I was looking for advice for upgrading my FMU and MAF. I've been having trouble getting my truck tuned right, I just ordered a wideband gauge. I keep reading/hearing about FMU and MAF upgrades, so I was wondering what I should get, something not too expensive lol. I'm thinking of running 12psi in the future so I want to get the right setup now.

So far on my 2004 5.4 3V I have:

vortech supercharger 8psi, HT0 spark plugs, 39# injectors, electric fans, SCT tuner, no cats (highflows to be installed this month).The FMU and MAF are stock, so is essentially everything else on the truck. 4.56 gears are going in at the end of the month to help turn my 35's!!

 

you are running an FMU with 39# injectors???


no wonders it isn't running right

 

I never got anything to change that with my kit, it was used maybe that's why!?


Do you have any idea what I should get to fix that, and where to get it?

Thanks!

 

you need a tune, remove the FMU, your stock MAF, fuel pump and the 39# injectors are enough for your power level

 

I'm working on a tune with a tuner now via e-mail, which is why I bought a wideband, so the tune part shouldn't be an issue. Honestly, I don't know anything about an FMU, let alone enough to remove it. Sorry for the uneducated response, but a lot of these things are foreign to me. Regardless, I'm always up to learn something new and get my hands dirty. A little more details would be helpful, thanks again for the advice!

 

it just clips into the fuel system, on the return side...


your truck is probably going pig rich under boost, taking countles miles off of your motors life span

 

yeah, I burned out my 02 sensors already, the new ones keep reading hot. I haven't been able to get it tuned for the life of me, and gas mileage is horrible to say the least. That's why I bought the wideband, haven't installed it yet. I'll try to dig up more information about the FMU, I'm still not sure where you mean lol. Thanks again

 

post some pics of your engine bay, and where the 2 lines for the FMU are hooked up

 

Here ya go, could be red or silver, probably attached to the firewall.



I don't think the O2s burn out, but excessive carbon from running rich will kill them. The widewand sensor doesn't like super rich either.

 

I downloaded the vortech manual and skimmed through it quick this evening and nothing caught my eye about messing with the FMU, it just talked about the bigger 39# injectors and how to install them. So basically I just remove the FMU and re-tune for that and I should be good to go?

It looks like 2 hoses go into the FMU and 1 come out, is there a proper way of coupling the hoses together, such as a barbed T connector?

 

the FMU should have 2 lines one from the Fuel rail and the other to the return line

basically you remove the FMY and plug the return line back into the fuel rail

 

His signature seems to indicate he has a later model with a returnless fuel system. Unless he has a heritage, there would be no return line.

 

There is no FMU in the Vortech 3 valve kit. Don't worry about it. Who is tuning your truck? Ask him. If he is unsure about the FMU run! Find another tuner. Your Kit should have had a Flash tool, aka hand held tuner, that plugs into the OBD2 connector. These kits are fine right out of the box. if you want more then you have to up the boost. that involves increasing the fuel and air entering the engine. At some point your fuel pump will not be able to supply enough fuel and the MAF will not be able to properly measure the incoming air. At that point you absolutely need to up grade. Now having stated that your truck will run better with the upgrades even before you increase the boost. But you will need to tune for these upgrades.

Think of a MAF as a counter on a turnstile. It counts the number of turns that it makes. If it allows one person (Think of an air molecule) at a time after 1 turn, 4 people will have passed. If you get a bigger turnstile that allows 2 people at a time 8 people per turn will have passed through. If you forget to tell the PCM that 8 people per turn are coming through it will only have 4 beers (think fuel) waiting. You will have 4 pissed off people and they will destroy the place. Engine runs lean and explodes.

 

Thanks for clarifying that. I was just hoping I could find something else that might be causing trouble with tweaking my tune, so I thought the FMU or MAF could be culprits. Once I have the wideband gauge installed I think things will go smoother. It sure is tough doing things via e-mail.