C1500 Misfire When Hot
October 28th, 2016, 3:27 PM
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C1500 Misfire When Hot
Hi all! I could really use y'all's help with a misfire issue I've been having. I've scour everywhere online (including here) and I can't figure out an answer.
Okay, here's my problem. Everyday, I start my truck up and head to work. When it first starts in the day, it runs fine. Purrs like a kitten. But after about fifteen minutes of driving, I start getting a random misfire CEO. I'm pretty sure it has something to do with the temperature, because it always starts right when the engine hits about 180 degrees. Everytime. Nothing overheats or anything, it just starts misfiring.
I've replaced the spark plugs, wires, distributor cap and rotor, and even the spider injector. Still have the issue. Does anyone have any idea where I could look next? Thanks for looking!!
Okay, here's my problem. Everyday, I start my truck up and head to work. When it first starts in the day, it runs fine. Purrs like a kitten. But after about fifteen minutes of driving, I start getting a random misfire CEO. I'm pretty sure it has something to do with the temperature, because it always starts right when the engine hits about 180 degrees. Everytime. Nothing overheats or anything, it just starts misfiring.
I've replaced the spark plugs, wires, distributor cap and rotor, and even the spider injector. Still have the issue. Does anyone have any idea where I could look next? Thanks for looking!!
November 3rd, 2016, 6:09 PM
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I have the same problem with my 99 4.8 liter first thing in the morning fires right up a runs like a top. My truck gives me problems after i shut the engine off. Its when i go to start it after it sits for about 15 min. I have to crank it over and over for it to start. Once it does start it runs horrible almost like theres water in the gas. Have you changed etc sensor? (Engine temp control)It sounds like maybe that could be ur problem.
November 30th, 2016, 10:05 AM
#3
ok #1 what you did is "throw parts at it until it's fixed", which is always more expensive and takes allot more time. put on your thinking cap and test each part of the system (air, fuel, spark, water, electrical grounds) until you find a definite problem THEN replace the part
be a little more specific. random misfire. how frequently? does the engine stumble? can you hear how frequently it misses a cyl and whether it's the same cyl that missing? (this would tell you if it's unrelated to spark)
background: usually air/fuel is adjusted by engine vacuum until/unless O2 sensors are active (note i assume you checked intake sytem for air leaks: battery, oil, water, air, fuel, spark in that order usually, dont skip battery check!). had you a vacuum leak when warm, that'd cause misfire. had you a bad "mass air fuel sensor" (adjusts air fuel by air effect on red hot wire not by vacuum pressure) that should show up early not after warming up.
what changes when hot? one (of many) things that can be hard to trace down is an O2 sensor. when the engine starts your in "cold mode" (ie maf sensor only). after O2 sensors warm up and begin giving the engine signal* the engine begins in feedback mode - it adjusts air fuel ratio according to what O2 reads as "result". (the engine computer now gets air before and air after to optimize ratio with). but dont replace O2 sensors until after you test it, like i said in #1.
unfortunately, there are other things. you really need to trace the problem to it's cause. is the misfire due to... "no spark / insuff. spark" or "fouling" or "lean or rich fuel adjustment" ? if you know which then you know which leg your on to trace back to (unless it's O2, which can be difficult to trace - so it's a good bet to measure it after checking battery for air intake leak)
so there's 2 things to try for "care misfires when hot". check for intake leak when warm (but this is not random per say), check O2 sensors when warm; O2 is also a likely suspect for "being random" - however many things are.
"air fuel spark"
_____________
* ie, test shows 0V-1V ac high freq when hot, you can measure just 1V when hot not the feq, but if you measure 0V after hot it's a bad sensor)
all the above is generic advice
be a little more specific. random misfire. how frequently? does the engine stumble? can you hear how frequently it misses a cyl and whether it's the same cyl that missing? (this would tell you if it's unrelated to spark)
background: usually air/fuel is adjusted by engine vacuum until/unless O2 sensors are active (note i assume you checked intake sytem for air leaks: battery, oil, water, air, fuel, spark in that order usually, dont skip battery check!). had you a vacuum leak when warm, that'd cause misfire. had you a bad "mass air fuel sensor" (adjusts air fuel by air effect on red hot wire not by vacuum pressure) that should show up early not after warming up.
what changes when hot? one (of many) things that can be hard to trace down is an O2 sensor. when the engine starts your in "cold mode" (ie maf sensor only). after O2 sensors warm up and begin giving the engine signal* the engine begins in feedback mode - it adjusts air fuel ratio according to what O2 reads as "result". (the engine computer now gets air before and air after to optimize ratio with). but dont replace O2 sensors until after you test it, like i said in #1.
unfortunately, there are other things. you really need to trace the problem to it's cause. is the misfire due to... "no spark / insuff. spark" or "fouling" or "lean or rich fuel adjustment" ? if you know which then you know which leg your on to trace back to (unless it's O2, which can be difficult to trace - so it's a good bet to measure it after checking battery for air intake leak)
so there's 2 things to try for "care misfires when hot". check for intake leak when warm (but this is not random per say), check O2 sensors when warm; O2 is also a likely suspect for "being random" - however many things are.
"air fuel spark"
_____________
* ie, test shows 0V-1V ac high freq when hot, you can measure just 1V when hot not the feq, but if you measure 0V after hot it's a bad sensor)
all the above is generic advice