What are your fuel pressure readings on a 95 LT1 Supply and Return

**beestoys** · 02-21-2014

Ok a little background here. Camino has a transplanted 93 LT1 running a 95 ECM it is a M6 setup. I have a Walbro 255 intank pump with a racetronix power harness and relay to give the pump full system voltage. The Camino is running fat all across the entire operating range. I did these pressure checks on the off chance there may be a restriction in the return line causing a backup and high pressure in the supply.

Did a check on fuel pressures and here is how it stands

Supply at idle 44#
Return at idle 3.5#
Vacuum line for pressure regulator pulled 50#
Return line for pressure regulator pulled 3#

Now I remember when I installed a Holley projection sytem in a Firebird anything under 5# on the return was not an issue.
Anyone have anything to the contrary from a manual or something that would say otherwise. There is going to be some return line pressure just because of the length of the return line and all.

Inputs or insights please

**steveo** · 02-21-2014

as i told you before stock regulator functioning properly is 43.5-45 with the regulator unplugged, and loses a bit for each inch of vacuum, so depends on your cam and idle settings what idle pressure is (usually 35 or something with a ton of vacuum in decel)

**beestoys** · 02-22-2014

Originally Posted by steveo

as i told you before stock regulator functioning properly is 43.5-45 with the regulator unplugged, and loses a bit for each inch of vacuum, so depends on your cam and idle settings what idle pressure is (usually 35 or something with a ton of vacuum in decel)

Agreed but was thinking if a had a high return pressure it could have been creating a raise in the supply. I am suspecting that the FPR is going south (it's the original equipment) and causing an over rich across the board. The above pressures confirm that now that I have had a couple people on another board come back saying 3 to 3.5 on the return is about normal. So good news is that my return line seems to be clear. I'll pull the old regulator and make sure its clear and get a replacement anyway.

**steveo** · 02-22-2014

yes it could be the return line, pull it, throw it in a bucket, and see what your pressure is

**brian617** · 02-22-2014

If the regulator isn't leaking (through diaphram into vacuum hose) and it drops the rail pressure with vacuum I don't see how it can be bad. In your other thread you mentioned having two fuel pressure gauges, did you use both of them to confirm accuracy? I tried to look the specs up on ShopKey but for some reason the information is way off the chart and for a different application (something wrong in there software). Maybe rent a fuel gauge from Autozone, O'Reillys, maybe a local shop etc as a third opinion.

**beestoys** · 02-22-2014

Steveo
I'll give that a shot next to confirm.
brian
No it's not leaking. That was my first thought for the possibility for the extra fuel. But it checks out good.
Thinking the spring has gone weak from age. The supply and pressure gauges are 2 different scales. I can't use them interchangeably (at least not for checking high pressure) I know and have verified both gauges are good.

**brian617** · 02-22-2014

If the spring was weak you'd have less fuel pressure than desired, effectively returning more fuel. The spring acts just as your thumb over the end of a garden hose, tighten you squeeze, more PSI. I see what your'e saying about swapping the gauges, wasn't thinking about the scale from 3psi to 50psi lol.

**beestoys** · 02-22-2014

Originally Posted by brian617

If the spring was weak you'd have less fuel pressure than desired, effectively returning more fuel. The spring acts just as your thumb over the end of a garden hose, tighten you squeeze, more PSI. I see what your'e saying about swapping the gauges, wasn't thinking about the scale from 3psi to 50psi lol.

Ahhh your right was thinking in reverse on how it limits. Well then It's looking more like a partial blockage on the supply side. I'll need to confirm but I am thinking the regulator is the last thing it see's before it dumps the pressure to the return line. If there is a partial blockage then it explains my high rail pressure on the injectors and the reason the thing is running fat. I have done a leakdown test on the injectors so I know they are all good. And I know it's on the edge because i had a vacuum line for the heater box controls off a couple days ago accidentally and the idle BLM's were better at 117. As soon as I found the line and hooked it back up they tanked again to 108.
I am still going to bucket it like Steveo mentioned. If the pressure only drops down the 3 #'s I am seeing with the return line hooked or not at all then I know to go looking before the regulator for my problem.

**beestoys** · 02-23-2014

Ok pulled the return line and dumped into a gas can. KOEO 50# running 45# so it's definitely not the return line. Pulled the regulator (what a pain) and didn't see anything blatantly obvious. So I am going to replace it anyway and we'll see where the pressure ends up afterwards.

**steveo** · 02-23-2014

hey man i had a failed regulator that made 47psi of pressure, and replaced it, it made ~43; i think it was just gummed up. i sliced it open after and it was full of crap. so that could be your problem

either way 50 is no damn good, and you can't trust it to reduce pressure based on map reliably either, right? throws everything off

**beestoys** · 02-24-2014

Originally Posted by steveo

hey man i had a failed regulator that made 47psi of pressure, and replaced it, it made ~43; i think it was just gummed up. i sliced it open after and it was full of crap. so that could be your problem

either way 50 is no damn good, and you can't trust it to reduce pressure based on map reliably either, right? throws everything off

Ok I am pretty sure my gage is on but I'll see if I can borrow another to be sure of the below readings.

I put a new regulator in and pressure is a little better 43# at idle Still 50# with regulator vacuum line pulled so unless the borrowed gauge shows otherwise I'm going to have to calculate an offset and trim everything back.

The only other option is a adjustable but I'm not sure that is really necessary. I should be able to offset for the extra pressure right or will the whole curve be wacked?

**steveo** · 02-24-2014

adjustable is ok but avoid aeromotive unless you're replumbing and going full external.

considering how rich your trims are, as i mentioned on the other forum, i suspect your gauge.

**beestoys** · 02-24-2014

Originally Posted by steveo

adjustable is ok but avoid aeromotive unless you're replumbing and going full external.

considering how rich your trims are, as i mentioned on the other forum, i suspect your gauge.

I'll see about another gauge then if it is at those pressures then is there a reliable solution. I have recalculated as stated for the 50 versus 43 or will I need to tweak another constant somewhere else as well?

**beestoys** · 02-24-2014

Ok
2 gauges same store both reading 38# idle 46# regulator vacuum line pulled so my gauge is off by 4#. That doesn't seem to bad now but I'll recal my figures and dump them in to see what happens.

I'll get the rest of the stuff and get the wideband in there and see if my 02's are cooked. Then I'll start tweaking once I know where I stand with those baselined.

Part of me wants to just start tweaking but I have gone down that road before and it usually creates more work than is needed LOL

Thanks for your inputs