Truck is a '99 tahoe, 198k miles. I have a P0304 that occurs only uphills under load. I have replaced the fuel filter, spyder injector, upper intake gasket, and distributor. The plugs, wires, coils, fuel pump, and compression have all been checked by a trusted mechanic. Based on my readings, the persisting P0304 seems to align with the crank position sensor. Ordered one to try- worth it for the cost. Mechanic just did spyder injector and upgraded to MPFI. He thouht the misfire was due to the spyder injector lines leaking into manifold and causing misfire in rear cylinder bank. After doing MPFI conversion, truck pulls harder than ever and feels great but still triggers the P0304 misfire but it is more difficult to trigger. Any other thoughts or obvious things I have missed?
Persisting P0304
- Thread starter gbsharon
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1998Suburban
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There's a TSB about tight valve guides. I don't know the number off the top of my head but the symptoms are a good match. My '98 does the same thing on occasion.
Snowbound
Jim
A P0304 points to #4 cylinder misfire. If it was a P0300 (random cylinder) I would suspect crank cam correlation issue. You can do cheap checks with no special tools. First swap plug with another hole and see if you still get a 0304. If so swap a plug wire and check again. Obviously you'll have to clear codes or disconnect negative battery post while performing diagnostic repairs. If problem still persists there's a number of things that can cause this issue. Compression test and leak down test will fill you in on condition of cylinder. If compression is low, put a little oil in cylinder and test again. If compression comes up, it's most likely ring related. If not it could be valve or head gasket related. The Vortec heads have been known to pull the rocker arm stud which would limit rocker travel. Could be a rounded cam lobe. System is pointing to what cylinder, up to you to pin point. Hope this helps.
Jim
Jim
parkerpress
TYF Newbie
Did you ever get this figured out? I have a 99 that is having similar issues. Last repair was to replace the Mass Airflow Sensor and fuel injectors and clean the entire fuel injection system. I still get the "stuttering" at speed under load on hills (at about 50-70Mph). Yes, my Tahoe makes noises and is getting old (just like my knees), but I love that truck and would love to see it continue it's life. It runs flawlessly in the city and around town and on flat highways. But that's kinda usless living in Colorado... 
I remember reading something in the past about possible bent or warped valve arms or something like that (where the arm was off by 1/8"). And I see above that somebody mentioned a TSB and a number of other things that I'll take to my mechanic next time in.
Does anybody have links to or know where to find that valve arms article, or the TSB? I've been searching the web, but haven't found either one yet.
TIA for any advice/opinions...
Steve
I remember reading something in the past about possible bent or warped valve arms or something like that (where the arm was off by 1/8"). And I see above that somebody mentioned a TSB and a number of other things that I'll take to my mechanic next time in.
Does anybody have links to or know where to find that valve arms article, or the TSB? I've been searching the web, but haven't found either one yet.
TIA for any advice/opinions...
Steve
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