6.2l fuel pressure

[dieselgetmethere]

Hello, a first timer here. I like to get a different view on a N/A 6.2l fuel pressure. I've purchased an 84' M1028A 1-ton 4x4 with the 6.2l (converted to 12V) and have installed a mechanical fuel pressure gauge. A short history, I've removed the mechanical lift pump and installed a 93' turbo electric lift pump on the right side frame rail (actually 2 - pumps, 1 as a back up) across from the only brand new fuel tank. I've also installed a RACOR 635 filter before the pumps and have retainded the origanal filter. The problem is fuel pressure drops off to less than 2 lbs. at throttle, say pulling a hill, then comes back up to an average 5 1/2 lbs. . I've bepassed the factory filter temporarily and found no difference. Any help would be appreciated.

[DmaxMaverick]

Welcome aboard!

Typical/normal fuel pressure will range 4-8 PSI at idle. It is normal for the pressure to drop at higher engine loads. The injection pump does not require anything more than just positive pressure, so anything above zero under any condition is acceptable. Higher pressure, such as can be had with "high performance" aftermarket electric pumps exceeding 12 PSI can have adverse affects. Positive pressure under all conditions, with sufficient flow to maintain that positive pressure is all that's required. Mechanical pumps actually do best, as they track engine RPM, with more closely follows engine load conditions. Electric pumps work well, but have a static supply environment, and they can fall short at higher load demands as they wear. The electric pumps offer the advantage of fuel system priming, without the need to crank the engine. I don't recommend running both, simultaneously, unless there's a specific need for it (such as a failing mechanical pump). A failed mechanical pump will usually leak externally, so a closed bypass is highly recommended if you are using the electric(s) as backup.

[joeq]

I've run an aftermarket (AC) electric pump for years along with the stock lift pump, solely for the reasons you explained, and haven't had any adverse reactions. my elect one did fail this summer, (for the 1st time in 15 yrs), and because the truck quit running, imagine the mech. one had been defective for (who knows how long?). Not sure what the pressure is in the system is, but believe the AC pump to be approx. 6-7 lbs max.(No fuel pressure gauge).

[johncarrol]

In my 1991 GMC 4X4 pickup I pull the fuel through my turned off, dash switched, stock electric pump with a mechanical. I had to relieve slightly the brace that holds up the front diff to install the mechanical one. When my stock filter starts to get plugged the engine will start to die on a steep grade. I hit the switch and the extra little bit of pressure brings the engine back to life telling me it's time to replace the filter which I will do soon after. Then the electric pump makes filter priming a breeze.