my 97 is starting and running good, revs good in park and can hold a constant RPM. however, while merging onto the interstate and at 70-75 miles per hour the truck will jerk sometimes 1 time and sometimes 3 or 4 times in a row for a couple of minutes and then it will be fine the rest of the day. it started this when it got cold. i have replaced the spark plugs, checked the wires (since all this stuff is less than 6 months old anyway) and replaced the fuel filter, took it to a trans shop and they said the 4l60e is shifting and functioning as it is supposed to.. it is very aggrevating. ive been told it can be anything between the spider injectors to the rear end having slack. but fuel consuption is normal and i got under it and checked the drive train, and it is all fine, there is no check engine light on. i work at a parts store and i have come across someone else with the same problem, but he has replaced his o2 sensor MAF, and MAP sensors and his is saying random multiple misfire. could this be a problem with the crank or cam shaft positions sensors? I'm completely lost and aggrevated at the truck. has anyone else run across this or is my truck retarded? please help.

 

Not sure how the rear end having "slack" would cause it to jerk while doing 70MPH on the highway...

This is most probably a misfire. When the injection system gets gunked up, the spray tends to not atomize properly and can cause a very random misfire that does not meet the requirements of the PCM to set a code. You could try running some fuel injector cleaner through the system.

Water in the fuel is another possibility, but I would think that you would notice this at other times, not just at high speed.

 

every now and then it will do it a 45 mph but its rare.i was running an octane booster during the summer. maybe i should atleast try the cleaner since i work at a parts store anyways.

 

When it does this does/glance at the dash...do all this lights come on ever so briefly? I had a 97 one time do this and ended up being the ignition switch. JP[:@]

 

dash stays normal, i first looked to see if the light was coming on, and then looked to see if it was affecting the oil pressure, speed, etc. nothing changes,

 

update. it got colder, the truck got more retarded. it now jerks between gear changes, and sometimes during a take off. a totally different trans shop wants the truck overnight to check it out while its cold. he put a computer on it and a freeze frame showed that the O2 sensors were messing around, but no code set. I swear i am pretty sure its the trans. the shop is gonna check it out for free and give me an estimate and tell me what the prob is.

 

just a thought-recently do a cap and rotor? Had one once that exhibited similar issues, I thought it was tranny. Took iit to my tranny guy and he said cap and rotor. Did it and whola...JP[:-]

 

its not a miss. at a rev it hold strong and fine. never misses a beat. i guess i need to pull it off and check it anyways.

 

I think i am going to change the filter and fluid in the trans. maybe this will help or make it worse. don't know. it has 127k miles on it and was owned previously by and elderly gentleman that pulled a small john boat every weekend and drove his wife to the docs office. i know judging from some papers i found in it he has owned it since 2000. if the truck decides not to move again. wouldn't it be a problem with the valve body? haven't done it yet just trying to be prepared.and what do you all think about trying this out to help the issue. im affraid that if i don't try something i will tear up the torque converter, rear end , or something else. feedback will be greatly appreciated.

 

I doubt anyone is reading this anymore. but i have run a 3 step fuel system cleaner through the engine. It is now really really responsive and seems to be doing extremely well on fuel economy and as far as the jerking goes it has slowed down alot. i put step 1 and aerosol can of throttle body cleaner in, sprayed it really well, got a lot of black junk out, and discovered that my blazer will not stay running with out the full breather assembly attached. step 2 was put in through the pcv valve vacuum line to run it through the intake. step 3 was poured into the gas tank which was then filled all the way up. so far i have only run a quarter tank out and it seems to be doing better. the product used was berrymans 3 step professional fuel system cleaner.