Fuel Pressure

[peterbylt]

On my 1989 MCI 96A3 with an 8V92TA (mechanical engine) I thought it was a little under powered, She runs pretty good and will cruise at 70 but will lose speed on even the smallest inclines on the interstate.
 
When I got the Bus there was an electric inline fuel pump installed before the filters that runs all the time, I know that is not stock but never saw the harm in it and the Bus runs pretty good.

After watching a YouTube the other day about the effect of Fuel pressure on Detroit's I checked the Pressure at the secondary filter and found 8 PSI at Idle and a little over 25 PSI at high rpm, Specs say it should be 20 – 25 at idle and 60 – 70 at higher RPMs.

I changed the Filters, they had not been in there that long, I also replaced the fuel lines from the Bulkhead to the mechanical pump, in the process of replacing the fuel lines I also removed the electric pump thinking it could possibly be restricting the flow.

The only change is dropping a few PSI with the removal of the electric pump, my next step is to replace the Mechanical Pump, I have ordered one From Luke at US Coach.

Anything else I should check?
 
Do you think this will add power on inclines?

Peter

[luvrbus]

The fuel pump may not have been the problem to begin with, it could be the wrong orifice size fitting in the return line, it is what controls the pressure by restricting the fuel return flow back to the tank.You always check the return which should be .9 GPM   

[peterbylt]

Just to follow up on this issue, I installed the rebuilt mechanical fuel pump I got from Luke, when I took the old one apart I found grooves worn into the shaft, the seals were also pretty shot.

I believe it was sucking air in through the seals, I had already removed the electric pump that might have been restricting the flow, replaced any of the fuel lines that looked questionable and replaced the filters. I also added a permanent fuel pressure gauge at the secondary filter.

This brought the pressure up to 30 at idle and 60+ at higher RPM.

I was not able to test until this weekend.

The power difference is substantial, a little quicker off the line, I no longer lose speed and can even accelerate on the smaller inclines that previously caused me to lose speed, it is also quicker to accelerate when merging onto the interstate and passing slower vehicles.

Peter

[luvrbus]

60 psi is ok that falls in the middle of the 50 to 70 psi range at 1800 rpm most of the time the new pumps do 70+ psi