I've been fighting a problem with an intermittent low boost problem. It would have basically no boost pressure until you hit a bump in the road while the you had a load against the engine then the boost guage would shoot up to almost normal until you lifted then it would go back to low pressure.

The turbo was replaced with a reman turbo about a year and a half ago. I removed the turbo last week and as far as I could tell the wast gate was tight. We aplied shop air and it took betweet 25 and 30 lbs to open it. While the turbo was out I made some test plugs and tested the intercooler. It had several sever leaks that our local radiator shop could not fix. I installed a brand new intercooler and a new set of hoses and clamps since the old ones had some rubb marks and minor cuts.

Since the install I still can not build more than 13 lbs at around 2500 rpm. It will some times shoot up to 20 lbs but that is nomally only in first gear which I will lose as soon as I shift gears. As most of you know you can't get very far with 4:10 gears in first gear!

My truck is mostly stock. The only mods I've done is a #10 plate and boost elbo. both done about 6 years ago.

Any ideas on what to check next or again would be apreciated. It's been along time since I've had consistant boost and power and I really need to get this figured out.

 

Have you done a boost leak test, it sounds like you might have a leak in the charge system.

 

did you check your primary fuel side from the tank to the fuel pump for sucking air. check all fittings and lines and did you change the fuel filter? rule out all of the cheep parts before replacing the exxpenceve ones. replacing parts only will tell you what the problem is not. brubaker57

 

Could also be a problem with the AFC. Tubing or problem with the diaphram in it as well.

 

This is what I'm thinking as well. Take the AFC off and remove the foot and take it for a drive. This will give you full command of fuel to your foot, so if your intake side is leak free, you should have more power and boost.

 

When you say remove the foot are you refuring to the tourqe plate I have in it? If I do remove it and it helps what does it meen? Is the diaphram bad as discussed earlier or is it somthing else. I'm going to get a new fuel filter for it also. I beleive the one in it I installed last year but the truck did not have alot of miles put on it last year. Thanks for everyones resoponses. I'm not bad with a wrench but I don't have alot of experience when it comes to diesel engines. Race season is about to start and man is it a long boring drive to the track with no power!

 

I too would pressurize the whole air intake system to check for leaks, after that I would start looking for a lack of fuel. It's quite possible that the shutoff solenoid isn't pulling up far enough to allow full fueling. With the truck shut off, you should be able to lift it manually and feel if it binds, then see if it lifts itself the same amount when you start the truck.

Checking fuel pressure and full throttle travel never hurts either.

I have seen the steel aneroid tubes break a few times. That is the tube that leads from the injection pump to the wastegate actuator. If boost pressure leaks there, the pump won't add fuel because it doesn't see any boost.

Your catalytic converter may be broken inside. A chunk of catalyst can turn sideways in there and block the exhaust flow, then when you hit a bump it can fall out of the way and temporarily allow flow again, the way you say happens. Drop the downpipe from the rear of the turbo and take it for a drive.

There, I've covered most of the possibilities. Hope this helps.

 

Take the AFC off the pump and take it to the bench. On the front, there is a screw that keeps a pin in place. Remove the screw, and pull the pin out, and the AFC foot will drop out. Put the AFC back on and go for a drive. If it is better, it means your AFC isn't moving. Could be a pinched line, a leaky fitting, or a ruptured diaphragm.

You can also pull the fuel shutoff solenoid off to make sure you are getting full travel on the shut off lever. The lever is in the run position normally, no need to wire it up. Press down on it to shut the truck off. With either of these being the issue, you should have a stiff pedal when you run into the AFC foot or the shut down lever. Do one at a time, so you know what changes and what doesn't.

 

Thanks for the replies. Yes I have checked the system for leaks and replace a bad intercooler and the hoses. As far as the exhoust it doesn't have much in that department. I have a straight pipe that dumps down in front of the rear axle.

After reading these posts I took a closer look around the AFC and the shut down solenoid and discoverd that solenoid's mounting bracket has toatally broken off and the solenoid is just hanging by the wire. Frankly I'm shocked it starts and stops at all! I'm going to stop by cummins tomarrow and see if I can get that bracket.

 

Thanks for the help everyone. I got my new bracket but before I put it all back together I tied up the fuel shut off lever and took it around the block. Man what a difference that made. I think it may be fun to drive my truck again!