surge at 35 mph

Rdnck84_03

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New to this forum. Have done alot of reading here over the last few years, usually find my answers through the search function. I haven't found anything on this exact issue.

At around 35-40 mph in 4th gear at light throttle cruising i get a light surging. if i hold that speed it get more severe, to the point i have to either speed up or slow down so it doesn't rip the driveline apart.As soon as you make it below 35 or above 40 it stops. I am not sure if it does it in any other gears as i don't have a tach to reference the rpm when it happens. I have learned to drive around it but would still like to find the issue.

Any help is greatly appreciated.

James
 

Thewespaul

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Hey James, welcome to the forum. What year is your truck and what transmission do you have?
 

Thewespaul

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Change your fuel filter, when you get the new filter fill it with clean atf, fire the truck up and let is idle for 20-30 seconds then shut it down and let it sit overnight. You likely have a fuel delivery issue, and the atf will help clean up the injection pump Incase it’s the metering valve sticking. Give that a shot and let us know how it goes!
 

Rdnck84_03

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I was actually planning to do that tonight. Bought the filter and atf, realized after i got home and ripped the plastic off the filter that the parts store gave me the filter for the newer 7.3 filter head. Will try again tomorrow and post the results.

Thank you for the quick response.

James
 

Rdnck84_03

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was wondering if the filter head from a 92 7.3 will interchange with my 83 6.9? I can see that the return from injectors hooks up a little different. Wasn't sure if i can swap just the head without needing to change lines or bracket? I have the complete 7.3 setup on an engine sitting in my shop. Thinking this could save me having to buy another new filter and give me the added bonus of having the water drain. The water separator was already bypassed when i got the truck.

James
 

IDIBRONCO

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Yes you can do that. The return lines on your truck are probably 3/16" while the return nipple is probably 1/4". You'll need to change that back to the 3/16", but that should be your biggest issue.
 

Rdnck84_03

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Thank you sir. If i get off work early enough tomorrow night i will get it switched over and try the atf in filter. Will report back with the outcome on the surging as soon as I can.

James
 

david85

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Hi James, welcome to the forum.

Not sure if you found the solution yet, but I was having similar problems all week. It got steadily worse until the truck was nearly undrivable.

Minor surge started off the line, then sometimes calmed itself as speed increased toward 30 MPH. Heavy acceleration would get away on me almost like air in the system. When I performed a load test by driving at full power up a 10% grade, it was very obvious the truck was surging near top end as well. Idle while in gear was also getting to the point where one injector would die, causing black smoke at the stop light. Slight foot on the throttle was enough to 'cure' it.

Light throttle cruising with the torque converter locked would also cause severe bucking in the drive train until I had to change speed. Sounds a lot like what you had with your stick shift.

I have a clear plastic fuel return line connected between the filter head and the injector return lines. Even after a morning and evening commute, I noticed air in the system would not fully purge. Yesterday I replaced the lift pump and installed a new fuel filter filled with ATF. Started it up and let it settle to idle but did not test drive it (this allows the ATF to sit in the injection system and do its magic). Today I had a callout, so I used this as the first road test. All seems to be well now and I am able to accelerate on a 10% grade to 70 MPH in 2nd gear until hitting the governor. Something the truck hasn't been able to do for many years. This coming week will tell me if the problem really has gone away for good.

I can't say for sure if the fuel filter or the lift pump were the culprit, but I had in mind to install a new pump for a while and figured this was as good a time as any. The filter was also not very old, which lead me to believe the pump might have been on its way out. I have no way of knowing if it was original or not.

Oh, and I've been running the 7.3 style filter/separator unit for many years, so yes it can be done.
 

Rdnck84_03

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I swapped the filter head out Friday evening, filled new filter with atf and ran engine for about 45 seconds. Came in Saturday morning and started it up (not nearly as easy as starting on diesel) let it idle until temp gauge hit bottom of normal range. Took it out and blew the cobs out of it on an old backroad.

So far I haven't gotten it to surge, but the wind was blowing so hard that it was impossible to hold a cruising speed steady. I did notice that my top speed seems a little higher now and it definatly accelerates quicker. I guess time will tell as the sticker on pump says it was rebuilt in 99, no idea of how many miles are on it or even the truck for that matter. Probably just prolonging the inevitable.

Thanks to those that posted info. I should have more info on results after driving it to work this week.

James
 

IDIBRONCO

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That's good to hear. Also what part of Kansas are you in? I'm always trying to see if there's members close to me. I'm about 70 miles northwest of Hays.
 

Rdnck84_03

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Caney. I am just west of highway 75 a half mile north of Oklahoma state line.
 
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