Code PO308 Even After Tune-Up

whiplash473 · Oct 19, 2016

As the title says - I just didn't a complete tune-up and still have this 308 code (cylinder 8 misfire). I cleared the codes after the tube-up just to see if it came back and it did. Any ideas on where I go from here? I was thinking it could be an injector since they're original.

I did a search on the forum and nothing came up at all, which I thought was weird but I searched through Tapatalk on my phone so who knows.

Sent from my bored/stroked iPhone 6S

Justin S · Oct 19, 2016

Does it feel like its misfiring, or are you just getting the code? If its not actually misfiring, it might need a crank relearn. I had that happen with my 01, but it just kept randomly throwing a p0300, and not a specific cylinder though.

whiplash473 · Oct 19, 2016

Justin S said:
Does it feel like its misfiring, or are you just getting the code? If its not actually misfiring, it might need a crank relearn. I had that happen with my 01, but it just kept randomly throwing a p0300, and not a specific cylinder though.

I had a P0300 a while back which straightened out when I did the tune-up (about 2 months ago) and now it's P0308. There's definitely no feel of a misfire, I was surprised when that's what came up on the code read.

What's this about a crank relearn?

Sent from my bored/stroked iPhone 6S

Justin S · Oct 19, 2016

Either need to take it to a shop, or to someone with the correct scan tool. I know @Jrgunn5150 recently did this with some cheap app and OBD plug also.

whiplash473 · Oct 19, 2016

I have access to a top-of-the-line scanner so that's good but I don't understand what you're even talking about with a relearn.

Relearning the PCM the crank position? I have no clue with this crap. I grew up on carbs and 4spd. Haha. Thanks for the help, Justin.

Sent from my bored/stroked iPhone 6S

slowburb · Oct 19, 2016

Yes, it's sort of like rebooting the whole engine system. I'm not sure it will help your problem though, but is worth a try.

If OBDII calls out a specific cylinder there's usually good reason. A misfire can be from a lean or rich condition. Rich most likely being from no spark, less likely a leaky injector. Lean from a clogged injector, vacuum leak, or valve sealing issue.

With a full function scantool you should be able to watch the screen and see when it misfires, whether at idle, part throttle, under load, etc. This may help with diagnosing.

whiplash473 · Oct 19, 2016

Great. I can check it at all three of those stages on load and see what happens. I've also got a P0430 for a catalyst efficiency bank 2. Might have something to do with it, eh?

Sent from my bored/stroked iPhone 6S

slowburb · Oct 20, 2016

They *could* be related; since bank 2 is the 2-4-6-8 side of the engine. It *could* be that you've dumped enough raw fuel through that hole to foul the cat.

Justin S · Oct 20, 2016

The P0430 is most likely the converter breaking apart. I had this same problem with my 98, I didn't have any misfire codes, but a big chunk had broken apart and lodged itself across the back end, which hurt power a little. I wasn't aware because I had just got the truck, and noticed an immediate difference after I gutted them. I also had/still have (too lazy to fix) a leaky cyl 2 injector that dumps extra gas in, so that could be what caused mine to break apart. I wouldn't have known unless I took the exhaust apart to gut both of them anyways. Anyhow, for the crank relearn, you just go in with the scan tool to where you can test things, and just select where it says crank relearn. I believe all it asks you to do is bring up the RPMs for a short time. Worth a try.

whiplash473 · Oct 20, 2016

I have dummy cats on the shelf in the garage that I'm waiting to put in until I get headers, then I'm doing the entire exhaust. Keeping the new Flowmaster Super 44 I just put on to replace the Super 10s I had on. So all in all it's kind of sounding like I should wait to mess with this until I fab up the new exhaust.

Code PO308 Even After Tune-Up

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Code PO308 Even After Tune-Up