Light misfire at 75mph

[JeezLouiseGMC]

Hey everyone, its been a while and it seems i only come back around when problems arise.

My truck is having a very slight misfire around 70-75mph under light throttle light load on the interstate. At times it is barely noticeable whereas others you'll feel a sudden deceleration and a pop in the exhaust. It drives perfect under 55mph with no misfires what so ever. I have no check engine light and all my vitals on the dash look great. This really doesn't affect drivability a ton but it does make me feel uneasy driving on the interstate because of this.

Shortly after this started I replaced my distributor (somewhat unrelated, had a no start condition), as well as did a tune up including new NGK plugs and wires, and replaced my ICM with an AC Delco unit.

The coil is also fairly new, having been replaced a year or two ago with an NGK unit.
I was reading on another thread that it could be the EGR valve being clogged up and that's my next step. I would like to know if anyone has had a similar issue and what their fix was?
Thanks for your help in advance!

1999 Sierra Classic, k1500 Vortec 5.0.

 

[Schurkey]

Verify fuel pressure, preferably when misfiring at higher speed.

Connect a scan tool, look at the data stream when misfiring at higher speed. Find out what the computer is trying to tell you.

A clogged EGR is not likely to cause a misfire. An EGR that's flowing at low speed might.

 

[JeezLouiseGMC]

Copy, I'll have to get a scan tool. I know there is a way to get it on an android tablet with a cheap obdII reader but I'll have to look into it again.

I feel like as long as I have owned and worked on this truck I should have access to a scan tool by now lol

On another note, any recommendations on a scanner to get? I've looked around and and it seems that I get a different answer anywhere I look

Although I should mention even at 70-75mph at anything greater than light throttle it doesn't stumble or anything. My thinking is that if I was having a fuel pressure issue that it would get worse with rpm and or load?

Thanks for your help!

 

[Schurkey]

Twenty+ years ago, when it was my money, I bought a Snap-On MTG2500, used, from a seller on eBay.

A couple of years ago, I had to replace it. Again, bought a used Snap-On Solus Pro from a seller on eBay.

I would rather have a professional-grade used scan tool, than a brand-new consumer-grade tool.

Other folks like the software + Cable solution for a laptop computer, or some similar method. Never used one, can't help there.

 

[harpo]

Mine is coming in tomorrow

 

[tpass]

yeah scan tool is the only way to go. I got tired of "guessing" at what was wrong with my vehicles. I bought an autel MK808 off amazon. It's a step down from their "pro" stuff, but it does everything i need it for.

Only problem I have with it is the yearly subscription fee for updates.