I. Started seeing problems with fuel pressure i have raptor 150 i cleaned the filter screen there was alot gunked up put back together same thing when im at idle i have 14-15 when warmed up at cold 12-13 regular driving i see 9-11 psi romping on it its gone to 0psi i wouldve thought the truck wouldve cut out but it kept pulling hard the vp was recently replaced along with lift pump and fuel filter i noticed at idle the lights will dim and fuel pressure will drop 3-4 psi and jump back up im some what new with this someone help i dont wanna replace the vp:(((

lights dimming could be the grid heaters cycling. check the battery connections as well, ensure no corrosion. also not sure if its the same as the airdog but there is a steel ball held with a spring that can get stuck open or something like that..?i also see a big drop in pressure when i get on the skinny, was at 19 idle and drop to ~11ish and this weekend it was idling at 19 but dipping down to 8 for some reason so i cleaned terminals and adjusted it to idle around 21, now it dips to 13 at most.

First, I would adjust the FP to be in between 18-20 psi at idle. Second, are you using the factory fuel lines fromthe tank to the VP? Do you have an isolator on your FP gauge? Are you running your fuel thru the old lift pump? (Not sure from the way you wrote the article. You mention Raptor150 and then lift pump.

You've got some restrictions in the fuel system. Do yo have 1/2" from VP44 to the fuel tank? Is there any factory plumbing and fittings left?Is there a possiblity of air leak on a suction fitting?

  Mopar1973Man said:

You've got some restrictions in the fuel system. Do yo have 1/2" from VP44 to the fuel tank? Is there any factory plumbing and fittings left? Is there a possiblity of air leak on a suction fitting?

Im not 100% sure if all the plumbing is aftermarket but the fuel lines are half inch its the raptor 150 the fuel lines need to be replaced they are getting dry rotted but were else could i be possibly getting a leak from?

AirDog's quick connectors are known to leak on the suction fitting most people have to give Vulcan Performance a call and talk to Eric about upgrading fittings to over come the problem.

  Mopar1973Man said:

AirDog's quick connectors are known to leak on the suction fitting most people have to give Vulcan Performance a call and talk to Eric about upgrading fittings to over come the problem.

Would that be causing the odd fuel pressure?

Possible. A lot of people have had issues with air leaks around the quick connectors. Since it a suction line it never leak outward. Even with the engine off air leaks inward draining the line out.

Seems like we are missing something here! If his pressure drops down to 0 at times. Then either there is a faulty gauge or a problem with an isolator. IMHO

  gassernomore said:

Seems like we are missing something here! If his pressure drops down to 0 at times. Then either there is a faulty gauge or a problem with an isolator. IMHO

Both are possible...

You said there was alot of gunk at the inlet screen....I would check it again and if its plugged up again you may need to look into where its coming from that could very well be restricting things and causing your pressure drop.

Or it could be like my air dog 150. The motor on the pump was intermitent. I don't understand the need of 1/2 inch lines on these small engines unless you are flat out racing. In days past my experience with 315 cummins engines that pulled 78,000 lbs and only got 6mpg only had 1/2 inch fuel lines and it would be 15 ft of suction befor the pump.

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I don't understand the need of 1/2 inch lines on these small engines unless you are flat out racing.

Volume and pressure stability. With smaller ID plumbing you get wilder pressure swings up and down. Mainly because Bosch VP44 injection pump requires 70% of all fuel to be return to the tank for cooling and lubing reasons. So this means even with a stock fuel system you would need a supply volume of roughly 70-90 GPH. So the stock plumbing is only rated for 75 GPH but that with 0 PSI at the Bosch VP44 Injection pump and 15 PSI at the lift pump. So the increase in ID of the lines aids in pressure stability so like on my truck I start at 19 PSI at idle and 17 PSI at WOT. With the old stock lines it would start at 15 PSI and fall to 8 PSI. So you got to remember the larger line isn't for the 30% being burned but for the 70% that required for cooling and lubing.