I have sent almost the same tread to the Computer Diagnostics & Programming board

I’m worried about the fuel pressure

My Autometer Fuel Pressure Gauge 0-100 PSI 6163 shows only 55 psi fuel pressure at 8 psi of boost (AUTOMETER Boost Gauge 6160 Cobalt Series 30 psi). I know that the fuel pressure should be 80-90 psi at 8 psi of boost. If I understand my DataMaster log, motor is not running lean? Maybe that Fuel Pressure Gauge or electronic sender is broken?

I logged some test data (DataMaster EE data) and wanted an opinion.

http://www.transam.fi/emc/Testi%203%202006-05-25.uni

Mods are:
Is there something wrong or not?

Thanks for your opinion.

BTW: Sorry for my english... I am from Finland

 

Someone correct me please if I am wrong. The pressure at the fuel rail wil be ~55 (actually 43.5 + 8 = 53.5) since your fuel regulator sets the rail pressure. I have heard FMU's up fuel pressure too.........I dont know. Maybe the FMU isnt working correctly...just typing out loud here.

 

FMU's can up fuel pressure anywhere from 1:1 to 8:1. Stock fuel pressure regulater is 1:1 with boost. In the procharger manual it recommends how many turns to open up the FMU based on injector size and engine mods. It sounds like your fmu is not upping the fuel pressure. How many turns did you open it up? Someone could be playing a nasty joke at the track by messing with your fmu setting.

 

You need to adjust your FMU.

 

FMU needle valve is turned close. I have cheked and cleaned FMU two times.
However I can see fuel pressure still rising from 40 psi to 55 psi?

 

Have seen that kind of truouble on a car there they had split the hose and run it both to the FMU and the bypass valve, the bypass had a leak so the FMU didnt get any pressure...

 

That may be the problem! They are in the same vacuum hose. Where should I connect those vacuum lines, any ideas?

 

I see fuel pressure like that without an fmu. Try pulling the fmu and see if you still see the same fuel pressure increase. If so, then you know its either the fmu, or booster pump. If you need either I have a known good one for sale.

 

Split the one to the stock FP regulator widh a T.

 

Thanks, i try it next

 

I have now connected the FMU vacuum hose the to the stock FP regulator, but no improvement
Factory fuel pump is working as usual, inline pump is noisy but it is working and FMU has never worked
Do you have any more ideas?

 

Start the car and hook air pressure from the shop into the fmu with a blow nozzle. If you see a large spike in pressure then the fmu is doing its job and you have a volume problem. The culprit is probably the inline pump. Check the ground and voltage to the pump.

 

Can't the pressure seen from an air compressor damage the fmu?

 

Can you verify this? Just a thought.

-Scott.

 

The story continiues

I have already new Racetronix LT1 F-body in tank (Walbro 255L/Hr) fuel pump & harness kit. I will install it next weekend. I will also order new Siemens / Mototron Deka 4 Flow-Matched 60 lb / hr injectors.

So, I ditch the FMU, factory in tank fuel pump and the procharger in line pump.

Of course i need new base tune after those modifications.
Bryan from PCMFORLESS make the tune.