'99 1500 5.2 Engine misfire

[quasarn01]

Ok... I've done just about everything I can imagine to do. Plugs, wires, cap, rotor, etc... I keep getting P0304 - Misfire on Cyl. #4... It's strange, though. I would use Seafoam through the intake and in my oil and gas and immediately after the treatment, the engine light would go out and she'll run better than ever before. However, after a couple of days, about 80 miles, the misfire code will come back and the #4 cyl. would begine to misfire again. I knew I had to change oil because of the Seafoam treatment so I changed oil and filter. I didn't even have the engine running for more than a minute before the P0304 code cleared and engine ran fine again. But, after another 60 to 80 miles, the dang light came back on and the missing started again. The wires were rerouted from the start and I checked the plug(s) and no signs of fouling. I've swapped injectors thinking I could narrow it down. Cyl. #4 still pulls a misfire code. Now, during all of this when the light came on there was a tapping coming from the area of the #4 cyl. When The light was out and the engine was running fine, no tapping sound. Would a lifter suddenly collapse and then start performing normal like that? Or would a valve stick, get unstuck, and stick again? I thought "plenum gasket" failure, but, why would the misfiring clear up after treatment and start over again after awhile if the gasket was blown? Any thoughts?

[fredjacksonsan]

My brother has the same problem with his 99 V10; cyl 7 misfire. He changed everything you did, and also switched the fuel injectors. Then he got a misfire on a different cylinder (which was not involved in the swap).

He said his truck runs fine, but he's considering getting a diagnostic done @ a delaer or other shop. I'll let you know what he finds if he does it.

[danwilliams]

That is strange. I'd guess an injector but you already checked that. It seems too new for it to be a problem with a valve but I couldn't say that fer sure. When I had injector problems same code came up. One thing though. the injectors intermittently worked. And until you reset the computer, the same codes will still come up. I unplugged each inj. one at a time when I checked mine, then ran the scan and every cylinder logged a misfire. Just a thought. Mine's a 99 and has blown 3 injectors already. Good luck.

[quasarn01]

Originally Posted by fredjacksonsan

My brother has the same problem with his 99 V10; cyl 7 misfire. He changed everything you did, and also switched the fuel injectors. Then he got a misfire on a different cylinder (which was not involved in the swap).

He said his truck runs fine, but he's considering getting a diagnostic done @ a delaer or other shop. I'll let you know what he finds if he does it.

Yea, my problem seems to be centered on the #4 cyl. Worse case scenario is going to be a burnt valve. I haven't eliminated that yet since I haven't run any compression tests. Hope to test it in the next couple of days...

[quasarn01]

Originally Posted by danwilliams

That is strange. I'd guess an injector but you already checked that. It seems too new for it to be a problem with a valve but I couldn't say that fer sure. When I had injector problems same code came up. One thing though. the injectors intermittently worked. And until you reset the computer, the same codes will still come up. I unplugged each inj. one at a time when I checked mine, then ran the scan and every cylinder logged a misfire. Just a thought. Mine's a 99 and has blown 3 injectors already. Good luck.

I agree. It shouldn't be a valve but stranger things have happened. Oil has been changed regular. I would have suspected the plenum gasket but there hasn't been any noticeable loss of oil. None... Nada... Just a little while ago I ran some 5 minute Engine flush. Ran for about 10 minutes and dropped the oil plug and filter. Put in new oil and filter and disconnected the battery for a few. Runs good, no missing and no code yet. There is a very slight tapping noise on the passenger side of engine but no where like it was before the oil change. I'll just wait and see if the missing returns and/or the light returns...

[BUYOUTS]

Did Anyone Fine Out What It Was. Mine Has A Cyl. 7 Misfire And I Have Done Everything..1998 5.9

[A97]

I have a 98 w/ 5.2 i seem to get a misfire on cyl. 8 did the plugs cap wires and rotor and after 10000 - 15000 miles the same plug would misfire looks ok when i pull it out but for some reason the same one goes bad avery time. no big deal on changing them often but i just wonder why. i never had a problem before until about 75000 miles my coil wire broke and i replaced all the wires then, i checked and rechecked how i routed them and everything looks fine maybe its a gremlin

[quasarn01]

Well, I finally went out and bought a nice compression tester. All the cylinders pushed between 110 ans 120 except for Cyl. #4 and it panned out at 60... No climb in pressure after several revolutions... So it's either a blown head gasket or a burnt/stuck valve... Sometime in the next week I'm gonna pul it all down and do whatever it takes to get it cleared it up... Got the gasket rebuilt kit yesterday so I'll start next weekend... I guess if I had run the compression test alot earlier then I would have saved all this time and money doing just about everything else to the truck to find out what was wrong... I'll post my results later when(if) I get my truck up and running....

[fredjacksonsan]

Good luck with it; let us know how it pans out.....