Lots of discussion, a while back, on higher fuel pressures being unusable...and possibly harmful to the VP44.

Many theorys were kicked around....was anything proven or generally agreed upon??

RJ

 

Nothing proven that I know of.....I have yet to see anyone be able to prove how high fuel pressure (10 + psi @ WOT) will somehow benefit the VP44.

 

I think its more of a safe state of mind thing for having higher pressures. I idle at 24-25 psi, and can't drop it below 15.I've read how many folk wouldn't go that high, but like people state, there isn't any evidence supporting how these high pressures are a negative influence on the IP. Granted, sometimes I wonder if I should get a new pusher pump to lower my pressures, but the way i see it is:

How many IP's have croaked because of low pressure? (lots)

How many IP's have croaked because of too high of pressure? (none that I have heard of)

Plus, I do agree that there are many more people out there with lower pressures vs. higher pressures (could be the very reason we've never heard of high pressure killing the vp).

Sorry I couldn't give you any actual rock hard evidence, just thought I'd throw my opinion out there.

 

In my hunt to find my lack of power problem I spoke to an injection shop here in NE Ohio that was supposed to be the best in NE Ohio regarding my VP (prior to the Blue Chip install) and mentioned to them that I was idling at 14psi and could not pull it below 13psi at WOT. They told me that anything over 8psi was way too much. I never called them back.

I'll agree with DD4x4, I have never heard of a VP failing because of too much pressure, but if there is anyone out there that has some info please speak up.

 

i thought i heard of hard start issues and it being bad for the vp seals if pressure is close to 30 psi. i idle at 21 and wot is 16 psi.

 

It is about cooling and lubrication. Higher pressure generally means a good movement of fuel. The more fuel you get through the pump the cooler it will operate and will also lubricate better.

 

I (edit: HEARD) that DD killed a VP with high fuel pressure-- at 45psi

The frustrating thing is that we just don't know. We BELIEVE that low FP from a bad LP causes VPs to die, but we have no proof at all. None. Some trucks go eons with a dead LP and the VP lives. Some of us have had VPs die with perfect FP (I did).

Likewise, we have no idea how much FP is too much. 20? 30? 35?

The only sense I can make of the FP situation is that you want as much as you can get, but not more than much over 14. If Bosch sets up a bypass valve to relieve FP over 14psi, then I'm forced to conclude that there is some reason they chose to do so. Why, I can only guess, but I'm gonna have to say that they had some rationale behind it.

The longer I'm around these VP trucks, the more I start to believe that VP reliability is a crap shoot. We don't want to admit that, because we want to feel like theres SOMETHING we can do, even if pump failures are completely beyond our control.

 

I will let you know when my vp bites it, it sees all of 30psi and does not seem to budge hardly ever, I have yet to see a pump leak at a seal it always seems to be electronics or vane thingamajobby.....so to the benefit of all I will be a marter

 

If you think about it the relief valve on the vp opens at 14 pounds. So max flow would be a 14 for cooling. Now how much fuel can it bypass? There is your differences in pressure. Low volume at 40 pounds would bypass. High volume would be a bigger problem. To hurt the pump it would have to flow more than the bypass can handle and build high pressure past the overflow valve.

How much is that? I really have no idea.

 

I know I am in the wrong section but I can tell you that I am obtaining some test equipment for the 3rd gens that can easily be used on the 2nd gens to see just how much fuel is being sent back to the tank.

The reason I am pursuing this is because of my in tank assembly being all melted and distorted from heat. Heat from super heated fuel returned to the tank. We feel that the CP3 pressure relief valve [not the pop off valve on the common rail], is either out of spec or sticking open. Hence, I am getting pressurized heated fuel sent back to the tank.

How did I determine this? I would get this intermittant stumble while cruising on the highway...I would normally have 10-12 psi at 70 mph. This stumble would be followed by fuel pressures going up to 15 and having no throttle response. This happened for quite some time and my Essex lift pump was being blamed. It was fine. Then I encountered the same stumble but the psi would drop to 7 and then another stumble and it would go back to 10-12. Eventually the stumbled started taking it down to 5, then 3 and then 0.

The dealer felt that the in tank upgrade would solve this. We put it in...now I have 7 at idle, 5 at cruise and 0 at wot. We did a test of the fuel pressures on the CP3 and they all came back low.
When we took out my in tank assembly it showed the problem...there where two holes in the pick up tube...melted through!
So my thinking says that the first round of stumbles was because the heated pick up tube was sucking shut and then the final round of stumbles was because of the sucking shut and eventually a hole in the tube.

Twice I used an infrared Therm on the tank and I got 176F and 181F !!!

I think some of this might apply to the VP-44 on a smaller scale.
Running high pressure does not always mean high volume. If you have fuel pressures in the 20-30 range, of course your VP is getting some of that to be safe but I bet a bunch of it is going right back to the tank from the bypass.
I wonder how long the relief valve will last?

Somehow, somewhere there has to be a balance between the pressures, volume and what the tolerances are in the CP3 or VP-44.

 

When healthy, my stock lift pumps (I went through three) would idle at 17 and cruise at 14-15. So I'm assuming that with the stock configuration that the pressure relief valve was always open except at or near WOT? If so, what's the difference now that I'm running the stock LP and a pusher pump at the tank, with 23 psi idle, 18-19 cruise, and 15 WOT? Unless I'm missing something, the differential stress on the pr valve seems marginal.

btw, 180* fuel in the tank? Wow. I gotta say, I've had my hands on the tank after a fair number of long, hot, summer runs, and I've never felt that kind of heat. Not arguing with you, just don't know what to think about it.

 

I'm riding with Hohn on this. They put the 14 psi bypass on for a reason. Timing pressure? The maintanance of the fuel pressure is SOMETHING we can do to try to exercise a certain amount of perceived control over the eventual dreaded demise of our VP's. It may be an exercise of futility on our part but most including myself are banking on the extra effort of maintaining a very good amount of fuel pressure and it's resulting additional flow to keep the VP happy to what we hope will be a long lived VP.

 

I have said it before and I will say it again.....we put an aweful lot of faith in fuel pressure as the cause and solution to VP problems.....yet MANY failures of the VP aren't related to the wear of the mechanical side of the pump at all - it is the pump mounted VP electronics that can't seem to survive anywhere near as long as the mechanical part of the pump. Then I seem to continuously hear that more fuel pressure will let the VP run cooler which in turn will let the electronics mounted on top of the pump run cooler.....does it? I have seen no evidence to support any of these claims - it is purely speculation. I agree with HOHN, the lack of knowledge about what actually kills these pumps and the amount of specualtion seems to be the worst part of the problem. FWIW, I seriously doubt the pressure and temperature of the fuel will have any effect on the VP electronics when it comes to the heat cycle related failures. It sounds like Bosch and Fed-Ex got on the right track with the updated VP44 electronics that are more durable......why hasn't DC?

 

Living in the South, with 6 months of 85*-100*days, Fuel temp has always been a question? For this reason, I have always filled my tank when 1/2 empty...other than hwy trips.
But I'm sure there are many in this part of the country that drive 100 miles past the warning light before adding fuel. Some of them must run high pressure pumps?
They don't seem to have a higher rate of VP44 failures; nor does the south in general....do they?

Doesn't that fact support the above quote?
AND, if the warm weather CTD's don't have a higher rate of VP44 failures...doesn't this also eliminate heat as a concern for the electronics?

If so, that leaves the mechanical concerns from higher FP....seals & valves.

Is my logic faulty?

RJ

 

Ok, that was a slight misquote from what I was trying to say.....I specifically implied that I doubted if fuel temperature and pressure would have any effect at all on the VP44 ELECTRONICS and their rate of failure.....I, in no way tried to imply that there would be no effect on the mechanical part of the pump. IMO, fuel temperature could quite possibly have a profound effect on the temperature of the pump internals, it's tolerances and the ability of the fuel to lubricate the VP mechanicals adequately. I was specically referring to the elctronic failures and the heat cycle related failures. Is it really the actual temperature of the heat that causes the electronic failures? Or is it the fact that the cycling of the heat is causing the solder to fail on the PC boards? I was under the impression that it was the cycling of the heat as I am well aware of how that can effect the service life of solder rather than the actual temperature.

No, I most certainly don't think your logic is faulty. We might be coming at this from different angles based on our experience with this pump. I do agree that there could be some issues with excessive pressure, especially with regarding the fact that the relief valve opens at only 14 psi. This means that ALL the addtional fuel that is over and above the 14 psi COMPLETELY bypasses the pump mechanicals and does not enter the pump to cool and lubricate it and goes directly back to the tank.