fuel pressure gm 454 1998 motorhome
 

Posted for transmission help on here for motorhome and need help with fuel pressure diagnostics 1998 gm 7.4l 454 8 injectors.

Checking fuel pressure today, turn on key, pressure goes to 54 then drops quickly to 49 and stays there, start cold engine 32 degrees outside and pressure goes to 50 / 51 and when you rev engine, moves 2/3 psi put under load in drive full throttle and stays same. shut off engine needle jumps for a second up then back to 49. will stay there with key of for 1/2 hour.

Do you think pressure is okay? Engine starts and runs great, just dealing with this transmission vibration towing, going to change wires, plugs and cap/rotor, but do not want to install if I have to take it all off to do other repairs

Re: fuel pressure gm 454 1998 motorhome
 

I am working on a 1999 3500 GMC and those numbers look about the same. I would hook up a gauge and test under load. ---Trevor

Re: fuel pressure gm 454 1998 motorhome
 

new data, I did replace the regulator in 2011 with BWD pn 24027, Noticed change next spring going to charlotte from phila. just did the following diagnosis

I can pinch vacuum line going to regulator. The following has happened

1 Start and pinch line goes to 57 psi and stays there. Under load drops 1psi
(in drive with 1/2 throttle) Release vacuum line drops to 46psi
Squezze again and no change release
Shut off goes to 57 then drops to 46 and stays there.

2 Start and pinch line goes to 57 psi and stays there. Under load drops 1psi
(in drive with 1/2 throttle) Squezze and shut off and sounds like a solenoid kicks in and drops to 47 psi and stays there

3 .Start and pinch line goes to 57 psi and stays there. Under load drops 1psi (in drive with 1/2 throttle) Release vacuum line drops to 46psi
Squezze again and no change hold and shut off drops to 37psi sounds like a electric solenoid releases
Release pinch and goes up to 40psi.


Thoughts? other tests?

Re: fuel pressure gm 454 1998 motorhome
 

I had a '96 GMC with the same driveline as your MH...

Started to have engine issues when it was only a few years old.

Intermittent loss of power and stalling.....

I did the fuel pressure test and your numbers are fine...

I changed a bunch of parts including the fuel pressure regulator....and the problem would come and go....


Problem persisted....and got worse...

I attached a fuel pressure gauge and taped it to the windshiled and drove it around untill it started acting up.....Fuel pressure was dropping.... a lot...

It turned out to be the fuel pump pickup filter sock....It had dirt.... and red silt in it and was causing the problem....

I replaced the pump....filter sock and can filter......and stopped going to the gypsy gas stations I was going to......Problem never occured again....

I kept that truck for 14 years and bought it new and towed with it all those years......