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1998 Mack E7 460 running bad when warm (long post)


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Hi, I've been a member here for awhile but this is my first post after scouring through multiple posts and not really finding the fix that I need. First I will give the symptoms of the truck and then I will post everything that I've tried to fix it, some things I've found on this site (great bunch of people) and other things from local mechanics and local Mack/Volvo or should I say Volvo/Volvo dealership.

- Bought the truck about a year ago from private seller, truck ran great on test drive aside from a lope in the idle which I have heard before on other Macks. Got the truck home and began working it (6 axle dump truck). Middle of the day when the truck was good and warm it began to run as though the fuel filters needed changed. Changed filters and ran fine the rest of the day. This became a common occurrence, was changing filters 3-4 times a week until it dawned on me that something else was going on.

- Tried to check codes using cruise control but soon found out check engine bulbs and electrical bulbs were missing. Kind of see where this is going huh. Put in new bulbs and truck had multiple codes, not going to name them all but replaced sensors that should have caused the code but code still showed.

- Engine wiring harness was kinda bad so I had a new one installed along with a used engine ECU that was reprogrammed at the dealership. This cleared all the codes and got rid of the idle lope but the same original problem exists, running like the filters need changed when the truck is hot. Truck runs strong until this happens.

Things that I replaced or checked.

-Oil temp sensor, air intake sensor, engine speed sensor on bell housing, cleaned engine position sensor on front passenger side.

-Cleaned all grounds on frame and starter.

-Cleaned engine ECU and VECU and made sure plugs were pointing down.

-Checked primary fuel filter for water and none was found.

-Truck runs this way no matter how much fuel is in the tank which makes me think its not a broken pickup tube. Truck only runs off of one tank, the other is used for hydraulic fluid for the dump bed.

-No water in oil or oil in water.

-When truck acts up oil level and coolant level are within range.

-Truck has no active codes which makes me think its mechanical.

-Engine fuel pressure is 80 ft/lbs.

-Engine oil pressure is 60 ft/lbs when going down the road and oil temp is 180 degrees.

-Truck doesn't overheat.

-No grey or white smoke under normal conditions. Seen grey smoke last time it started to run funny.

-Tried Mack and Baldwin fuel filters, truck runs funny with both.

-The 3 power fuses in the glove box seemed to get really hot so I changed them and the new ones still get hot.

-Overhead ran last year.

Sorry if this post is long but I'm trying to be thorough. Again, truck begins to run funny when the cab temp or under hood temp is high. Truck ran fine last November when the temps here in Ohio were low.

Vin# 1M2AD62CXWW007770


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  • 2 weeks later...

Take the fuel line off at the primary filter that comes drone the tank. Blow shop air back through it make sure there is no restriction in it or pickup tube. I have had this happen before it was aggravating. It was the rivet out of the fuel cap it would suck it up the tube but not past the 90 at the top. When you shut truck off it would fall down. Then when you start it and not till you got on a hard pull would it suck back up in there. So I'm thinking every time you change the filter it is falling out of pickup tube.

This is just a guess worth a shot if you haven't tried it yet !!

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