The Diesel Stop banner
1 - 7 of 7 Posts

·
Registered
Joined
·
29 Posts
Discussion Starter · #1 ·
I have a 7.3 PSD from a customer that has been giving me absolute grief. Came in with intermittent shutdown faults, like it was running out of fuel. I scanned the ECM and found a few codes, patched all of that and fixed the wiring. Further diagnostics then pointed to the lift pump on the chassis rail. I replaced this and plumbed it up with clear fuel hose. After about 10km (I'm in Australia) the truck started to slowly lose fuel pressure again, eventually showing zero on the gauge and stalling. I fitted an auxillary fuel supply and it started straight back up again and got me back to the shop. Suspecting an in tank issue I pulled the tank and sender and found the suction foot broken off the tank, and the mix bowl screens badly blocked.
I modified the pickup to eliminate the screens and fitted another filter between the tank and lift pump. Started the truck again and off we went, returned it to the customer and they drove for about 4 hours before the same problem started again. Limped the truck back to my shop, removed the supply line from the back of the lift pump and used a smoke machine to search for any further pin holes that may be allowing air into the fuel. This test revealed a pin hole in the flexible line that goes from the sender to the steel line on the chassis. Replaced this and went again. I personally drove the truck for 3 hours with the fuel pressure never dropping below 60psi, before allowing the customer to collect it again.
Customer rings again today telling me that he managed to drive approx 12km before the fuel pressure dropped and the truck stalled again. I'm leaning towards maybe a sticky fuel pressure regulator? This is definitely the hardest diagnostic job I have had through in a while.
 

·
Super Moderator
Joined
·
26,677 Posts
It may be that there's still crud in the fuel system that's either blocking your pre-pump filter or the screen on the inlet of the fuel pump itself.

I think you've done everything right so far, but what was in the system may have caused it to block fuel delivery again.

I doubt if the fuel pressure regulator at the filter is causing a problem. If that was plugged, the fuel pressure would go higher as it plugs.

One question. When you deleted the in-tank filter screens, did you also delete the mixing chamber and reroute the fuel return line away from the inlet? If not, aerated fuel may be getting back into the supply, causing a loss of pressure. Just a thought. Strictly Diesel has their Hutch Mod kit instructions available here: https://www.strictlydiesel.com/images/PDFSpecs/Driven Diesel_DD-73FS-TKF-v3.pdf You should review them if you haven't already.
 

·
Registered
Joined
·
29 Posts
Discussion Starter · #4 ·
I removed the sender after doing the hutch mod and smoked both the inlet and return lines to confirm that they had sealed. Also made sure the return was way out past the float for the gauge. Only reason I was suspecting the FPR is that I thought it may be sticking partially open intermittently causing a drop in fuel pressure?
 

·
Registered
Joined
·
1,436 Posts
Can you run 12v directly to the fuel pump and see if the truck keeps running? Maybe it is a wiring or control issue on the fuel pump.
 

·
Registered
Joined
·
29 Posts
Discussion Starter · #6 ·
That's the thing. As soon as it drops pressure I have been able to fire it straight back up on an auxiliary supply. The electric pump is brand new also. The truck will hopefully be back here next week so I can try again
 

·
Registered
Joined
·
1,436 Posts
That's the thing. As soon as it drops pressure I have been able to fire it straight back up on an auxiliary supply. The electric pump is brand new also. The truck will hopefully be back here next week so I can try again
The ECU cuts power to the fuel pump if it doesn't seen an RPM signal. Sounds like a control issue or wiring problem between the ECU and the pump.
 
1 - 7 of 7 Posts
Top