Hello all looks like another quality forum. Sorry this is going to be a long post.. I was refered to this forum from the fullsizechevy forum. I have a 2003 Silverado 2500HD 4x4 w/ the 6.0L (LQ4) running an out of the box 9psi Intercooled ATI ProCharger, and a FastChips tune. Like I said it is an undynoed out of the box install, using the stock fuel injectors and the FMU that is supplied w/ the kit. I have Fuel Pressure, Boost, and EGT gauges in the A Piller. It has been on the truck for about 10,000 miles and so far no issues other than I don't care for the intake being positioned over the exhaust manifold, and the noisy bypass valve.

My questions are around Fuel Management:

Recently it was brought to my attention that the FMU and stock injectors are not the best way to keep a good A:F ratio and I may be risking the engine at WOT. I was told that I should ditch the FMU and go with larger injectors.

1. Just how bad is the FMU really? Obviously I don't want to fry my engine but I really don't desire to spend another $1000 between new injectors and another tune. What should I look for as signs of problems, I have not heard any detonation even under heavy towing loads and I need to keep the vehicle smog legal.

2. If I do decide to go with larger injectors can I just get a reflash from FastChips or maybe Westers or should I dyno tune it? This is my daily driver not a project vehicle and I need it on the road. My main concern is keeping the motor healthy but I wouldn't turn away better performance if it is available.

3. (Not FMU related) I also plan to regear to 4.56's (to compensate for lift and Tires) and was thinking about some long tube headers from The Other Guys. I suppose I should wait on tuning until these are done, any pro/con comments on headers?

I want the truck to be turn key simple and I don't really want to tweak with it constantly (not that I wouldn't like to, I just don't really have the time)

Thanks for any help you guys can provide....

 

Anybody? C'mon I know I am a new guy but I have read enough, to know that the experts are here...... please?? somebody please help the

 

don't know much about your unit. is the fmu equivalent to the aux inj's and computer on a whipple ? if so get rid of it. if it is doing an adequate job of fueling the motor and you are happy with the performance why mess with it. if you're worried, get some sort of logging tool that will show o2 readings and kr, or find a shop that will log it for you, but keep in mind if the fmu works like the whipple those numbers won't be accurate. the problem with the whipple system is basically it does'nt work on our trucks. there are flat spots, lean spots, rich spots, and you can't get accurate info with their computer in place so you can't tune it out. from what i've experienced with the piggyback on mine, i would never get another one, no matter who makes it. they are completely unnecessary, overcomplicated, and can't handle the task at hand. the stock pcm with correct tuning does a great job. for me the money spent on the inj's and tune was well worth it, i have had zero issues since i did them, and "retweaking" is not necessary. though you may not hear detonation, you may still be way off on your fueling and timing. your pcm will adjust the fueling as it sees fit to attain the proper fuel ratio,but the closer you get it to start with the less it has to compensate for, if for some reason the fmu goes bad, the stock inj's won't be able to compensate at high rpms. if it senses knock through the sensor it will pull timing to eliminate it, which kills performance. unless the fmu actually interfaces and is controlled by the pcm, pulling timing is it's only course of action once the stock inj's have reached 100% duty cycle. sorry if this isn't much help, if it was a whipple i would say with complete confidence that you should ditch the electronics. maybe somone with your system will chime in. definately regear for larger tires, you"re losing alot of torque. if you are concerned about smog better check on the legality of the long tubes, i think the edelbrock tes are legal, don't know of any others. i went with the edelbrock ceramic coated shorties, i'm happy with them. they don't require any modification to the exhaust and reduce the radiated heat you were talking about dramatically. they are also relatively inexpensive. you could take the money you save and put it towards the inj's and tune. anyway good luck, let us know what you decide, if you go with the tune< allen nelson has got these blown trucks down. e

 

You happened to post your reply right as I was checking posts. Any way let's see how good I am at explaining the way this thing works. The FMU on the Procharger is purely Vacuum/pressure controlled (no electronics) As a matter of fact Procharger claims that the system is designed to be used with the stock PCM. Basically the FMU is installed inline with the fuel return line after the stock fuel pressure regulator and works in conjunction with an auxilary high pressure fuel pump. The fuel pump runs constantly and during normal driving the stock fuel pressure regulator directs uneeded fuel back to the gas tank, as the boost begins to build and more fuel is needed the FMU constricts the fuel return line, overriding the stock fuel pressure regulator and forcing a linear rise in fuel pressure to the stock injectors & supplying more fuel. You can watch it happen on the fuel pressure guage: normal driving = about 55-60psi, 2lbs boost = 65psi, 4lbs boost= 70psi, and so on until it maxs at 9lbs of boost and about 90PSI of fuel pressure, then the tranny shifts and you start all over. The feedback I get is that this is very inconsistant, unreliable, and hard on the fuel injectors.

I guess what I forgot to ask in my original post is, if I want to go with larger injectors and a tune what size/brand is recommended? I am guessing w/larger injectors and a tune, then I can just ditch the FMU? Am I supposed to expect about stock fuel pressure with the larger injectors, being that the fuel volume is coming from the larger injecter instead of a higher pressure.

Recomended tuners? Nelson, FastChip, or Westers.

Also, definetely will be doing the gear swap, still not sure about headers.

BTW - You guys got some seriously impressive vehicles here....

Here's terrible pic of mine

 

No, the FMU isn't the best way to add fuel. Everything you've heard about it is true. If you don't plan on raising the boost, the cheapest way to make sure your fueling is adequate is to dyno with a wideband, keep an eye on your fuel pressure, and leave it alone. My FMU kept the air/fuel ratio around 11-1 cranked all the way rich.

If you get new injectors, you'll want a dyno tune also. 43lb injectors are $400 plus the cost of a dyno tune. Then you get rid of the FMU. You won't gain too much performance, but it will be more reliable.

Are you looking to get better performance/ better track times? Or are you happy with the power where it's at?

 

Well as you can see the truck isn't exactly what I would have bought if my primary concern was perfomance. It's a heavy sucker for sure. I know 11 sec 1/4's aren't in this trucks future with out major $$$ and I am not even gonna try. I wouldn't mind a little more power but, I want a solid reliable set up. If I can stomp a Hemi or a Ricer or two here and there all the better. With the FMU set full rich I see well over 100PSI of Fuel pressure at max RPM/WOT, I think that is too much for the stock injectors so I backed it down to the recomended 85-90PSI and that was all I did for tuning. I did have the PCM flashed by FastChips for the Charger, and to firm up the shifts.

I don't know, Tune it with the FMU and be done with it? or new injectors ditch the FMU, tune it and be done with it? Either way I am getting gears in the next month or two and am gonna need a reflash anyway, might as well get it all dialed in at once.

 

I think if you arent going to up the boost, then get it on a wideband to make sure you're not lean, and be done with it. A mild stall would make it alot quicker down low. I'd get a 2600 for that truck.

 

thanks for the explanation. sounds like someone trying to reinvent the wheel, or the fuel system as it were. i know all these companies are trying to come up with a bolt on kit that does'nt require a custom tune, but unfortunatly, noone has nailed it yet. i personally would get the larger inj's and probably get it dynoed rather than a mail order tune, if i did'nt have the efi and edit. tuning by ear is definatly a thing of the past. you said you had it flashed, if it was'nt a custom tune on a dyno or at least logged, there is probably power still to be had. i would get all your ducks in a row, gears, headers and any other exhaust or intake mods, inj install, and shop to tune it as all these things will affect your tune and dyno time isn't cheap. get it the way you want it then tune it. i know it's easier to say than do considering the expense all at once, but it's cheaper in the long run. at least you didn't get whipple. nice looking truck btw, good luck. e