HOME FORUM RULES CONTACT
     
   
   

Go Back   CLASS RACER FORUM > Class Racer Tech > Support Tech


Reply
 
Thread Tools Display Modes
Old 11-01-2011, 06:30 PM   #1
Doug Domm
Member
 
Join Date: Apr 2006
Location: canada
Posts: 242
Likes: 26
Liked 26 Times in 17 Posts
Default engine misfire on 350 vortec

I have a 98 z71 1500 350 vortec that shows a misfire on #4 cylinder with a Snap-on scanner. This misfire occasionally goes away but is there most all the time. It will show as #4 cyl. and once in a blue moon will swap as #3 cyl. Shows only at idle and will go away if you turn on the air conditioning or if you just break the throttle of idle. It runs fine on the road and has as much power as it ever had before. Sometimes at idle it will get so rough it'll almost shake your fillings out. Replaced plugs, wires, cap, rotor and has good compression. Help!!!! Thanks Doug
Doug Domm is offline   Reply With Quote
Old 11-01-2011, 10:37 PM   #2
FED 387
VIP Member
 
Join Date: Jun 2006
Posts: 3,347
Likes: 309
Liked 279 Times in 149 Posts
Default Re: engine misfire on 350 vortec

got a 99 Tahoe 105,000 miles---gonna replace the injector on #5 did everything ya did same symptoms nothing else to do---mine doesnt jump around tho same cylinder all the time
FED 387 is offline   Reply With Quote
Old 11-03-2011, 01:59 PM   #3
buzzinhalfdozen
Senior Member
 
Join Date: Sep 2006
Location: Bellevue Ohio
Posts: 985
Likes: 0
Liked 12 Times in 9 Posts
Default Re: engine misfire on 350 vortec

Change the dist. cap, #4 &#3 are next to each other in the cap you'll see what I mean when you flip the cap over and trace the terminals. I see this quite often and can almost never SEE an issue with the cap, I suspect it's burning thru internally. While you're at it replace the rotor also. Though I can't guarantee it I'm quite sure this will resolve your issue. Joe
__________________
Joe Buchanan SS/BX 3117
buzzinhalfdozen is offline   Reply With Quote
Old 11-03-2011, 10:01 PM   #4
Mark Ruset
Member
 
Mark Ruset's Avatar
 
Join Date: May 2006
Location: Southwest Florida
Posts: 250
Likes: 23
Liked 35 Times in 25 Posts
Default Re: engine misfire on 350 vortec

Doug you didn't mention if this miss began after work was done on the motor such as having the intake manifold off. If so, check the injector lines for correct order. It is possible to swap two injectors and end up with a miss. GM has posted a service bullitan about this condition after having the manifold removed and replaced
__________________
Mark Ruset 2048 STK
Mark Ruset is offline   Reply With Quote
Old 11-04-2011, 11:26 AM   #5
buzzinhalfdozen
Senior Member
 
Join Date: Sep 2006
Location: Bellevue Ohio
Posts: 985
Likes: 0
Liked 12 Times in 9 Posts
Default Re: engine misfire on 350 vortec

Sorry didn't see you had replaced cap. Have you looked to see what your camshaft retard is? This is the degrees the cam sensor triggers at, if it's off you can move the dist. just like setting timing and set to 0 degrees... you must rev the engine to over 1000 rpms after adjustment to read the new setting. Could be the rotor phase is off and you're getting spark cross in the cap. Kind of a long shot but easy to check and adjust, just seems odd that it's those 2 cyls having miss fires since there not in direct relation to each other. Mark is correct that installing the nozzles in the wrong hole will cause a miss though hard to believe they could have crossed nozzles to other bank. Have you performed an injector balance test yet, if not it may tell you something, not sure if the scanner you're using has this as a special function or not. Typically "harsh" misfires are Ignition related where "subtle" rough idle are more fuel related in my experience. Joe
__________________
Joe Buchanan SS/BX 3117
buzzinhalfdozen is offline   Reply With Quote
Old 11-04-2011, 12:38 PM   #6
Doug Domm
Member
 
Join Date: Apr 2006
Location: canada
Posts: 242
Likes: 26
Liked 26 Times in 17 Posts
Default Re: engine misfire on 350 vortec

Yes the intake was off some time ago but this problem only started recently. Twice this week it performed flawless then the next time driven acted up again. It will run perfectly cold and only act up after operating temp. reached. Soft miss vs harsh miss, well it is a soft miss most of the time but occasionally goes to HARSH !! and I mean shake your fillings out harsh. I've had replace the spyder suggested but most have seen that item usually affects all cylinders?
Doug Domm is offline   Reply With Quote
Old 11-04-2011, 12:45 PM   #7
Doug Domm
Member
 
Join Date: Apr 2006
Location: canada
Posts: 242
Likes: 26
Liked 26 Times in 17 Posts
Default Re: engine misfire on 350 vortec

When it goes to harsh miss it still only shows #4 cyl. with intermittent swap with #3 cyl. not multiple cyl. as it feels that rough.
Doug Domm is offline   Reply With Quote
Old 11-04-2011, 01:29 PM   #8
buzzinhalfdozen
Senior Member
 
Join Date: Sep 2006
Location: Bellevue Ohio
Posts: 985
Likes: 0
Liked 12 Times in 9 Posts
Default Re: engine misfire on 350 vortec

This engine you can replce individual injectors, you don't have to replace the entire assy. I have replace a few injectors on these engines, easy to do. as I said by doing an injector pressure drop test you may see a problem that you can verify, rather than just throwing a part at it. You can do this test with a tech 2 but unsure on the aftermarket scanners.Joe
__________________
Joe Buchanan SS/BX 3117
buzzinhalfdozen is offline   Reply With Quote
Old 11-07-2011, 11:29 AM   #9
FED 387
VIP Member
 
Join Date: Jun 2006
Posts: 3,347
Likes: 309
Liked 279 Times in 149 Posts
Default Re: engine misfire on 350 vortec

we just fixed my buddys Tahoe Sunday(yesterday) bad intake gaskets also replaced the injector(#4) while we were in there---took about 5 hours to do the whole thing PAIN IN THE *** job if there ever was one---runs like brand new now---not saying this is your problem but spray some starting fluid along the intake manifold along the valve cover see if the engine picks up speed could be the problem bad intake gasket
FED 387 is offline   Reply With Quote
Old 11-10-2011, 08:28 PM   #10
JWhalen58
Member
 
Join Date: Aug 2010
Posts: 105
Likes: 7
Liked 98 Times in 19 Posts
Default Re: engine misfire on 350 vortec

Just went through this with my wife's 98 buick century. Kept having a miss in 4 and 5. Replaced the coils and put new wires and plugs in. Then did some checking on internet and found something helpful. This is gonna sound dumb but it worked. I got a long extension and put it right on top of the fuel injector on 4 and lightly taped it while the engine was running, I used the handle on a screwdriver, killed the engine but started it up and did it on 5. The miss went away and I reset the computer so the check engine light would go out. The car ran great, I did go and have the injectors cleaned out on a machine at my buddies shop, wife says it runs like new. The injectors must have had a little crud in them. There is a you tube video on this.
JWhalen58 is offline   Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 02:06 AM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright © Class Racer.com. All Rights Reserved. Designated trademarks and brands are the property of their respective owners.