mustang gehl engine problems 4tn98

[beauthemechanic]

hello all... got another fun issue with my 2014 mustang 2100rt engine
machine has 2500 hrs .
has the yammer 4tn98
machine is throwing code for low fuel rail pressure 157-18 dealers have no idea, local yammer shop has given up...

has new injectors, new injection pump, new filters, new fuel lines, new lift pump,
im going in circles..
if I pull fuel pressure valve out of common rail and rev engine to full throttle I've got gallons of fuel dumping out of the pressure regulator valve.. is this normal? tried to swap with a spare I had out of a common rail cummins "same Bosch design" with no change...
any experts out there have any clues. thanks

 

[BigWrench55]

The only way to narrow down the problem without software is to isolate your fuel returns and measure what returns back to tank. You will have to measure the fuel that returns from the head and common rail. You shouldn't get any fuel returning from the common rail.

 

[beauthemechanic]

thanks for the reply, yea injection pump is new from Bosch, so are injectors.. 0 hrs on them... fuel return measured from injection pump head is minimal as is fuel from new injector return hoses.. weird thing is machine only throws the low rail pressure code when ran up around 2200 to 2500rpm and after about 3 min.. then drops off to limp mode 1800 rpm and sets the 157-18.. read a lot about these Bosch common rail designs. so if I unplug the common rail return line and block it off I can measure volume directly off the common rail and its probably 3/4 gal per min as soon as engine goes above 2200 - 2500 rpm .. but at idle or high idle the pressure relief valve doesn't leak anything? so it is closing and opening somewhat.. like I stated I also swapped with a common rail cummins pressure valve with no change?

 

[BigWrench55]

You have one injector returning to much fuel. I went through this last year with a deutz engine. You will need special block off fittings in order to determine which injector is returning to much. The injectors will need to be blocked of one at a time and return measured at high rpm. Does your engine have injector lines direct to the injector or does it have lines from rail feeding the injector through the head. If it is the latter. Then it is possible that the high pressure pipe inside the head is misaligned with the injectors. And those should have been replaced with the new injectors.