454 Vortec P0300 Multiple cylinder misfire code. Troubleshooting and solution.

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Mangonesailor

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Hey guys.

I'm all about trying to spread out info of my personal experiences on things, and trying to help the masses that may end up having a problem that I (or they) can't rely on the good ole' Google to help them solve. This left me scratching my head for a little over a month, and tied up quite a few weekends trying to figure out what's going on. So I thought I'd share what I found, how I did it, and my end result.

So gentlemen. I've been fighting a P0300 (random multiple misfire) check engine light for the past month.

So here's some past info: Plugs (.050" gap), wires, cap & rotor (MSD), coil (Accel), intake gaskets, FPR, 19lb Bosch injectors, EGR & TB gaskets, all installed 1yr ago. The truck idled with a little roughness, and I could feel a miss every once in a while, but I didn't have any codes and got 13mpg. About 2mo ago I replaced the fuel pump and fuel filter. In the beginning of July I did a 0411 install... and that's when I received my P0300. I did not perform a crank relearn as every dealership I went to was unable to perform it, however I have since gotten it taught. Just drive up to the dealer (Shop) and tell them to program their Tech 2 (Scanner of whatever flavor) for an '02 Chevy Express van with a 5.7 or 8.1 motor and it'll be able to perform the crank relearn.

So, using an OBDLink MX dongle with Torque pro and Dash Command I decided to try to figure out what in the hell is causing all of this. Here's my counts:
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I also have no comms with my ABS module.
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Here's when they happen: Engine warm, idling in P or D, A/c on or off, with NO accelerator applied. If I accelerate the engine, they stop. Any bit of gas I give it and the engine runs flawless and will not miss. I do not have any lifters ticking and the engine internals sound fine (Via stethoscope).

Here's what I've done:
1. TPS sensor had read (way in the past) .4% open when the throttle was shut. So with Torque Pro running and the engine off I set the throttle closed position to 0% using the slop in the screw holes. After I started having my miss at idle I suspected it was the TPS or IAC valve. With the 0411 and Dash command I was able to see the TPS was showing -2.1* with the throttle shut, so I set it to 0* with the throttle shut. This did not help.

2.Then I looked at IAC counts and they were "0," so I replaced the IAC. They were still at 0, so I played (and counted turns of) the idle stop screw to see if I could get counts in the 25-75 range. They did not increase. I have verified the IAC is receiving a signal from the PCM by unplugging the IAC in the engine and plugging the old IAC external to the TB. i can feel and see it moving.

3. I then suspected a vacuum leak, so I unplugged the IAC and sprayed everywhere I could with starting fluid and used propane under the intake. Nothing.

4. I then started looking for loose vacuum hose connections, because why not anyways? I replaced the PCV's hoses and put a clamp on the breather tube's hose.

5. Cleaned the EGR valve. Lots of carbon fouling. No change.

6. Replaced the oil fill cap, and dipstick O-rings.

7. I checked fuel pressure: 58PSI KOEO, 54PSI KOER, then clamped the return line and jogged the pump. I stopped when I saw 68PSI, so I have pressure and volume.

8. I pulled cyl 4's plug to see what it looked like:
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Gap was still at .050", regapped to .045", no change.

9. I pulled the upper plenum and had a look around. The intake runners all look evenly "washed" from fuel from the injectors. I wiped their tips clean, jumped the fuel pump for 15min, and checked for leaks with a paper towel. No leaks.

10. I pulled the dizzy cap and found this:
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So i replaced them with a new Accel set, and used locktite on the rotor screws. I also found the old screw in the housing. I checked backlash in the rotor and it was fairly tight, so I left it there.

11. Replaced the FPR for the hell of it.

12. After sealing everything back up and test driving, I still got a p0300, with the same set of cylinders missing, and only doing it at idle. So, I fabricated a blockoff plate to verify the EGR wasn't leaking. Nope.

13. Changed #3 and 4 spark plugs, gapped to .050", nothing.

14. Put 8oz of marvel mystery oil in crankcase to rule out sticky lifters. No change.

15. 8oz of MMO in gas, no change.

16. Ran that tank out and swapped from 87 to 89 for two tanks. IT GOT WORSE.

17. Changed crankshaft sensor and cleaned pickup wheel to verify that was working properly. NOPE.

18. I had thought about the cylinders in relation to the firing order, and they are all next to each other. Yesterday I decided to pull the dizzy and check the gear. Good thing I did:
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Camshaft looks OK too, and I checked the whole thing.
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I replaced the dizzy with an entire unit from summit. It came with everything from the Gear to the Cap. I had to index the oil pump drive so that the rotor and it's pickup wheel would be properly aligned when I slipped it in. I used the old dizzy shaft, sans gear, in the old housing for that.
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So, After all of that, I have no more misfires. Zero. None. Nada. The engine still kinda has a funky idle when cold, and it feels like it has a light miss when warm. However, I'm content with that.

I did get the P1336 code (Which is crankshaft angle variation not learned) after installing the new dizzy. I got that taught and no I have no more issues. I also unblocked the EGR valve, and all seems to be operating normal.

Hopefully this will help out someone in the future whenever they try to use their McGoogle skills.
 

Ttoyota

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Damn.If I have to do all of that to try and fix this pig, my wife will have me sleeping in it. So the 411 didn't have anything to do with it, you just had a worn out distributor gear? I do like all the other things to look for though. Thanks
 

Mangonesailor

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Damn.If I have to do all of that to try and fix this pig, my wife will have me sleeping in it. So the 411 didn't have anything to do with it, you just had a worn out distributor gear? I do like all the other things to look for though. Thanks
Yeah, basically the 0411 made it appear. The problem was there, it's just that the black box didn't detect it.

I think it's good data and helpful for those that may be at their wits end and want to know what else to check.

From what I've read here and elsewhere the dizzy gear is a common wear item. They'll take about 100-150kmi before they become problematic, kinda like the fuel injectors being an Achilles heel as well.

You can change the dizzy with the intake on BTW. Just remove the ignotign module and coil, pull the dizzy cap, and it'll come out and around via the very back side of the motor. Dizzy bolt is 14mm, and yoully need 14mm and 9/16 for the rest I believe... IF you have to do the dizzy.

Do you have torque or any other way to log cylinder misfires like I did ?
 
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Ttoyota

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Your write up was awesome. I'm still trying to rationalize how I would go about all the things you did. To be honest the truck seems to be running pretty decent if not good. My original problem was the leaky intake gaskets and hard start so I changed out distributor injectors fpr wires plugs and 411 all at the same time. I was pretty sure I had one if not multiple issues you had worked thru with my truck afterwards. I listened to Christian and checked dropped my plug gap down from 55 to 45. That made it really run like doo doo. Good thing was it changed the symptom enough to lean towards conventional plugs and factory .060 gap. After doing this I feel like it's running a whole lot better. Pretty much the same as it was before doing all this. I think my next step is to get tuning equipment and try and see what it needs. Thanks again. Got plenty of questions about this or that and your write up pretty much explains what it takes sometimes to find the gripe. Ttyl.
 

Mangonesailor

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Your write up was awesome. I'm still trying to rationalize how I would go about all the things you did. To be honest the truck seems to be running pretty decent if not good. My original problem was the leaky intake gaskets and hard start so I changed out distributor injectors fpr wires plugs and 411 all at the same time. I was pretty sure I had one if not multiple issues you had worked thru with my truck afterwards. I listened to Christian and checked dropped my plug gap down from 55 to 45. That made it really run like doo doo. Good thing was it changed the symptom enough to lean towards conventional plugs and factory .060 gap. After doing this I feel like it's running a whole lot better. Pretty much the same as it was before doing all this. I think my next step is to get tuning equipment and try and see what it needs. Thanks again. Got plenty of questions about this or that and your write up pretty much explains what it takes sometimes to find the gripe. Ttyl.

Maybe your coil or ignition module is going? That's strange that going to .060 from .045 would help it run smoother.
 

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It's possible. I was reading thru some threads last night and it sounded like the consensus was if you go cheap distributor route you should replace your rotor and cap with a.c. Delco. I tried a new coil. Removed the new coil I had and swapped in anew coil. Results were the same. Btw when I pulled my original distributor it was way worse looking then the one you had.
Fortunately it was still working. Who knows, maybe my cam sensor is Chinese garbage or my cap and rotor.. I haven't done a crank relearn but my oh so special 411 computer hasn't told me too. That said I did pull that sensor too. Appreciate the help though. Let me know what I should try next and I'll update.
 

Mangonesailor

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It could be. Heck, I got a crank relearn code after running mine for a while. Turned out the summit cap/rotor terminals oxidized (they're aluminum come to find out). Replaced with MSD (MAKE SURE YOU LOCTITE THE ROTOR SCREWS WITH FRESH LOCTITE, I've had two loosen up on me, and others have... so yeah) and blew out the crud. Code went right away.
You can have the ignition module checked at an auto parts place to make sure it's good.

So, do you have torque or ANYTHING to get you some cylinder misfire data? Even dash command would give you some feedback one which cylinders are giving you issues.

I think once you get that data we'll be able to continue.
 

BowtieBrody

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It could be. Heck, I got a crank relearn code after running mine for a while. Turned out the summit cap/rotor terminals oxidized (they're aluminum come to find out). Replaced with MSD (MAKE SURE YOU LOCTITE THE ROTOR SCREWS WITH FRESH LOCTITE, I've had two loosen up on me, and others have... so yeah) and blew out the crud. Code went right away.
You can have the ignition module checked at an auto parts place to make sure it's good.

So, do you have torque or ANYTHING to get you some cylinder misfire data? Even dash command would give you some feedback one which cylinders are giving you issues.

I think once you get that data we'll be able to continue.

How did your truck run after the MSD cap?
I've just got stock AC Delco on mine, but I'm probably going to have the whole distributor replaced with a billet shaft when I do my 0411 because I've noticed two other members who have had issues with the distributor shafts after swapping computers.

I was gonna go back to Delco but I'm curious if you noticed any difference in performance.
 

Ttoyota

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First and foremost, thank you for the time and help. I have gauge pro or something like that. I have tq as well but haven't been able to talk to dongle with it. I 've had all right gauges up and just seen the missfires count up mostly during deceleration and idle. I would think when I give it gas as well. I can check tomorrow to confirm. I was in empty parking lot and had tires up against curb in drive. When it would miss the truck would basically let up the pressure on curb for a sec then return. I turned as off and on to induce a load and the misses kinda councided with that. Had distributor checked at AutoZone and they said it was fine. It's the original I'm pretty sure. I do run a front aux pusher fan as well as the fleas lite monster fans so I know I'm drawing some significant current. I need to look at gauge app while I'm doing all this to try and give you better data. My po300 only flashed once other then that I have know cel. But the mail does show up in my bosch obd1200 .Scannee.
 
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