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catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2244
Experience:  Field service technician for CAT 19 years.
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Would a bad spray pattern on injector cause high idle

Customer Question

Hi, would a bad spray pattern on injector cause high idle miss on 3306di (D5B).Machine starts ok and runs fine at low revs, at high idle the more you load the engine up the better it goes - as in you can make a push with full blade of dirt in 1 gear with slight miss at full throttle,go up into 2 gear and engine runs fine, when you reverse out their is heavy miss at medium to high revs under none/slight load.
Submitted: 7 months ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 7 months ago.
Yes, worn injectors can cause strange misfires. Other items can also cause issues with injectors as well.Depending on the type of injector, it could have been installed too tight and have damage to the nozzle.Pencil type could have the wrong washer or two washers under them. You should have more smoke than normal too. (Assuming the fuel screws have not been played with.)A dirty air filter can be a problem too. (If this engine naturally aspirated?)What have you done so far?
Customer: replied 7 months ago.
Hi, sorry about not getting back sooner. I have cleaned fuel tank, repaced fuel lines including return line and air and fuel filters. Machine is 1984 d5b s/n 48x -engine is 3306di - i think engine no is 10z. Not blowing any smoke, as for fuel screws the cover on pumps looks like it has been removed recently (have only just brought machine).
Expert:  catmastertech replied 7 months ago.
Since you have just purchased this machine, I would recommend a complete service. Change all your fluids and filters. Save the old filters and cut them open for inspection. Examine drain plugs for metal and if possible, purchase oil sample kit to detect serious issues like water or fuel in the oil. (Just to know the condition of the machine.) I would first begin by adjust the valve lashing. (.015 intake and .025 exhaust)Next check the fuel pressure and look for signs of air entering the fuel system. (sleeve metered engines are known to have problems)These older engines you can have the injectors pressure tested and that would also help isolate an issue. If you need further details, please provide the full machine and engine serial numbers. (If you can find the tags.)

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