Hi I have a 1992 ford motorhome with a 7.5 superduty engine I have replaced fuel pump not assembly just the pump and the filter. My motor home cranks up and gets 32 psi at crank up remove the vacuum to the regulator and goes to 40 psi. With vacuum on you pressing the gas or taking off you it rises from 30 to 40. After driving a half mile the pressure will drop while just pressing the gas or taking off the pressure goes from 30 back to 20 and after this happens you can kill it for a split second and the pressure will go back to acting normal. But after that every time you crank it the pressure will not go back to normal but it will go from 30 to about 32 then soon there after it will go back to dropping back to 20 while hitting the gas. And it makes no diffrence with the vacuum line off besides it will go from 40 to 30 psi while pressing the gas. And one thing I did notice was when you crank it back up and pump the brakes it felt spongy and the first rev would go from 30 to 32 but go to from 30 to 20 every time after just thought it was weird.
There isn't much question that you are still having a fuel pump or fuel tank issue and it's going to have to be investigated more thoroughly. Confirm there is no voltage drop at the pump and nothing in the tank is restricting the pump pick up. I'm assuming the issue was the same before the pump change.
December, 6, 2012 AT 6:37 PM
Hi I was reading about changing the oringal pump assembly to a new style made in 1997 that suppose to be made better and it was a turbine pump and has a four wire harness. The old assembly has a three wire harness and was told it was a gerotor pump. Now I changed the pump in my old assembly and the company I bought it from said it was a new style turbine pump. Allright my question is if its the new style does that mean it was made for the new style assembly. They said it was for the old style. Not sure if they just sais that to get me to purchase it or not. Also since it is a new style then would that suggest it needs the four wire connector harness for some reason. Also what is the fourth wire for on the new style pump. Just trying to figure out to see before I go buying the $320 pump with the $40 harness to make it fit. And being that I only have 3 wires going to my pump what would I be hooking the fourth wire to.
December, 6, 2012 AT 8:47 PM
You need to ask the parts people that question. It could mean upgrade or it could mean there was a mid year modification and you need to know which one you have. The number or wires should not change.
January, 17, 2013 AT 1:49 PM
Hi I was doing some other checks and I was checking the resistance on my injectors and on the analoge multimeter and I checked 3 of the injectors and stopped because not sure if they were right or I was reading wronge but the resistance or ohms on the 200 setting was on the 4th bar back between the o and the one and if I went up to the next setting it was on the 5th bar back. Is this correct. And if the engine gets to operating temp will this change. When I checked it the temp was 44 degrees and engine was not warmed up. I was also told the injector connector would read 12 volts key on one side and nothing on the other side. I was getting 11.47 on both sides. Then the said the terminal side that read nothing would jump from 0 to 12 while cranking. I did check that to and while cranking on both sides I only got like bouncing from 6 to 8.5 volts on both sides. I am going to put light on anyway not sure if the meter can read as fast as the voltage comes in and out just wondering if that is ok. I was also wondering how to test them if I am doing something wronge. Also dont believe the egr Valve is opening at all. Was wondering if between the o2 sensor and the map sensor could they effect the fuel pressure. If so how should I check them properly. I did check voltage at connector and the drop going to the back. Guess it stop there for the shorter chassis. The voltage drop on one side was.3 and the other.1. Voltage was high 13.5 and turning on every thing I could it went down to 13. The engine was only idle and rev n the engine. Just wanted to know about these things before I drop the tank and do voltage drop at pump and possibly change to a 350 dollar pump. Oh I did a check on the air temp sensor and the ohms said it was almost no resistance I think same as injector will have to check again and it never went to no resistance after warmed up. The temp outside when checked was in mid 50's