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Old 07-09-2014, 11:12 PM   #1
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Default Misfire Assistance (P0300)

So two days ago I was driving home and began to notice a hesitation when accelerating. In addition to the hesitation I noticed some sort of odor, I could not pin point it at that time, but kind of like something burning. I have since started the car a few times and it smells like a burnt out firecracker or rotten eggs. During this episode the SEL came on. I noticed it would flash if I attempted to accelerate hard. Checked the manual (I had not seen this before) and realized it indicated a misfire. I got the car home and indeed scanned it for a P0300 cylinder misfire (does not indicate the cylinder). That is where I began my search on this site to help troubleshoot this. I have gone through a few things on suggested from the site but am still looking for any additional advice that people might have.

Below is what I have done so far:

1. Checked all wires resistance, checked at around the 3,000 ohms mark (a little higher for the longer ones).
2. Checked the resistance at the coils, this checked at about 5.5-5.7 on all coils.
3. Pulled the three "easy" spark plugs (front ones) and did not notice any issues with them. Spark plugs were replaced with standard Bosch Copper plugs 20k miles ago (along with the wires (AC Delco, I believe).
4. I went to start the engine at one of the many instances (after sitting for awhile) and it chugged a bit to start, so I began to check the fuel system. First checked fuel injector leads with Noid lights, all looked good.
5. Checked fuel pump pressure, and was around 42 PSI, all good there.
6. Checked the resistance in all fuel injectors and measured 12.7 ohms for all.
7. My wife last put gas in the car and put in the mid grade. I have done this before with no issues on rare occassions, but typically use the 93 Octane. Due to this I filled up with 93 Octane, but have not driven enough to "cycle" that fuel through.
8. I have ordered a fuel filter to replace, as I am due, but I am not convinced this is the issue.

Some additional things to note:

1. In the past month my electronic leveling has not been working so I have been running with the relay removed after I am satisfied with the level of the car.
2. On a couple of occasions (not every time) when starting the car I get the items highlighted below (all at once):
a. Air bag service
b. Service Stability system
c. Service theft system
d. Security light is on
e. SEL light is on
f. no reading for tire pressure monitoring system
3. Upon first looking at the engine I noticed that my coolant reservoir was below the level to feed the engine.
4. Still notice some sort of odor while the car is running (firecracker/rotten egg smell). This order is noticeable from the exhaust and at the engine compartment.
5. Water (or some liquid, feels and looks like water) drips from the exhaust while running.
6. It also appears like there is some "liquid" (looks like oil to me due to viscosity and if it was fuel, I would assume it would evaporate fairly quickly) around fuel injector for the 5th cylinder. Also further in behind the fuel injector for the 3rd cylinder, there is a small area of liquid that I can't quite get too (again, looks like oil based on the viscosity and lack of evaporation). See attached pictures for this.
7. I also noticed a rattling on the idler pulley for the belt that runs the back belt (non supercharger belt). See video at the following link:

https://drive.google.com/file/d/0B5N...it?usp=sharing

I am looking for some additional things to check. I am almost to the conclusion that it is my manifold gaskets that need to be replaced. I last replaced them 40k miles ago while changing to green antifreeze. I used a Fel-Pro gasket. I am just hoping this is not the case, again, but I am not looking forward to doing it again...

Any other information is appreciated.
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Misfire Assistance (P0300)-fuelinjector1.jpg   Misfire Assistance (P0300)-fuelinjector2.jpg  
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Old 07-09-2014, 11:32 PM   #2
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I'm betting you lower intake gaskets are leaking coolant and the engine is trying to ingest it. Is it using coolant? You might consider doing a back pressure test to see if the cat is starting to plug up.

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Old 07-09-2014, 11:40 PM   #3
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Thanks, 75 racer. I think that is what I am leaning towards as it seems I have to add coolant periodically. Not exactly what I wanted to hear, but at least I have another person that believes what I am thinking.

Is there a better gasket than the Fel Pro that I should use (I thought I read something about aluminum ones??)? Maybe I didn't do a good job 40k miles ago, although it quit consuming coolant after that repair...
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Old 07-10-2014, 02:55 AM   #4
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Yes fel pro has since updated the gaskets to a aluminum gasket with injected silicone seals.
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Old 07-10-2014, 09:21 AM   #5
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I 2nd the gasket failure. Yank em both out and upgrade the bottom ones. Those are very prone to failure.
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Old 07-10-2014, 09:59 AM   #6
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regular green coolant is not good for anything in your engine. it doesnt have the corrosion inhibitors for the plastic and aluminum. i dont like dex though, i use prestone ext life, walmart has it pretty cheap. and 20k is about it for standard plugs, alot of the guys run those in that engine but they change them often

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Old 07-10-2014, 10:30 AM   #7
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Thanks, guys for the info, it at least confirms my hunch that it is the gaskets...again.

I will order the parts from Rock Auto today and begin to disassemble.

jwfirebird, sorry to not be specific (I thought green is green...), I have been using the prestone extended life coolant since the last gasket change.

Are there other plugs that I would not need to change as often that still work? I just used the bosch copper from reading the consensus on this site. I am open to other options and might as well change them while I am in there.

Thanks again everyone.
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Old 07-10-2014, 12:11 PM   #8
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I would still do a coolant pressure test first....just to make sure it'* not an external leak....

How much coolant do you leak? On a cold engine first thing in the morning, top off the radiator and bring the reservoir level up to the cold mark.....this will give you some idea of how much and how fast it is leaking.......

It'* quite possible your misfire is not being caused by a coolant leak.....I always use oem plugs.....If you feel the misfire at 55mph, up a slight grade, with moderate acceleration, that'* usually a secondary ignition problem....plugs, wires or coil(*)....

I would do a spark output check using a spark tester, like an ST-125.....
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Old 07-10-2014, 03:39 PM   #9
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Good call on the coolant pressure test leak. I will likely give this a shot. I am assuming there is not an exterior coolant leak as I have not seen any evidence of coolant leaking. I don't drive the car much, as I typically commute by bike, but I would assume there would be some sign of drippage with an exterior leak.

It seems I had been adding a little every month or so when I actually remember to check the reservoir, but I feel like it has been more lately.

As for the misfire at 55 mph, I am not really driving the care, as you can tell driving it all together that there is an issue even at 15 mph (very low gas mileage based on the computer). I can feel the loss in power on any acceleration.

I will look to purchase the spark tester, as I still have a hunch this could be an issue (even after checking the resistance in the coils and wires). I will report back.
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Old 07-10-2014, 07:26 PM   #10
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Just tested the ignition system with a spark tester (one of the simple inline LED testers, obtained from harbor freight - $4.99).

Turns out that cylinders 1 & 4 are not getting anything. Thus, it seems the coil is the issue. I have ordered the replacement coil (Rock auto of course) and will report back that this indeed solved the issue.

Once back running, I will at some point probably do the LIM again with the metal gasket. Fortunately I can do it on my own time at this point and determine how much coolant I might be actual losing.

Thanks to the guidance thus far.
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