miss fire conundrum
miss fire conundrum Ok fellas, I'm at my witts end. Car runs amazing for 15 minutes and then bam grows a miss fire. So far I've replaced the 02 sensors, icm, coil, plugs, and opti. Unplugged the maf when it started doing it to confirm that it's doing it in closed loop too. I can't figure it out. I was really hoping that the opti which I changed last would fix it. Any help would be awesome.
I had this happen and found out the water pump would only leak on the opti once pressure was built in the cooling system. It would run great until operating temperature and then start to stumble.
Check the resistance values on the coolant temp sensor in the water pump yet? See if it's where it's supposed to be cold/ ambient and check it again when it starts misfiring. You should be able to do it in the driveway. Stuff gets hot of course- it's easier to get at it from below when it's warm (ramps). See if the value it has when it's warm is where it should be for the range of 180-215 degrees. Resistance value table here:
http://shbox.com/1/4th_gen_tech2.html#ect
Something to eliminate that it doesn't sound like you've checked yet...
http://shbox.com/1/4th_gen_tech2.html#ect
Something to eliminate that it doesn't sound like you've checked yet...
I notice you didn't mention replacing plug wires...did you? It's pretty easy to burn them on the headers causing misfires if you don't have the over the valve cover wire conversion.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Topdon ONE vs. Artidiag 800 BT2: Which is the Diagnostic Tablet For You?
Pouria Savadkouei
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
What happens when you unplug the MAF is the car will die if it's running. But it will still go into closed loop while running speed density. Only way the car will go open loop after it's warmed up is if an O2 sensor is completely dead or unplugged. If you want to check if it could be an O2, either hook up a scanner and check the sensors switching or crawl under and unplug them, one at a time. If you unplug one O2 sensor and it smooths out, check the connections for any corrosion, breaks in the wires, and finally swap the O2 sensor.
Also, what brand O2s did you swap into it? Bosch are sheet.
Also, what brand O2s did you swap into it? Bosch are sheet.
TECH Veteran
Joined: Apr 2008
Posts: 4,985
Likes: 113
OP
I would REALLY check for any arching at plug boots. It can be hard to see and you may need to look from below also while car is running. Even though you replaced plugs/wires one may not be on all the way or a plug boot is arching to exhaust. or arching between heat shields over boots (if you still have the OEM ones on).
You really need to use dialectic grease on both ends of plug wires
I chased a misfire and replaced everything you did only to discover a plug boot arching with a heat shield boot cover. Could not see it from up top even in dark while spraying wires with water mist.
It certainly could be another cause but REALLY check for arching from wires.
I would REALLY check for any arching at plug boots. It can be hard to see and you may need to look from below also while car is running. Even though you replaced plugs/wires one may not be on all the way or a plug boot is arching to exhaust. or arching between heat shields over boots (if you still have the OEM ones on).
You really need to use dialectic grease on both ends of plug wires
I chased a misfire and replaced everything you did only to discover a plug boot arching with a heat shield boot cover. Could not see it from up top even in dark while spraying wires with water mist.
It certainly could be another cause but REALLY check for arching from wires.
Fuel pressure is good. Rechecked for arcing plug wires and came up with nothing. It's really driving me crazy that it only does it when it's hot i.e 15-20 minutes of driving. Until then it runs awesome and then the miss has a slow onset until it's just down a cylinder. I've found from searching that numerous people have had this problem but nobody on any site ever posts the fix.
I did notice that when it starts missing my fuel trims go from left 128 right 128 to 120 126. I don't know. I'm about ready to just get rid of this thing. It's driving me batty.
So I want to be a guy that finishes up and posts fixes to elusive problems. My buddy called his guy at gm and they suggested the PCM. I figured what could it hurt and bought one for $100 and whamo we seem to have a fix. Going to drive it around on a good long cruise and make sure but drive for about 30 minutes tonight and nothing. Runs strong.
So I want to be a guy that finishes up and posts fixes to elusive problems. My buddy called his guy at gm and they suggested the PCM. I figured what could it hurt and bought one for $100 and whamo we seem to have a fix. Going to drive it around on a good long cruise and make sure but drive for about 30 minutes tonight and nothing. Runs strong.
