Fuel pressure goes up on Accel?????

[JAG1]

All new Mechanical gauge, big line kit, Draw straw, just tried second brand new Raptor 150 and fuel pressure goes up with acceleration and rpms.

 

I adjusted to 18 psi but the dang pressure drops back and forth between 18 and 15 at idle..... you can time it with a watch, back and forth. Then when you rev it the pressure goes up way too high. Grid heaters are disconnected and I checked with a volt meter for voltage fluctuation but it's charging steadily when engine is running

 

 I switched to a different new raptor 150 today thinking it was the pump regulator... weird... because after you adjusted it to the 18 you get going down the road and the dang pressure goes up  as high as 25.

 

My 02 does not do this........ pressure is steady till you get on it and it drops to about 16 which is normal.

 

Any thoughts....?

Edited May 5, 2017 by JAG1

[dripley]

The fluctuation sounds just like the grid heaters cycling. Do you have them disconnected at the battery?

 

Can you check the voltage going to the pump when rev it to see if the voltage is spiking? That is spit balling from the electrically challenged.

[Mopar1973Man]

I think Dave hit it on the head. 

[Hawkez]

Does it happen at idle as well?  I can't imagine the grid heaters would do that as you accelerating down the road.  Have your verified your gauge is correct?

[JAG1]

Grids are disconnected and lift pumps hooked to the battery with the ECM controlling the relay. Voltage is steady at the batteries so I better check the relay control coming off the ECM.

 

It's weird.... you get going down the freeway and all of a sudden the pressure is way up to 25. Come to a stop and it goes to 21 that's after adjusting to 18-19 at idle.

 

Fresh start in the morning it bounces slowly like a clock pendulum back and forth between 18 and 15.

16 minutes ago, Hawkez said:

Does it happen at idle as well?  I can't imagine the grid heaters would do that as you accelerating down the road.  Have your verified your gauge is correct?

The higher pressure happens under increased rpms

after trucks sits for awhile, 18 at idle but swings between 15-18 just sitting idling. No grids.

Get going down the freeway and it goes to 25

Get to a stop after the freeway and it goes to 22 at red light idle.

25 again when truck gets going again.

 

I better get a another new gauge to compare. I did not think that Isspro Gauges would have problems. I thought they were the best.

[Me78569]

Is system voltage increasing as you accelerate?  

[IBMobile]

Restriction in the system between Raptor fuel pump →VP44→tank.  Return valve sticking?

[Mopar1973Man]

1 hour ago, IBMobile said:

Return valve sticking?

Raptors don't have a return line. Just a return port within the pump that returns the flow to the input side. Only the AirDog or FASS have the 3rd return line to the tank. This is a reason I'm not fond of the Raptor pump because it's possible to cavitate the pump. 

 

 

[IBMobile]

 The restriction is after the Raptor acting the way a fuel pressure regulator does in a gas fuel injected engine. 

[jlbayes]

15 minutes ago, IBMobile said:

 The restriction is after the Raptor acting the way a fuel pressure regulator does in a gas fuel injected engine. 

 

Dis. It is also post the gauge location.

Edited May 5, 2017 by jlbayes

[notlimah]

I had issues with one ISSPRO mechanical fp gauge. It would increase pressure until it got until 14psi and it would just stick. If I knocked against the gauge it would move up slowly, but never up to where I'd seen it prior. Called ISSPRO and they had a new gauge sent out to me by the time we hung up the phone. Didn't need to get the old gauge back or anything so if that's something you really suspect being the issue, you shouldn't have a problem getting a replacement.

 

I tend to agree with IBM and jlbayes, in that flow is restricted somewhere. Could be the return valve sticking at the VP, could be the a kink or something in the fuel lines or line to the gauge.

 

If all of that checks out ok, then I'd say something internal with the pump. When my FASS was doing the same, it was the return spring and ball that was causing it.

[JAG1]

Grids are disconnected and lift pumps hooked to the battery with a relay. voltage at the battery is steady.

 

Cannot understand why the above statement shows up just to post a reply.

 

Matt, just want to say thank you much for that information. It's got me baffled. The dang gauge is doing different not understandable things. I will look for restrictions like IBM and you say and go from there. I have all weekend to do some testing but no new gauge till Monday. I will find it and report back, but thank you to you all for the help. Is there a half way decent way to test the overflow valve here at home? do a by pass or something to see if I can affect the strange pressure readings?

Edited May 6, 2017 by JAG1

[notlimah]

As far as I've read there's no real way to check the overflow valve. I imagine if you have a regulated air pressure hose you could possibly check it but really don't know if you could verify it's functionality just by looking and blowing air through it.

Edited May 6, 2017 by notlimah

[JAG1]

 I could attach a hose to the return line and run it down the fuel fill neck. Easy to hook up on a flatbed and can watch flow and gauge at the same time.

 

Going to go over all the new fuel lines and make sure all is right plus look at the F/P gauge line.

 

Mopar Mike told me a long time ago to NOT use a 60 gph primary filter. That's my faul,t I got cheap so that's getting changed to a 90.

[JAG1]

On ‎5‎/‎5‎/‎2017 at 6:50 AM, Me78569 said:

Is system voltage increasing as you accelerate?  

 Will check today as I finally went back to the job and got the volt meter I left there.

[Mopar1973Man]

Like to told @JAG1 to check the output line with clear tubing and see if there are air bubbles in the line heading to the VP44. 

[JAG1]

Update; after running return line in a bucket which revealed no restriction and doing some tests on the electrical (found minor voltage drop from bad alternator/ engine grounds) I went ahead and changed primary and factory filters. I found amazing amount of crud in primary with the factory filter discolored after just two weeks of short runs and about 700 miles.

 

Started truck this morning and gauge is steady like it should.

 

Goes to show it's best to drop the tank when upgrading entire fuel system. It will afford the opportunity to clean out and rinse the tank. As it is I will need to change the filters again hear soon and it's nice to know what the gauge will be doing when needing a change.

 

Previous owner must have been buying stagnant fuel. Nice to have a primary filter to help polish the fuel as it circulates with return fuel. Also that return line going into the fuel basket causes only the cleaner fuel up the draw straw leaving more stagnant unfiltered fuel outside the basket nearer the ends of the tank.  Better to run the return fuel elsewhere, down the fill neck perhaps to help filter the fuel in general and not let the hotter newly filtered fuel return so quickly

[dripley]

 

Good to see you found the problem, no matter what it was. I will take my electrically challenged hine end to the wood shed. 

[JAG1]

Funny thing about wood sheds whatever is wrong it's plain to see what the problem is.

 

Electrical stuff is slowly coming to me. The more I learn the more time it takes to sink in and get thru that thick skull of mine.

[Mopar1973Man]

That is one thing I like about the draw straw. There is no way to plug it up being there is no screen. So any debris is captured by the prefilter and water separator on the AirDog. Then the AirDog will pump through the 3um filter then push up to the stock 10um filter which I know my fuel is polished clean. Then nice part is I can unscrew the prefilter and rinse it out and reuse the filter again.