DragonSlayer

With 1000's of random misfires, it may be a coil......

LRB

It only happens under load, usally climbing a steep hill. I could go for weeks with no problem, but come a hill and the light starts to flash. My mechanic thought maybe a coil but did some checking on that. But when I have him replace the injectors I will check the coils too.

Thanks all!

99swatburb

So i am having the same problem with my 99 suburban 5.7L 4wd. But it does it intermittently instead of under load. It almost seems like a mass air flow sensor. What will happen is sometimes when I start it the engine will buck or knock and then start but the idle is rough between the 1000-2000 rpm mark. Sometimes it drives fine then will start to misfire and not accelerate and when i give it gas it sputters and almost sounds like a back fire in one of the cats. Then if I park it the idle will drop and almost stall and then go back to regular idle and do this over and over. I have about 198 thousand miles on it. Havent had a tune up and it is due for one and i plan on putting a new fuel filter on it. The fuel pump sounds fine but I dont have a pressure guage to test it. Just recently put some fuel system cleaner in it now I am having this problem. But I have heard that other people have done the tune up and it then leads them to the fuel pump or filter cause the tune up didnt solve the problem. Also my sender must be bad as well because ever since I have owned the car the fuel guage needle has a really fast vibrating almost movement all the time. It reads correctly just flutters. So my question is does anybody think it is 1.bad mass airflow sensor 2.bad cat 3.fuel filter 4.coil 5.fuel pump 6.injectors. The thread never said what the problem was and if it was fixed. Any help would be great thanks guys

20redfrogs

I had my 99 Yukon give me the same issues of random misfires, and bucking/no power up hills. The issue ended up being clogged catalytic converters.....

99swatburb

Well it has been a long road but the burb is fixed. The seafoam worked for about 3 days and then it was back to the misfire. So i bought the magnaflow direct fit cats and had them installed by midas which took about 5 days and then I get it back with an oil leak from the timing chain cover. Great huh? So even after the cats it still is running like crap so I decide to do a tune up which consisted of: cap, rotor, plugs, wires, cam sensor, and crank sensor. When I was done it fired right up and ran great but then there was the issue of the oil leak. I could have done the timing chain cover myself but was worried if I did it that it would end up leaking again or I would break more stuff then I fixed so I left that to the pros at the GM dealership. Yeah I would pay more but it is worth it to have it done right. So GM had it for about a week. So they started with the timing chain cover and once they got into they said that the chain had play so they replaced the chain and gears. Then they tell me my oil cooler lines are leaking, ok replace those too. Then I asked them to put a new fuel filter on it well guess what, the gas lines were leaking. So they put a new return line and replaced the feed line from the filter forward. I had them sand and lube the driveshaft and yoke to get rid of the clunk. Then they tell me the oil filter adapter gasket was leaking well damn might as well fix it all. So this is the total cost.
Cats and installation $550
Tune up I did myself $318
Alll the work GM did $1719
Total $2587 I could have took that money and traded my burb in on a new one but hey I love my truck.