bgilbert

Anyone know of anyone that has tried a true 2nd gen 3936316 piston lift pump on a 1st gen with a VE pump? From what I've read it is a 18-24psi at idle, 30-38psi cruise, with some guys seeing up to 55psi downhill. With my lower pressure piston lift pump 3936320 I see 14-18psi idle, same for cruise, but haven't really seen a WOT psi reading. IIRC I might have seen as low as 11psi at WOT. I want to use a 3936320 LP for my new 91.5. But instead of just buying another, I'd like to possibly try something different for my 89 and then use the old LP for the 91.5. As far as finding a 2nd gen LP, I figure I'll pull one off a core engine CHEAP at my local junkyard if I choose to try one out. I see Stomp is running as high as 22psi with his FASS, and KTA is running more than that?? Just don't want to kill my 14mm pump next month on the dyno. Ideas?

G1625S

I've often wondered why one wouldn't run a 2nd gen LP with a regulator after the filter? Seems then one could custom tailor their fuel pressure for their individual needs with virtually no limit in pressure.

apwatson50

I don't see why you couldn't do that as long as you used a regulator with a return and maybe just plumb it into the return coming from the IP and injectors.

Alec

It would seem to me that a thrifty fellow could get a second gen pump, weaken the spring, and have a "first gen" pump . . . If you are too cheap to buy the regulator, that is.

Only problem for me is there isn't any local junkyard with these engines . . .

wannadiesel

I wouldn't run the 2nd gen pump without a regulator. The problem with excessive pressure seems to be that it puts thrust load on the vane pump (and tears it up), not that it causes case pressure to get too high. A bypass regulator (post filter) a 2nd gen pump would be a good solution.

I can drag my piston pump down to 5 psi under heavy load in 5th. I'm sure you can do the same, Bill. When the filter was new it wouldn't drop below 8 psi. I don't think force feeding the VE accomplishes anything, as long as it has positive pressure it is getting adequate flow.

RCW

Do not run a second gen lift pump on the VE injection pump as the comment by Wannadiesel is right on. What happens is the pressure and volume of fuel required by the P pump creates a lot of microscopic air in the fuel. That is just fine on the P pump with its tough pistons and large clearances, but on the VE pump the extra air and fuel will cause the vanes to cavitate and they simply go away after a while.

If you installed a system to eliminate dissolved air from the fuel, it would not hurt a thing but spend money for something that really gains you nothing relative to performance in the long run.

G1625S

So the next question is: does the turned down piston pump for the VE address the air issue separately, or is the lower volume/pressure enough in itself to eliminate a problematic amount of air entering the VE? Had anybody who's tore up a VE ever checked the vane pump to see if it may have been the root cause of internal pump damage on down the line? Maybe a post-filter FASS-type system is in order to keep the big 14mm plunger heads happy...

bgilbert

I think I might try Alec's idea of fooling with the spring in it. I can pick up one off an industrial p-pumped engine core cheap, course I'll get the part number off it first before buying it or trying it out. Might get lucky and get one with a happy medium- right between the 3936320's low pressure and the 3936316's high pressure.

I really am looking for someone that has tried one and if their VE survived or dumped fuel into the timing cover. This would only be for dyno or drag strip events etc, not daily driving. Sure don't need all that pressure driving around town.

blueberry

Why not just add an electric pump on the frame rail that you can switch on and off?

Stomp

I don’t see a big problem with running a second gen lift pump with a regulator. I have taken my new Fass pump as high as 29psi with no ill effects. I think KTA has the right idea since he has his pressure controlled with a boost regulator. The higher the boost the more pressure/fuel his supply pump gives to the injection pump

Here is some food for thought.

I now have a case pressure gauge installed on my pump. My mechanic drilled and tapped the governor area of the pump to get accurate readings of what is happening inside of the pump. On the return I took the orifice out of it and installed a regular banjo bolt along with an adjustable regulator. I can now adjust the case pressure to what ever I want to set it at. Right now at idle it reads the same as my fuel pressure gauge 24psi. Then when you raise the rpm's and the case pressure starts to rise. At 2000rpm's it sits right at 80psi. When I put the hammer down going down the road at 2000rpm's I watch it drop back down to 40psi until I let off on the throttle and then it will jump up to lets say 100psi at 2500rpm's. It all depends on high the rpm's are when I let off. Ok one more thing worth noting if you activate the KSB the case pressure going sky high. It pegs my 200psi gauge at higher rpms. I don’t know what it is at idle. I still need to do some more testing with the case pressure and the inlet pressure.

Ok with that being said I think we all know that you will loose the timing advance that the VE pump gives us at anything less than 60psi of case pressure. Usually the timing advance is somewhere between 60-80psi well that is what I have read anyways. (Someone can correct me if I am wrong.) So if I want to keep the timing advance all I need to do is play with the regulator. I can also raise my fuel pressure to the inlet side of the pump and it will also raise the case pressure to a certain point plus it won’t drop off as fast when I hammer on the throttle. So positive pressure and adequate flow might keep your stock pump alive, but you could be loosing out on power (timing loss) in the process if the inlet pressure drops to low. Then throw a KTA Special on there and you need all the help you can get. I did not get to check the pressures with a KTA head/rotor all these readings are from my old worn out stocker. I don’t even want to know what would happen with the KTA pump I think the case pressure would probable go down close to zero if you don’t have a way to keep it up. Maybe that is why I have had so many problems?

The only ill effect that I and a couple of other guys see happening if you have too high of pressure going to the inlet would be blowing the seal on the pump shaft and pushing fuel into the front cover and diluting your oil.

So put a second gen lift pump on Bill and just keep checking your oil. If you’re motor starts making oil you will know what the problem is. R&D pretty fun huh. Let us know how it works for you.

Stomp

bgilbert

Thanks for sharing your R&D Stomp. I'll post something when I get something figured out.

G1625S

Very interesting stuff, Stomp. Thanks for the writeup. Sounds like maybe the vane pump or, more likely, the spool valve in front of it can't keep up with the huge pressure/volume demand swings of a heavily fueled truck?