Truck Repairs: Cummins L10 STC Smoking and Rough Idle Part 1

We try to get to the bottom of this Cummins L10. It starts and runs well, but when cold it will not idle correctly and has a lot of white smoke.

[stevecanny]

I love a good episode of Mechanical Mystery Theater! :) The STC valve had means and opportunity, but no motive. The injectors are looking very suspicious, but they keep their internal operations well concealed. Tune in to the next episode where (we hope) misbehavers will be brought to justice and order will be restored!

[sfordguy]

Wes, NO unqualified person should disassemble a STC injector nor any other injector for that matter due to “class fit” tolerances being observed in a clean room. If the STC valve is working as you showed and all injectors are bypassing air except a clogged injector then the Cummins procedure is to R & R the injector(s) as necessary.

I was laughing when you did your initial testing but, I was very glad to see you found your mistake. Then you stumbled on the injector check valve issue while explaining and thinking. Your a good mechanic man and don’t talk bad or second guess yourself, your a very thoughtful and read the theory of operation type of guy.

[keeganwebber]

"if you said 100 dollars, you must work for cummins" giggled audibly at that one

[jimmy_olds]

I worked at a pre owned truck dealer, we bought out a fleet of old Ford L9000 quad axle dump trucks from a local contractor. They were time capsules. All powered by L10 Cummins backed w 8LL. The phone rang off the hook about those trucks until the last one was gone. I sold one to this old timer, he “tuned” the injection pump in the parking lot with his pocket knife just before he took off. The L10 Cummins will always remind me of those old Fords and that old guy

[michaeldunagan]

Thank you for the schematic.of the STC system.

Visual aides—I guess I am more of a visual learner—really helps me understand technical jargon just as you laid out in this video.

[alanrobison]

Menards is outstanding! I hauled many a load to their stores throughout the mid west.

[SteveSummers]

Nice detective work Wes👍. That stuff is testing and brain twisting at times. Always makes sense after a good hard look and some rest. I'm not sure I could have controlled myself. That injector would have been in pieces on my bench. Keep up the videos. 👍

[bcbloc]

I looked the boxes at Menards over pretty good and the Harbor freight ones seem better. We have guys in the shop with both and the harbor freight one feels more rigid. This is only on the big boxes. The 44" box at menards was better built than the HF in the store. The Kenworth dealer was the cheapest place for me to buy Cummins parts. Typically I find the recons are cheaper than getting what I have fixed.

[paulcooper]

I know this is a year late .. but ... 16:45 .. nothing on 5, nothing on 6 ... I thought I had somehow changed channels and started watching LPL!

[James-fsrn]

If u can't fix it, it ain't broke!
Have a great holiday!

[omegalpha]

I know this is an old video and shipping would be a long way but I can't tell you enough good things about a place here in texas called M&D distributors formally texas fuel injection...they can rebuild any injector I've taken them so far and even Bosch fuel pumps.

[JourneymanRandy]

Use a butterfly impact on the exhaust studs. It doesn't have enough power to break them but it may shake the rust out. It worked on 7 of 12 for me. I had to buy a set of twelve point sockets when I came across a 12 point bolt.

[kevinbelcourt]

I don't like the idea of a 24" deep toolbox. Very easy to tip if you have a few drawers open. 30" deep is better. Looks like the ultimate toolboxes are made in the usa. Just my thoughts. Keep up the great videos you have a great channel.

[ActiveAtom]

Great video I have no thought on the tool box we have 5 models around here maybe 6 and they each have a purpose for us of course you need to hold more stuff then these two micro-machinists. I like to understand this diesel mechanical work as we have no diesel knowledge so we are all eyes learning everything we can. We do know a good truck when we see one your truck is something we would love to have one of for personal use (pick up small vintage machines) only of course.

[robertquast]

Last time I did a injector in a big cam 855 I had to go to town and buy a 3/8” 12 point socket

[stevencox]

the thing most people don't get is Chinese products are only as bad as the person ordering them, they can make you state of the art for anything but the people buying the products in bulk to sell to us cheap out to make money out of us

[terryezzell]

Used to have several Mercedes straight trucks at Roadway Express Atlanta GA. Those diesels covered the loading dock like fog during the winter while idling a couple of hours before dispatch. They were brutal

[neadialain]

The masterforce toolbox is really well worth the money

[clarencewiles]

Thumbs up 👍 great video and explanation.

[sfordguy]

Wes your close to the problem but, not quite there bud. I’m a cummins tech and I primarily work on common rail engines but, I’m the only guy at my shop that knows the earlier fuel systems. Honestly, all the way back to the mechanical engines including the V8 903’s and I work on anything from 2.8L to 19L engines. So pretty much everything that came in trucks or smaller.

The old L10/10.8L, 855/14L and K19/19L STC engines which became the M11, N14 and K19 Celect engines. These engines all suffered this problem in variation and all had issues with the check valve in e top of the injector sticking. The fact you couldn’t stick a 0.040” wire in the injector lube Port is incorrect because, the check valve ball is what’s stopping the wire from entering the injector.