P0300 - what to look for (NA motor)

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Hi. Got myself a 98. Non ultra, so NA.

I will be doing a simple tune up with new plugs, wires, I will make sure all the coils are properly cleaned and attatched to the module and all that good stuff. The fact its a P0300 and not a specific code makes me think it could be something like a vacuum leak or spark plugs or the wires maybe. I know when under slight load, so not idling, it does seem to go away and isnt even always present at idle, if that helps.
 
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2007 Lucerne CXL, 1995 Lesabre currently, past 1973 Riviera, 1968 Riviera
The P0300 is that kind of wildcard code so scanning it after the wires and plugs, which seems likely is code related, would at least eliminating the most common. If it comes to the coils this is a pretty detailed site with steps, if you know already maybe it will help someone else.

Part 1 -How to Test Ignition Coil Pack -Misfire Troubleshooting Tests (GM 3.8L)

If the code still pops up here's a list of other possible items.
OBD-II Trouble Code: P0300 Random/Multiple Cylinder Misfire Detected
 
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Way back when there were distributor caps that supplied the spark and a single coil you wouldn't be able to tell where misfires were comming from so you had to test each plug and test each wire until you find the dead one. As for misfires that jump all around it would have to be the dist cap, but generally if a cap is cracked it won't even start at all. Now fast forward and there is no distributor Or cap and there are THREE coils rather than just one. This really helps to seperate a problem and make it easier to locate.
Way Back When, a coil either Worked or Didn't work, very very rarely If Ever would a coil work, but work crappily and usually the actual problem was the balast resistor and not the coil at all. The Ignition Control Module in my opinion is very much like the older coils in that they either work, or they Don't, so if it is not starting at all then this might be the case, but with misfires and especially Random, I would look elsewhere.

Having three coil packs is great for hunting down misfires because if it is in a particular cylinder you can narrow it down to two spark plugs, two plug wires and ONE coil pack. If you have a P0300 Random Misfire, this means it is happening across ALL THREE coils and is so extremely unlikely to have all three coils go bad at the exact same time, that I would look elsewhere for the cause.

Much the same can be said of the plug wires, if it was any One Plug Wire Individually then it would Not be a P0300, it would be a P0301, 02, 03 etc and fairly easy to locate. Since plug wires will never give a P0300 unless All of them are Toast at the same time, which is Really Unlikely, I would look Eslewhere for the problem.

It may not be factual, I am not sure here, but it is to my experience that Idle Voltage from the coil packs MUST be a little lower, than when the engine is running at a higher RPM. The engine might stall while idling, but then start right back up again on the first try, it might even run a little rough at idle, but then smooth right out when you apply throttle. So it is either variable voltage from the coil packs or it is a result of the different amount of fuel octane in the cylinder differing between idle speed and anything higher then that, I'm just not convinced yet which it might be that causes this symptom but generally speaking, the spark can't seem to make the jump across the span between the contacts at an idle, but will make the jump just fine under throttle. Various voltage? Or different level of combustability? Hard telling But any way you slice it the P0300 is norrowed down fairly specifically in the above explanations and I am all but certain your spark plugs have a fairly stubby fillament on them resulting in a large spark gap that at times will not spark.

Like I said in the other post, I have a feeling that when you change the spark plugs this code , once erased, should not return.

I hope this information was helpful, Guido
 
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1998 Buick Park Avenue
Way back when there were distributor caps that supplied the spark and a single coil you wouldn't be able to tell where misfires were comming from so you had to test each plug and test each wire until you find the dead one. As for misfires that jump all around it would have to be the dist cap, but generally if a cap is cracked it won't even start at all. Now fast forward and there is no distributor Or cap and there are THREE coils rather than just one. This really helps to seperate a problem and make it easier to locate.
Way Back When, a coil either Worked or Didn't work, very very rarely If Ever would a coil work, but work crappily and usually the actual problem was the balast resistor and not the coil at all. The Ignition Control Module in my opinion is very much like the older coils in that they either work, or they Don't, so if it is not starting at all then this might be the case, but with misfires and especially Random, I would look elsewhere.

Having three coil packs is great for hunting down misfires because if it is in a particular cylinder you can narrow it down to two spark plugs, two plug wires and ONE coil pack. If you have a P0300 Random Misfire, this means it is happening across ALL THREE coils and is so extremely unlikely to have all three coils go bad at the exact same time, that I would look elsewhere for the cause.

Much the same can be said of the plug wires, if it was any One Plug Wire Individually then it would Not be a P0300, it would be a P0301, 02, 03 etc and fairly easy to locate. Since plug wires will never give a P0300 unless All of them are Toast at the same time, which is Really Unlikely, I would look Eslewhere for the problem.

It may not be factual, I am not sure here, but it is to my experience that Idle Voltage from the coil packs MUST be a little lower, than when the engine is running at a higher RPM. The engine might stall while idling, but then start right back up again on the first try, it might even run a little rough at idle, but then smooth right out when you apply throttle. So it is either variable voltage from the coil packs or it is a result of the different amount of fuel octane in the cylinder differing between idle speed and anything higher then that, I'm just not convinced yet which it might be that causes this symptom but generally speaking, the spark can't seem to make the jump across the span between the contacts at an idle, but will make the jump just fine under throttle. Various voltage? Or different level of combustability? Hard telling But any way you slice it the P0300 is norrowed down fairly specifically in the above explanations and I am all but certain your spark plugs have a fairly stubby fillament on them resulting in a large spark gap that at times will not spark.

Like I said in the other post, I have a feeling that when you change the spark plugs this code , once erased, should not return.

I hope this information was helpful, Guido
Wow very detailed. Thanks. I'm hoping it's that
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I think any old timers would agree that with the onset of computerized auto's, it singlehandedly signaled the demise of basic troubleshooting skills. Skills that were once acquired over years or even decades of dealing with symptoms and having to Find the cause. You Always Remember what those symptoms and causes were and file them away in your brain for future retreval. Although being able to use a code reader to locate the problem is friggin awesome and anyone can do it, experienced in troubleshooting or Not, but imho I think that there is a Lot that gets lost in translation.

One of my old favorites was a Ford symptom where it would fire right up and rev to the moon with no problem, drop it into gear and at an idle it would buck and kick and sputter and DIE. Start it right back up on the first click and rev it all you want, no problem. Drop it into gear and at idle buck and sputter cnd die. Repeat as desired. What the hell ?? Must be something inside the carburetor, The Main Jets seem to be working fine becouse it revs nice, but maybe the Idle Circuit has an issue since it won't idle? Time to get a Carb Rebuild Kit and go through that 4bbl carb on the Big Block 429? NO ! Unscrew the Fuel Filter that was inexplicably mounted directly on the carb and replace it. LOL Fun Fun.
 
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I clicked on the link in the post above just out of curiosity, it is a little like the one I posted for you in the other post about P0300 just a different web site design but basically the same info. The part where it lists "Other Possible Causes", If you have a good troubleshooting library in your head, you will notice that All of those other possible causes Also have Other symptoms attached to them, even #2 Faulty coil packs (Gen only One goes bad) would also be accompanied by other codes specific to those two cylinders. When I read Burned Exhaust Valve I actually started laughing. You got a burned exhaust valve you will get the cat conv filling up with Fuel and there Will be other symptoms.
Picking the brains of old farts can lead to a wealth of good info lol
 
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Seriously, if the plugs don't do the trick I would ignore that entire list of "Other Possible Causes" and go Directly to inspecting the wires leading into the coil packs and look for possible shorts. eg. "shittiest quality electrical wires in the industry" Because when they get a bit of heat, ..... the insulation dissintigrates and you get BARE wires all over the place.
That would be My Shortcut to finding the prob anyway. Heh.
 
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Wow very detailed. Thanks. I'm hoping it's that
Well, in the other post I supplied a link and said I was pretty sure that changing those plugs would do the trick. When I saw this new post I figured you were looking for a more definitive answer, so I felt the need to be much more specific and describe the logic as to exactly why I was so sure that plugs was it. lol
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I know that feeling. I am gearing up to do that 4T60E Trans Shift Kit, The one that everyone seems to be affraid to do. I have read too many discussions where people have stated they bought the kit and Only used the springs and spacers for the 1-2 and 2-3 accumulators under the bottom pan, which to me is silly because you can do That with $5.00 worth of hardware store material.
I have the Air Intake removed, the shift linkage unhooked, The steering rack unbolted and wired up to the brake master cylinder (The Best Way imo), The Steering Fluid Lines unbolted from the subframe, The Trans mounts unbolted, The Drivers side Ball Joint seperated, The Tie Rod End Seperated, The Brake Caliper wired to the strut spring out of the way, The Front Left Spindle removed, The Left Drive Axle Off and the Sub Frame unbolted and lowered and all the side cover bolts removed. And it is all primed up and waiting for me to remove the side cover.

I decided that since it such a Beast to get into the side cover on this thing, that with 193K miles and never a failure, I should replace all the shift solenoids and the PWN Solenoid and both pressure switches, the Fluid Pump Bearing as well as the Channel Plate Sleeve and the Internal Wiring Harness (Since people say the plastic connectors crumble apart with heat exposure).

But just like the Steering Column Pinch Bolt and thick Rubber boot that is such a pain, (and I decided taking the 5 bolts out of the rack and the fluid lines from the subframe made Much More Sense) I am going to also do the shift kit in an unconventional way, possibly because others haven't thought of it and also possibly because they were too affraid to go that deep into the unit, but since it is required to install the Total Shift Kit I want to try to remove the Channel Plate with the pump and the Valve Body still attached to it.and now I have all the parts, the last of which just showed up.

Now what is holding me back is that I can't do it on the weekend because my 5 yr old daughter will NOT let me work on anything while she is at home. I mean I could try, but I know for a fact it would only end in frustration because every couple minutes would be Dad, Dad, Dad, Dad, DAD, DAD DAAAAD!!! lmao so I just refrain from working on projects until the weekdays when she is at school. so it is going to be a Looong Weekend waiting to get started.
 
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1998 Buick Park Avenue
All right, I got it fixed.

Basically, there were a few main issues: the spark plugs had inconsistent gap, (.040 on one to .075 on another), two of the rear spark plug wires were partially melted on the insulation (also the wiring harness protector on the back of the motor), and the spark plug wires were hooked up in the WRONG firing order!!!! Two of the back cylinders were swapped, so right there should have been an indication whenever the plugs were done.

I got new wires, plugs, gapped them at .060, and routed the wires so they can't melt. Runs like a kitten now and has great power, idles perfectly!!

And I did have a vacuum leak which I posted in another forum I'm sure contributed.
 
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Yikes !! I bet that was one Rough running beast with that many Non-spark issues.
LOL Or I duess Great Spark in all the wrong places?

It must seem a World Of Difference.


If the plugs with the tighter gap were in the back against the firewall, then when the last person was trying to put them in using a short extension and a spark plug socket, doing it by hand, I bet they got dropped or at least tapped against the exhaust manifold and didn't recheck the gap before a second try at getting them in there. If they were in front, then there is just no excuse I can think of to get them off the hook even a little bit.
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1998 Buick Park Avenue
Yeah the ones in front were like .040, .070, .065. In about that order lol. The ones in the back were similar. And it ran surprisingly well for having the wrong firing order on 2 cylinders(both rear) and messed up gap. But my oil had a lot of gas in it which tells me it probably ran like that for a while with gas pushed past the rings into the crankcase.

Also my oil filter was on way too tight... hmmm...
 
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