The stumper.

I am currently running a super FMU from Vortec.
The diaphram split.

Sent it to Vortech, they rebuilt it.

While the FMU was out, I put back in the stock FMU from the S-trim kit. At anything approaching WOT, 7psi of boost and 5,500 rpm it would send the fuel pressure to 75 psi in a heart beat, and lay a cloud of black smoke.

I get the super FMU back.

Re-install with the same ring as before ... 2.2" ring ... was expecting to see around 60 - 62 psi at 6000 rpm +/- 9psi of boost. That would be 10 - 12 psi more than the 50 psi I have with no vacuum.

No added fuel pressure, just topped out at 50 psi where the adjustable fuel pressure regulator is set at. Boost guage topped out at 9psi at 6300 rpm. Scan master O2 reading says I went lean on the top end.

HHHmmmm .....

Get hand pump out and a bunch of tees and hose ... tie into boost guage, fuel pressure guage, FMU and an aux pressure guage.

At idle ... apply 6psi as seen on car boost guage and aux pressure guage ... get an extra 4 or so psi of fuel pressure. Pump up the pressure to 10 psi and see an extra 12 psi of fuel pressure. So far so good??

Put in a new line from manifold to FMU ... nice and big Try again at WOT, still no fuel pressure.

No big deal ... I'll just go with a bigger ring and get the fuel pressure that way.

Install the next size ring, and hit the throttle again expecting to see some fuel pressure. Nothing again, not a drop of excess fuel pressure on the WOT run, again, 9psi of boost at 6300 rpm.

WTF?? Is the T-rex pump dead??

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Plan B ... ditch FMU and run straight of the SVO 42# injectors which are running on 50 psi of fuel pressure and have the injector constant set at 47#

I see 16.7 milliseconds at 6000 rpm and 16.1 milliseconds of pulsewidth at 6300 rpm ... that's where it goes lean. Anyway, by my calculations I'm right at the 85% duty cycle.

Can I add ... how many more % fuel to the PE curve and hopefully be rich enough to stay safe??

My PE table is stock to 6000 rpm, so it peaks at 10.9% at 5200 rpm and then declines to 6% by 6000 rpm, I have added 3% fuel on the 5800 - 6500 rpm zone.

I'm thinking I should go to something like 12 - 14% enrichment from 5500 rpm and on up in the PE table ...

One last thing ... dyno run on wide band today ... A/F ratio was 11.8 - 12 to 1 untill it got near the top end and then it did start to lean out ... got to around 12.7 to 1

What do you think??

thx for any input.


LWM

 

ttt

not so fast you guys ... the mystery deepens.

Went back to the shop and had a pow-wow with the groo ...

Disconnected the FMU circuit.

Hooked up an aux pressure guage where the FMU was ...

Saw the expected 7 - 9 psi of boost where the FMU boost signal originated from, the passenger side of the manifold. Thus we acertained that a pressure signal was being generated from the manifold while the engine was under load.

OK

Went for a drive ... saw 50 psi FP at 7 psi of boost.

Back in the garage, disconnected the vacuum to the Fuel pressure regulator at the back of the engine. Hooked up the hand pump to the Fuel pressure regulator ... and applied 8psi ... watched in suprise as the fuel pressure rose from 48 psi with no vacuum to 56 psi with 8 psi applied via hand pump. Just exactly what a 1:1 FP regulator is supposed to do.

I never see more than 48 - 50 psi on the FP guage, even though the fuel pressure regulator on the engine should supply some extra fuel pressure. The vacuum signal is good and I'm seeing 7 - 9 psi of boost.

The boost guage is tied in to the same line as the fuel pressure regulator.

So ... the engine sees vacuum ... because the idle FP is 42 psi and a quick blip runs it up to 50 psi, about correct for my altitude and all.

But ... on that same circuit ... I don't get a manifold generated pressure signal that will get the FP regulator at the back of the engine to generate a FP in excess of what I would expect atmospheric pressure to invoke.

I suppose I'll change out all the vacuum lines tommorrow and see what happens.... but in the mean time... have a read and see if this makes any kind of sense.

thx

LWM

 

I think you are on the right track with the injectors,maybe try larger injectors and eliminate FMU and reprogram your computer?

 

I think either your T-rex or the intank pump is dying on you.