.  99 Deville D'Elegance.  I love it, even if it's got an ac leak so I have to run windows down in the summer. 

[CAP1]

I don't know beans about working on cars.  Just wanted to say that I have that exact same car in the exact same color.  99 Deville D'Elegance.  I love it, even if it's got an ac leak so I have to run windows down in the summer. 

just taking a shot in the dark......evap cores, and compressors are common on them.

[maddafinga]

just taking a shot in the dark......evap cores, and compressors are common on them.

Yeah could be the core.  Compressor was replaced just before I bought it, so that's not too likely I don't think.  It hasn't been used to speak of.  I looked into the evaporator and it's about 1200 bucks to replace, so if that's it, I'll be keeping the windows down until the gar gives up the ghost.  You know, another 10 years or so.  I do love the car.