Ditching FMU require burning a chip?!

[1sickgt]

If you ditch the FMU, do you have to get a custom chip burnt? I dont want to run the FMU, I would like to go bigger injectors and utilize my already intank 255high press.(without uning the T-rex)

Also, would 42's and a 255 intank be overkill for 8-10PSI on a stock motor? Or should I go with a smaller injector?

Any advice appreciated!
Thanks.

[speedytang]

Most with 42lb injectors have warm start problems without a Chip or Tuning Device. You can bypass the problem by holding the gas pedal to the floor when starting the car warm.

[1sickgt]

Most with 42lb injectors have warm start problems without a Chip or Tuning Device. You can bypass the problem by holding the gas pedal to the floor when starting the car warm.

Good to know!

[1sickgt]

So does this mean that I DONT have to get a chip burnt? Will the system run fine without the FMU and without a chip, solely relying on the MAF and the Fuel Pressure to get the correct mixture?

[speedytang]

The MAF will do the job if it is calibrated for 42lb injectors. You are always going to need a tuning device at this point because of your timing and fuel ratio to boost reference to get the most power and MPG.

[1sickgt]

The MAF will do the job if it is calibrated for 42lb injectors. You are always going to need a tuning device at this point because of your timing and fuel ratio to boost reference to get the most power and MPG.

Yeah, I have wideband access so I will set the A/F That way. I also have a BTM so after I set initial timing the unit should handle the rest(under boost), correct?

BTW do you set the A/f at idle? or is there a way to simulate WOT? or is there another way?

Thanks

[speedytang]

You must drive and have someone help you since you need to use real world driving habits. This is why a Dyno is so handy. How are you going to adjust A/F since you said you don't have Tuning Device.

[1sickgt]

You must drive and have someone help you since you need to use real world driving habits. This is why a Dyno is so handy. How are you going to adjust A/F since you said you don't have Tuning Device.

I was just going to use the AFPR to set A/F at WOT. I am looking into getting a tweecer RT.

[speedytang]

That idea won't work because your going to be building boost from 2500rpm and up. The AFPR won't help since the FMU is what will building up and adding fuel.

[1sickgt]

That idea won't work because your going to be building boost from 2500rpm and up. The AFPR won't help since the FMU is what will building up and adding fuel.

Im not planning on using a FMU. Just bigger pump and injectors. Does that make a difference?

[fanglemeister]

If you run an accurately calibrated MAF meter, the Fox EEC will command 11.78:1 at wide open throttle, and you should get close to that if you have a good meter installed. If you need or want to run a lower a/f ratio than that, you will have to install a tuning aid or a blower-calibrated MAF to get it.

Adjusting a/f ratio by fuel pressure for any running mode other than closed loop is not the best idea, once you get into closed loop, the O2 sensors will detect the added fuel instantly and start clipping the commanded pulsewidth to bring the a/f back in line. Eventually the EEC will decide it needs to clip the pulsewidth a similar amount in every running mode including WOT. Now, if the only thing you do with your car is make runs at the track, then this tuning method can work just fine, since it won't be running in closed loop long enough for the EEC to start clipping the fuel in all operating modes. Again, a tuning aid comes in handy, because you can run higher fuel pressure and simply tell the EEC via programming that you have a bigger size injector installed.

On the 42# injector question, the main problem is that the EEC has a fixed "minimum pulsewidth" wired into it, so at startup and at idle, it is commanding too big a pulse. You can clean up this problem some by running the disc-type injectors from Lucas or Accel, but these don't like having their fuel pressure spiked up much above 50psi, which you will get at 10-12 psi boost, from a manifold-referenced FPR.

[1sickgt]

Alright, So from what Ive read here and on a few other sites, Im going to go with a 36Lb injector, and a MAF calibrated the same. After I get it running, I will stay out of the boost, take it to the dyno and get them to tune it. What should initial FP be set at for the 36lb'ers(ballpark).

Thanks!

[fanglemeister]

Anywhere from 39 to 45 should get you close to where you need to be. You probably know this already, but in case you don't: the fuel pressure is set with the manifold reference line disconnected from the FPR.

Anecdote: back in the day we used to set our carb idle mixture screws with a vacuum gauge-- start at the recommended baseline, fine tune to get the strongest vacuum signal possible, and then readjust back @ 1/4 turn toward rich. We can do the same thing today with the fuel pressure adjustment, can even use the manifold referenced pressure as an indicator if you don't have a manifold vacuum gauge handy - adjust in small increments to get the biggest pressure drop (highest manifold vacuum) when the manifold reference line is reconnected, then turn it back up just a pound or two toward rich.

EDIT: if your idle fine tuning takes the pressure outside the 39-45 window, you need to re-clock your MAF meter to get the element closer to where the bulk of airflow is at idle.

When you go in for your dyno tune, make sure to first reset the EEC's Keep Alive Memory back to all zeroes by disconnecting the battery leads and pressing the brake pedal - you'll end up chasing your tail if the EEC is already making internal adjustments when they start to tune on it.

[1sickgt]

Anywhere from 39 to 45 should get you close to where you need to be. You probably know this already, but in case you don't: the fuel pressure is set with the manifold reference line disconnected from the FPR.

Anecdote: back in the day we used to set our carb idle mixture screws with a vacuum gauge-- start at the recommended baseline, fine tune to get the strongest vacuum signal possible, and then readjust back @ 1/4 turn toward rich. We can do the same thing today with the fuel pressure adjustment, can even use the manifold referenced pressure as an indicator if you don't have a manifold vacuum gauge handy - adjust in small increments to get the biggest pressure drop (highest manifold vacuum) when the manifold reference line is reconnected, then turn it back up just a pound or two toward rich.

EDIT: if your idle fine tuning takes the pressure outside the 39-45 window, you need to re-clock your MAF meter to get the element closer to where the bulk of airflow is at idle.

When you go in for your dyno tune, make sure to first reset the EEC's Keep Alive Memory back to all zeroes by disconnecting the battery leads and pressing the brake pedal - you'll end up chasing your tail if the EEC is already making internal adjustments when they start to tune on it.

Thanks for all the info Chris, I'll keep it in mind!

[greenlantern]

Good info guys but there was a question that went unanswered. I too am running 36lb injectors with 8psi of boost. I am running the 190 in tank with the T-rex. Can I ditch both of them along with the FMU if I go with a 255lgh intank?