hello fellas, got a weird one for ya.....not broke down on the side of the road, but suppossed to leave this evening to drive 18 hours for my wife to see her grandpa before he passes and sure as hell don't wanna break down halfway there...so I hope y'all don't mind me putting this in this section of y'alls forum!

....I'll try to make this as detailed as I can so as not to waste any of y'alls time....

Truck: 99 auto 7.3 PSD 250 Superduty 4x4, 344,000 miles, no mods other than KN air filter....truck has been in the family since 80,000 miles and has been all highway miles pulling a 5th wheel until a year ago when we moved out in the country and now drive bout 6 miles a day on really rough unpaved and dusty roads

Problem: a bit over 3 months ago, was sitting at drive through and truck started feeling like wasn't getting enough fuel and within a minute she was shaking HARD from side.....pulled outta the line and popped her in neutral and gave her fuel and straightened out until I'd let off the pedal; so I took off to try to get back to work, pulled out in traffic and didn't think I was gonna make it into the next parking lot...as in not even registering on the speedo and literally going down hill.......this is where it got weird....shut her down, popped the hood thinking real bad **** (temp guage don't work after a new radiator put in at 280,000) and everything seemed fine, couldn't find nothing so finally after a coupla minutes started her back up and had way more power, still rough though, tried to get to work and by the time I got to work she seemed to be running right as rain..

...got off work that night and ran home like a new truck....next morning did an oil change/new fuel filter/cleaned the air filter, and started using 2 cycle oil like I do in my old 1st gen Cummins......next few weeks, not a problem at all.....

.....take off one day on a trip outta state bout 2 months ago and she started acting like she wasn't getting no fuel at 75mph about an hour into the trip and had to pull her over and she wouldn't even do 20 mph, everything seemed fine under the hood, after bout 2 minutes started her back up and ran just a bit rough for about 20 seconds and then blam, hauling butt at 75mph like a new one....

...30 minutes later same thing, except this time she died at about 15mph on the side of the road trying to limp her in somewhere....let her sit turned off for about 5 minutes and started her up and she started and ran perfect from the second I hit the ignition...got into an oreillys and seemed to be running great but changed the fuel filter anyway and added some sea foam in with the filter....13,000 miles later and not a hint of the problem again....although a coupla weeks ago the check engine light started coming on but only sometimes and only when ya first fired her up and then it'd go off after 3 to 10 seconds but she was running and starting great....

....then 3 days ago coming home from outta state she was running great, pulled off the freeway to get fuel and when I slowed down to about 30mph she started running real rough again, pulled in to get fuel, filled up and took off and was rough until got to freeway speeds, then smooth....400 miles until home and no more issues the whole way.....running around town last coupla days and no issues, then last night started again....run rough at low speeds for about 5 miles and then runs great again....

wth is going on with this old girl???

any help would be awesome fellas, racking my brain here and aint coming up with nothin....thanks in advance for y'alls time and help!!!

 

Try replacing the CPS.

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Sounds like the UVC harness on one side or the other is coming unplugged or shorted out.

Not a CPS, CPS works or does not, it does not cause run issues like this.

UVC is Under Valve Cover Harness... There is also the UVC gasket which is the same, but the gasket. Both have wires and plugs on them that will go bad, get loose or just plain break.

 

so the UVC harness could be becoming unplugged minutely?

if it is shorting out, where could that be happening at other than the plug?

thanks!

 

Most times the plug will get melted or burned on the inside connection.

You have three connections happening there... One from the main truck harness to the gasket, one from the gasket to the under valve cover harness and then on to each and ever injector and glow plug... So more then three but you get what I am saying. The most common one is inside the valve cover from the gasket to the harness.

 

thank you for the help, been outta state with no internet access and just got back home yesterday

all the connections underneath the valve covers seem to be just fine....so still scratching my head

since the original post we have put over 3400 miles on her and not a single issue until yesterday when it had 3 problems back to back to back and has seemed fine since...

...got off freeway and the saw the station didn't have diesel so kept on straight from the off ramp to the on ramp and nothing outta the usual at all....picking up spped like normal...hit resume on the cruise at about 40 mph but kept accelerating with my foot and a second or 2 after I hit the cruise she started loosing power and took about twice as long to get up to speed....

....ran 75 for another 15 of 20 miles til we stopped for fuel....had to wait on a pickup that was fuelng up and I literally did not think she was even gonna pull herself forward to put fuel in her....shaking bad and running ruff as hell....a hail storm hit and place turned into a circus, probably about 7 or 8 minutes before I got to start putting fuel in her and she kept getting rougher by the minute....tried revving her up and she would do that and then idle ruff as ****.....starting putting fuel in her, went inside to pay and buy some Howe's, come back out and she was purring like a damned kitten and sounded, and ran, just like the day I bought her....she had just under a 1/4 tank when I pulled in........and on the trip I had let her fall below 1/4 tank probably every single fill up and no issues at all.....

...350 miles later getting home and just under 1/4 tank again and got off the freeway and running ruff again...head to the fuel stop and by the time I got there she was running normal....sat at the pump for a few minutes and no hiccups so went ahead and filled her up...running just fine still...shut her off, started right up...let her idle, did just fine...

....also, when the above things happened I never shut her off, so it wasn't like something was "re-setting" once turning it off...

any ideas???

 

Does this seem to happen when the tank gets below 1/4 full?

 

well, it definitely does not happen every time that it gets below 1/4 tank as most times I let her get as close to empty as possible just cause the wife and daughter always make a fuel stop into a 30 minute event....so virtually 100% of the time it gets below 1/8th of a tank and it wasn't doing it except for on occasion

...now has it been below 1/4 tank every time she has done it.....I can't say yes because I honestly never even thought about that until yesterday when that happened......but thinking back I would say it is very likely that it has in fact been below 1/4 tank every time that it has happened....can't say for sure though....

thank you for your help sir....any ideas bud?

 

running your tank low all the time I might suspect plugged pick up screens. Might be time to drop the tank and check the screens and just gut it.

 

thank ya sir, I appreciate the help!