Low fuel pressure
 

1996 f800 ford with a 8.3 cummins and a Allison mt653.

Fuel gauge fluctuated wildly when first installed between 5 and 15 psi.

For a test of the fuel pressure I pinched of the return hose, which produce 80 psi, burping the throttle very little showed 100 psi and blowed off the return hose so I believe I have a good pump.

Installed an overflow valve from tork tek and it raised the #'s by 5 psi.

Installed a clear hose after talking with Rob at TT to check for air, no air, but the gauge quit fluctuating so wildly, just a steady pulse at idle. I took it for a drive and noticed the boost was slow to come up and then the fuel pressure went nuts again.

Just replaced the hose from the afc to intake hose (found it was worn through) and the boost is back, 20 psi, but the fuel still fluctuates.
After I changed the hose was the first time this truck has ever had a fuel smell from the exhaust, so I've gained something.

At idle gauge pulses slightly now between 10 and 20 psi, when held at a high idle 25 psi steady. In reverse #'s are the same. In drive, I loose fuel pressure and the gauge goes nuts again.

Im asking for input on what to check next.. I am thinking the diaphragm, not sure why.

I want to adjust on the fuel plate, but I want to get all the other problems lined out first.

yeah sound like you might have a pump issue ... at WOT what kind of numbers are you seeing ?

the 8.3 ..... not a real screamer .... but good torque ... never seen too much HP ... 450 ish .... wonder what they will do ..... :humm:

Well I took it out tonight, high idle is 25 psi. When actually pulling it went down to around 10 psi.

I have to tell all here for future reference, I installed my gauge in the rubber fuel hose, seemed to be the easiest way to install the sender. Tonight after posting the above long post, I realized the sender NEEDS to be grounded. Grounding the sender took all the fluctuation out of the gauge.

Tomorrow, I'll clamp return hose again and see what my pressure says .

I'm not really wanting a screamer, but I would like for it to be comparable to the duramax that it has replaced.

well not as many rps's for starters .... wich will give you the impression of low power ( hence the amount of torque they produce ) ... so gearing will be important to keep the cummins in its power band ... wich is narrow as all get out ... 1400-1700 or so ..... you have your work cut out for ya ...... so what did iu put this in anyways ? duramax came out and put an 8.3 in .... box truck ? ...... did u have one of those 6N duramaxes ? .. lop of junk .......LOL ......:s:

The dmax was a 2005 4 door that I sold. This truck is an 1996 f800 ford that came with the 8.3 . Just trying to get the bugs worked out of it.

oh I thought you took a D-max out and put in a ISC .... LOL :s:

also check your fuel lines ... may have collapsed or have debris in them and also pull ur filters and blow out the lines...and possibly change filters.. just for insurance purposes .. :tu:

might also want to check your pick up tube as there could be some sludge in the tube due to long time sitting ...

Had a haul to make tonight. Going with an empty trailer, truck ran better than ever (since I've had it). Loaded around 5000 lbs and it ran just as good.

Engine even sounded different. The hose I replaced, from the afc to the intake, just what does it do? I realize the worn hose was leaking boost and I did notice the boost gauge responded quicker, but not over 20 psi just like before.

Fuel filters have been changed. This truck has a racor filter and has 1/2 inch hose from the tank to the racor, then 1/2 inch to the lift pump. From there it all stock.

I am going to change the lift pump. When on the throttle hard the pressure drops to less than 10psi. If the pump helps as much as the hose replacement did, I'll be a happy camper err,,, driver.

We may get thing figured out.

Occasionally in the rubber hoses (with the cloth braid on outside) where the fittings go in the hose or where they are crimped on .... its called a flapper .... have seen it a few times , seems to be more common with the bigger hoses after some time ... and they get really loose and squishey on the inside and you may not feel it on the outside due to the metal braided stuff between the rubber and the cloth... just know that it can collapse and have you running in circles.......:s:

Installed a new lift pump, 10 psi steady.

I bypassed the racor filter and get a steady 20 psi. Guess the racor has an air leak.

Truck runs real good :jump: with the racor bypassed, pulls good enough that im not going to slide the fuel plate just yet.

Thanks for your help.

Whats a racor?