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I would start with this video from RealFixesRealFast.
It could be a voltage leak. Those seem to pop up when ever the engine is under load, such as in towing.
Thanks for your input, That guy at real fixes is an amazing tech. My car shows by the code it is misfiring but there has never been a running problem. I have never felt it misfire.
RealFixesRealFast is excellent so defiantly check that out. In addition I’ve made a video that might help in a similar vehicle. I’m also going to link my power balance video to help nail down the effected cylinder(s)
Thanks Eric. I watched those two videos of yours (again) and I got alot more out of them the second time. I tend to dread getting that deep into it and I will admit that I tend to jump to conclusions. the threshold thing that bugs me is that my car doesn’t seem to have an actual miss. After watching your videos I feel that is a little naive on my part. I will say I have taken long towing trips with this car since it has been doing this and I have another trip this next week. After i get back i shouldn’t need to use it for a few months so I will devote some time to it. Question: I watched you do the compression test on a suspected bad cylinder, but if you want to do the test on the whole engine do you pull all the coil pack connectors when you pull all of the plugs? Is there another way to assure you don’t get zapped by the dangling plug wires?
Ignition misfires tend to happen under a load. The best way of isolating the cylinders is by a cylinder balance test as already posted above. You can do this via a good scan tool or by following the same practice Eric shows in one of his video’s.
A good scan tool will also show you how many misfires each cylinder has had if you jump deep into the scan tools functions.
You could possibly start diagnosing the issue your self by stress testing the ignition system by using a good brand adjustable spark tester. I would also be looking at fuel pressure issues as well as vacuum leaks. Again the correct tools will make diagnosis alot easier.
For the compression test, just complete one cylinder at a time. I would pull the fuel pump fuse so the vehicle will not run nor flood the engine of raw fuel.
Hope this helps.
P0300 is random missfire detected and the flashing mil light is because it is catalyst damaging meaning the only thing missing is the lean codes of p0171 and 174 before total meltdown of the cats.
You need to check the fuel trims and find out how far out they are and then check for confirmation with propane around the intake manifold gaskets.Yeah I like the high tech stuff he has .
Here’s another one to look at:
http://www.youtube.com/watch?v=CR32Lpt6 … re=related
Quoted From silveralfa:
Thanks for your input, That guy at real fixes is an amazing tech. My car shows by the code it is misfiring but there has never been a running problem. I have never felt it misfire.
Here is a link to the compression test video.
The results of checking the power balance are that there is no difference between cylinders. When each coil connector is removed there is a skip created that goes away when I put the connector is replaced. Question: how do i check my fuel trims?
Fuel trim can be read from a real-time ODBII scan tool that can display live engine data.
I have a video myself on reading live data on an engine here:
http://www.youtube.com/watch?v=d0ucS4RydkA
And here’s a video from realfixesrealfast that talks about how fuel trim works.
http://www.youtube.com/watch?v=mzsOY_AhgY4
Quoted From silveralfa:
The results of checking the power balance are that there is no difference between cylinders. When each coil connector is removed there is a skip created that goes away when I put the connector is replaced. Question: how do i check my fuel trims?
Can you actually feel the misfires and the engine running bad? It may be as simple as having a crankshaft variation relearn done. I had a 2005 2500HD in the shop this morning with a P0300, when the RPM’s got over 2700 or so it’d say about 4 cylinders were missing like crazy, couldn’t feel any misfire whatsoever. I did a crankshaft relearn on the Tech 2 and the problem was solved. Crank sensor must have been out of sync just enough to think it was misfiring when it really wasn’t. Might be something to have done before throwing parts at it. If it still is throwing codes after that, then continue diagnosing the problem.
thanks Shaun. I can not feel any misfires and the engine is not running bad at all. I have never heard of a crankshaft relearn before, but that sounds interesting. Is that to do with mechanical age like timing chain? I assume that I can not do this relearn myself.
Thanks pcmdJason My 1st scan tool was defective out of the box. the replacement scan tool came today and the data stored for the code showed that both the long term and short term fuel trims were between 0%and 1.5% which I gather is good.
Yes it could be a slightly stretched timing chain. I wouldn’t be too concerned about that though. There are many notches on the reluctor wheel for the crank sensor, doesn’t take much to throw them out of whack. I’d get the relearn done and go from there. Not guaranteeing that’ll fix it for sure but I’d definitely try that first if you can’t feel any misfires at all. It has to be done with a scan tool, not sure if some of the aftermarket ones can do it or not or if you have to have it done at a dealer with the Tech2.
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