EFI Fuel Pump Problem

[ScanmanSteven]

23 gallon BCBroncos fuel tank with in tank pump. Last outing after running for several hours it started backfiring due to lack of fuel. We added a frame rail pump to supplement the intank pump but that didn't help. Seems the 1 year old filter was clogged. Replaced that and it ran about a mile and died again. Left it but later picked it up and ran all the way back to camp.

So I dropped the tank, cleaned the pealing paint off the walls, removed the in tank pump, after pumping out almost 20 gals with no problem. Dropped and secured a hose for a pick up and mounted the frame rail pump permanently. Ran fine, well almost. Now I drive a mile or so and starts back firing. Turn off, cycle the pump a couple of times, then starts up and runs fine. What gives? I going to hook up a light to see if the pump is running all the time. Could it be the pump isn't supplying enough fuel? 351EFI, 19# injectors, mid 80's TBI pump on frame rail to get it home. Several members use this pump, which is why I bought it.

Thanks and Help.

 

[Viperwolf1]

Sounds like pump isn't pumping enough fuel. Do you have a fuel pressure gauge?

 

[ScanmanSteven]

Yes, but with the GT40 upper intake, the adapter and hose won't fit so I usually have to do it under the Bronco. I called to find a permanent gauge to mount but the local parts house didn't have one. That is also on my list of things to try and monitor is fuel pressure.

 

[chuzie]

Fuel pressure gauge mounted so I can see it is one of the vest troubleshooting tools I have.

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[jim3326]

I mounted an electric gage in the dash so I could monitor the pressure. When I first started the engine, it was running about 39-40#, after taking it on the maiden voyage, about 12 mi., it's at about 36-38# and it died on me in my driveway when it went to 4#. I thought maybe the pump was getting hot and shutting off but it was still running. Then I was thinking maybe the regulator was the problem, nope. I think what the real problem is, is that the vent line is too small creating a vacuum in the tank. I tried to re-create it by running it at high rpm at the shop, but it must take a lot longer than I gave it. The only other thing I can think of is the LP pump can't keep the accumulator filled.

Aaahhhh the fun and games of troubleshooting a new system%)

Jim W.

 

[chuzie]

Any chance of vapor lock? What accumulator u running? How bout removing gas cap and see what happens with vent theory.

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[ScanmanSteven]

Problem solved, bad fuel pressure regulator. Once we rigged the gauge up and drove it, the fuel pressure would start dropping to 0#. If I cycled the key the pressure would build and bleed off instantly, but after several cycles it would hold pressure and run for a while. We replaced the regulator and it starts and runs fine, haven't driven it as someone removed the steering column to replace the dash and upgrade the system. Thanks for all your help and suggestions. Chuzie, I don't have an accumulator as I'm running a high pressure pump right outside the tank.

 

[stlo]

Glad u got it figured out steve