freddy2pipes

OK guys, see if you can help with this one. My buddy has a 92 ctd thats giving him some grief. Lift pump has been changed and still acting up. Squeeze on the throttle and she wont make any power. Foot to the floor and 2 psi on the boost gauge. Back out of the throttle and hammer it to the floor and she makes 15 psi but then drops off to 2 psi again. We checked the intercooler and plumbing for leaks and all is well. About 2 months ago we adjusted the full fuel screw and it performed well but the idle could not be adjusted so we set it back. The truck ran ok after that and then suddenly this started to happen. We are at wits end with this. Any advice would be helpful. Thanks P.S. No other mods done to this truck besides boost gauge and its an auto trans.

Bushy

This sounds like the fuel 'guide pin' is sticking...
Your initial shot of fuel when you get on the throttle will give a moment of high boost due to the initial fuel shot, then quickly drop back down.
This problem is fairly common, assuming that is the problem. You can attempt a repair with the pump on the truck to start with.
You need to remove the AFC housing on top of the pump. Once that is off, remove the large rubber diaphram by lifting/jiggling it up and down... sometimes you need to rotate it while lifting it. If the guide pin is sticking the diaphram will take a bit of tugging and wiggling to get it out.
Once it is out look down into the hole it came out of... while looking down, manually cycle the throttle wide open. At about 1/3 throttel the little pin should pop out of it's hole down near the bottom. If it pops out cleanly, use a small screwdriver and push it back into it's hole. Repeat the process a few times and make sure it is moving freely.
If not, you can spray it with a light machine oil and keep doing the wigglies in and out... after a bit it should free up.
If after all that, it still doesn't want to operate crisply and quickly, then it's time to remove the pump top and take it in and have a new seal installed.
I think there are some decent pictures of the parts on the site...take a look around and maybe one of the guys can add more info from here....

Pastor Bob....

freddy2pipes

After following Paster Bob's advice, the truck ran much better, but still had the same problem just not as bad. The pin was very sticky and we were able to free it up. Some more investigation and 2 pots of coffee, the trouble was discovered. On the throttle shaft that goes into the top of the pump, there is an inner shaft that actually connects with the innerds of the pump. The shaft was slipping and when accellerating lightly it would not allow full throttle until the shaft was returned to idle and then mashed to the floor. Must have been just enough friction to catch it and force WOT. Thanks for all the help and hope this saves a rebuild for anyone else with the same trouble.

Bushy

Hmmmm..... if I'm thinking right .... the only way that could happen is if the large 8mm allen head cap screw is loose and/or the throttle shaft has dropped downward a bit and has fallen out of the serated indexing slot in the throttle plate.

Did you find that this thing was loose??? What was the deal/fix here.....>???

bob..

freddy2pipes

Not sure. Another friend of his used to work for cummins I think. He found it while getting ready to remove the pump to have it rebuilt. When my buddy returns from work, I will find out what the fix was but I suspect it was the allen screw.