| Author | Message | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 12 Registered: 1-2010 Posted From: 58.6.44.92  Rating: N/A |
G'Day all, Can anyone enlighten me on the correct fuel plumbing for a 6V92. Currently fuel enters the inlet side of the primary filter via a non return check valve, the outlet here goes to the inlet on the fuel pump, then outlet of the pump goes to the inlet on the secondary filter, then both outlets on this filter go to the injectors. There is a balance pipe on the fuel rail between the two. Is this plumbing correct, I think it might be BUT..... not 100% sure Main problem.... what or where does the fuel return line go. At the moment there are fittings on the chassis for the fuel return line and the pipe itself is there but blanked off so no fuel is returning to the tank as it stands now. Any assistance here would be greatly appreciated. Dirk | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 438 Registered: 3-2006 Posted From: 216.198.139.38  Rating: N/A |
Dirk Check very closely. There has to be a return line from the heads to the tank. The pump runs constantly and the fuel cools the injectors as it returns to the tank. It goes through a restrictor fitting (usually .80) then to the tank. If you open the fuel fill cap when the engine is running you should see the fuel returning to the tank. Bill | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 13 Registered: 1-2010 Posted From: 58.6.44.92 Rating: N/A |
G'Day Bill, Hope I am not duplicating here but my reply post seems to have gone into cyber space. My thoughts exactly. At the moment there is only fuel going into the heads and the balance pipe connecting both heads but that's all no sign of a return from there. I was thinking there might or should have been a return from one of the filters but no there isn't. At the moment no fuel returns to the tank at all. The excess must just bypass or hold off from the pump. There are fittings on the chassis but not connected as is the return line. Dirk | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 444 Registered: 12-2000 Posted From: 72.187.35.208  Rating: N/A |
The fuel return should come from the back of the head(s). Your supply side sounds like it is done correctly. If the return has been plugged, then you could be in for some serious problems. The return is part of the injector cooling. I would find someone who knows exactly what he is looking for to check it out. | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 14 Registered: 5-2009 Posted From: 65.92.54.2 Rating: N/A |
On my bus the plumbing is the same as yours, and the return is from the rear of one head (the passenger side head) only. On my industrial engine, the plumbing was completely different, but accomplished the same thing. The heads have ports for the fuel in rail and the fuel return rail at both ends, and it matter little which end you use as long as you get fuel from the filter into both heads and out of both heads via a single restrictor, as far as I can see. Brian | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 439 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Dirk The main reason to return the excess fuel to the tank is cooling off the injectors and to keep a constant supply available for the injectors. Look carefully as there has to be a return line. I have never heard or seen any other system on a detroit. | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 14 Registered: 1-2010 Posted From: 58.6.44.92 Rating: N/A |
Thank you everyone for the replies. Think I have it sussed now. The motor is a replacement and it looks like when it was stripped out someone just screw the fuel lines onto the filers again anywhere. So have that sorted now as per a workshop manual. The return line blanked off is from the old installation. No idea why its been done like that as the motor was running when I bought it. I didn't drive it far just from the road from the tow truck to the yard so probably being blanked off didn't worry it for that short trip. Might also explain all the smoke at the time, over pressurized system if that's possible. Again thanks heaps fellas. Dirk | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 445 Registered: 12-2000 Posted From: 72.187.35.208 Rating: N/A |
That is really strange that someone would do that, it would make me very suspicious of what else you might find on that bus. When you properly restore the return line, be sure to use the correct restrictor in the return to make the correct fuel pressure. | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1385 Registered: 12-2000 Posted From: 71.3.72.124  Rating: N/A |
When I called DD to get a new restrictor fitting (I cross threaded the original one), they asked for the engine serial number to make sure I got the correct size. I am pretty sure it was a 0.70 for our 8V71 NA. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1043 Registered: 8-2006 Posted From: 98.167.198.235 Rating: N/A |
Orifice size depends on the fuel pump when I replace a fuel pump on a 71 or 92 series I change to the high capacity type that feeds both heads without a cross over line and use no type restriction on the return JMY | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 15 Registered: 1-2010 Posted From: 58.6.44.92 Rating: N/A |
This is a brilliant place to get information, thanks heaps to everyone. The restrictor fittings are these the screw in unions at the front of the heads or on outlet side of the fuel pump. Dirk | ||
| Bob MacIsaac (Wildbob24)
Registered Member Username: Wildbob24 Post Number: 122 Registered: 5-2007 Posted From: 184.36.242.102  Rating: N/A |
Dirk, The restrictor fitting, in order to work, needs to be installed after the injectors. So, they are usually installed on the back of the cylinder head where the return line is attached. Bob | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 16 Registered: 1-2010 Posted From: 58.6.44.92 Rating: N/A |
Bob, Thanks for that, appreciated. Dirk | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 17 Registered: 1-2010 Posted From: 124.171.2.97 Rating: N/A |
Well finally go to the bottom of my plumbing problem. Found the fuel return line is at the back end of the motor. Only by chance I found this line while trying to work out why there wasn't a spare connection for the return up front. The fuel manifold holes are identical on the other end of the heads, obviously they might be reversible, which makes sense. I was wondering what this other spare line was as the open end was dry and clean but when I unscrewed a join union further up there was diesel in it and traced it back to the manifold ports. Dirk | ||
| Dirk De Bakker (Kelvin12)
Registered Member Username: Kelvin12 Post Number: 18 Registered: 1-2010 Posted From: 124.171.2.97 Rating: N/A |
Bob, Should have read your post properly, missed the back of the head bit. That will teach me not to just breeze over it. Dirk |