1998 bizarre 0300 code

[John Dolschenko]

OK I have an interesting problem.

1998 D'eville, 215,000 miles. I have a Random misfire flashing MIL with only a p0300 code @ anything above idle, but still idles ruff. 6000 miles before the P0300 it had a slight random became a problem, I was on the road. It tossed a few codes, low fuel secondary, bad upstream O2, random misfire, bad cat efficiency and torque converter slip. After changing the Fuel pressure regulator, it only has the 0300 code. (The car idles at 2000+ rpm in park/neutral. I does not use coolant, or over heat. 3000 miles before the problem, the engine was overheated (still had coolant in it) with a flashing over temp light for less than 4 miles. (again on the road) that was due to a bearing grenading on the water pump idler pulley. I changed that on the road and drove the car issue free for another 200 miles the same day.

I sprayed WD-40 around the intake and MAF seals without any effect on idle quality.

When the engine was cold, it would back fire slightly in drive with your foot on the break. I changed the fuel pressure regulator and the car will cruse blinking the Mil lite at 80 mph. With as many bad miles and at least enough power to run down the highway, I was thinking that it may be the ICM, A fubared EGR ( no codes) or ? The only physical thing I can see, is the Harmonic balancer has a noticeable wobble to it. Is it possible that the Crank or cam sensor has an issue with no codes? It has never had the head gaskets change. A accept for a alternator,a power steering pump I rebuilt, idler pulley at the nose and the water pump idlers changed, the engine has not been touched. I guarantee the Cat is not plugged. The car runs like it has a HUGE vacuum leek. It makes very little difference or effect idle if you pull one of the valve cover vacuum hoses. One more thing. The car has for a decade made a squealing noise that sounds like a high pitched vacuum leak....... it still does when it is cold. Any thoughts?

Yes I know driving the car like that is a bad idea, BUT family court was out of state and 338 miles away. And Yes I did have to get back to work. nearly 450 miles back. I have been a motor head since birth, an Electronic tech for 20 years, and am now A CNC and robotics mechanic in a die cast factory. I have never had a car in the shop for anything, and am paying 1560$ a month in child support. This cady is not going to a shop. I am confident it will run correctly again, I am just trying a cut down on the head scratching. I would guess, that it is not a burned valve and confident it cant possibly be running with jumped timing condition. I am planning on checking compression in the am, so any help would be appreciated. It seams if the heads tossed the gaskets, it would have spit parts on the street a few hundred miles ago. thanks. To fair and honest, I have not read the plugs yet, but they where changed for the second time in the cars life, maybe 2k ago.

[Cadillac Jim]

Anything that make the MIL light flicker or turn on is saved in an OBD trouble code. The first thing I would do is, after driving the car but before turning off the key, running the OBD codes, writing them down, and posting them here. Be sure to note which ones are CURRENT.

The reason to the codes after driving the car is that all the codes go to HISTORY when you turn off the key, and won't be CURRENT when you turn the key on again unless the problem is detected then, too.

Between the squeal and the seems-like-a-vacuum-leak and the age and high miles, I would suspect a crack in the rubber coupler between the throttle body and the intake manifold. But it's important to see the codes first, in case they show us a smoking gun.

There are other possibilities, like plug wires arcing, or even a coil, perhaps a bad ground, etc. But check the rubber throttle body mount and look at the codes first.

[John Dolschenko]

No; that squeal you cant find. It sounds like a three phase inverter that has seen better days. After replacing all coils and the ignition module, I made extension cords to get the entire ignition system out of the way. Pocking around with a stethoscope, did not pinpoint anything. That was 5 or more years ago. I said hay, the car verified by a gas station fuel pump and GPS and a little math was within 1% of the dash getting 28.2 MPG on the highway. The car had no mis- issue, and had impressive set you back in your seat acceleration from about 40-80 where an over the road driver wanted it. Your advice did reveal some thing interesting that I have never seen on any car or LT before. After taking your running code read advice, I did get one additional code. Upstream bank 1 O2 heater NFG. I am confident that is not causing the random misfire ( maybe amplifying the problem, not causing it). The other day, it was raining. Today, I am going to do a compression check, and read the plugs. ( miss the days of leaded gas before my eyes needed a magnifying glass.)

A couple of things upset me though. I have a complete known good coil and ignition module at my home in NY 578 miles away. Due to work schedule, I am stuck here in on the S. Ohio, Indy boarder till January. I am fairly confident this is an electrical problem. A year or so ago, in Wyoming, a fresh rebuilt alternator (by me) cut out. The L2 ckt opened. After a couple of hrs in a parking lot; a cordless soldering iron, and some 14 guage wire from an Ace hardware store, I was on the road again. I ran a NASA Space shuttle mission 134 fix. I ran a jumper wire from the alternator to the fuel pump side of the pump relay. I never bothered tracking the real problem past a new pin and plug on the alternator. right rear window has no UP or down its not the motor regulator or driver/passenger switch cluster, and I jumped out the auto headlight off relay a few years back. There was a fault in the coil ckt some place. There was also a heater A/C issue a month ago. after replacing a surface mount fuse in the heater programmer, I had to re-solder a couple or resistors on the climate control portion of the digital dash. For some reason, they melted the solder for an intermittent connection. No wonder GM needed a bail out. There is no way that a three phase inverter, digital driven heater motor will save enough gas over the lifetime of the car to pay for the engineering or an appropriate increase price of the car. I would rather see Glass headlight lenses that don't require annual. attention. Dont get me wrong, I have had this good old hoer for a very long time. She has been good to me. Right now, I am just a little more than pissed off. I wish I still had my Merc 240DL. I ran that car on anything from a 75/25 mix of used motor/heating oil, to an 18 dollar, 5 gallon jug of corn oil from sams club when diesel was 4.25 a gallon.

Any who, 0300, and Bank 1 O2 heater, dont forget the expected alternator, brake switch and fuel gauge code. I did do a resistance check all 4 coils post to post only with rock solid across the board 5.57 K ohms. Who knows? i dont. but I wish I could get my hands on a CTS V sport wagon cheap. I wish I had an O scope with my to look for some funky wave forms on my crank, and cam sensor. As far as Cady programming goes, is the cam sensore function just like the Ford? all it does is: one crank and one cam to intiiate the first ignition and fuel injector puls, then is associated only with injector timming? I know that in GM type I II 3800s, after it starts, you can disconnect a cam sensor. if the engine runs better, your cam sensor (without codes) is probably being stupid?

[BodybyFisher]

Too much to read so I will ask a couple of questions. When were the ignition wires and plugs changed last. If you had the ignition module and coils off, did you replace the ground wire that attaches to one of the bolts?

I couldn't follow your alternator hack because I didnt work for NASA :-) but you need to make sure the coils are supplied with sufficient current to fire them, clean the battery connections and grounds and load test the battery.

[Logan]

Couple of thoughts...

2000 rpm at idle massive vacuum leak.

Flashing SES lamp is a misfire bad enough to damage the cat.

WD-40 is just about the worse material to use to check for vacuum leaks...has silicone in it.

[BodybyFisher]

Because there was so much to read, i missed the details. No one really had time to dig through narrative for symptoms, I saw a jury rigged alternator and P300. In the future bullet point the symptoms. As a matter of fact it might help to bullet point the symptoms now. It would help to post ALL codes now to see what you are getting (lean codes, service TB, etc)

The 98 does not have a rubber plenum behind the throttle body so that is not the problem.

Has the throttle body been cleaned? Dirt in the throat and edges of the plate can hold the plate open.

As logan said look for a large vacuum leak, check the backfire valve behind the power steering pump for a leak its in the intake manifold. All vacuum hoses, look at the plastic adapter at the brake booster. Check the ISC to be sure there is no leak maybe the ISC is faulty, post codes.

Make sure the throttle plate fully closes.

[James Woods]

The o2 code is most likely not a bad o2 sensor.It's not toggling like it should due to the massive unmetered air leak (vacuum leak) o2 sensors do go bad. Normally the heater element but you'll have a code for the heater circuit. If the o2 is working then it'll be pegged at lean and set a code for that. Most people interpret a lean our rich o2 code as a bad o2.

Same goes for the cat efficiency code the cat can't work when engine is so lean. Most likely not a bad cat converter.

The bad balancer wobbling can set a misfire code. Basically the computer uses the crank speed and position to sense a misfire. When the crank slows down at certain point when a cylinder is supposed to fire then it knows that cylinder didn't fire. The wobbling can slow crank or give a bad reading to crank sensor showing misfire.

1st thing is to fix the high idle. Going by the codes I would search for a huge vacuum leak. Follow the under hood vacuum diagram and check all the connections to the throttle body. Also the throttle body mounting gasket/o-ring.

Also could be a bad mass air meter not reporting the correct amount of air our a bad intake air temp sensor and then computer is giving you much fuel do the idle is high. but those 2 items are far down the list of possible causes.

Good luck on fixing your problem

[John Dolschenko]

You guys are funny. I will get back to you. You all did get what I said. It drives like it has a huge vacuum leak but does not. I assure you . all plug wires are below 500 ohms, and do not arc . I even meggered the plugs. plugs and exahust smell tell me the car is running rich. Front O2 heago is all over the place. back... is doing what a open heater, O2 sensor does. go ahead tell me to R&R the bank one O2 and see what happens.

[James Woods]

bad sensors providing incorrect parameters to the computer will cause over fueling and high idle. With a scan tool use a PID check and see if any thing is providing bad data. A freeze frame or live data stream will do.

Like I mentioned a bad balancer can cause the p0300 code with no specific cylinder identified because it's random.

[BodybyFisher]

The engine will run rich when the system is in open loop if there is an current emission related P code it will stay in open loop and run rich.

The engine runs in open loop till warmed up and the O2 sensors take over air fuel management and then it is in closed loop.

Think of open loop like a 60s car with the choke on when the engine is cold it causes a rich mixture (open loop), till warmed up and the choke spring opens the choke (closed loop) and the mixture leans out.

Lots of people run their cars with P codes that keep it in open loop rich and destroy their o2 sensors and CATS

[BodybyFisher]

Good info about the bad balancer jwoods! What if, work was done and the balancer was not indexed correctly on installation? Thx

[brmurph]

I have a 1998 deville and have fought the po300 twice. First time new plugs and wires (even though they were not that old) fixed the problem. Be sure to use AC Delco wires (lifetime warranty) and plugs. Last time turned out to be a coil. I was able to use an inductive timing light to see which plug was misfiring (it was very obvious), the plug was torn up so I replaced it then swapped coils to see if the miss moved, it did so replaced the coil. Each time I was sure it was something more LOL. I also found out that coils going bad are pretty common on these vehicles. That being said the car went from running great to barely running, I believe you said your vehicle runs ok.

Hope this helps.

[Cadillac Jim]

Be sure and check both grounds on your ignition module. If one is bad or loose, the car may run OK but there may be an occasional miss and it's hard on the ignition.

If you take the beauty cover off, and especially if the spark plug wires are moved or changed, be sure and lay them out exactly as shown in the FSM. They will not touch or cross, or touch any ground anywhere. Otherwise the wires will eventually break down and cause missing or even cross-firing, probably sooner rather than later.