Fuel pressure goes up on Accel?????

[JAG1]

That's what I do too, is get rid of screens down in the fuel tank so dirt will go to the primary filter where I want it and can get to it.

 

Dave Ripley, just make sure you don't have more than 3/10ths of a volt drop in voltage when you go from the back of the Alternator and then see what you have at the batteries. I had 14.8 at the alternator and only 14.2 at the battery. Had to take a rest yesterday so I've improved that some, about half by cleaning grounds. might have Tuesday off and will finish cleaning PCM grounds and one other battery ground on the block behind the oil filter.

 

I want to pull the pin connector off the ECM and inspect also. What's nice about this 01 truck is everything seems to be original. Lucky deal in my book when it's just minor things so far wrong with it. I'm amazed that the guy traded the truck in this way cause it's very nice with only minor stuff I suppose others would think are major if all you have to rely on is the dealerships.

 

 

[dripley]

Last time I checked mine I dont remeber any voltage drop. Have not checked that in a while though.

[JAG1]

Another update; I put on a 90 GPH primary filter and new factory filter and as said before, seemed to solve the problem since they were clogged with debri from P/O buying marginal fuel.

 

I next got to thinking about how I still have dirt and debri in the tank and wanting to use up the only new 60 gph filter I have left... you know... a lot of junk in the tank will quickly clog another filter so I put the new 60 to use temporarily and help clean the fuel. So now the problem of fuel pressure immediately comes back with pressures going well above the desired 19 psi, it is jumping to 24 psi on acceleration. I do not understand since a slower flow filter before the  lift pump should cause a drastic drop on acceleration rather than an increase.

 

I'm lost on this one everyone. The only thing I can think of is having weak batteries, they are old btw, would cause low voltage at first until the charge system could build up the batteries and drive pressures up with engine revs.

 

Another issue is the return fuel getting warmer and dumping in the basket where the pick up tube is..... as I accelerate the F/P increases as the fuel warms up, hot fuel getting dumped into the same basket as the pick up tube.

 

I need to get the return dumping elsewhere, possible new batteries, and after fuel is cleaner change back to the 90 gph filter.

 

But for the life of me cannot understand the amount of increase on acceleration with a slower flow pre filter.

[notlimah]

I know these raptors don't have the same returns as the airdogs and FASS systems but when I was seeing the exact same thing it was because my return spring and ball was all messed up. Makes me think that maybe your return line is clogged with debri. If it were I could see that higher resistance in that line causing higher pressure in your supply line. 

 

Does seem weird that filters seems to make the problem appear or disappear. Again, maybe just be due to a higher or low resistance in those filters causing some irregular pressure fluctuations. 

[JAG1]

Thank you matt it is acting a bit more normal with the new filters on there and adjusting the pressure down. I think when I go back to the 90 gph pre filter it will be better like before when I reported above.

 

I need to get the return 'Td' to go into the tank fuel fill vent line which puts the hot fuel elsewhere and not into the basket as the draw straw. I think the hotter fuel makes for easier fuel flow and causes pressure to rise on acceleration. Combine that with weak batteries in the mornings and higher voltage when the engine runs, is contributing to the problem. I'm also going to clean more grounds which seems to be helping more normal pressure changes, such as going down when on accelerating.

[dripley]

FWiW both my return lines go to the fuel basket with the pick up and I have never seen a pressure rise on acceleration. 

[JAG1]

What about cold mornings isn't it a bit lower than average and then increases as it warms? Mine acts like that only a lot more radical.

[notlimah]

I agree with @dripley, I don't think the fuel going back directly into basket makes that noticeable of a difference. Yea fuel pressures seem to increases slightly once the trucks been run for a while but that's more likely just the entire fuel tank warming up. I have a raptor pump on my 99 and it'll gain an extra psi or 2 after driving for a while.

 

It seems like something is restricting flow which in turn is raising your supplied pressure more then it should. Maybe that higher flow filter really is all that's causing it.

[JAG1]

I know leaving it dump in the basket is a good thing in colder climates. I ran the return into a bucket to check the flow and was surprised how quickly  it was getting warm even with the engine still cold and parked overnight.

 

Next test is a clear piece of tubing to check for air in the lines.

Edited May 10, 2017 by JAG1

[Haggar]

Jag,

 

Have been having trouble sleeping thinking about your issue.

 

Air dog doesn't have head/flow curves for their pumps.  I have been thinking about developing some.  (I would really like to know the NPSH requirements!!!!)

 

I think part of your problem is the 150gph pump being fed by "60 gph" and "90 gph" filters on the suction side.  It appears from the parker catalog (depending on the racor part number) most of these 90gph use 1 psi drop across the filter to establish their flow rate.  Since you are moving more fuel through than their design, the differential pressure needed to pass that fuel through goes up.  Just how much it went up I can't find.  (looking for flow/head diagrams as I type this)   (ok found this one .pdf is attached)

 

Notice the flow head for the 490R series.   That is 1 psi differential to get 90gph...  But look at the shape of the curve,  it is going over 2 psi to try to perform at 150gph (assuming it follows that curve and does not go more exponential)....  (notice the shape of the curve for the 120 is completely different, the design is different apparently.) 

 

The whole thing is you are in a suction throttling situation.  You just happen to be right on the hairy edge of the NPSH required for the pump to operate.  I think you are cavitating and making vapor.  This is why the regulator in the pump starts wandering... (it is designed to regulate liquid, not vapor) 

 

I don't think changing output pressure will help much either.  since the pump internally recirculates, the temperature is already increasing, which makes cavitation occur more easily.  (this is why some of the regulators return to tank....  to try and cool this fuel.  (Though a closed system will eventually heat the complete tank too....) 

 

I hope this helps.  If you really want to know what is going on, you will need to add a couple absolute pressure gauges across the inlet.  You may be able to pressurize the fuel tank and see if the problem goes away.  If it does you know for a fact it was suction throttling.  (assuming the filter can even flow that rate irrelevant of the differential pressure.)

 

Hag

Racor 490R flow head.pdf

Edited May 12, 2017 by Haggar
spelling...

[JAG1]

I think you are right on with this and will have more time to work with it and run some tests next week or so. It's interesting you came up with the term ' suction throttling' as I was thinking along the same line that causes an imbalance across the regulator.

 

It's interesting also that my 02 truck with a 90GPH pre filter and the Raptor 100, the fuel pressure does not fluctuate and behaves normal. 

 

With the 01 truck I have gotten it to behave almost normal by getting rid of the dirt clogged 60 and going to a new 90 gph, but wanting to use up the 60's I have stored up first, till I get rid of the dirt in the tank, I changed back to a new 60 and it's behaving badly again but not nearly as bad as the dirty one. I had no idea there was that much dirt in the tank and is my fault for not dropping the tank when I changed to the 1/2 inch drawstraw and be able to flush it out.

[Haggar]

Jag,

 

Let me know how your tests turn out.  I started thinking about some of these problems with my current setup...  When I drain the system, the FRRP that I use will NOT self prime.....   Unless, I disconnect the outlet of the pump at the inlet to the filter manager.....  The pump will then self prime, and if I re-connect it while it is flowing, never have another problem with it. 

 

Apparently, with the head of the filter manager, IP and return lines, it doesn't have enough NPSH to self prime, but once primed is fine.  ( the FRRP is in the stock location, so Centerline of pump is at or above fuel level.)

[Mopar1973Man]

Here is a good article on this...

http://www.pumpschool.com/applications/NPSH.pdf

[Dieselfuture]

I wonder if it's possible to do some kind of VFD (veritable frequency drive) on a pump. That way you could run cheaper filters and just adjust speed of the pump acordingly. Just an idea...

[Mopar1973Man]

17 hours ago, Haggar said:

When I drain the system, the FRRP that I use will NOT self prime

 

Because there is no return line to the tank. There is nowhere to vent off the vapor. Like an AirDog pump with the 3rd line to return fuel the Raptor's are just 2 line pumps. The regulator just routes the excessive pressure to the inlet again so it's impossible to self-prime a Raptor. The outlet has to be open because there is too much restriction on the injection pump to pass the vapor.

[JAG1]

So all this discussion has helped me understand that the gauge swing (high and low gauge confusion) is from cavitation caused by too much restriction on suction side.

 

So  when the flow on the suction side is greater than the restriction on the pressure side, restriction being fuel pressure, the cavitation stops and the gauge should read steady and make it easy to properly adjust the regulator.

 

   The above is a simple way of explaining it, but is a 'lite bulb experience' to me. Thank you all.

 

I think there may be a lot of dirt in the tank possibly clogging the pick up tube or too small of filter rapidly becoming clogged as discussed previously.  Also the pre filter mounting base  has a manual pump for priming the system which may have a problem.

 

I will report back when I have time to do more tests/ work on the system in a week or so.

Edited May 13, 2017 by JAG1

[Mopar1973Man]

One reason I love my drawstraw and AirDog. Suction tune cannot become clogged nor do I have to worry about dirt in the tank. Being the excessive flow is returned to the tank and it's constantly filtering the fuel.

Edited May 13, 2017 by Mopar1973Man

[dripley]

Pretty interesting stuff, fellas. Learned more about pumps today than I knew to start with.

[JAG1]

Funny thing.... this morning I drove around to a couple places. Dang thing is starting to.... what I believe, steady itself. Will know for sure Monday, job takes me a lot further.

 

Edited May 14, 2017 by JAG1

[notlimah]

Haha wonder if it was just air stuck in the system taking its sweet time to work itself out!!??