After driving 300-400 miles at the start of my trip on Sunday, I noticed I had very low boost. I had boost but took a LONG time to get up to full rated boost. I had almost no boost at all until I reached 1800 RPM then it came on and would go to full (20 lbs) and to my surprise, would actually go 2 lbs over what I normally see at full throttle. I could still run all day long at 70+ MPH once there. Temperatures all normal.

First thought was turbo or some airflow related issue. My air cleaner is a bit old and I do have some indication from the filter monitor that it is time to change. Most people are surprised that I still have the original turbo.

Going thru some trouble shooting procedures, the first thing I noticed was NO SMOKE! OK this is NOT a boost related issue. This is a fuel delivery related issue. If fuel is available but no boost from the turbo or related plumbing, I would have copious amounts of smoke

Thinking about fuel issues, first thing comes to mind is fuel filters, followed by lift pump, followed by injection pump issues. (man, I hope not!)

Thinking further if I can run at 70+ MPH and EGT is close to normal I don't think I have a fuel delivery problem. I had a loss of boost problem similar to this last year and it was the fuel shut off solenoid that was not fully pulling in and would restrict fuel delivery but in that case I could only get to 35 MPH.

After a rest, on Monday opened up the engine compartment and did some checking. Checked the fuel solenoid, was good, engine would start right up. Checked the tubing going to the waste gate, no problem there. Looked and did some checking around the injection pump-----OH OH-----!

On the back of the injection pump is a throttle modulator, it controls how much fuel can be delivered depending on the boost. It is only effective at low RPM and is there for emission purposes, SMOKE. As one applies throttle the the injection pump can only deliver enough fuel to accelerate (slowly) and when boost comes on, will allow more and more fuel.

What I found was that the small line from the intake back to the modulator was loose at the modulator. There is a "T" fitting and it is threaded into the modulator housing. A tapered pipe thread, but it was very loose. The waste gate pipe also comes off this "T" fitting.

With this fitting very loose, the modulator could not move with small increases in boost so therefore very low fuel delivery at low RPM and very slow acceleration and of course no smoke. It takes fuel to make heat and without heat, no boost. Further, with a small leak in this line, the waste gate was not getting the proper pressure to open up so the boost at the upper RPM range would go 2 lbs higher.

Turning the "T" fitting in 1 full turn tightened it up now I had smoke on throttle application and good boost response. The boost at upper RPM was now back to the normal 20 lbs. When I return I will disassemble the modulator to find the root cause of the the fitting loosing up. I also think there is a seal inside that may now be damaged or missing.

Will have pictures after I return.

SIDE NOTE:

Many years ago, I opened the adjustment cap on the modulator and turned the adjustment crew in about 1 turn. Started with 1/2 turn, tiny bit of smoke and a tiny bit of increased acceleration, Going to 1 turn made a tremendous improvement in off line acceleration. YES, I am getting more smoke when throttle is first applied but goes away quickly. I also have to watch the EGT more closely as it is higher than before at higher RPM. "P" pumps on all Cummins engines 5.9L, 8.3L can be adjusted for better performance off line.

You're one member I really don't worry about when heading out on the road. Excellent write up for our members to check.

To all... just because the fuel shutdown solenoid releases and it starts right up it doesn't always mean that it's not the problem. Also check the placement on the arm to pivot of the solenoid and at the shaft of the pump. They sometimes loosen up enough that it'll start but it is internally keeping it from fully releasing thus limiting your real ability to go to full throttle. Same holds true for throttle pivots and arms loosening up on the pump shaft.

The 3208 Cats won't show linkage placement so you'll have to read this writeup. Fuel Shutdown Solenoid 3208 Cat

After tightening the connection on the injection pump AFC things got beck to near normal but later, boost was still not back to what it had been. Has good power and full boost at upper RPM ranges but still not giving me good boost at lower RPM.

On the last leg of the trip, for some reason I had good boost at low RPM and a more stable engine temperature. There is something else in the turbocharger system that is not right and is changing. I have 5 months to work on it.

The first thing I will do is remove the complete radiator system. I intend to take out the trans cooler for the MD3060 and remote it away from the engine driven fan. With a sandwich of 3 cooling radiators it is impossible to clean the center radiator. I will also check the intercooler radiator for any leaks, replacing if any found.

Injector pump will come off and rebuilt with new higher rated springs timing advanced and a few other HP improvements. Not going crazy, just a few common sense changes to a crappy design and some over the counter upgrades.