Chevrolet Tahoe Misfire
I have a 99 tahoe with a 5.7 vortec that missfires on #4 cyl. under heavy load (pulling a hill) I have replaced the fuel filter, air filter, cap, rotor, plugs and wires no change I also replaced #4 injector no change. I have sprayed the intake looking for a vacum leak no leak detected. I also checked the compression it's good. Anyone have any ideas where to go from here I do have access to a tech 2. When it missfires bad I get a p300 random misfire code
Analyzing Ignition Misfires
Analyzing Ignition Misfires
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.
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.
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.
:confuse: 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?
I have a 99 tahoe. It has the 5.7L 8cyl engine and is 4X4. I have had problems with it misfiring under load. It seems to only happen when going up a steep hill. When I give it gas and reaches about 50mph, it vibrates. Then, when I slow down to a stop, it bucks like it's going to stall, but then it smooths right out. It was throwing the PO300 code (I had it scanned and am aware that this is a misfire code for all of the cylinders). I had the fuel pump replaced, intake manifold gasket replaced, the valve cover gasket replaced, new wires and plugs, new cap and rotor, fuel injectors cleaned, new fuel filter, checked for vacuum leaks, checked for electrical shorts, and had the timing checked. Still have the same problem. Any ideas???????? Other then the misfire under load, everything else runs great!!!!! It idols smooth and the code resets itself and doesn't come back until I go up a hill! Please help. Thanks.
check the fuel pressure, and flow.
email me when you verify it [email protected]
New heads are about 1500 dollars and that's just for the parts so even if they "assisted" me the bill is more than what I am going to pay for a random misfire. I am only upset because I had this complaint while my vehicle was under warranty and they just threw parts at my Tahoe until my warranty expired. Live and learn, let me know what you fnd out though. I hoped this helped.
I now have the dreaded misfire code p0300 then p0306. Has 160k and always been sweet running until inspection time. The garage which I won't name, attempted to fix this problem. $1200 later only to receive an inspection sticker and the service light to return as I'm driving away, bummer. I've done every possible tuneup part twice also, 2 new highflow magnaflow cats, injector nozzle change#6, two out of the 4 new O2 sensors replaced. The rough idle appears 20 secs after first starting, blinks the service light and stays on. I can shut the truck off clear the codes and drive away, only to return the next time I start it up, same codes. Multi misfire and cyl 6, what do you do next, replace the remaining two o2 sensor. Is it worth it? I'm reading your posts and getting discouraged.
Ok, just put in 4 brand new O2 Sensors, 3 of them looked like caked on chalk. When started the first time, engine light blinked, misfire P306 and P507 Throttle position sensor. Cleared the code drove about 60 miles hasn't returned yet. I also haven't started it cold yet. I'm also running can after can of seafoam, I still think misfire in 6 has faulty fuel delivery, clogged injector? What do you think next? Grrrrrr!
Took it to my mech Mike Tieg, Tieg Automotive, Greenwood Mo. He had it three days and called me stating he thinks he figured it out, 99% confident, but it isn't cheap. He replaced the fuel distribution spider to the throttle body fuel injection under the intake. He was spot on!
Put another 100K on it and sold it earlier this month w/ 224K on it.
Loved my Tahoe for 10 years, now I love my Denali 6.2 L.
How do you guys clean your own injectors?
As far as I'm aware the CSFI 'spider' poppet injectors can't be cleaned without removal. This means the upper half of the intake manifold needs to be removed.
If you're going to that trouble....you'll do well to replace the whole injector setup with one of the 'mini' injector units. These are 'proper' injectors....not ball bearing valves at the end of hoses (poppets).
The other common issue with these trucks/SUV's is the distributor gear wears unevenly and gets 'knife-edged' on one side.
which all check out working correctly. I have an good scanner and it shows the upstream 02's working (Correctly I'm not sure of the parameters) I have even removed the upper plenuim to check that the new injectors were seated properly. The motor cost a little over 2k plus a new distributor and injector spyder and all filters and fluids and knock sensor and temp sensors and gaskets.
Thanks for the input and we will run with it, Any other thoughts let us know
I have a 97 chevy 1500 withh a 5.7 vortec. I started developing a misfire every once and a while. maybe every 3 0r 4 weeks to 6 weeks apart, Then started getting it everytime i accelerated a little more than usual or going up an incline for a decent amount of time. First of all changed the fuel filter to see if it was clogged, no help. Second the plugs and wires which have been changed 3 times currently with ac delco double platnum irridum. no help still have a missfire. Changed my distributor cap and rotor cap 2 times to make sure no cracks, still misfire after going down the road and accel to higher speed. Pulled off the upper intake expecting to find poppers in there but no, it had spider already installed, but guess what, I pulled it and put a new one in, making sure all injectors are in correct cylinders. Checked this 3 times before putting upper cover back on.Still misfire continues. Then the fuel pump goes out, how convienient. Replaced the entire assembly. still missfire continues. I replaced the ignition coil, no help. finally discusted after having the caty convertors checked and testing the 02 sensors which all checked out fine, I had a new distributor put in yesterday. took of from the shop and got 3 miles away and missfire on #5 has once again returned. NO vacume leaks and not bad compression. Idles great and starts perfect runs great until you accel too much or going up a hill or sometimes out of nowhere it starts in again. I have gone 2 to 3 days without it doing it off and on , but it comes back. Crankshaft sensor , camshaft sensor timing on dist, plugs all on the mark. what do you think about this one????? Contack me personally if you like at [email protected]
With 215K original owner miles, i’m actually okay with changing the engine out, but having spent big dollars in new fuel injector Spider, new distributor, plugs, wires, O2 sensors, cats, a new computer, all other items listed in this forum — and more, and a huge number of diagnostic labor hours, I’m still concerned this “gremlin” may not be solved even with a new engine! I understand the O2 sensors and fuel injector assembly are primary culprits and solved some folks’ problems, but for those that it did not help, did anyone ever resolve the persisting misfire problem? Did the bad injector problem ruin a valve over the years? stuck valve? could pulling the head and replacing to fix one damaged valve work, even though we all know if you pull one head we should go ahead and do both? could the bad fuel injector design have damaged a cylinder?
Thanks for any info you can share for those that didnthe Spider assy swap and other items suggested but the misfire persists. By the time i pull both heads, I bay as well replace the motor and have the “low end” all new. I let you all know what i find when i pull the head as that pesky cylinder 8 has been a bad gremlin for years now but we can’t surrender just yet as I can’t see spending big bucks for a new vehicle of this capacity or taking on someone else’s problems with a used vehicle. Thanks. Usually GM 350ci motors don’t present such mysteries!!
Curios, did you ever discover the problem?
Part No. 12530283
5.7L/350CI L31 LONG BLOCK CRATE ENGINE WITH VORTEC HEADS
It turns out that after a careful examination of cylinder 8 there was a tiny hairline crack that was allowing the slightest bit of moisture (from the water coolant pathway to get into the cylinder and cause the combustion chamber to not fully fire correctly. No way to have found that without tearing down the engine and rather than try and repair it, my decision was to install the new motor. Now i have a brand new motor and upgraded other peripherals while I was at it to where this truck will now outlast me. good luck and i hope others have success with the other less costly maintenance options articulated above, but it’s now no surprise none of those worked for me and i’m not sure this sort of thing would be able to be diagnosed as there was no evidence of water (rust, moisture) at the spark plug. live and learn.
sorry for other typos above:
*...what it took to address my MIS-FIRE and HAVE an engine where all cylinders are firing...”
glad to have the lower end all new as there were some oil leaks in front and rear seals and other issues that were on the “to do” list if i was going to commit to keeping this vehicle for the long run.