Bottom Line
Maintenance Q&A
Diagnosing sputtering step by step

By Paul Abelson
senior technical editor


Q:  I have a 2000 International with a Cummins 525 hp. I am having an engine miss on cold startups and when shifting gears. The computer shows nothing. Killing the injectors does not change it at all. It always does it when it’s cold, but may go all day without doing it again. Also, I get lots of blue smoke when it misses while shifting gears. Any suggestion would be appreciated. 

A: I went again to my “brain trust,” two TMC members who earned their Silver Spark Plug awards through their leadership and contributions to truck maintenance. Tom Tahaney retired from Kenworth as a field service manager. Carl Tapp is maintenance VP at a large truck load fleet. Here are their diagnoses:

First of all, have you checked your oil consumption? A little is normal, especially in a 10-year-old engine, but any excessive consumption could indicate other problems and might account for blue smoke. But their consensus is that your injectors might be over-fueling.

You should take this step-by-step, running a week between steps and comparing fuel mileage  before and after each step. First get a baseline by recording fuel use for a week. Then make sure valve clearances are within tolerance and valve timing is accurate. Tolerances could be excessive.  If you have an engine brake, make sure it is properly calibrated. Run for a week and compare.

If that’s not the answer, have Cummins recalibrate the fuel pump. Don’t trust this to a mechanic without proper factory training or equipment. See if that corrects the problem. If not, put in a set of factory remanufactured (not locally repaired or rebuilt) fuel injectors. The old ones may be dribbling, creating an over-rich condition causing your blue smoke.

Q: Last fall I traded my Century Class for a used Columbia. Lately, drivers have shouted on the CB that my headlights were blinding everyone. I could aim the round lights on the Century with aiming tool, but I have no idea how to set up aerodynamic lights, Can you help?

A: When they did away with mechanical aiming to allow better aerodynamics, TMC developed a Recommended Practice, RP 161, dealing with “Forward Lighting Aiming Methods.” Manual adjustments still use the adjustment screws. There are two per side, one for vertical aim and one for horizontal.

You’ll need a screwdriver, a roll of masking tape, a 25-foot measuring tape and a level. Find a flat parking area, 25 feet away from a vertical wall. Park perpendicular to the wall. If the lot is contoured for drainage and your truck isn’t level, your aim will be off. Use the level to check your truck’s position. Make sure all tires are properly inflated and have someone seated in the driver’s seat.

Measure from the ground to the center of the bulbs on the headlights and measure the distance between the low beam lamps. If the height of the headlamps is between 22 and 36 inches above ground, tape a horizontal line on the wall the same height as the headlights. If the headlights are between 36 and 48 inches above the ground, tape the horizontal line 2 inches lower on the wall than headlight height.

Then tape a vertical line where your truck’s center line intersects the wall. On each side of that vertical line, mark a vertical line that is equal to half the distance between the low beam headlights. The intersections of the two outermost vertical lines and the horizontal line are your aiming points for the center of each headlight beam’s hot spot.

Cover each headlight in turn with cardboard. Use the two screws to adjust the hot spot so it’s centered on the aiming points.

Make sure the hood is securely latched each time you adjust and measure, or the hood will be angled downward and the aim will be off. For more specifics, refer to the Recommended Practice. LL


Paul Abelson can be reached at