Intermittent Missfire???
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
Melting Slicks
Joined: Mar 2002
Posts: 2,164
Likes: 7
From: Beringen
Just to offer a possibility : I was going thru the same thing on my engine and just found out an aftermarket PCV valve was upsetting my air fuel ratio so much that it ran way too lean causing missfires. You may want to look into that and unplug the pcv to see if makes any change. (if the pcv is hooked up to manifold at least)
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
That is exactly what my 35 year pro mechanic said after 4 weekend mechanics, including myself checked the cap, rotor, ignition module, plug wires, egr valve, timing, carb, gas, vacuum, etc, etc ! He said most older hot rod engines that have not had the seals changed have this problem to some degree but the owners don't notice it or it is masked by other issues! If this does not get any worse I will wait until late fall to replace the seals. It is not a huge job but we all know how when you open something up one thing leads to another then another and the driving season is short enough already 
It is going to be electrical or fuel delivery causing that miss not a valve guide .......
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
I do get smoke out the tailpipe...sometimes! After the car sits overnight or for any extended length of time there is no smoke. If I start the car after it is shutdown for less the 20 minutes or half an hour there is no smoke. But if the car sits for 30 minutes to about 2 hrs. there is definitely black/blue smoke. I have been told that this is probably from the carb leaking, when very hot it vaporizes, when just warm it accumulates and loads up the car, after a couple of hours it evaporates. This does explain my symptoms exactly, and others have the same issues. I have just changed my oil back to 20/50 from 10/30 and it seems to help but I have not driven enough yet to tell. One of these days I am going to pull the carb and check for leaks but it has not been enough of an issue to justify it yet!
Also last winter when I rebuilt the HEI and did plugs and wires, 2 or 3 plugs showed some evidence of oil. The car starts, runs, and drives very well, just has the intermittent miss which now seems to be happening very infrequently
Also last winter when I rebuilt the HEI and did plugs and wires, 2 or 3 plugs showed some evidence of oil. The car starts, runs, and drives very well, just has the intermittent miss which now seems to be happening very infrequently
Last edited by BPHORSEGUY; May 25, 2013 at 03:45 PM.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
You did not get my post ,,if u had bad valve seals you would blow a big puff of old whitish blue when you cold start ..every time .. and if a valve seal leaked enough to make a miss fire you would be smoking all the time . To me at least a valve guid seal is something your motor may need but not why your getting a miss fire.
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
You did not get my post ,,if u had bad valve seals you would blow a big puff of old whitish blue when you cold start ..every time .. and if a valve seal leaked enough to make a miss fire you would be smoking all the time . To me at least a valve guid seal is something your motor may need but not why your getting a miss fire.
quart in 3k. But the guy I trust the most and at least 2 board members here say that is what I have. Read my posts carefully, this problem is so mild that some think it isn't even happening.
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
I think I did get your post, and the fact that my car does not have the classic symptons! I am not a pro but we have all seen issues w/ out all of the classic symptons. My car does not burn oil either only maybe 1/2
quart in 3k. But the guy I trust the most and at least 2 board members here say that is what I have. Read my posts carefully, this problem is so mild that some think it isn't even happening.
quart in 3k. But the guy I trust the most and at least 2 board members here say that is what I have. Read my posts carefully, this problem is so mild that some think it isn't even happening.
Yep that's classic .
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
If your trying to talk your self into a motor or convince a wife to get the wallet opened that's fine, BUT that an HEI fired GM could leak the smallest amount of oil into a cylinder and it cause a misfire ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha ha
Yep that's classic .
Yep that's classic .
PS I wouldn't kick a new ZZ4 out of the garage!
Last edited by BPHORSEGUY; May 26, 2013 at 06:39 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Melting Slicks
Joined: Aug 2012
Posts: 2,548
Likes: 379
From: Woodinville WA
You have low standards .... tell your wife you need a LS9 to solve your current woes.
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
Thread Starter
Melting Slicks
Joined: Jul 2010
Posts: 2,762
Likes: 820
From: SUFFIELD CT USA 2023 C8 CORVETTE UN-MODIFIED FINALIST
2023 C8 of the Year Finalist - Unmodified
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Some years ago I installed an '89 truck roller engine in my '72, along with a POS ZZ9 cam from TPIS....in Minnesota....engine ran perfect with a nice smooth idle for about a year....then it developed a ragged idle that would be there most of the time, but not ALL the time, some days it would run fine, drove me crazy for years, then I finally got tired of it and decided to change the cam for fuel economy reasons, about 3 years ago, when examining that roller cam, I found 6-8 of the lobes had lost some surface, and the rest looked pitted, I maybe still have pix of it, I did post them on another forum.....at any rate, the lifters were perfect, so I installed the stock L98 cam I had, and sure enough, engine has not missed a lick since.....
I wonder if similar crap can happen to a flat tappet cam???
an intermittent mechanical problem, I would NEVER have guessed it was that cam, I played with that missfire for YEARS, went through ignition, wiring, plugs always looking normal, several sets of plugs, Jacobs ceramic wire caps, dizzy's, injectors several times, wiring, computers, chips, you name it....freeking CAM SHAFT......go to hell and how to figger....
I wonder if similar crap can happen to a flat tappet cam???
an intermittent mechanical problem, I would NEVER have guessed it was that cam, I played with that missfire for YEARS, went through ignition, wiring, plugs always looking normal, several sets of plugs, Jacobs ceramic wire caps, dizzy's, injectors several times, wiring, computers, chips, you name it....freeking CAM SHAFT......go to hell and how to figger....