| Author | Message | ||
| Jim Blumenthal (Jimblu)
Registered Member Username: Jimblu Post Number: 1 Registered: 11-2008 Posted From: 63.136.113.138 Rating: N/A |
Does anyone know the idling fuel pressure on a mechanically injected 6V92TA, and the effect of low pressure (currently 25psi at idle, I'll bet it should be 45). The pressure then tracks RPM and goes above 125 psi at 1800 (as high as my test gauge measures). Is there supposed to be a pressure regulator or is this a restricted return problem? I don't have my book handy! Thanks for the help! | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1020 Registered: 12-2000 Posted From: 71.3.157.139  Rating: N/A |
My 8/V71 shows about 20 at idle and about 65-70 at the governor. My old 8V71 showed about the same numbers. Jack | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 1407 Registered: 10-2003 Posted From: 71.58.110.9  Rating: N/A |
I didn't find the pressures in the DDA book, however, they specify for a turbocharged engine with a .070 fuel return restriction (spill orifice), disconnect fuel return line and insert into a suitable container with at least 2 gallon capacity to start and run engine at 1800 rpm for one minute and measure amount of fuel flowing from the fuel return line; 1.4 gallons is specified. Observe fuel line immersed in fuel in container; any bubbles indicate air is entering the suction side of fuel pump. if so, tighten any fittings between pump and tank If less,change fuel strainer or filter and recheck. If still not up to specs, check for kinks in fuel lines; try another known good pump. If still not satisfactory, could have a bad fuel injector. There is a procedure to check them, however this should be enough for now. | ||
| niles steckbauer (Niles500)
Registered Member Username: Niles500 Post Number: 915 Registered: 11-2004 Posted From: 173.78.29.189 Rating: N/A |
Jim - either your gauge is incorrect or something serious is wrong with your mill's lube system - Are you saying these are the #'s at operating temp? FWIW | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 247 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Jim Jacks numbers are right on. There is a pressure relief valve in the pump that releases the fuel at 65 to 75 psi at 1800 rpm. It sounds like the valve isn't releasing or your gauge isn't working right. The restrictor in the return line is .070 so you might want to check that as well. | ||
| Jim Blumenthal (Jimblu)
Registered Member Username: Jimblu Post Number: 2 Registered: 11-2008 Posted From: 63.136.113.138 Rating: N/A |
My gauge is accurate so the problem might be in the pressure relief valve, is it part of the pump? And where are the restrictor fittings, is it the discharge elbow on each head? I'm measuring at the intermediate filter. The book is on it's way. Thanks to all for the information. | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1021 Registered: 12-2000 Posted From: 71.3.157.139 Rating: N/A |
Jim, Just to let you know, I have my gauges (mechanical in engine compartment, electric in dash) connected to the input side of the secondary fuel filter. When I installed the new (to us) 8V71, I was getting these pressures, but discovered a pinhole leak in the return line from the engine to the check-valve on the bulkhead. I purchased a new 5/16" return line and pressures dropped (against the governor was 45-50 PSI). I then checked the old (leaking) line and found it was 1/4". I replaced the new line with a 1/4" and pressures were once again 70 PSI against the governor. Jack | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 249 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Jim The pressure relief valve is built into the fuel pump. On one side there is a large nut and if you remove it there are springs etc. When you get the book it will show it quite clearly. The restrictor is a 90 degree brass fitting in the return line to the fuel tank. There is a number stamped into the end of it. The number indicates the size of the small hole in the fitting. you will have 2 lines coming from the fuel tank. One has a 1" x 2" round thing in the line. That is a one way check valve that prevents the fuel from returning to the tank on shut down and the other line will have the 90 degree brass fiting in it. That is the restrictor fitting. Hope you can understand this. Bill | ||
| Jim Blumenthal (Jimblu)
Registered Member Username: Jimblu Post Number: 3 Registered: 11-2008 Posted From: 63.136.113.138 Rating: N/A |
Thanks for the help. There is a return line from each head, they join together and continue to the tank. I should pull the pump since it shouldn't be putting out 125 psi even if the restrictor fitting is restricted. | ||
| Clint Hunter (Truthhunter)
Registered Member Username: Truthhunter Post Number: 137 Registered: 1-2009 Posted From: 24.129.235.190  Rating: N/A |
Your not dead heading the pressure (to get that 125 psi)are you? The gauge must be tee-into the line at the right place and the pressure measured with the flow through the orifice, ideally into a bucket to measure volume per minuet. | ||
| Jim Blumenthal (Jimblu)
Registered Member Username: Jimblu Post Number: 4 Registered: 11-2008 Posted From: 208.168.246.169 Rating: N/A |
No, fuel is flowing through the return line. I opened it into a bucket and it was reduced by 25 psi. It is flowing at a gallon per minute through the tee into the bucket at idle. Thank you. Haven't found the location of the orifice yet. Maybe it is clogged. | ||
| David Lower (Dave_l)
Registered Member Username: Dave_l Post Number: 129 Registered: 11-2007 Posted From: 67.58.201.132  Rating: N/A |
Jack your numbers sound good for oil pressure, 50 to 70 psi at 1800 to 2100 rpm with a minimum of 25 to 30 psi. For fuel pressure 45 to 70 psi at the same rpm range and 0.9 to 1.4 gpm depending on the oriface size 0.080 or 0.106. I will add the at idle fuel pressure when I find it and the location of the oriface. These numbers are from the DD overhaul manual. Dave L | ||
| Jim Blumenthal (Jimblu)
Registered Member Username: Jimblu Post Number: 7 Registered: 11-2008 Posted From: 206.48.230.222 Rating: N/A |
Turned out to be the fuel pump. The restrictor fitting was farther out, not on the head. Pressure now steady 60. Thanks to everyone for the help. |