Truck Surging at Freeway Speeds on WVO

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Truck Surging at Freeway Speeds on WVO

Postby Tmaxxrox97 » Mon May 18, 2015 3:24 pm

Hello all,

I just recently finished my 1998 Dodge Ram Conversion and everything seems to be working fine besides the problem the title suggests. While taking a trip this weekend I was driving on WVO and the truck started to surge. RPMS and speed would drop and all power would be lost for a few seconds then it would pick up again for 10-15 seconds then it would surge again. I am trying to figure out why this is happening. I'm not sure if it's a weak (original?) mechanical lift pump struggling with oil, a worn/ tired overflow valve, a clogging filter (I changed it on the trip to see if it would help), or a combination of the three causing my problem. I don't have a fuel pressure gauge and am looking into getting one. It doesn't happen at lower speeds or any other place just on the freeway. It doesn't happen on WOT acceleration so I'm quite stumped.

Any help would appreciated.
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Re: Truck Surging at Freeway Speeds on WVO

Postby SunWizard » Mon May 18, 2015 4:46 pm

Besides the 3 ideas you list, even more likely is an air leak, or a clogged screen in the tank pickup or the pre-filter just before the lift pump. A pressure guage is the best tool to find the problem. I would need to see a diagram of the plumbing to give more ideas.
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Re: Truck Surging at Freeway Speeds on WVO

Postby Tmaxxrox97 » Mon May 18, 2015 5:21 pm

Thanks for the reply.

An air leak is entirely possible and I should probably go through and double check and triple all my connections. There are a lot of them...

The system is plumbed the exact same as yours with the only difference being that I used solenoid valves rather than manual ones.

And something I didn't mention in the original post is what I mean by freeway speeds. This only happens at 70-75 MPH. Not 50. Not 65. Not even 68. Just above 70 does it happen.

Thanks again.
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Re: Truck Surging at Freeway Speeds on WVO

Postby David » Sat Jun 13, 2015 8:15 am

Simple, had the problems endless times. Its fuel starvation.
In my case it's when the filters clog. Your system may have different problems but tracking back from the filters to the tank pickup is the way to go.

The reason it is happening at sustained speed and not WOT is because you aren't keeping your boot in in long enough to cause the starvation. The pump may in fact be sucking down fuel lines of vaccing down filters. It might get away with this for under 10 sec at WOT but keep the demand up for a minute or 30 and it's a whole different ball game.
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Re: Truck Surging at Freeway Speeds on WVO

Postby White99z » Thu Jul 02, 2015 9:05 pm

Our bus was doing this the longest time and I couldn't figure it out for the life of me. I had a predicted on our line coming out of the tank. It was horribly restrictive. Took it off and no problems since. Our problem was on WVO only. Is yours happening on diesel too? Our bus exhibited the same behavior when the WVO filter was clogged.
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Re: Truck Surging at Freeway Speeds on WVO

Postby Tmaxxrox97 » Thu Jul 02, 2015 9:15 pm

It was just on WVO thankfully. It started to do it while I was pulling a trailer at 45 mph and then wouldn't do it again when I wasn't towing. I also noticed a fuel leak that started to get worse and worse. So I fixed that by replacing it with a much simpler way of doing it, which removed multiple connections, and since then haven't had an issue. So it was definitely an air leak causing the problem.
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