Help! Towed back to shop

[EWB555]

1995 RD688S E7-400. Shut off today, while driving. Seems to be a fuel problem as it will start and run on either. All accessories are coming on when turning key so ecm should be getting power. Thoughts on what to start with to trouble shoot? This engine is computer control but not an etec. Appreciate any suggestions!

[41chevy]

I'd check to see if the fuel pick up tube in the tank may have cracked or broken off. Also the ECU is very sensitive to voltage drop. Anything below 11.5 volts and it has running issues, its more of a problem on those as the cab and chassis electrics are 24v and the engine is 12 volt. Check to see if you have a battery on the way out.

 

[EWB555]

Ok, so this evening I checked every single fuse, circuit breaker and relay, all good. No malfunction light on. Voltage was 12.5 in the fuse panel. Turned key on  and had 12+ on on one pin at the round fuel  pump connector, and an even 3 volts on another. Looked in both tanks, pickup tubes seem in tact, cracked fuel line at the pump and there is fuel. Thinking it has to be something with ecm or pump electronics. When cranking it doesn’t even try to start, shoot it with either and it will run a few seconds. Not sure where to go from here, appreciate any suggestions. 

[hatcity]

fuel filter?

 

 

 

[OldRedMack]

We have had an eecm take a crap on us out of the blue on 1 of our cat motors.  The truck was running great, shut it off on a job site and it would not start.  Spent 2 days trying everything under the sun to no avail.  Finally got an eecm out of a wrecked truck and it fired right up.

[Mack Technician]

I use to have a steel fuel line I’d hook to the pump with a tester jig and injector. Kinda like those spark testers used on you lawnmower engine only for diesel. Gives you a quick answer on delivery. Put your cigarette out though. Crack a line and see what’s pumping out one of the six top delivery ports. Stick a fuel pressure gauge in-line after fuel transfer pump. 

[EWB555]

Well, we know it's not the fuel transfer pump. Dad talked to a mechanic who suggested we try that, he picked one up and put it on today, nothing changed. I am going to mess with it Sunday, it's going to rain here all day Saturday. We didn't want to put the truck in our shop since it's loaded. Will definitely crack one of 6 lines on the pump and see what we have.

From there I'm going to start checking wires in the harness. Does anyone know how to check the sensor in the side of the pump or the one in the flywheel housing? Will these make it not run if they fail?

I have a multimeter and can check voltage, resistance etc. Just not sure what I need to look for.

I do appreciate everyone who has chimed in with suggestions!

[EWB555]

Figured it out. Should have known that when I cracked the fuel line at the pump and some fuel dribbled out that didn't necessary mean it was getting fuel to the pump. First thing I did today was pull the filters, neither one was full. Put 2 new ones on full of fuel, hit the primer on the new transfer pump until it was hard to pump, and it fired up after about 5 seconds. Let idle hoping that maybe it actually was the transfer pump and it just needed a good prime, but I had a feeling that wasn't it. Anyway after a few min I could tell the idle had changed and it was clearly not right, hopped in the cab gave it some fuel to confirm it was missing then shut it off. Disconnected the main line from the  primary fuel filter, slid under the truck and stared tracing it, when I got to the back of the trans where it crosses over I discovered that it had a hole in it from rubbing on something. Pulled the line off the truck and will have a new one made tomorrow. Thankful it's  not an electrical gremlin however frustrated that I didn't pull the filters when I first checked the truck out last week.

 

[j hancock]

Glad you found the issue and thanks for reporting back with an update.