tracking down a intermittent cylinder miss, or a miss at a certain rpm range problem is ALWAYS a P.I.T.A.
you can always isolate the issue by breaking it down into , remember to logically look at the indications, or symptoms
example , if a miss only happens in third and fourth gear but your fine in the lower gears at the same rpms thats sometimes an indication your fuel pressure and volume is not keeping up with demand.
if a miss happens only after the engine heats up, it could indicate a electrical circuit failing as it heats-up
The ignition control module in the distributor is another item that normally fails when hot, that needs to be replaced is you suspect its defective
but you won,t be able to tell much without testing, drop back to the basics,and don,t assume anything, test and verify.
theres a bunch of good informative links and easily dozens of sub links in each link, it might take a few hours of reading and time spent testing, and reading a shop manual, and looking thru trouble codes. but you can locate your problem with logical testing
IGNITION,FUEL,MECHANICAL,EXHAUST BACK PRESSURE, and sensor or control failures
Id suggest you start by pulling trouble codes and isolate the cause thru a few tests,check fuses, verify your engine grounds, etc. a shop manual will be very helpful , tools like noid lights to test injector connectors and verifying your sensors are working correctly will help
GUYS I NEVER SAID I,M A GREAT MECHANIC, BUT I HAVE LEARNED THAT IF YOU TAKE THE TIME TO BREAK THINGS DOWN INTO THE SIMPLEST PART AND DO A BIT OF RESEARCH, FINDING ANSWERS IS FAR LESS INTIMIDATING OR DIFFICULT
like the old saying how do you eat an elephant ?......one little bite at a time!
all the answers are readily available, theres known testing procedures and listed test results you can expect, and procedures listed in the shop manual for isolating and testing components, you don,t need to be a genius, you just need to be logical and persistent and not afraid to learn new things while getting your hands dirty at times
and posting clear pictures of each spark plug labeled as to its cylinder number,
doing a vacuum leak test,do a fuel rail pressure test
do a compression test getting the compression number from each cylinder
check voltage on the coil input lead and alternator
http://www.helminc.com/helm
http://www.harborfreight.com/5-in-1-dig ... 98674.html
so you need to find the cause thru testing and correct it.
you'll need to isolate it to,the individual cause and if you have a non-stock cam installed it could easily be indexed wrong or you may need to change the cars rear gear ratio,compression ratio, ignition advance or timing,or converter,stall speed to use the more radical cam
MECHANICAL--things like worn cam lobes , badly adjusted valves ,vacuum leaks, rusty distributor advance weights and springs,
FUEL DELIVERY-- things like clogged fuel filter or defective fuel pump, bad fuel pressure regulator, wrong power valve or jets, defective fuel pumps and accelerator pumps in carbs
IGNITION-- things like incorrectly set,timing advance curve or bad wiring , old spark plugs , burnt ignition wire, the wrong plug gap, cracked distributor caps etc.
the basic tools youll need, are common mechanic hand tools plus....
the correct matching SHOP MANUAL
TIMING LIGHT
IR TEMP GUN
VACUUM GAUGE
MULTI METER
FUEL PRESSURE GAUGE
COMPRESSION TEST GAUGE
http://www.professionalequipment.com/ex ... ermometer/
Wide temperature range from -58 to 1832°F (-50 to 1000°C)
https://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html
https://www.jegs.com/i/JEGS/555/W89...MIoLGlpLnz3gIVDFYNCh36aAK4EAQYAiABEgKTIvD_BwE
BACK PRESSURE IN EXHAUST
viewtopic.php?f=56&t=495
you can,t rule out anything yet, it might be as simple as water in the fuel or a bad ground, or a bad electrical connector or defective sensor,it can be something major like the computer controls, the ECU,the connectors or the sensors or something minor like a bad ground, but it can be something really difficult to locate, that only happens when two different things happen at the same time, I had a miss like that once that was caused by a carb that only malfunctioned on hot days if I hit the brakes real hard, I only located the cause after rebuilding the carb, AND finding a vacuum leak in the brake booster, I won,t get into details , but crud in a carb and intermittent vacuum can mess with your mind when your low on experience and only about 20 years old, todays real time data logging scan tools make this far less of a guessing game, try to determine if its ignition or fuel related as that narrows the suspected source of the problemmost larger dealerships have diagnostic computers that can test your CPU,
and that cars old enough that some local salvage yards can probably supply a replacement, very reasonably, that you can use to test/replace your current cpu, but before Id go that route ID try to find and use a real time data logger and cable to use to isolate the exact cause
the action ID suggest is to beg,borrow, buy, a scanner that puts out real time data logs, and have the wife or a buddy drive while YOU watch the data on a LAP TOP , or have a dealer do it for you
https://www.scantool.net/obdlink-sx/#customer-reviews
http://www.auterraweb.com/dynoscan.html
http://www.mercedesmanuals.com/Live_Data_OBD2_Deluxe_Automotive_CAN_BUS_Code_Scan_p/u581.htm
http://www.obd-2.com/
http://www.moates.net/product_info.php? ... ucts_id=54
http://tunertools.com/proddetail.asp?pr ... CMSCAN-KEY
http://www.scantool.net/
http://tunertools.com/proddetail.asp?pr ... ata-Logger
http://www.innovationhouse.com/products ... _tool.html
http://www.moates.net/aldu1-and-cabl1-xtremealdl-and-newcabl1-combo-p-127.html?cPath=49
you can always isolate the issue by breaking it down into , remember to logically look at the indications, or symptoms
example , if a miss only happens in third and fourth gear but your fine in the lower gears at the same rpms thats sometimes an indication your fuel pressure and volume is not keeping up with demand.
if a miss happens only after the engine heats up, it could indicate a electrical circuit failing as it heats-up
The ignition control module in the distributor is another item that normally fails when hot, that needs to be replaced is you suspect its defective
but you won,t be able to tell much without testing, drop back to the basics,and don,t assume anything, test and verify.
theres a bunch of good informative links and easily dozens of sub links in each link, it might take a few hours of reading and time spent testing, and reading a shop manual, and looking thru trouble codes. but you can locate your problem with logical testing
IGNITION,FUEL,MECHANICAL,EXHAUST BACK PRESSURE, and sensor or control failures
Id suggest you start by pulling trouble codes and isolate the cause thru a few tests,check fuses, verify your engine grounds, etc. a shop manual will be very helpful , tools like noid lights to test injector connectors and verifying your sensors are working correctly will help
GUYS I NEVER SAID I,M A GREAT MECHANIC, BUT I HAVE LEARNED THAT IF YOU TAKE THE TIME TO BREAK THINGS DOWN INTO THE SIMPLEST PART AND DO A BIT OF RESEARCH, FINDING ANSWERS IS FAR LESS INTIMIDATING OR DIFFICULT
like the old saying how do you eat an elephant ?......one little bite at a time!
all the answers are readily available, theres known testing procedures and listed test results you can expect, and procedures listed in the shop manual for isolating and testing components, you don,t need to be a genius, you just need to be logical and persistent and not afraid to learn new things while getting your hands dirty at times
and posting clear pictures of each spark plug labeled as to its cylinder number,
doing a vacuum leak test,do a fuel rail pressure test
do a compression test getting the compression number from each cylinder
check voltage on the coil input lead and alternator
http://www.helminc.com/helm
http://www.harborfreight.com/5-in-1-dig ... 98674.html
so you need to find the cause thru testing and correct it.
you'll need to isolate it to,the individual cause and if you have a non-stock cam installed it could easily be indexed wrong or you may need to change the cars rear gear ratio,compression ratio, ignition advance or timing,or converter,stall speed to use the more radical cam
MECHANICAL--things like worn cam lobes , badly adjusted valves ,vacuum leaks, rusty distributor advance weights and springs,
FUEL DELIVERY-- things like clogged fuel filter or defective fuel pump, bad fuel pressure regulator, wrong power valve or jets, defective fuel pumps and accelerator pumps in carbs
IGNITION-- things like incorrectly set,timing advance curve or bad wiring , old spark plugs , burnt ignition wire, the wrong plug gap, cracked distributor caps etc.
the basic tools youll need, are common mechanic hand tools plus....
the correct matching SHOP MANUAL
TIMING LIGHT
IR TEMP GUN
VACUUM GAUGE
MULTI METER
FUEL PRESSURE GAUGE
COMPRESSION TEST GAUGE
http://www.professionalequipment.com/ex ... ermometer/
Wide temperature range from -58 to 1832°F (-50 to 1000°C)
https://www.harborfreight.com/11-piece-noid-light-and-iac-tester-set-97959.html
https://www.jegs.com/i/JEGS/555/W89...MIoLGlpLnz3gIVDFYNCh36aAK4EAQYAiABEgKTIvD_BwE
BACK PRESSURE IN EXHAUST
viewtopic.php?f=56&t=495
you can,t rule out anything yet, it might be as simple as water in the fuel or a bad ground, or a bad electrical connector or defective sensor,it can be something major like the computer controls, the ECU,the connectors or the sensors or something minor like a bad ground, but it can be something really difficult to locate, that only happens when two different things happen at the same time, I had a miss like that once that was caused by a carb that only malfunctioned on hot days if I hit the brakes real hard, I only located the cause after rebuilding the carb, AND finding a vacuum leak in the brake booster, I won,t get into details , but crud in a carb and intermittent vacuum can mess with your mind when your low on experience and only about 20 years old, todays real time data logging scan tools make this far less of a guessing game, try to determine if its ignition or fuel related as that narrows the suspected source of the problemmost larger dealerships have diagnostic computers that can test your CPU,
and that cars old enough that some local salvage yards can probably supply a replacement, very reasonably, that you can use to test/replace your current cpu, but before Id go that route ID try to find and use a real time data logger and cable to use to isolate the exact cause
the action ID suggest is to beg,borrow, buy, a scanner that puts out real time data logs, and have the wife or a buddy drive while YOU watch the data on a LAP TOP , or have a dealer do it for you
https://www.scantool.net/obdlink-sx/#customer-reviews
http://www.auterraweb.com/dynoscan.html
http://www.mercedesmanuals.com/Live_Data_OBD2_Deluxe_Automotive_CAN_BUS_Code_Scan_p/u581.htm
http://www.obd-2.com/
http://www.moates.net/product_info.php? ... ucts_id=54
http://tunertools.com/proddetail.asp?pr ... CMSCAN-KEY
http://www.scantool.net/
http://tunertools.com/proddetail.asp?pr ... ata-Logger
http://www.innovationhouse.com/products ... _tool.html
http://www.moates.net/aldu1-and-cabl1-xtremealdl-and-newcabl1-combo-p-127.html?cPath=49
Last edited by a moderator:
