97 5.7 vortec P0304

[donwon37]

I have a 97 tahoe 5.7 vortec.The engine light came on,pulled the codes stated P0304 cylinder 4 misfire.This weekend had a guy replace the intake gaskets.While he was doing the work we replaced the number 4 injector,thinking this would fix the problem.Got the intake back on the engine,started it up,The engine light came on again with the same codes.I replaced the plug wires,distributor cap,spark plugs,I thought it might be the distributor cap so i pulled the #4 wire off with it running and the wire was popping at the plug.The truck runs and idles but you can feel the skip at idle.And runs very strong on the highway.I read in a post that the distibutor plate is possibly shorting out.Does anyone have any idea what this problem could be.I'm ready to push the m$%^&**&##**&%^% in the fish pond and say the heck with it.

[wafrederick]

Pull the distribitor out and inspect the distribitor gear.A worn out distribitor gear will cause a miss on the vortec 350s.I have seen this happen and look for shiny spots.

[donwon37]

Thanks for the reply.I thought i stumped everyone on this one.My mechanic took the distributor out and checked everything on it.It lloked ok.Called the Chevy service dept.They told me the same ole shit,(could be anything).

[777stickman]

Looked up that DTC P0304 in my GM '98 C/K service manual and found it. Trouble is the manual says that code is only on the 6.5 diesel and not on any of the gas engines. Another mystery???

[donwon37]

Yes another mystery!Now i'm stumped.I talked to a buddy that worked at the chevy dealership service dept.He said there was an update for the computer but he didn't know exactly what year it was for.I've done all i know to do!I know if i take it to the dealer all they will do is change parts and rip you off.I guess all i can do is just keep waiting for posts because i know i'm not the only one with this problem.The mechanic i use is an intelligent guy that knows how to diagnose problems before just ripping parts off to swap them.We're going to do a compression check next to see if it's something internal.....Just an update in case some one out there has this same problem.

[2000CAYukon]

Originally Posted by 777stickman

Looked up that DTC P0304 in my GM '98 C/K service manual and found it. Trouble is the manual says that code is only on the 6.5 diesel and not on any of the gas engines. Another mystery???

P0300 is a generic code for misfire. P030X is the code for a particular cylinder where X is the cylinder. This applies to both gas and diesel.

//2000CAYukon

[LastOne]

Ask your contact at the dealer to research Mechanical Sticking of the valves on the 5.7
My 98 has this problem. I think it is a result of the intake leak causing a gum up in the valve stems, just my opinion. I switched to Mobil 1 full syn oil, did a Seafoam treatment through the brake booster vac hose, and in the oil and fuel.
After about 2500 mikes the miss was and is still gone. Easier than rebuilding heads.

[donwon37]

Originally Posted by LastOne

Ask your contact at the dealer to research Mechanical Sticking of the valves on the 5.7
My 98 has this problem. I think it is a result of the intake leak causing a gum up in the valve stems, just my opinion. I switched to Mobil 1 full syn oil, did a Seafoam treatment through the brake booster vac hose, and in the oil and fuel.
After about 2500 mikes the miss was and is still gone. Easier than rebuilding heads.

Interesting reply....I talked to my mechanic tonight,he said it was probably a valve too tight,he wanted to adjust the valves.But i will mention this to him.I run full synthetic oil and it seemed to start this after i switched to the synthetic oil.It probably is something to do with the intake leak we will check and i will post the results.Thanks!

[donwon37]

Update........Checked compression on cylinders 2,4,6,& 8
All 3 cylinders except the # 4 cylinder was 150 p.s.i.
The # 4 cylinder was 120 p.s.i.
Mechanic said it is probably a valve not seating...
Will post with the results.

[BigBlackBurban]

Had this code intermittently for past 4 years. Changed out the injector on #4 as well as spark plug, wires, rockers, pushrods, Seafoam treatments, etc- all w/o success. Would usually get the code at about 10-15 mph, decelerating. Compression always checked out okay on all cylinders, but always had a slight miss. Did not seem to affect mpg or power. Before Christmas was doing a number of maintenance repairs, including putting in new fuel injection. After installing, did a quick round the block & noticed significant increase in power- the old injectors were worn badly @ 132k mi. Next morning, got about 1/2 mi from house @ 15mph & had a bang & engine wanted to stall out. Took compression check- cyl #4 was 0 (brand new #4 injector's tip was melted & singed brown). Pulled valve covers, #4 exhaust spring was broken in 4 pieces, pushrod bent & valve unmoveable. Took a while, but finally had engine tell me what the problem was. Most likely had a weak spring all along. Fortunately only a couple of scrapes on top of piston (no fractures) & minor damage to head. After heads were rebuilt, put back together, followed GM shop manual for setting valves & engine sounded as bad as at the breakdown. DO NOT follow GM directions- valves will be open all the time- they say to check lash by turning pushrod in fingers- very subjective as some have stronger fingers. Ended up resetting all the rockers in order suggested in shop manual, BUT checked for lash by getting play out of rocker & NOT tightening any further. Then did old fashioned valve adjustment while running to take out any remaining lash. Now am getting P1345 code each time engine is started. Will post results of 'repairs' to get rid of that code on P1345 thread.

[j cAT]

Originally Posted by BigBlackBurban

Had this code intermittently for past 4 years. Changed out the injector on #4 as well as spark plug, wires, rockers, pushrods, Seafoam treatments, etc- all w/o success. Would usually get the code at about 10-15 mph, decelerating. Compression always checked out okay on all cylinders, but always had a slight miss. Did not seem to affect mpg or power. Before Christmas was doing a number of maintenance repairs, including putting in new fuel injection. After installing, did a quick round the block & noticed significant increase in power- the old injectors were worn badly @ 132k mi. Next morning, got about 1/2 mi from house @ 15mph & had a bang & engine wanted to stall out. Took compression check- cyl #4 was 0 (brand new #4 injector's tip was melted & singed brown). Pulled valve covers, #4 exhaust spring was broken in 4 pieces, pushrod bent & valve unmoveable. Took a while, but finally had engine tell me what the problem was. Most likely had a weak spring all along. Fortunately only a couple of scrapes on top of piston (no fractures) & minor damage to head. After heads were rebuilt, put back together, followed GM shop manual for setting valves & engine sounded as bad as at the breakdown. DO NOT follow GM directions- valves will be open all the time- they say to check lash by turning pushrod in fingers- very subjective as some have stronger fingers. Ended up resetting all the rockers in order suggested in shop manual, BUT checked for lash by getting play out of rocker & NOT tightening any further. Then did old fashioned valve adjustment while running to take out any remaining lash. Now am getting P1345 code each time engine is started. Will post results of 'repairs' to get rid of that code on P1345 thread.

THIS IS an old posting 4yrs old ..start a new one with your issues..

but since I'm here 1345 is distributor gear worn..common with these engines..get the GM gear ..don't use the brass/bronze one..