9ft vacuum line to FMU, any problems?

[bmxunderground]

on my daily driver I am using the vortech FMU. I have a 9ft -4 rubber vac line from the intake manifold, running back to the FMU mounted just beside the FPR. Attempts to hit WOT result in a complete lean state under boost unless I let off the pedal a bit. The car will then go rich. Aside from other possible problems, has anyone here had problems with this set up?

fuel pump: walbro 255
boost level: 5-8psi
injectors: stock
fuel: 92

 

[VelocitàPaola]

on my daily driver I am using the vortech FMU. I have a 9ft -4 rubber vac line from the intake manifold, running back to the FMU mounted just beside the FPR. Attempts to hit WOT result in a complete lean state under boost unless I let off the pedal a bit. The car will then go rich. Aside from other possible problems, has anyone here had problems with this set up?

fuel pump: walbro 255
boost level: 5-8psi
injectors: stock
fuel: 92

The length of the vacuum line shouldn't be your problem. Pressure acts on all points in a system equally. The Megasquirt developers have tested the response of a MAP sensor on the end of a 30ft. vacuum line and found no noticeable propagation delays. I would double check how you have the FMU connected to the fuel system, and then verify the disk size.

 

[bmxunderground]

Thanks for the reply. I knew before I posted that the line woudln't be the issue. I always kinda hope something small will be the answer, but as usual, I spend my mornings before work putting in Di time.

After a short test with a fuel pressure gauge, it appears that randomly under boost the FMU does not react to the pressure. Although I'm boosting, there is no increase in the fuel pressure. Then at other times, boost pressure (of up to 8psi) increases the fuel pressure to upwards of 100psi. (12:1)

The FMU is hooked up just as your diagram shows. Is it possible for the FMU to fail?

In the mean time I'll be checking other variables, fuel pump, vaccum fittings, etc.

 

[VelocitàPaola]

The FMU is hooked up just as your diagram shows. Is it possible for the FMU to fail?

Sure, it's a mechanical device. It's prone to failure just like any other mechanical thing.

 

[rstchris]

Check the pump too. If you can hook up an amp meter and a fuel pressure gauge and just let the pump run to see if it acts up even under high psi. Look for unstable amp draw from the pump and psi changes at the same time to diagnose a failing pump. It is more common for a pump to go than an fmu.

 

[bmxunderground]

once again, I am victim of my own lack of editing. I know everything fails, what I meant was, fail this soon. The FMU has only seen about 1000 miles of use now, really nothing much at all.

I'll get the equipment out tomorrow morning (Monday) and see about the amperage and fuel pressure. I'll report back.

 

[LD25Delta9]

I had the same exact problem about 1000 miles after my turbo build, too. But mine was a junk no name knock-off, not Vortech. It turned out that it was the FMU and after replacing with a BLOX it works fine....for now...hope that helps.

 

[bmxunderground]

for the sake of those searching posts like this for answers, I regret to say I have sold the car before ironing out the problems. New owner will be using HAHN portfueler so bye bye FMU.