Engine stumbling/ cutting out

[Jcode]

For the past week or so I have been having problems with my engine "surging" at hwy speeds (50-55). It feels like I am up and down on the throttle. When I drop back to 40-45 it quits. It does not seem to do it until the engine is completely warmed up. It cranks fine, idles fine, runs fine in every way except cutting out at 50-55mph when the engine is warm. It feels like I'm running out of fuel. I thought at first it may be fuel related, but it runs so good all other times I kind of doubt it. If my IP is going south wouldn't there be other symptoms like hard starting, etc.? Any help would be much appreciated.

[NH2112]

Replace the fuel filter. If the vacuum switch isn't hooked up your WIF light won't come on, and the feeling you described is a textbook definition of fuel starvation at higher RPM.

[Subzilla]

Yup, more than likely a clogged fuel filter. I usually try to change mine once a year and always carry a spare. Coming back from a trip last year, I experienced your same vehicle symptoms. It was lunch time so we found a Burger King and I told the family to order me something. 15 minutes later the new fuel filter was installed and purged of air. Ran perfect after that.

If that doesn't fix it, then maybe the IP. These vehicles will do different things with a clogged filter. My 6.2's actually act differently from each other. My Blazer will start fine and run fine until I hit the highway speeds, then the surging starts. My Sub will have extended starting times and will surge like crazy from idle up to high rpm's. And then not run so bad on the highway. Seem to be opposite of each other but a filter change eliminates the problem.

Try the easy, cheap stuff first.......

[Jcode]

That was the first thing I thought of, but the fuel filter is pratically new with about 500 miles on it. Anybody ever have a fuel filter problem with so few miles on it? The truck has been sitting alot lately, but I try to drive as much as possible to keep the batteries charged, etc... If water is in the fuel, what would be the best way to treat it? I use power service with every tank. Thanks.

[TheDubs]

I had the same problem at about 55 60 mph I changed the fuel filter and havent had a problem since.

[Jcode]

I went ahead and changed the fuel filter, I think that was the problem, seems to be running fine now. I didn't consider the fuel filter because I changed it a few hundred miles ago. How many miles do you guys normally get between filter changes? Does water actually collect inside the square filter, is there a way to bleed off the water without having to change filters so often? Appreciate the help guys.

[NH2112]

On the bottom driver's side of the filter there's a drain valve that will allow the collected water to drain off. Inside the filter, at the bottom, are a bunch of fine filaments that cause water in the fuel to coalesce and adhere to the filaments. I believe the WIF sensor turns the light on when there are about 30 ml of water collected, but it can hold more that that before water starts going to the IP. I used to drain about 8oz of fuel off once a week (with the engine running.) In the wintertime try to keep the tanks full as much as practical, heated fuel is circulated back to the tank and any air space in the tank is going to produce condensation as the fuel cools.

When I had my 6.5l, I was on a 3500 mile oil drain interval and changed my primary filter (OEM one) every 3rd oil change, and my secondary (2 micron Racor R45S) every 3rd primary whether or not they needed to be changed. Shopping ebay can get you some great deals, I once got a case of 6 R60S filter elements for $80, and 6 6.2l air filters for $15 shipped. I know I got similar good deals on OEM fuel filters (Wix 33136) and extra capacity oil filters (Baldwin B7, Wix 51794, etc.)

[Subzilla]

What Phil said! I change mine about once a year (that's about 10k to 15k miles) and try to do it before cold weather sets in. Yes, if you have a bad batch of fuel, they can clog immediately. Like I previously said, throw a spare or 2 in your emergency kit. You will need it at some point in time.

[Jcode]

I spoke to fast. The cutting out has returned. It does not do it all the time, it comes and goes. When it does it, it is always at around 45-55mph. It starts fine, idles fine and runs fine except for periodically cutting out and or surging at hwy speed. If it was bad fuel, wouldn't it constantly cut out? Is there any thing I can add to the fuel to dry up any possible water problem (like sea foam, etc)? The fuel in the tank is about 2-3 months old, but has been treated with power service and 2 cyc oil. Appreciate the help guys!

Thanks for the info Phil. I'll try to perodically bleed off some fuel from the bottom of the filter assembly to see if that helps.

[Yukon6.2]

Hi
My truck used to have a surge while driving,i disconnected the timing advance switch on the rear of the passenger head and the problem went away.Installed a new switch and it hasn't returned.
Easy fix,easy to try just pull the wires off after you have it running.
Good Luck
Thomas

[Jcode]

Thanks yukon, I'll give that a try. What does the timing advance look like on the back of passenger cyl head? What color wire?

[Yukon6.2]

Hi
Not to sure about the color of the wire's,but the sensor use's the same hole that the temp sensor uses on the drivers side head.It should be near the rear of passenger head,just a little above the glow plug holes,i think,i can have a closer look if you don't find it.
Good Luck
Thomas

[vstech]

this sounds like what mine was doing.
turned out to be a leaking o-ring on the wif sensor in the filter boss. pressurize the fuel system and look for leaks in the lines.
my truck was doing this exact thing, and plugging the air leak turned my truck into a different animal!