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Showing results for tags 'misfire'.
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I have been having trouble with my truck, 5.7L, running properly at low speeds. When I go to start the vehicle sometimes it will take 2-3 cranks before it will start but not always. When I accelerate from a stop it will shudder on take off but then level off. I notice it the most while I am accelerating and turning a corner but that may just be coincidence. Also while I'm driving at a low speed in town I can feel it fluctuating in speed slightly but on the highway it seems to be fine. The only major repair I had done to the truck was I replaced the intake gasket. The only thing that was different after that was every once in a while when I started it I would get a grinding on the starter as if the starter didn't release after the engine started. I figured this was a result of the timing being slightly out of spec. I recently had in to the Chevy dealership, the first time it was reading a misfire so they cleaned the spark plugs and said to try that, $50. The next time was a day later because it started doing the same things it was when I brought it in no more then 2 miles after I left the dealership. This time they re-timed it and put a new distributor cap and rotor on, $300. It ran great for a few days then I started to notice the same symptoms. It is not as bad as it was before I took it in but it is getting more noticeable. I also still get a slight grind on the started every once in a while when I start the engine. Items I have changed recently: Fuel Pump(10 months ago) Fuel Filter EGR Valve PCV Valve Cam Position Sensor Crank Position Sensor Throttle Position Sensor -
2004 Chevy Silverado 5.3 Bad Intermittent Misfire
MichaelAllen31 posted a question in Ask the GM Technician
Hello everyone, I've got an issue that's been bugging me for the past month and a half or so, and would like to get some help figuring it out. This happened out of nowhere, just backing into my spot at school. I felt my truck starting to shake, and smelled a lot of fuel in the exhaust, and i didn't think anything of it. Anyways, i got in my truck, started it up, and i could feel it shaking and lurching at idle at first, then i'd bring it to a stop and it would almost stall. I got it home, and thought it had sprung a huge exhaust leak somewhere, that wasnt it. It would hesitate only at idle, with check engine light, (Sometimes Blinking) And i was stumped when i'd take it down the road at hard throttle and it wouldnt misfire at all at first. Me and my dad replaced the spark plugs and wires about 2 weeks after this started, didnt fix it, but bank one was extremely black, and bank two almost looked lean. I did the injector test with a screwdriver to listen to the ticking, all seem to be working fine. Now, i just unplugged the battery for about an hour, took it down the road, and it made the same bang that it did to start the whole problem, and it ran perfectly fine for less than an hour afterwards. I parked it, came back out to start it, and the battery was dead (My fault), but got a jumper hooked on it and it started right up, running like trash, that was just tonight. Since we changed the sparkplugs, its been misfiring all the time, and the check engine light has gone away. It used to average about 18 mpg, now maybe 9-10 mpg. The check engine light was blinking the whole time i drove it after the battery died, and im stumped of what may be wrong. I need to have the codes read, but Napa wasnt helpful with that, and our local Autovalue is almost never open, and im not sure if they would read the code for us. Im thinking it might be an o2 sensor on bank one, but cant discern why the truck runs fine sometimes, then runs like garbage other times. It does have a nasty hesitation when taking off from a stop, and it chugs when off the brakes and just idling along. I ran an entire bottle of fuel injector cleaner through the truck with about 1/4 tank, and it didnt seem to help, but it changed what the exhaust smelled like. Any help would be appreciated as to what might have gone bad, or wrong, thanks in advance! If you need any more info, just let me know. -
Yesterday on the way to work my 2000 Chevrolet Silverado 1500 4WD with the 4.8L V8 Vortec engine started flashing a check engine light. I read it and it was a P0300 Random/Multiple Misfire. I had experienced a slightly rough idle previously (nothing serious) and had been unable to track it down. I replaced the PCV valve as a course of standard maintenance and it seemed to help get the idle back down, but still slightly rough. I also replaced the spark plugs and plug wires, and replaced the alternator on warranty for an unrelated issue. After I got the check engine light, I started doing some more diagnosis with a bluetooth-OBDII reader which is when I found that I had misfires only on cylinders 2, 5, 6, and 8. Since it was on separate banks, I could find no commonality of items to replace, so I tried the following things. replaced coil pack in cylinder 2 because it had the highest misfire count, no effect replaced the EGR valve, also with no effect. did the carb test to look for vacuum leaks in a few places on the intake manifold with no results unplugged to MAF to see if the idle improved and it did not (although I didn't try a load test with the unplugged MAF.) So I guess I'm stuck and about ready to give up on this one and take it to my mechanic, but I was wondering if there was something else I should try or if anyone has any thoughts. Side note: I only see the misfires at high RPMs (>1500), so could I drive it home if I take it very slowly and rarely open the throttle? -
I'm in need of some serious help: So I've had a heck of a time trying to get my 03 Envoy to run properly. I've been experiencing a misfire, when it gets to about 80 km/h and 1500-2000 rpm's the misfire is pretty bad until I accelerate over 2000 rpm and then it runs fine until I fall under 2000 rpm again. I brought the envoy to a shop and they said it was some pedal sensor or something which I paid $300 for the part and labour to have it replaced. Nevertheless the problem didn't go away. I ended up thinking it might be the spark plugs because they hadn't been changed since I've owned the vehicle. I replaced three of them (cylinders 2,3,4). The threads of the old ones were covered with oil and looked terrible. I had to go somewhere so I planned to do the other three the next day. After installing the 3 the envoy ran better and still had a misfire but not as bad. The next day I installed the other three, one of the plugs had the insulation casing cracked on it. I only realized after pulling the plug out. I looked into the hole and saw the little missing piece sitting over the plug hole. I vacuumed the piece out and I'm pretty sure I got it out. I heard it go through the central vac hose but I couldn't find it in the central vac tank so I don't know what happened. Once I installed those three plugs (cylinders 1,5,6) I started up the envoy and it was bad. It was making a very loud knocking sound and I immediately turned it off thinking I didn't want to do any damage. I tried to start it after that and it wouldn't turn over. Today I turned it to use an OBD II scanner and it started up but still had the very loud knocking. The scanner said there was a misfire in cylinders 4,5, AND 6. I'm completely lost as to why all three would show a misfire considering 5 and 6 at a different time as 4 and the spark plugs are all the same. I realized tonight after pulling out one of the new spark plugs I got that they are different from the original. The thread is about 1/4" longer and the overall spark plug is 1/4" longer. I looked online and it says this is the right spark plug and the parts store is the one who gave it to me so I'm not sure if this is normal or what. The old spark plugs were AC Delco 41-981 and the new ones I got are Champion 7437. If anyone knows of what could be the problem please let me know. I would greatly appreciate it. I just wanted to fix a misfire and thought changing the spark plugs could do no harm but clearly not. Thanks -
My truck's check engine light came on so i had a local mechanic shot diagnose it. They told be Cylinder #4 was missing a lot and something about that being just at idle rpms. And cylinder #3 was missing a tad to. Anyone have any idea what it could be? valve maybe? idk.. And i already checked basic stuff like plug and wires.. HELP! -
My truck's check engine light came on so i had a local mechanic shot diagnose it. They told be Cylinder #4 was missing a lot and something about that being just at idle rpms. And cylinder #3 was missing a tad to. Anyone have any idea what it could be? valve maybe? idk.. And i already checked basic stuff like plug and wires.. HELP!
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Hey guys, I'm new to the forum and am in desperate need of help. In the past two weeks my truck has been low on power, my fuel economy sucks, and it feels like its hesitating or misfiring. I've already replaced spark plugs, my cap and rotor, coil, and coolant temperature sensor and nothing has fixed this misfire/hesitation. When I took the plugs out a few of them had a white/grey build up that I've never seen before and I figured that had to be it but it wasn't. Do I need a distributor next? I also recently put in a new fuel pump and filter so that's not the problem. Help me out guys, if yall need anymore info just ask! Thanks!
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I recently replaced the cap, rotor, spark plugs, and crankshaft position sensor on my 1999 tahoe (police) and it runs great! But... when I'm driving up slight inclines giving it about 1/4 to 1/3 acceleration, it starts to misfire and run really rough. It goes away immediately if i gas it and it downshifts,or if i let off the gas a little.. does anybody have any advice on how to fix it? Its a 5.7 4x4. I didn't reset any codes or anything when i changed the crank position sensor and i don't have any check engine lighht on (even when it misfires). -
This is my first post so I am not sure if this is where I need to be posting this but here goes anyways. Bought 1999 Silverado 5.3 used last year everything worked great, just some minor issues that I fixed on my own (brakes, rotors, brake lines). I am no mechanic, just a guy with a garage and a few tools I would like to add. Currently it has 225,xxx miles on it and is my daily driver. Here are the problems I have had in the past few weeks. Idles rough, worse when engine is cold but otherwise always there. Misfires slightly only when under a load but ses does flash, only flashes after the engine is on and in drive at same exact time every morning and only once in a while in the afternoon. SES light was on so I had it checked pulled up misfire on cylinder 7 and p0300 code as well as the code for the EVAP and passenger side o2 sensor. This is what I have done so far, Replaced Fuel pump, fuel filter, fuel pressure regulator, all spark plugs, all plug wires, #7 cylinder coil pack, local mechanic replaced a part on top of the engine towards the front, it has a connector running to it, not sure what it is or called. Ran lucas injector cleaner thru it, and seaform also, no change. Cleaned the MAF sensor, retightened all my vacuum hoses and done a self vacuum leak test while engine was running, no change in idle and the misfire is still there. Also my temp gauge is running above normal but not overheating either when I have my a/c on or a/c off and drive for more than 45 min straight, unless it is in the morning when the air is cooler outside then the temp stays normal. Its NOT leaking antifreeze or oil. replaced thermostat twice, not sure why. What do I do next? Sorry for the long post but im sure I also forgot to mention something. If I think of it I will repost.
