Does anyone know where/how is the best place to hook up a gauge to test the fuel pressure on the 6.6 diesel? I do not see any type of schrader valve. Also, what should the pressure be at idle and under load? Thanks.

 

According to my 6.6/7.8 manual, it says to measure at the fuel filters. Pressure at the filter inlet should be min: 15psi and max of 28psi. Outlet side of the filters should be min: 15psi and max of 30psi. It doesnt say what and where exactly on the housing, but I think there is pipe plug ports on the filter housing you may be able to tap into. I would say at idle you should have 15 and no more then 30 at 2600rpm, loaded or unloaded. Are you chasing a problem with this truck?

 

Thats great info. Thanks. Yes, the problem is highway power. I have none going up a grade. Slows down to 40 mph. I have changed the two fuel filters and the moisture seperator filter already. I am getting around 18 lbs of boost but then it starts to dwindle as the rpm and speed go down. I will check the fuel pressure and post! Any other thoughts would be much appreciated.

 

That sounds pretty normal for what it is. If the fuel settings are all stock, they slow down a lot on hills.
There's 2 ports on the firewall side of my 6.6. One has the bleeder, the other has some quick coupling. You could swap out that coupling for a schrader valve. Looks like 3/8" pipe thread, so a pipe bushing for 3/8 to 1/8 pipe should do it. You'd need to test at max load, up a hill to duplicate it.

 

Thanks Dale. Mine has two ports on top, along with the bleeder, but they are not threaded. Looks like it could possibly be drilled and tapped, but I am a bit nervous of messing that housing up. What about puting a compression tee in the line between the filter housing and the pump inlet, would that work?

 

It could work, but a compression fitting isn't ideal, nor the most reliable seal. A double flare would be much better, and flare fittings are available everywhere.

 

I've got one of these 6.6's in my L7000. Thanks to Dale, I turned up the pump a little bit and it really came alive. Turned the fuel screw and the AFR only. I'm pretty happy with it now, but before, it was pretty numb. If your fuel pressures are where they should be once you figure out how to get inline with it, I would say refer to Dale's step by step video and turn it up some. I didnt go all the way, and I was very happy with the results. Keep us posted.

 

Ok. I was able to install the fuel pressure gauge after the double filters, before the injection pump. At idle it is steady at 18 psi. At 2600 rpm sitting still its at 18 psi. Going up a grade at 2500 rmp it did not go over 20 psi. Pretty much consistant at 18-20 psi. A couple times coming to a stop the psi went down to 12 or so but then came back up to around 18. How crucial is it that it does not hit the 30 psi range under a load?

 

That doesnt sound too bad for pressures. Remember, 30psi is a max, and you probably shouldnt be hovering there. Ive never recorded my fuel pressure, but that sounds good, along with your boost for a stock. Again, to get more power, try the fuel screw and AFR adjustment. Woke mine right up. Remember too that with there being no air to air cooler, it doesnt cool the air or make it denser. So unless this condition is something that just happened, I'd say its runnin well for a 6.6.

 

I will look at the video and give it a try. By the way what does AFR stand for? Thanks for your help. I will let you know how it works out. Probably will have some more questions once I get into it.
Russ

 

AFR means Air Fuel Ratio. Its a diaphram and screw in the back of the pump, hooked to the rack that allows more fuel to be sent as the boost pressure rises. One of the first steps toward emmission control back when. Pay close attention to the video. Its very well presented. Is this an auto or manual trans?

 

Most of the time, I dont even mess with the AFC(AFR), star wheel, unless I'm trying to cut the smoke back after cranking out on the screw.
I generally go by the term of AFC(Aneroid Fuel Control).

 

Ok, great. Its an automatic with an allison. Do I do anything different if its an auto tranny?