[Phoenix]

I have a 2005 Cat C-15 engine with about 635,000. Since I bought this truck (Freightliner XL) used two years ago I have no idea if anything was done to the injectors. I had an overhead done about 10 months ago at a FTL dealer and they said the injectors looked good. My fuel mileage has been averaging 6.3-6.6 until last week. I heard what sounded like a small backfire under the hood and since it never repeated I thought it was water condensation in the fuel or in the fuel line. I added some Howes fuel cleaner but noticed that my mpg has dropped to 5.3. I bought fuel in the southwest and so didn't think it would be a mix. The mix used when I run up north in the winter does cause my mileage to drop. How can I tell if one of my injectors may have gone. The engine sounds smooth when I idle and I just changed my fuel filters.
Thanks..

[Dejanh]

If the engine runs smooth and it isnt puffing smoke, youre OK as far as i know. MPG varies...

[Fredog]

have your engine running, turn the cruise control off, then hold resume until the check engine light flashes. you will get a certain amount of flashes then a pause then some more. this is your fault code. code 55 ( 5 flashes, a pause then 5 more) means there are no codes. if you get anything else, call a cat dealer and give them the code and they will tell you what it means, I suspect you may get a code 92 which is a bad intake valve solenoid actuator plug, everyone I know with this engine has had that problem, the part is 20 bucks and if you cant do it yourself about a 100 labor ( 1 to 1 1/2 hours) they can also do an injector test with the computer while it's there, if you do happen to have a bad one, it is very dangerous to let it go, if it drops you will be buying an engine

[CanTech]

I work on Cat, Cummins and Detroit engines. I am a tech at a Western Star/ Freightliner dealership.

Issues with a injector flutter are hard to diagnose with Cat ET. System tests usually come back normal when injector cutout tests are performed. When the Top end set was performed and they told you the the injectors "look good" meaning they were set correctly will not give you accurate analysis of a injector spray pattern.

Needle valves and solenoids fail over time as well as injector tips. Unfortunately when maintenance is performed on a engine the injectors are overlooked. Most of the time a injector is replaced one at a time as they fail. This in poor maintenance since injector tips wear over time causing the atomized fuel to "clump up" producing excessive carbon build up and overall fuel consumption increases due to poor engine performance.

It sounds stupid to most owner operators when explaining the above, but it is a proven issue with all engines especially diesel engines. It is expensive maintenance to replace all injectors at once but when your engine hits a million miles and keeps on going it is worth it in the long run.

Fuel injector cleaners are a waste of money! they will not restore performance of a injection system or clean the injectors. Excellent way for them to make money by misinformation to their customer's. A fluid cannot replace missing material from a fuel injector tip! Diesel is an excellent detergent cleaner as long as your filter system is maintained. As low sulfur diesel was introduced the sulfer which was excellent lubrication was replaced with a alternative additive to prevent wear.

just my two cents!

[Phoenix]

Thanks for all of the replies. I appreciate the advice and information. My mechanical abilities ended when I sold my John Deere A farm tractor but I'll try finding that check engine code first. I have a pretty good CAT mechanic on my way home so at least now I can sound semi-intelligent when I talk to him. Thanks again.

[solo379]

Originally Posted by Fredog

I suspect you may get a code 92 which is a bad intake valve solenoid actuator plug, everyone I know with this engine has had that problem, the part is 20 bucks

Solenoids sold and replaced in pairs, I've just relapsed all 6, cost me $685 total, parts was $487. Funny, but engine ECM didn't show any codes, not even nonactive, but test showed 2 working wrong. So I've decided to replace all 6, since they got upgraded from 2005.