Fuel pressure adjusting

[2500avalanche]

I just put on a fuel pressure gauge. I have a question about how to check my pressure.mindonhave an adjustable regulator. When I start it, at idle it is at 31 lbs. stock injectors, stock turbo.
How don't check it? What is the correct lbs? Also, how donjon adjust the regulator ? Thanks!

 

[Slyclone]

Re: Fuel pressure adjusting

Hey.

I think it goes like this..


Stock idle pressure is 40 psi with hose off. 50 psi idle pressure.

Hose off is vac hose on top of regulator.

If yo do have a adjustable unit there is a Allen head threaded stud with a nut that holds it from moving. Back nut off turn in threaded Allen head stud.

 

[dgoodhue]

Re: Fuel pressure adjusting

Stock fp is 43psi without the vacuum connected. At 20" HG idle that works out to 33psi at idle. The stock injector ulimate fp was 50 psi w/o vacuum. The 50# ultimate was 40psi.

 

[2500avalanche]

Re: Fuel pressure adjusting

Stock fp is 43psi without the vacuum connected. At 20" HG idle that works out to 33psi at idle. The stock injector ulimate fp was 50 psi w/o vacuum. The 50# ultimate was 40psi.

Thanks. So I do have the ultimate with stock injectors. My pressure at idle without disconnecting the vacuum should be 50?
Also, what is the reason for disconnecting the vacuum as well as if I need to, can someone assist with the exact ones to disconnect?

 

[dgoodhue]

Re: Fuel pressure adjusting

Thanks. So I do have the ultimate with stock injectors. My pressure at idle without disconnecting the vacuum should be 50?
Also, what is the reason for disconnecting the vacuum as well as if I need to, can someone assist with the exact ones to disconnect?

It should be 50psi with the vacuum disconnected. The fuel pressure regulator only has one vacuum line come out the top. The reason to disconnect the vacuum line is to isolate the fuel pressure, so the engine vacuum isn't affecting the fuel pressure.

BTW 50 psi is just a starting point for the ultimate chip, I adjusted mine based on datalog's, I ended up running less fuel pressure to lean out the WOT fuel mixture.

 

[fivetodrive]

Re: Fuel pressure adjusting

Stock fp is 43psi without the vacuum connected. At 20" HG idle that works out to 33psi at idle. The stock injector ulimate fp was 50 psi w/o vacuum. The 50# ultimate was 40psi.

Ugh.... I totally forgot about the vacuum line... No wonder I'm running so rich. Had it at 43 with the vacuum connected.

 

[Sean Krupa]

Re: Fuel pressure adjusting

Do you guys set FP with the truck off and fuel pump jumpered and line connected? Or is that wrong?

 

[Slyclone]

Re: Fuel pressure adjusting

Here is a pic of a FPR The vac. port is the taller one.

 

[Quickstop [UK]]

Re: Fuel pressure adjusting

FP jumped, truck off. :tup:

 

[dgoodhue]

Re: Fuel pressure adjusting

I use Long Term Trim or BLM indication in Closed Loop to give an idea whether fuel pressure is high or low of what the program is looking for.

BLM < 128 = pressure too high, system is reducing IPW.
BLM > 128 = pressure is low, system is adding IPW.

A couple side notes about the BLM's.

The factory ECM programing will only add fuel from the VE calculations at WOT, it will not lean the fuel mixture out. So if you have cranked up the FP and the BLM is 110, it will fuel it at 128.

Their is two BLM is the factory code. One for idle and one for everything else. (The BLM corresponds to the two VE tables)

 

[dgoodhue]

Re: Fuel pressure adjusting

Do you guys set FP with the truck off and fuel pump jumpered and line connected? Or is that wrong?

Normally it would be set with engine running.

I set mine at idle, I think I ended up doing 33psi at idle with the vacuum line connected, I knew that I was doing a completely custom tune, so it really didn't matter. My first tuning experiment which I screwed up so I set it at 30#, because my experience in the past was that some injectors need at 28psi to open properly, so I knew I wanted it higher than that. I up the FP a few psi on my second attempt because I know that I had a lot of lean spot in the upper Rpm the first time around.

If you have already done a bunch of tuning already (most likely in open loop), I wouldn't touch the FP unless it is way off... Changing the FP shifts the all fueling in open loop.

 

[fivetodrive]

Re: Fuel pressure adjusting

Thanks for your input Dave and Dave. Sorry to hijack but as I was liking at my logs tonight it looks like I still need to lower the pressure on crispy some more. Got it at 40 ish and I am still getting a reading of 124 all the time and down to 105... I am also having low voltage issues so I will fix that first. Probably getting a 26r battery...

 

[2500avalanche]

Re: Fuel pressure adjusting

Dave,
I am sorry, but what is blm and IPw. I am new into adjusting it, and I want to try to figure it out , while not hurting anything. How can you measure the long term trim?

The factory spec is actually 38-43 psi. Not "42".

I use Long Term Trim or BLM indication in Closed Loop to give an idea whether fuel pressure is high or low of what the program is looking for.

BLM < 128 = pressure too high, system is reducing IPW.
BLM > 128 = pressure is low, system is adding IPW.

For engines with custom programs, the ideal pressure doesn't have to be any value other than that the value is the same as it was when the tune was developed.

Lowering the pressure and retuning can improve idle quality on engines where the injector size is too large. And Increasing pressure and retuning can richen mixtures at high output on engines where the injector size is too small.

There's a lot more to fuel pressure than "set it to 42 with the hose off". BWTFDIK.

 

[dgoodhue]

Re: Fuel pressure adjusting

BLM - Block Learn Multiplier (long term average fueling)
IPW - injector pulse width

 

[fivetodrive]

Re: Fuel pressure adjusting

Go to www.powertuneplus.com

Best site for learning datamaster!

go to this page and look at # 11
http://powertuneplus.com/syclone/tunersguide_dm.shtm

Also does anyone have dig's patch for the wideband? I wanted to add it to my stock chip for crispy but I lost it in a hard drive crash...

 

[dgoodhue]

Re: Fuel pressure adjusting

I might have wb02 patch; I will look through some old.emails tonight. Its been a long time since even thought about ptaching a $58 BIN.

 

[TurboSBC]

Re: Fuel pressure adjusting

The factory spec is actually 38-43 psi. Not "42".

I use Long Term Trim or BLM indication in Closed Loop to give an idea whether fuel pressure is high or low of what the program is looking for.

BLM < 128 = pressure too high, system is reducing IPW.
BLM > 128 = pressure is low, system is adding IPW.

For engines with custom programs, the ideal pressure doesn't have to be any value other than that the value is the same as it was when the tune was developed.

Lowering the pressure and retuning can improve idle quality on engines where the injector size is too large. And Increasing pressure and retuning can richen mixtures at high output on engines where the injector size is too small.

There's a lot more to fuel pressure than "set it to 42 with the hose off". BWTFDIK.

This is a pretty detailed description of how to PROPERLY set fuel pressure. Thanks DaveP :tup: