97 chevy a miss at speed

[Greg T]

I have a 97 chevy k1500 Z71 4X4 auto 350 vortec 85,000 miles. Last 2 times I drove it when you get at steady road speed I could feel a series of light surges or "jerks" once in awhile. Just seems to do this on the flat ground at cruising speed. Once while it was doing this I held the throttle steady & slipped it into neutral it continued to miss. I tuned it up about 4,000 miles ago, new plugs, wires, cap & rotor, fuel, air & tranny filter. Any ideas on whats causing this would be appreciated.

[re-tired]

Since it has not been that long since tune up , i would make sure plug wires are not chafed or touching exhaust. all ok , I would run a few tanks of super and some injector cleaner.

[DanD]

What brand of spark plugs where the replacements?
This is just my opinion, but it’s also backed by a lot of other GM techs.
AC Delco Platinum spark plugs or don’t bother, for a GM product requiring platinum plugs.
A lot of the after market labeled spark plug manufactures will lump two or three applications together in an attempt to lower inventory.
The heat range and design is very close and using their theory should work. NOT ALWAYS!
Before anybody else says this, AC Delco spark plugs are (I believe) made by Autolite but they are built to Delco specifications.
I’m just speaking from experience, after chasing down light ( very Small) misfires all day, which turned out to be the “new spark plugs”. There is one manufacturer that comes to mind, that are very appealing due to their low costs, I believe they have a German heritage. LOL the things just don’t seem to work all that well, with any longevity anyway.
OK the spark plug rants is over. LOL
I do agree with what re-tired suggested and maybe take it one step further, by having the fuel system professionally cleaned. The pour in the tank cleaners are great as a maintenance item but won’t do anything if the system has gone past maintenance and needs to be cleaned to cure a lean misfire. The motovac fuel and cardon cleaning system seems to be the choice around here, it’s a machine with concentrated cleaners that connects to the fuel system which the engine runs off of during the cleaning.
It would be interesting to see what the scan data is, while driving down the road and the truck is doing its thing. Especially the misfire counters, that would be the easiest way to tell if it even is a misfire. It wouldn’t tell us whether it was fuel or ignition but maybe what cylinder to look at, if any at all.
If we knew that the ignition and fuel systems were not the cause the next thing I would do is retrieve the calibration code from the PCM. You’ll need a scan tool to get the calibration (program) code that your computer is running on.
Then go to this site tis2web.service.gm.com/tis2web
Enter your VIN number and see if there has been any updated programs that may address this issue or any others that may have been a problem that you haven’t noticed.
If there is you can take the computer itself or the vehicle into any GM dealer or an AC Delco store and have them reflash (program) your computer. Also if there has been a number of updates you’ll get the latest which will contain all of the previous.
Sorry for the long post, it’s Sunday and I’m board. There’s no safe ice around here to go Perch fishing yet. LOL
Dan.