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Chevrolet Tahoe Misfire

11 messages,  Last post on Nov 09, 2009 at 8:53 AM

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#2 of 11 Re: #4 Missfire under load all new plugs/wires and inj. [rmkak] by auditech2005 Mar 03, 2009 (10:10 pm)
Replying to: rmkak (Mar 02, 2009 11:31 am) O.K. I feal your pain I have a 99 5.7 tahoe 4x4 with the same exact issue only the misfire is sometimes on cyl 3, I bought my tahoe in 2003 from a dealer and they tried to do everything, it was hard to duplicate so I understood why it was so hard to fix it (which they never did), I am a certified Audi technician so I know how to diagnos and work on cars but this is a tuff one, long story short I think my Tahoe is finaly fixed, this weekend my Tahoe broke doen in L.A. during a little road trip, the fuel pump went out, I asked the mechanic if that might have been my misfire concern under load and he said he would bet on it, he said those fuel pumps are very sensitive. I researched this topic months ago and all I found were a bunch of a--holes who think they know everything and none of which helped me, I received my Tahoe back on Monday. I have driven it about 300 miles since (some of which was up long hills under load) and have had no issues, and my Tahoe feals a little stronger than it ever has, I think this is the fix, if my problem comes back I will update this forum, sorry this is so long I just thought you might want to know, take care and good luck. Oh I don't know if it matters but I currently have 81000 miles on it and the first time I had the issue was at 44000. Good luck. Replies to this message: kiawah (Mar 04, 2009 5:30 am) rmkak (Mar 04, 2009 8:28 am)
#3 of 11 Re: #4 Missfire under load all new plugs/wires and inj. [auditech2005] by kiawah Mar 04, 2009 (5:30 am)
Replying to: auditech2005 (Mar 03, 2009 10:10 pm) You'd think if you had a fuel pump problem, that it would have an effect on randomn cylinders as opposed to always just one cylinder, wouldn't you? Certainly a miss under load can be a symptom due to fuel supply problem, just hard to imagine that it's always the same cylinder that gets starved. Hope the pump really does fix your problem, but it wouldn't surprise me if it's a head gasket, intake gasket, or some sort of problem like a defect in the head on that cylinder. Replies to this message: rmkak (Mar 04, 2009 8:28 am)
#4 of 11 Re: #4 Missfire under load all new plugs/wires and inj. [kiawah] by rmkak Mar 04, 2009 (8:28 am)
Replying to: kiawah (Mar 04, 2009 5:30 am) The scan tool I used did show a few miss fires on the other cylinders during different times but just a couple compared to the thousands on #4 pulling a hill. Next I think I may change the egr and check the fuel pressure and also try un hooking the cat just for some more ez eliminations before I pull the head and look for a sunk valve or a bad intake or head gasket maybe even a flat cam. I will let you know what I find.
#5 of 11 99 Suburban slight miss at Idle by danel2 Apr 25, 2009 (12:17 pm)
My 99 Surburban misses at Idle sometimes. changed wires, plugs twice, cap and rotor. but still does it. any Ideas? Replies to this message: dbrown6 (Aug 24, 2009 7:37 pm) kiawah (Aug 24, 2009 7:52 pm) arrie (Aug 25, 2009 8:33 am)
#6 of 11 Re: 99 Suburban slight miss at Idle [danel2] by dbrown6 Aug 24, 2009 (7:37 pm)
Replying to: danel2 (Apr 25, 2009 12:17 pm) I have a 98 with 205k miles. I've had the intermittant and #4 show frequently. I have replaced the plugs, wires, cap, rotor, o2 sensors (contemplating Cat converters). Most recently the engine showed signs of clogged cats, but bought a couple bottles of Sea-Foam, one in the tank with 1/2 tank showing and the other through the brake booster. Runs great now! But, when the engine gets warm on a hot day, it starts the misfire routine. Appears to be heat related as it will run well all winter. This has been going on for years. I have ignored the check engine light for the past 5 years with regard to O2, cat and ignition issues and only recently started paying attention when the transmission finally gave out. If I had a bad valve, I would think the power thing would be bad all the time, but I did put in 1 yr parts rather than premium or Delco parts which may make a difference.... I like my Suburban too much to let it go down like this, but what could it be? Replies to this message: kiawah (Aug 24, 2009 7:52 pm) arrie (Aug 25, 2009 8:33 am)
#7 of 11 Re: 99 Suburban slight miss at Idle [dbrown6] by kiawah Aug 24, 2009 (7:52 pm)
Replying to: dbrown6 (Aug 24, 2009 7:37 pm) Have you thought about a bad intake manifold gasket?
#8 of 11 Re: 99 Suburban slight miss at Idle [dbrown6] by arrie Aug 25, 2009 (8:33 am)
Replying to: dbrown6 (Aug 24, 2009 7:37 pm) I do not know where crank shaft position sensor is located on a '98 model but if it is the same way as on my '04 tahoe I would have a look at it. In my car crank shaft position sensor is mounted at the side of the engine block at rear of the engine as it reads teeth on a wheel mounted in the back end of crank shaft. The sensor gets very hot as it gets hot engine oil thrown on it and this could make sensor heat sensible, i.e. when it is colder outside the oil pan helps cool engine oil down while on hot days this cooling effect is less.   I changed my crank shaft sensor once and it did improve idle "jerking" but did not completely fix it though.   If your sensor is mounted in the front of the engine and reads teeth on a belt pulley like I have seen on some other cars then your issue probably is not with the crank shaft position sensor.   Another very easy thing to try: Again, I don't know if you have the aluminum heat shields around spark plug boots like my Tahoe did but if you do remove those and drive around a few miles and see if it helps. The shields caused quite bad spark leak to engine ground in my Tahoe and I fixed this by replacing spark plug wires with racing wire set that does not require use of the heat shields. I bought Taylor wire set for $75, which is about the same price as dealer asks for the set of garbage they use, which you can get for $25 at car part stores.   Arrie
#9 of 11 Re: #4 Missfire under load all new plugs/wires and inj. [rmkak] by dave778 Nov 01, 2009 (4:36 pm)
Replying to: rmkak (Mar 02, 2009 11:31 am) you could need a new computer they have bin known to get a glitch which will efect any thing on it aND OR THE FUEL PUMP IS WEEK
#10 of 11 1997 Silverado 5.7L missing and rough idle by kkrause44 Nov 03, 2009 (8:52 am)
hey guys, I have been reading the threads and it seems like there is some knowledge here, so this is my issue. 97 chevy silverado, 5.7L I have had a rough idle here for the last year ever since I had the intake manifold gasket replaced by a mechanic because it was leaking coolant into my oil. Have also had a stumble when taking off, seems like the truck misses right once i press on the gas and then drives just fine. Just lately it has started to throw P0131 codes (O2 sensor, bank 1, pre cat). I replaced the sensor, bosch, not the universal one, no change. It then threw a p0300 code and a p0305, with the blinking SES light when driving at 25-30 mph, missing pretty badly. Looked at the plug (#5), it was black and sooty, so i swapped the cyl 5 plug with the cyl 1 plug just to see if it was the plug. Sure enough, next code was a p0301! I replaced the spark plugs with the autolite platinums, after reading other posts i now know i should have done the acdelco, but its too late now. By the time I changed all of the plugs, which was one week after I swapped them, the driver side bank of plugs (1,3,5,7) were all black and sooty while the passenger side plugs were completely normal looking. With new plugs for a week, i checked them again and sure enough, driver side plugs are sooty, passenger side are normal. Still having the rough idle and random misses, usually right on takeoff. It doesn't make sense to me that the O2 sensor giving the code is on the opposite side of the engine that I am having issues with the spark plugs being sooty, which i am presuming is a rich condition. I checked the fuel pressure at the engine and it goes to 63 psi with a turn of the key, after 2 seconds when the pump shuts off the pressure immediately jumps down to 55 psi within a second, and then bleeds down to 30 psi within 3 minutes. When it is running, fuel pressure stays constant at 54 psi, but again once when shut off it bleeds off down to 30 psi. I have read that the fuel pressure needs to stay within 5 psi for 5 minutes or there is a leaky injector or a fuel pump check valve. I am on a budget here in michigan and enjoy working on it, but don't enjoy burning money on parts that don't need to be changed. I read the post about paying for quality parts and agree 100%, have been burned too many times by reman/cheap parts. I am thinking about swapping the injector pack for the mpfi upgrade, but is there any additional diagnosis i can do to pinpoint it further? Have a new fuel filter and had a dealer do their fuel injection system cleaning right after the intake manifold was changed when they also reset the timing. However since then I have played with the timing trying to get it to stop missing after the dealer adjusted it. My dad has a scan tool that gives real time readings on all of the engine vitals, (fuel trim, o2 sensor readings, etc.) is that what i would need to set the timing? Have sprayed starting fluid around intake (while engine is cold) while running, no changes in idle. Thanks for all of your time, advice, and help on reading this long post, i just wanted to give a good background.
#11 of 11 Wow! This has been very, very ugly and painful by mcgyver2k Nov 09, 2009 (8:53 am)
My 99 Tahoe with 5.7 Liter Vortec has had the same problem (rough idle at low RPM only when warmed up) for the last few months.       I've done a full tune-up, replaced the fuel filter, cleaned the fuel injectors, replaced O2 sensors, replaced the passenger side catalytic converter (clogged), tested for leaky intake and a few days ago my fuel pump just went out on me so that's new as well. I've taken it to three shops (it's currently in the third shop). I'm pretty good with cars but this one has me at a loss.       It WAS stored for 3 years in my Dads barn while I was in Iraq and Europe but he started it once a week for me and this problem didn't start until I had put about a thousand miles on it after getting it out of my Dads barn.         I'm getting the random misfire code. It went away after changing the O2 sensors then reappeared. It also went away after replacing the fuel pump but now is back. I'm getting monster amounts of carbon build up on bank 2 (passenger side).   Please, if anyone has truly solved this exact problem let me know what it took?   Thanks,

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