Fuel pressure gauge fluttering under boost??

[Flyin Brian]

My cowl mount fuel pressure gauge flutters +/- 4 psi at WOT. I have my base fuel pressure set at 44 psi and at 15 psi boost it flutters around 55 psi. It should be steady at 59ish. What could cause this??
I put a new filter in, the old one was fine. I checked the hot wiring to the fuel pump, it seems good. My stock lines are modified from the frame to the rail. -8 feed and -6 return. Saginaw fitting on the return has been cut off to allow the fuel pressure to be set low enough with the Deatschwerks pump. Saginaw fittings are still on the feed line at the filter and near the motor so I know I only really have about a 1/4" ID feed in spite of the -8 from the frame to the rail. It was that way when I bought it. At 5300 RPM in third my injector DC is at 85% with 15 psi boost and an AFR of around 11:1 as read on the gas scale. I figured the 80 lb injectors should get my motor to 20 psi boost (that is what the TT chip is burned for) and still keep the AFR down near 10:1 assuming I have enough fuel pump. I know I need a double pumper, better lines, and possibly to dual feed the rail eventually to run real boost but shouldn't the Deatschwerks pump be doing a little better than this? Or is my motor really moving that much air?? I have checked my gauge against other gauges and it checks out.
Thanks for any input.

 

[Hot Air]

My guess would be that either your fuel pump or fuel pressure regulator have issues. Do you have a voltage booster? Can you log fuel pressure and boost?
Conrad

 

[Flyin Brian]

My guess would be that either your fuel pump or fuel pressure regulator have issues. Do you have a voltage booster? Can you log fuel pressure and boost?
Conrad

I have a Caspers volt booster. Voltage under boost holds steady around 15 volts on the Powerlogger. I can not log fuel pressure yet, just have to look at the cowl gauge. I can log boost. Boost log is not perfectly flat at WOT but only fluctuates a pound or so. I just installed the Accufab FPR a few days ago and the Deatschwerks fuel pump is only a few months old. Pressure was fluttering with the Bosch regulator too. Maybe the 80 lb injectors are draining the rail and the pump can't keep up?

 

[marleyskater420]

Your lines only flow as much as the smallest restriction. If you have the stock lines from the pump, then that is what they'll flow. If you have an incorrect filter size, that may cause some restriction as well. However fluttering sounds like some not hooked up correctly. Perhaps the wiring is not as perfect as you suspect, or the FPR is not working as well as you have hoped.

Is your stock rail dual feed? With a 250ci stroked and a big cam, you're going to move a lot of air. I would dual-feed your stock rails and put on a nice FPR.....coincidently I have a dual-feed stock rail and a new aeromotive regulator F/S..

Either way, check the wiring to the pump, like Hot Air suggested, and dual-feed the stock lines. When you dual feed them, you can put on an external regulator on the front of the rail and run the return from there. It'll clear the alternator, as I have my regulator in front of my champion rails right now.

...but seriously I do have a dual-feed rail and brand new aeromotive A1000 -6 regulator f/s with the braided lines already for the stock rail.. I also have a Y adapter that is -6 in to two -6's out (use it to dual feed the lines if you want to use a stock-style regulator).

 

[Flyin Brian]

Your lines only flow as much as the smallest restriction. If you have the stock lines from the pump, then that is what they'll flow. If you have an incorrect filter size, that may cause some restriction as well. However fluttering sounds like some not hooked up correctly. Perhaps the wiring is not as perfect as you suspect, or the FPR is not working as well as you have hoped.

Is your stock rail dual feed? With a 250ci stroked and a big cam, you're going to move a lot of air. I would dual-feed your stock rails and put on a nice FPR.....coincidently I have a dual-feed stock rail and a new aeromotive regulator F/S..

Either way, check the wiring to the pump, like Hot Air suggested, and dual-feed the stock lines. When you dual feed them, you can put on an external regulator on the front of the rail and run the return from there. It'll clear the alternator, as I have my regulator in front of my champion rails right now.

...but seriously I do have a dual-feed rail and brand new aeromotive A1000 -6 regulator f/s with the braided lines already for the stock rail.. I also have a Y adapter that is -6 in to two -6's out (use it to dual feed the lines if you want to use a stock-style regulator).

My stock rail is not dual feed. U looking to sell your dual feed setup? I will probably re-do the hotwire setup as it is old and possibly add the intermediate and in-tank harness that Racetronix sells. That should eliminate any question about wiring. If I still have the problem I will keep looking at pump, lines etc. Just can't seem to get enough E85 into this thing. Could just go back to race gas or start spraying methanol I guess.

 

[marleyskater420]

My stock rail is not dual feed. U looking to sell your dual feed setup? I will probably re-do the hotwire setup as it is old and possibly add the intermediate and in-tank harness that Racetronix sells. That should eliminate any question about wiring. If I still have the problem I will keep looking at pump, lines etc. Just can't seem to get enough E85 into this thing. Could just go back to race gas or start spraying methanol I guess.

Sent you a PM. Lets see if we can get this thing working! If you can't get it working with E85, going to methanol is only going to make things worse. meth takes 2x's as much fuel, whereas E85 only needs roughly 30% more fuel (compared to gas).

 

[Chuck Leeper]

It could be that the gauge is not equipped w/ pulse dampener..What size line is feeding the gauge? A shutoff valve that would allow you to "tune out" the pulses could/would make the gauge more stable.

 

[marleyskater420]

It could be that the gauge is not equipped w/ pulse dampener..What size line is feeding the gauge? A shutoff valve that would allow you to "tune out" the pulses could/would make the gauge more stable.

Perhaps he should look into Julio's fuel pressure transducer? That would give him exact numbers on his PL. No guessing there.

The 80's with a 300lph pump @20psi *shouldn't* be maxing out with a te-61. That pump should be fine, and those injectors will flow for a lot more horsepower than where he is at.

Wouldn't fluttering mean either there is a restriction in the lines that is getting clogged/freed, or that the pump is not getting a constant voltage to it? If the return line is only 1/4" at certain points like he stated, then perhaps that could be affecting the flow.

Try changing the fuel lines where the 1/4" restriction is. Change that to be a 1/2" fitting and connect it to your -8 to see if that helps anything. Start simple.

 

[Flyin Brian]

It could be that the gauge is not equipped w/ pulse dampener..What size line is feeding the gauge? A shutoff valve that would allow you to "tune out" the pulses could/would make the gauge more stable.

The gauge is the cowl mount style with a -4 an line going to the fitting on the end of the fuel rail by the regulator. It is an old Ashcroft gauge. I just took it off and looked in the connection on the back. It has a much larger hole than the tiny hole you see on the back of electric fuel pressure transducers so it is not really damped very well. Shutoff valve is a good idea for tuning out the pulsation, I may try that. It is hard to read that gauge when it is fluctuating rapidly like it does.

 

[Flyin Brian]

Perhaps he should look into Julio's fuel pressure transducer? That would give him exact numbers on his PL. No guessing there.

The 80's with a 300lph pump @20psi *shouldn't* be maxing out with a te-61. That pump should be fine, and those injectors will flow for a lot more horsepower than where he is at.

Wouldn't fluttering mean either there is a restriction in the lines that is getting clogged/freed, or that the pump is not getting a constant voltage to it? If the return line is only 1/4" at certain points like he stated, then perhaps that could be affecting the flow.

Try changing the fuel lines where the 1/4" restriction is. Change that to be a 1/2" fitting and connect it to your -8 to see if that helps anything. Start simple.

An electric fuel pressure transducer for logging FP to my Powerlogger is definitely on the list. Trying to read that cowl mount gauge and remember what it said after a run is hard for me to do. When I am at the track I tend to just floor it and drive. I only listen and look for the knock detector.
I agree that the pump I have should feed the 80 lb injectors up close to 20 psi boost. I may try and eliminate the 3 remaining restrictive saginaw crimps in the feed line next and see how that does.
Thanks for the responses!

 

[marleyskater420]

An electric fuel pressure transducer for logging FP to my Powerlogger is definitely on the list. Trying to read that cowl mount gauge and remember what it said after a run is hard for me to do. When I am at the track I tend to just floor it and drive. I only listen and look for the knock detector.
I agree that the pump I have should feed the 80 lb injectors up close to 20 psi boost. I may try and eliminate the 3 remaining restrictive saginaw crimps in the feed line next and see how that does.
Thanks for the responses!

The transducer will eliminate any guesswork. Get rid of those 1/4" feed restrictions. No point in having a -8 feed if your smallest diameter is more like a -4. You are only as strong as your weakest link.

 

[Flyin Brian]

Problem Solved.
After I installed the Racetronix double pumper, ran -8 from tank all the way to the rail, and used the stock feed line as the return I have no more fuel pressure gauge fluttering. I also installed the fuel pressure transducer and my fuel pressure readings are right on according to my base pressure and boost. I guess the 80 lb injectors were just draining the rail with the stock lines and single fuel pump. Now I can get back to tuning.

 

[Hot Air]

Glad you got it figured out! Learned a few things along the way, didn't you. Go get em.
Conrad

Problem Solved.
After I installed the Racetronix double pumper, ran -8 from tank all the way to the rail, and used the stock feed line as the return I have no more fuel pressure gauge fluttering. I also installed the fuel pressure transducer and my fuel pressure readings are right on according to my base pressure and boost. I guess the 80 lb injectors were just draining the rail with the stock lines and single fuel pump. Now I can get back to tuning.

 

[Flyin Brian]

Glad you got it figured out! Learned a few things along the way, didn't you. Go get em.
Conrad

Thanks Conrad.
I did learn a few things along the way. I learned that it is VERY important to have a properly modified fuel system when running E85 on a thirsty stroker motor.