Need help with FPR

[oc192]

Hello All, I need some help diagnosing a fuel pressure issue. My current walbro fuel pump and accufab FPR are about 8 years old. My fuel pressure was set to 43 line off and everything seemed to run as expected however the pressure would bleed off to 0 in just a few seconds after shutting the car off. I happened to have a dw300 sitting on the shelf so I went ahead and installed this pump. The pressure immediately jumped up to 55psi and the pressure would hold about 30psi for an hour or two after shutoff. At this point I thought everything was good.

The following weekend I turned the car on and attempted to adjust the pressure back to 43 line off however the FPR would not respond. Turning the top screw CCW to the point where it almost unthreads did not lower it all, and likewise, turning it CW didnt raise the pressure. It seems to be stuck on 50 now and when you shut the car off, it immediately drops to 10 and then bleeds off to 0 after a few minutes.

I ordered a rebuild kit for the accufab and installed the diaphragm (flat style), it still behaves the same as above but now seeps gas out of some of the diaphragm bolts. Should I just buy another FPR or do you think the issue lies elsewhere?

Also, when I add the vac line back on, it has no effect on the pressure, it still stays at 50.

 

[TexasT]

The dw300 does a lot of volume. You will probably need to drill out the return fittings as they hold the pressure back. Common occurrence.

 

[dank GN]

its not the fuel pressure reg its the check valve in the pump. and yes your return line is the most restrictive part in your fuel system . you can drill out the fitting like suggested the cheap way or just upgrade your fuel lines to a -8 supply and a -6 return and never have to deal with it agian that is unless you are trying to make 1000 rwhp in the future

 

[michael evans]

To me it sounds like there is other damage to the return ling as to why it will not lower for 50 psi.

A 300 will not normally produce enough volume to cause the issues you are describing.

First follow the entire return line to the tank and look for damage.

 

[BRAD_PADGETT]

I had the same problem with a DW 300 and stock fuel return line. Despite opening fittings pressure would not go below 41 line off. No visible restrictions on line to tank. Mine was solved electrically. I have ECU Gn. Beatav8v installed a relay and had the ECU lower pump voltage until full pressure is needed. Slick solution in my case without changing fuel return lines.

 

[Anthony P]

The dw300 does a lot of volume. You will probably need to drill out the return fittings as they hold the pressure back. Common occurrence.

@oc192, can't tell from your sig, do you really need that DW300 pump? a supersized pump only causes problems.

recall being on many threads like this. bigger than needed fuel pump overwhelms stock return line when fuel demand is low. some swapped to a fuel pump that better matched their performance level. some swapped the DW300 for a DW200. maybe that will work. that member drilled out the Saginaw fitting at the frame crossmember to mixed results - got fuel pressure lowered to 43 or so static but did not get the corresponding 9 psig fuel pressure drop when vac line re-connected (engine pulling 18 in hg) as fuel volume pushed by pump still too great.

another member had the same scenario. when drilling out fitting and smaller pump did not solve the problem, I suggested the Delphi pump used on the Syclone's and Typhoons. solved the problem as he needed 61 psig fuel pressure (static + boost) and the Delphi FE0114 output met that requirement .

read all about those cases and solutions here:

https://turbobuick.com/threads/fp-regulator-bad.459565/

 

[oc192]

Hello All, here is a quick update. I ran a -6 return and now the pressure is over 100!! When I turn the key on to just prime the pump, it jumps up to 80 instantly, then on to 100 when running. I put another fuel gauge on the rail just to make sure the gauge isn't wacked, getting the same readings. After some more inspection, we did find a kink in the feed line?? I am going to replace the feed line with -8 anyways but do you think this is causing the issue?

Thanks,
Don

 

[mikestertwo]

Hello All, here is a quick update. I ran a -6 return and now the pressure is over 100!! When I turn the key on to just prime the pump, it jumps up to 80 instantly, then on to 100 when running. I put another fuel gauge on the rail just to make sure the gauge isn't wacked, getting the same readings. After some more inspection, we did find a kink in the feed line?? I am going to replace the feed line with -8 anyways but do you think this is causing the issue?

Thanks,
Don

No...a kinked feed line will not give you higher than normal pressure. Your problem is either the return line or the regulator.

 

[RmvBfrFlght]

Hello All, here is a quick update. I ran a -6 return and now the pressure is over 100!! When I turn the key on to just prime the pump, it jumps up to 80 instantly, then on to 100 when running.

Thanks,
Don

Sounds like you picked the wrong line at the sending unit. The return line is the smallest of the three (the 1/4" line). If you connected it to the CCP vent line (5/16" line) there is a restriction orifice in that line at the sender.

RemoveBeforeFlight

 

[oc192]

Sounds like you picked the wrong line at the sending unit. The return line is the smallest of the three (the 1/4" line). If you connected it to the CCP vent line (5/16" line) there is a restriction orifice in that line at the sender.

RemoveBeforeFlight

you are right, I have the line connected to the middle size line. I assumed the large line was feed, the middle line return, and the smallest line was the vent.

 

[RmvBfrFlght]

you are right, I have the line connected to the middle size line. I assumed the large line was feed, the middle line return, and the smallest line was the vent.

It would have been much better if GM did it that way. But EFI was still being worked out in '84 - '87, so there is that.

RemoveBeforeFlight