Missfire under hard acceleration? Please help???
04-19-2006, 10:09 AM
#1
Missfire under hard acceleration? Please help??? I did a cam swap and valve springs, push rods, timing chain ect. in March. Car was running fine. Ran about 3 tanks of gas. The other day it sounded like I blew up the motor. It backfired and shut off at around 4000 RPMs Started back up and drove ok untill I hamer down and it backfires and sputters and shuts off sometimes. I have no SES lights. So I am assuming it is a misfire. I checked all the plug wires, valve terain, 4 of the spark plugs, (they were just changed 1000 milse ago). Every thing looks ok. Could I have a bad coil pack or fuel injecter? If so shouldnt I get a SES light? How do you check a coil pack or fuel injector? What the hell is wrong with this car? Please help.
04-20-2006, 01:37 AM
#5
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I was having the same problem last week. I changed the plugs and wires, and now everyhting works great. I found one broken plug, and one torn wire. Mine did throw a code, but only a misfire code.
04-20-2006, 01:45 AM
#6
Sounds like you might want to get someone to log the data when you are running WOT like that. That will definitely show you what is happening. Is this thing pretty much stock minus the cam? That was how I solved a problem similar to this. It was an Oxygen issue though, so it is hard to say what is happening if you have checked everything. I would get it tuned if you havent already and figure out your A/F ratio. You might be leaning that bitch out everytime you jump on it.
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04-20-2006, 08:53 AM
#8
Car has SLP headers and y pipe, MAF, lid, and custom tune by Texas speed. Cam is 228,228 on 112LSA. Cheap Flowmaster exhaust. I aslo get codes for the front 02 sensors the rears are deleted. Thanks for all the input so far. Do mass air flow sensors go bad? Is there a way to test them??
04-26-2006, 09:30 PM
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I gotta agree with the guys above....start with the low-level stuff....cracked plug, loose plug wire, bad coil pack, etc. Spark plug insulator faults can be so minute, you can't visually detect them. Plugs are just about 100% perfect these days, and since yours have only 1K on them, I'd find it hard to believe you had a bad one....BUT, even if you buy a new set of plugs, and the car still doesn't run right, you're not out that much money, and you've cheaply eliminated a problem area. If all the basic, low-level stuff checks out,
Check these out:
MAF wires....the bare ones running through the ID of the MAF...they should be squeaky-clean...oil, grease, dirt, or any kind of crud on the wires will cause the MAF to send bogus air flow values to the PCM. This will cause inaccurate fuel delivery. Your 02 sensors just monitor free oxygen in the exhaust....the free oxygen values then signal the PCM to richen or lean the mixture. You can try checking these, but from the way you describe the problem, it sounds more like an ignition/timing thing to me, than an air/fuel delivery problem, although at some point, all of these values (mixture, fuel delivery, timing/ignition) reference each other in the PCM's look up tables.
Crank position sensor...if this is malfunctioning, it will not consistently sense the crank location in relation to each individual cylinder, causing the PCM to fail to provide precise spark & fuel delivery. Less likely, but maybe possible is the cam sensor. I gotta believe, though, that if either one of these sensors were malfunctioning, you'd set some kind of code, especially if it were the cam sensor...one of the main functions of the cam sensor is to detect misfires, which you think would set a code. But I could be wrong.
Right now, the only other sensor I can think of that has anything to do with timing/fueling curves, is the Intake Air Temperature Sensor.
Other than that, all I can think of (assuming all your plugs, wires, and coil packs are okay) is a dirty/plugged fuel injector, or a bad MAP sensor. To control injector pulse width, the PCM has to "know" the base pulse width, which it finds in a look up table. Base pulse width is a function of RPM, and load. Load is calculated via the MAP sensor, so I guess it wouldn't hurt anything to look there, too.
You didn't happen to have any PCM tuning done after your cam swap, did you?
Check these out:
MAF wires....the bare ones running through the ID of the MAF...they should be squeaky-clean...oil, grease, dirt, or any kind of crud on the wires will cause the MAF to send bogus air flow values to the PCM. This will cause inaccurate fuel delivery. Your 02 sensors just monitor free oxygen in the exhaust....the free oxygen values then signal the PCM to richen or lean the mixture. You can try checking these, but from the way you describe the problem, it sounds more like an ignition/timing thing to me, than an air/fuel delivery problem, although at some point, all of these values (mixture, fuel delivery, timing/ignition) reference each other in the PCM's look up tables.
Crank position sensor...if this is malfunctioning, it will not consistently sense the crank location in relation to each individual cylinder, causing the PCM to fail to provide precise spark & fuel delivery. Less likely, but maybe possible is the cam sensor. I gotta believe, though, that if either one of these sensors were malfunctioning, you'd set some kind of code, especially if it were the cam sensor...one of the main functions of the cam sensor is to detect misfires, which you think would set a code. But I could be wrong.
Right now, the only other sensor I can think of that has anything to do with timing/fueling curves, is the Intake Air Temperature Sensor.
Other than that, all I can think of (assuming all your plugs, wires, and coil packs are okay) is a dirty/plugged fuel injector, or a bad MAP sensor. To control injector pulse width, the PCM has to "know" the base pulse width, which it finds in a look up table. Base pulse width is a function of RPM, and load. Load is calculated via the MAP sensor, so I guess it wouldn't hurt anything to look there, too.
You didn't happen to have any PCM tuning done after your cam swap, did you?
