3406b Not making hardly any power

Brought the Pete to a great mechanic here in CT. He had me send him the parts list from Johnston RI peterbilt yo see exactly what parts were used on the inframe. He said something along the lines of some 3zj's we're actually 350's from the factory and not 425's. After researching we did Confirm mine is a 425. He pressure tested everything had my driver go for a ride. Checked the afrc diaphragm, afrc valve,. Both of which looked good. He ended up turning the fuel up %25 and the boost is now reaching what I believe is normal range. Prior to turning fuel up the boost wouldn't go above 10 or so psi and that was hammering on it and now it is well over 15 psi while climbing hills loaded. The manifold psi is getting to about 18 psi now when maxed. Very similar power to my Western star which doesn't have a gauge and has same motor, but climbs hills at same rmp and speed. I still am planning on scheduling the truck to go in for a day to check timing, the rack and cam, have everything gone over etc. They did what they could in a quick stop by appointment. All in all it's running pretty good since he turned the fuel up. He also said maybe when they did the motor they left it right at spec for warranty purposes or even below spec a tad. Not sure just how much you can leave the fuel pump down and have truck still run but it was really low

 

After replacing the diaphragm I should really check the afr in a bit to see if the oil is still present.

 

Sounds like it's running better. How come I don't remember you saying that it was fresh off a motor job? That would be my mistake if you did. The B motor is all about that pump. Timing, adjustment on fuel and air, and pressure. When they do motor job, they always set the pump on the low side. For warranty yes, but also because every motor is different and it's always better not to over fuel the pistons on a fresh motor job.
Have to ask did you put any money into the fuel pump, or did you do motor job and set the pump. You would def know if you did pump work because it's expensive. Can easily spend 4,000$ just on that pump.

 

No I bought the truck with about 125k on inframe a few months ago and just started running it

 

Motor was done and truck picked up the first of the year 2015 from Johnston RI peterbilt

 

Truck sat for a few months at a time while previous owner tried to find a driver etc.

 

I own a 91 star with 5kj b model and as soon as I loaded this Pete I knew it had no where near the Power or boost that my star does and my star is only turned up %10 over spec at H O Penn cat in CT.

 

I know Wayne and the guys in Johnston fairly well. They are good, for the most part. I've been buying parts from them and stopping through for over 25 yrs. I don't go through there as much since they moved to where they are now.

The turbo they put on your truck, is it wastegated or no?
Do you have a working pyro gauge in the truck?
If your pyro is not working properly, fix it right away.

You may have to turn that pump way up, to get your best fuel mileage and best power. You also may need to cut it back some. It's gonna be trial and error until you find your sweet spot. Your westernstar will be a good gauge at least you'll have something to compare it to.

On the plus side there may be absolutely nothing wrong with your Pete, fuel pump may just not be tuned right. Odds are you will need to advance the timing a hair, and turn both screws out an additional turn or two. But I'm just guessing, you'll have to make your adjustments over the next few weeks to get her right. Good luck man

 

Think we narrowed it down on pete. Pressure tested the fuel pressure and vacuum pressure off the injection side. Mechanic helping me said vacuum pressure won't even get to 1psi. Should be around 3 or 4. Explains the loss of power on the high side of tranny and top end. He's checking the exact specs but thinks it's the fuel transfer pump. 2 bolts right under the front of the pump assembly.

 

Quick question, is the truck losing prime? If it sits for a few days when you go to start it does it crank for a little while before starting?
If so then that transfer pump is your issue. Sounds like your mechanic has a pretty good handle on it. Hopefully you got it.