mid-throttle surging

[bleucrew6.2]

I have a 1989 6.2L that starts quickly every time, but I experience an occasional "surge" at mid-throttle, highway speed. Sometimes it feels as if the motor has gained power, other times it feels as though it's losing power.
I have been using fuel conditioner for the past year, and tried different fuel sources as well. The surge situation only lasts for about 5 seconds. Anyone have any ideas?

[john8662]

Are you getting any smoke when this happens?

What are the details of your truck, 1/2 ton 3/4 ton (light or heavy).

Could be an EGR mal-function.

Or possible a fuel related issue with air in the fuel system. These are just things to check!

J

[Yukon6.2]

Hi
My truck used to do the same thing.Try disconecting the sensor on the rear of the passenger side head,on the glow plug side.It is the cold advance switch,it will advance the timing while driving causing a surge.on mine a new sensor solved the problem.
i would unplug mine after the truck warmed up then the surging went away.
good luck

[bleucrew6.2]

Thanks for your suggestions! The truck is a 1989 4x4 3500 Cheyenne Crewcab, non dually. It belonged to the USAF before I bought it. Truck has about 95,000 miles on it, and runs really well except for the occasional surge situation. I recently tracked a fuel leak to one of the ip fuel line fittings. Apparently the pump was replaced sometime before I bought the truck, and someone cross-threaded the one fitting. I was able to find a replacement fitting locally (Arundel Fuel Injection, Baltimore MD. 410-525-3700), and luckily the fuel line nut was okay. No more leak. While under the hood I found a small vacuum line that looked pretty bad, so I replaced the whole thing. Fuel economy is good, and like I said before, it starts up quickly in the morning (even in the winter, if it's plugged in).

[gavio]

You didn't mention whether you've already addressed this, but....... I've had similar symptoms turn out to be fuel filter issues.

One time, I only had a few hundred miles on a new filter so I ruled it out. Tried everything I could think of - even poked around inside the IP, still that surging was making me crazy - in fact it got so bad I had to stop driving the van. It turned out a bad batch of fuel had lunched my filter.

I learned: unless it's obviously something else, try the fuel filter first! It's advice many have stated before, but it's worth considering.

Good luck!

[murphyslaw]

fuel filter. phew please its NEVER the fuel filter.

















J\K

[bleucrew6.2]

Thank you all for your input and suggestions. The truck has had this same surging issue since I bought it. Its really not that bad, just something that annoys me and leaves me wanting an explanation. FYI, I have changed the fuel filter twice in the past year. One filter change was from a crappy batch of fuel that I bought in Western Maryland. The other filter change was just for curiousities sake. I keep a new one in the truck at all times...just in case.