BGrahovac

Purchased a 2005 Express 2500 with the 6.0 about 2 months ago. It was missing a catalytic converter and had a flashing engine light above 45MPH when got it. I replaced the converter and also an evaluation solenoid that was bad. I went through and replaced the plugs(gapped properly) and wires. I testes the coils with an electric spark tester and they all seemed to be ok. Everything seemed OK so I replaced the blown exhaust manifold gaskets and rusted out oil dipstick tube. The flashing engine returned. The engine is running slightly rough at idle.i went through and made sure all the spark plug wire boots were firmly attached to the plugs and coils. They were.
They only code being generated is a generic P0300. Mileage is 253K.
I did test fuel pressure at the rail with a gauge and it's near perfect.
Is there a way I can bench test each coil for a more accurate and sure reading? Anyone have any advice on testing the fuel injectors?
My scanner does not have the capability of testing misfires.
has anyone dealt with this type of issue on their van?
Im at a loss on this at the moment.
​​​​​Any advice or direction to go in would be greatly appreciated
Thanks!

mountainmanjoe

does you scanner provide live data? A readout of the basics might provide some clues.

with that kind of mileage, common culprits will be vacuum leaks at the tubing, or intake manifold

Injectors are diagnosed with a balance test (need bidirectional tool for that)

Easiest way to test ignition is remove EFI fuse, pull out spark plugs one by one (leave plugged in), ground it, and just visually confirm strong spark.

BGrahovac

My scanner does do live data feedback. I guess I'm just not schooled in what I should be looking for. It does sound like there may be a vacuum leak, I just can't pinpoint it. I've sprayed brake clean around to see if the idle changes but didnt really notice anything. Any info you can provide would be great. Thanks again

mountainmanjoe

just the basics for now ECT, MAF, Fuel trims, ignition retard
snapshots at idle and during misfire

be careful with brake clean. It's very aggressive and damages some plastics on contact. Smoke tester is the most foolproof way.

BGrahovac

I just got hoke from picking up a more sophisticated scanner. I will be able to look at each cylinder when it's running to see where the misfires are. I will check it out tomorrow after work and report back

I dont have a smoke machine so I will have to get creative to try and push smoke through the system

mountainmanjoe

oreillys, advance auto , and autozone all have loaner tools

BGrahovac

So i borrowed an Autel scanner and played around after work. I was able to test all 8 injectors and they are functioning fine. I then check live misfire data. Cylinders 1, 5, 6 and 8 were misfiring like crazy. 8 was the worst I believe.
I did a crankshaft sensor relearn and then checked the live data. There was maybe 1 or 2 misfires here and there. I put it on the highway and no engine light. I checked misfire data again when I pulled in the driveway and all cylinders were clear.
I'm not 100% sold that took care of the issue so I will drive it again tomorrow after work and check data again.
Anyone have experience with crank sensor relearn issues in these?

tech2

whenever the crankshaft sensor or pcm are replaced...a relearn is needed as there are variances in the waveform that must be compensated for. If not done the result will be false misfires at high rpm.

BGrahovac

I didnt change the crankshaft sensor. I had read a few things online that people had done a relearn on it and it "cured" the p0300 misfires

Can i look up online what the fuel trims should be on the 6.0 engine?

mountainmanjoe

as close to zero as possible on any engine