First I have 1999 trans am auto.. When I'm in fourth gear just cruising and I push the throttle just a bit to gain a little speed to pass or going up a hill it seems like it misfires... How do I fix this?

 

It could be several things could be plugs and wires could be low fuel pressure do to bad filter of pump could be a bad engine sensor or could me more serious like engine damage get it scanned first to see if any dtc are being set and check fuel pressure to make sure its rite if both come back good I would start with a good set of plugs and wires and a new fuel filter if it still does it run a compression check to make sure the engine is in good shape

 

I had the same problem. Plug wires were the problem but I also changed the fuel filter and plugs.

 

Is it throwing a code? If so get it read and see if it's ignition or O2 sensor related. Again check all the plugs and wires. Probably isn't your case but I had a tiny crack in a spark plug boot that was letting it arc to the coolant sensor and was causing a random misfire.

 

I just fixed this problem.

Went through a fuel filter per oil change, would fix it for a day or two, and then would come back.... Bla bla bla

Did headers on the car, finally.
I found 3 plugs that had bent boot tips, #6 was only finger tight, and #2 was cracked. Cracked to the point it fell apart when the plug boot was removed.

Once I replaced the plugs I haven't had a misfire since. It's damn aggravating though, I know what you mean.

 

yea i would inspect plugs, and if you have stock wires, i would get some MSD's for the simple reason you can remove those things countless times with no problems. the stock wires do not like to be removed and re-installed more then a couple times.

 

I have tr55 with msd wires installed in June this year when I did headers. Maybe fuel filter/pump? It's only in 4th gear... Before I did headers plugs and wires it threw a misfire code... Maybe need to tune out rear o2's? I'm not sure don't have a scanner and parts stores here in Hawaii don't read codes( bullshit I know) so I'll try to find a code reader and get back to y'all won't be for a week yet I got the family out here till Sunday... Thanks for the input keep it coming please

 

got a code reader and no misfire codes soo any thoughts?

 

Typically misfires under load with no error codes are ignition related, specifically plugs, wires, or the related connections. You can check the wires for general leakage by observing the engine in the dark. You can also test the wires with an ohm meter for resistance levels. The plugs require visual inspection for cracks, fouling etc.

Misfires can, of course, come from bad fuel, fuel filter. or injector, but those usually trigger a lean error code under full throttle.

 

misfires under load are almost always ignition related. it sounds like your torque converter is locked (wich causes extra load on the engine) thats when the ignition system will fail. brake torque the car and you will proably have the same result. find someone with a good scan tool and check the misfire counters, that should help you narrow down wich cylinder it is. or you could get real fancy and find someone with a lab scope and check the ignition wave forms to see where the fault is. if all that is out of reach for you then go to a shop. if you can do a tune up yourself i would do that first. but if its a coil then you will need to wich cylinder acting up. good luck bro.

 

fuel problems almost never cause a miss under load (from my exp.) but there is a first for everything.

 

i have found that a ignition misfire will through a P0300 for multiple or P0301 - P0308 depending on cylinder #

generally if their is a NO CODE misfire it is fuel related

and before i get bashed here......I work on LSx motor all day in my fleet of vehicle and have 20+ years with automotive work in the professional field to back this up......my 2 cents worth

 

A P0300 code will only set if the misfire occurs while the engine is between 450 and 5,000 rpm. Thus, ignition-related high-rpm misfires will not necessarily trigger the P0300 code.

 

the engine will only throw a code for a misfire if it happens frequently enough for the pcm to determine that the event is a catalyst damaging misfire. this will usaully be accompanied by a flashing MIL while the misfire is happening.when you load up an engine either through a brake torque or when the torque converter is engaged, like at crusing speeds, there is a higher volume of air in the combustion chamber. as a result of this increased pressure it takes more kv's for the spark to jump the gap on the plug. we all know that electricity takes the path of least resistence, so when you have a worn component like a bad plug or wire the spark will find its way through the bad spot in the insulation to an easier ground source. this will be evident by a black carbon track left by the arc. if the problem is internal like the secondary winding on one of the coils shorting to the primary winding there will not be a carbon track to see. sometimes you can take a bottle of water mixed 50/50 with rubbing alcohol and spray the wires and it might mess upat idle, just a cheap easy test. (the water and alcohol make it easier for the spark to escape). if you can get a good scanner on it will show you plan as day what cylinder is misifiring. it will be a lot easier to diagnose it then. i am very interested to know if bones has tried to brake torque it yet to see if it misfires. when you do it just push the brake real hard and rev the motor as high as you can with out the wheels spining. you should feel the engine miss. if not spray the water/alcohol solution on the wires and do it again.

also, nobody should ever bash anybody giving their opionion to try and help someone with a problem on this forum. whats so great about this site is that there are so many talented people on here willing to share the advice they have, based on the experiences they have had.

ASE Master Tech with 13 years as an electrical and drivability technicain.

 

i also would not worry about the rear O2 sensors. they do not have anything to do with the air/fuel ratio. they only report to the pcm the health of the catalytic convertor. if it were a fuel filter or pump there would be a serious lack of power and probably a lean code. get a fuel pressure gauge from your local parts store, i think you can rent them, and check the fuel rail presssure. its real easy to do. should be about 55-60 psi with a slight increase when you snap the throttle. if your problem only happens at crusing speed then duct tape the gauge to your windshield and drive it around to see of the pressure drops. i have personally seen these engines run all the way down to 20 psi so it will have to be a big drop to make a diiference not just a pound or two. good luck!

 

Off subject but blumaroz28 why do you mix the water with alcohol? I always used strait water in a spray bottle and did it in a dim area to see the spark jump.

 

I will try to brake torque it tomorrow and see but it's only when cruising and I hit 4th in my a4. I'll be cruising and push the throttle a tid bit to go up a hill or
The like and it jumps... Seems like a misfire to me but honesty I don't know

 

that sounds to me like a torque convertor

fords had and still do have this problem af the convertor locking up at certain speeds and in certain gears

GM hasnt had this problem to often

but something else to keep in mind

 

mixing the water with alcohol just makes it that much more conducive, but strait water will work too sometimes.

 

its happening at crusing in 4th gear becuse the torque comvertor is on. that causes an increased load on the engine. if it is torque convertor "chuggle" which does feel exactly like a misfire then it will only happen as the torque convertor is engaging and disengaging.

without driving the car its hard to say wich one he is feeling. thats why i suggested the brake torque. if it does mess up then we can eliminate the torque convertor. but you are right lemkerailroad it could be the TCC.