I have a crate LS3 / 430hp in my /61 bubbletop, It has done a lot of sitting in the garage while working on things. There's been a couple 9 mile drivers over the winter.

So I'm noticing a P0300 engine code. With regard to how it's running, when it's been sitting for several days, when I start it , it is a rough idle...sounds like a wild cam in it. After warming up, it smooths out. If I start it up again maybe next day, it runs smooth.

I've been thinking that the lack of driving has affected things. I have a LS1 in my '56, and find that given a lot of down time, I ultimately have to replace the plugs. It will run and drive rough if I don't.

So I decided to take a 25 mile drive, get it up on the interstate for a few miles. Hoping if I give it some time running, it may blow out the crap.

Here's the strange thing: I have Dakota Digital gauges in it, and the indicator for ENGIINE is the same light section in the gauges as the transmission gear indicator. So after about 20 miles, the indicator flashed back and forth between the gear and ENGINE. Whenever I've had a code, it just takes over that indicator, and says ENGINE all the time.

......

I just went out and checked for codes, and it now has a P0303. That's better, at least it localizes the problem.

I'm considering purchasing new plugs and changing them all.

If anyone has any other thoughts, I appreciate the feedback.

 

Bad gas? Stuck/ clogged injector on the cylinder that's misfiring? If the cat sits a lot the gas won't keep forever

 

What plugs installed? Check #3 plug condition. Look at wear, burn condition and carbon tracking on outside insulator. Compare with good plug. Swap plug, coil, and wire with different cylinders and see where problem moves.

 

Thanks for the suggestions. friends. Some of that I'd never have thought of.

I'll post back on what I find. But just a bit more info after your comments:

I have two things driving my thoughts about the plugs: My 56 with LS1 and 4L60e has had the plugs just get all screwed up with few miles, but installed a long time. No codes, but the engine ran very rough and missed a lot. The '61 LS3 had had the plugs in a long time as well, 5 hears, finished and driven for over 3 years. Given that I will be changing all plugs.

The gas should be OK. It was down to very little, and I bumped it up to full last week.

I'll keep an eye on this thread. It may be a week before I get the plugs changed.

Thanks again for taking the time to help out. ;-)

 

Your gas MIGHT be OK. IF it was very low, and had any decent amount of sediment, filling it stirred that up, and if you drove it right after, that suspended sediment likely got caught in the filter (as it should), clogging it.

 

Below are a couple pictures of the plug attached. Frankly I don't think the plug looks too bad. But I think I may replace them anyway giving the experience I had on my 56.

To some extent I probably exaggerated how long it had been sitting. The gas that was less that was in there I don't think was put in that long ago. I don't know how long it would take for gas to " go bad".

The P0303 has only happened once whereas the others were P0300, I don't know that the codes were consistently against the plug three. I'm going to follow the advice about swapping this plug with one out of a different cylinder and see if the error continues and continues to be on plug 3. I'll post back how the test goes.

 

I just got back from another 25 mile test, and no codes this time.

I did run a test script form the Torque app which hooks to my ODBII scanner (BT), and there is some info here that may be of consideration.

Here is a link to a Youtube screen video showoing the scanner report:

 

I was going to post the text, but it's too long to post

 

So last update other than the test script results that got no reply, the latest at that time was suggested swapping a plug if it received an error, so I swapped plug 3 with plug 5. Today on another short drive, immediately leaving home I got a P0300. Then after putting approximately 10 miles on it and heading home, I felt it mis, and heard what sounded like a backfire. Engine light came on.

Checking that code it was P0305. So, the plug that had mis fired while in cylinder 3 now did the same in a different cylinder. So, I have some plugs on the way from Rock Auto.

Another interesting development: the trans is acting up. It upshifts too slow, and downshifts too easily. This was greatly exaggerated after the P0305 misfire.

So, even with new plugs, I don't know if I'll have a fix or not.

 

Those deposits up in the shell around the center insulator can/will promote misfire. Appears like some excess oil in that cylinder. How do the other plugs look? Stock heat range?

 

Thanks for noting it. I'll check tomorrow. Frankly, I didn't pay much attention to 7 when I pulled it. I'll be looking at all of them in more detail when I get the new plugs.

I can't imagine that assuming this is a plug issue that it would affect the transmission. Thoughts otherwise?

 

Resolve the misfire and then see how the trans responds. Factory PCM will use engine load to adjust trans shifts but that is likely not your issue.

 

I really appreciate your input.

I am going to replace both plugs and wires. I have no concern that the plug wires are bad, but they aren't that expensive, so going to do it. Going ACDELCO on both.

Assuming that the trans still is off I'm not sure if I should take the car to a trans shop, or a tuner. I should know fairly soon. Plugs and wires are on the way.

 

I aput in the new plugs and wires tonight. I only took it for a short drive, because of the transmission issue. It did not get any codes, but I really need to drive it further to allow that.

But I'm son't 2000 rpm at 20mph, so the shifting is all screwed up.

Here is two sides of one plug, all of which pretty much looked the same:

 

Well, the transmission issue was that the shop that had done some work on it screwed up majorly: they left out the trans fluid temp sensor; and the bigger thing...they did no use a gasket on the pan, they used some type of silicon or RTV. Some of it got into a solenoid exhaust channel and blocked it. Transmission burned up.

So I just got it back today. The P0300 codes came back, along with others. I'm wondering what the chances are that pulling, rebuilding, and reinstalling the trans may have caused one or more of the current codes. Those are:

• P0606 - Powertrain ECM/PCM Processor
• P0300 - Random/Multiple Cylinder Misfire Detected
• P0335 - Powertrain Crankshaft Position Sensor A Circuit

It now is slow to start, ie. cranks over for maybe 3-4 seconds before it starts. When it was first started at the shop to bring out for me to take home, it started slow, it sounded like there were some pops in the exhaust, and it responded slow to the pedal, not much power.

Driving it home 45 miles, it smoothed out, but the slow start is the same, and it is definitely way low on power.

I cleared the codes, and the P0335 came back.

I need to research those some, With just a bit of reading, I'm thinking that the P0335 may be related to the P0300 code.

If anyone has any thoughts, I'm appreciative.

 

What vehicle is the PCM from? I don't remember about the P0606 code. I would focus on the P0335 Cranks sensor code first. It is likely inducing the P0300 Random misfire code.

 

I was thinking the same thing on the codes.

The PCM is 2009 Chevy Silverado, as is, of course, the TCM.

 

The P0606 is a problem. If all PCM power and grounds are good, you likely have a bad PCM.

 

Well, I have positive news to report.

From what I gathered from researching info on the 3 codes, it seemed logical to first address the P0335 code, Crankshaft Sensor. It being very central to timing on the car, it made sense that it could be causing the misfire and the resulting P0300 code. Another fact that I think I didn't mention, when those 3 codes came up, my tachometer had quit working.

Having installed a new sensor I can report that the car is running great. Only around 30 miles on it with no codes. I'm feeling optimistic.

Thanks for the input everyone.

I'm

 

If you continue to have issues, there are two further things you can try that will resolve a P0300 code - 1. Perform a crank position sensor relearn procedure (usually requires a higher end scan tool to perform) or 2. Replace your Primary O2 sensors.