VP truck starts hard warm or cold

J

jedeka

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A guy called me today about his truck. He bought it back from the guy he sold it to a while back. Head gasket was leaking, so he had that fixed and runs well now, but is having starting issues. I think I know the problem but need confirmation before I call him back. There is an Air Dog 165 on the truck. When he turns the key on, the gauge shows 30 psi on the 0-30 psi gauge. Once it starts, the gauge runs at 25 psi and seems to run fine, until he shuts off truck and tries to start it 10-15 minutes later. I hear too high of fuel pressure can cause starting issues and possibly rupture the VP44 diaphragm. I haven't looked up the Air Dog 165 to see if the fuel pressure is adjustable. Thinking he needs to lower fuel pressure to 20-25 psi, with key on. Truck should have around 16-18 psi with truck running down the road. Am I on the right track? Thanks.

Edit: He also mentioned that he thinks his fuel tank is pressurizing. He can take off the fuel cap and gets a mist of fuel fumes coming out of the tank.
 
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Check for issues in the fuel return. Ive seen return line restriction causing some problems like that.
 
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take the fuse out of the air dog before starting and see if that helps. mine only bumps to 10psi on the key cycle.
 
not to change subject but how do you adjust fuel pressure on a fass 150 titanium series i have this same problem constant 22-25 psi and hard starting if it sits for 10 or 15 mins
 
The plugged tank vent would be a great place to start. Pull the cap from the fuel tank and try starting as usual. Regardless of the outcome, the vent should be taken care of.

Also '98 to early 2000 ECMs (pretty sure on the last year) ran the lift pump longer during key on. Newer ECM programs just operate the lift/transfer pump for a very short "blip". If it's not the back pressure from the plugged fuel tank vent, it's the very early warnings of an injector pump issue - albeit a very early sign. I didn't see a year, so if the year you're talking about runs in that range, he could turn the key on, wait for the lift pump to quit, give it an extra 10 second count and see if it starts easier. If so, you could consider updating the ECM program with a Smarty by just programming in any Smarty level and then returning to stock.
 
There is no rubber diaphragm any more. What concerns me is pressurizing the tank. That leads me to improperly seated injector & it will cause issues.

Ed
 
Is this mist while running or not? Also lower the pressure below 20 on the ad, see what happens then. Also if it's really over pressurizing the tank I'd say the copper washers where not replaced or injectors where not properly seated. If the tank is pressurizing then you know the return is not clogged.
 
You should check you cranking pressure. Typical good cranking pressure is 7-12 PSI. No more than 12 PSI is need! Ed is right there is no more diaphragm in the VP44's.

Harden steel plate with a plastic back that holds the o-ring in place.
5338s2.jpg
 
Injector O-Rings was the trick for me...I know, I know, usually not the injector O-rings but rather the connector tube. Well after starting at the back and working forward ie. tank vent, tank to lift pump fuel line replacement, lift pump tear down, lift pump to FF line replacement, FF O-Ring, Banjo's at FF and VP, return fitting at back of block, Spring at VP Bleeder, connector tube O-Rings and again adjusting to make sure they were seated good... I finally tore open and looked at injectors...I noticed that the O-Rings were almost PLASTIC like. Zero elasticity and not round anymore, they were damn near FLAT and even with the body of the injector. This was found on #'s 2,3,5. They were so bad that I didn't even need to apply pressure when lifting them out. Replaced them all..and when putting them in got that nice POP/Click on the seating, tightened them down to 8 and put it back together....

3 months now and not a single issue. Cold or Hot she fires right up.

I remember a few years ago everyone wondering if this new ULSD would cause problems....I think that combined with the heat had dried them out and then caused them to become hard like plastic....

IDK for sure but it kinda makes sense.

N0RCAL

PS...tried the LP relay disconnect too that was my moment relief that it wasn't gonna be a 1000 dollar fix.
 
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