I'm working on a 1994 12 valve 5.9 that resides in a small Business Class Freightliner. The truck runs fine once it gets rolling. The problem is that it doesn't want to move or accelerate from a stop. It seems to not be building sufficient boost off idle/under load. The truck will accelerate when the boost gauge reaches 5 psi.

I need a starting point to diagnose the problem. Any help would be deeply appreciated.

I don't know if the AFC Air Fuel Control affects this part of the performance. The AFC on my pick-up is controlled/referenced by one plastic tube from the intake to the rear of the high pressure pump. the one on the large truck actually ties the wastegate, intake and high pressure pump together through three air tubes.

Thanks,
Don

 

My AFC is plumbed the same way. If it isn't a hung up brake, or something like that in the drive line that is holding you up, the pre-boost fuel screw could be adjusted up a bit till you see a little smoke on take-off. It is on the back of the afc under a small stamped metal cover that looks like a big pencil eraser. There should be at least one tamper proof screw preventing you from removing the cover. After that, loosen the lock nut and thread the adjustment screw in a little. Tweak that until you are happy with the "just barely moving" smoke levels. For fueling from "just a little" boost to maybe 4 or 6 PSI, you can play with the star-wheel. You said it isn't moving to your satisfaction till it hits 5 psi, so taking tension off the AFC spring (adjusting the star wheel) should help you. The star wheel is under a plug in the top of the AFC that is removed with an 8mm hex key. Remove the plug, then rotate the top of the wheel towards the engine. This allows more fuel to come on at low boost.

 

Yours is plumbed with the three hose set-up? I need a photo of this plumbing set-up if possible. The factory Cummins manual doesn't show it and this one has been previously messed with. I have all new parts that I ordered from Cummins. I need to see how they tie together near the rear of the pump at the AFC housing.

I haven't played with the star wheel and I am unfamiliar with the setting behind the small plate but I will play with it.

 

This might help> http://dieseldatabase.com/read.php?id=58

 

i dont think itll be running fine for much longer ...that exactly what my 94 ram 2500 was doing ....now all of a sudden it will stall while im driving repeatedly (forwarned with a little shudder)starts up right away but surges and wanes and wont go above 50 mph. i changed the filters except for the fuel/water separtor (thats tomorrow) nd put some diesel booster and injector clener in the tank didnt stall today but the rest of the problems remain

 

If you pour cold water on the injection pump when the engine is acting up and it pulls out of it you have the infamous '94-'95 warped injection pump bore syndrome.
Only cure is a pump rebuild.

 

im a bit green....where do i find the injector pum...and is it expensive/difficult to rebuild...iverebuilt alternators before but tats pretty straightforward lol

 

The Injector pump is on the front of the engine, on the driver's side. It has 6 little steel tubes coming up out of it that go to the 6 injectors on the engine. The pumps have to pump to an insane amount of pressure... about 14,500 psi as I recall--(if I'm wrong somebody will correct that number). As a result the injection pumps have to be built to exceedingly small tolerances. They operate at half the engine speed. The pumps are pricey new, and a little less pricey rebuilt. I have sometimes added soybean oil to my fuel and at other times diesel lubricity additive as insurance against poor lubricity in the fuel.

 

okaythose tubes are CAKED with oil and grimeas my dipstick tube is ?loose?and spews gunk everywhere. as well as the injectors

 

Time to hit the car wash with some engine cleaner.