Seafoam is a very safe cleaner/additive for any engine they say you can pour it directly in a vacum line or intake. It works very well I once added an entire bottle to about two or three gallons in my cars gas tank and drove around in 1st gear at almost redline for 10 minutes and it cleaned out 2 clogged injectors and the motor ran like new afterwards. Mechanics I have talked to say it is safe for any engine. If it didn't fix his injectors this time do it again and add 2 cans to a full tank of diesel, that might fix the sticky injectors.