Hey all. well, i think ive finally reached a conclusion as to the cause behind rough starts, smoke and rough idle that improves as engine warms, but never really clears. Truck engine has about 310k. recently installed new motorcraft glow plugs x8, dieselsite waterpump and the 203 termostat (def recommend to all who have not done this). heres the scenario: cold start, truck starts right up but misses badly, smokes. let oil pressure build for a min then floor it WOT. will only reach about 2100 rpm for several seconds then after studdering a bit will shoot to rev limiter. while its missing, smokes like crazy. for the longest time i was thinking (praying) fuel issue. narrowed down miss to p/s rear two cylinders by unplugging injector harness plugs (two per bank). replace both injectors with known good injector and new rings TWICE. issue persisted. did remove stopped up ebps tube, cleaned out and reinstalled. got pissed and drove the hell out of it. (just installed 3.55 gears) had some fun. just trying to shake loose another piece of the puzzle. even removed valve cover, observed engine while running. injectors were spitting oil about the same. ohmed out injector harness and checked connection to valve cover pins, all ok. finally notice oil leaking between head and exh manifold confirming worst fear.......bad rings, loose piston or worn cylinder. does this sound reasonable? any viable options? or is it teardown/rebuild time? the only thing i did not do was check pushrods (which i hear are prone to bending) and valve guide (not really sure how to check or if they are even prone to wear that causes these symptoms) thoughts anyone?

 

Have you done a compression test on either of the two cylinders?

That stumble at 2100 sure points to injector o-rings.probably on another injector. have you checked the fuel filter for blackness?

 

i currently lack the tools to perform a compression test. did change the filter a while back, but very recently checked it. no blackness.

 

Sounds like you have bad injector orings with another issue.

If you have oil coming out of the manifold at the head that means you have leaky manifold.
Having oil in the exhaust is normal after changing injectors

 

yeeeah, ive been driving the truck for a while since those injectors were swapped out. and then oil leak is a recent development. ive re-ringed all injector on the passenger side, but havent disturbed the drivers. is it that unfathomable to have a worn out cylinder? and what about the valves/guides? anyone ever have one wear enough to loose compression through?

 

And if you need an engine, I've got one sitting out back. Had a '97 but trashed the body on it...

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would love to get it from ya!! i actually installed the engine thats in the truck right now. it was the first time i ever laid hands on a diesel! 5 years later ima detroit diesel certified tech. i work on diesels all day, thou theyre normally much larger.

 

not unheard of to find low compression but not real common either. most of the time it is a symptom of something else like extended use of a k&n (bad filtration) or oil supply issues.

you can make a cheap tester from the harbor freight kit...

Richard

 

i admit that i am using a k&n knockoff-type conical air filter. i have it hose clamped onto a sch80 pvc pipe union (4"od) and then clamped onto the intake piping. i keep forgetting to mention that this truck is not driven regularly at all. averages very few miles per month. anyway, i guess ill just start prepping core engine for rebuild. and getting back to the oil leak, i guess some oil might have made its way down into the cylinder during gp changeout. i used compressed air to blow all that oil off of the top of the gp. not nearly as messy as you think and way faster than the last way i tried to get the oil out. i have access to freightliner grade air filters and housings. might try to fab my own tymar style filter set up...

 

Run a compression test and report the numbers. The numbers will show any issues very quickly.

Richard

 

I'd suggest getting the compression tested, or making your own kit and performing yourself. An easy way of testing compression when hot is the amount of blowby you have (result of ****ting rings). Pull your cap off whi e the truck is running and see how much pressure your getting out of the valve cover. I have done a lot of commonrail cummins recently that will blow the capoff the cover due to holes toasted through pistons on failed injectors. We have a couple 400k plus 7.3 motors on original rings that puff when hot a good amount out of the CCV to atmosphere, but still will start in the dead of winter of straight plugs. Compression has to be pretty low to cause those issues. I have seen turbo wheels on trucks that look like a bag of rocks went into the motor, and even though they were prematurely failing and had poor compression, truck would not miss, and would still start in the cold just fine if the rest of the systems were in check.

Do this well before you rule out bad o rings. A if you are getting a stutter on cold start and then you can feel an injector kicking in, this can also be a sign of worn poppet valves on specific injectors. This will usually happen in the cold to the point that you won’t ever be able to start it when very cold. I know this may only be applicable to certain areas, but this has resolved the issue on 6 trucks in this last month. Between gelling and -25 degree temps, even when they were plugged in they failed to start. New injectors and they would start off the plugs in -40 within a second of cranking on the same fuel. Almost sold a truck a couple years back that had all new orings, gps, wiring, idm, injectors, gpr, batteries, starter, and the list goes on….turned out to be a set of injectors that had bad poppets, and were overlooked in the rebuild process.

Others can disagree , but I can usually take a truck for a drive in the morning when Ice cold and feel 1-3 injectors come to life once it warms up or stepping on it hard, I have even had others let it go till they will not start at all when under 40 degrees. Truck runs fine all summer(smokes a bit more than usual on startup) but once fall hits, and its plugged in it will simply will not start at all. Buzz testing is also helpful, but after disassembling injectors that tested null, and checking poppet valve tolerance, its not always a tell all test.

Hope this helps but I’d put your money on orings that are failing, or injectors that are worn. Not compression. But to make it easy on yourself, compression testing is the easiest out of all three. I do my tests on a hot test, not with an Ice cold block. Try that first and come back with the numbers. Most shops will charge around a 100 to do it…

 

thank you very much nossliw!!! i can never have too much information when it comes to diag. its always harder than normal to start during the coldest parts of the year, but its never actually failed to start aside from from weak batt/slow spin. i will def get to work on a compression tester. ive done the oil fill cap blowby test before but was never really clear on what exactly means "blows the cap off". i mean, yes when i take the cap off, i dont hear a "pop" and i do have puffs of white smoke rising out of the oil fill hole. when i turn the fill cap up-side-down and set it on the fill hole, it kinds slides off air hockey puck style, heavily assisted by the motor shaking with a miss. really thinking about a whole set of injectors, as this motor has a good mix of aftermarket and factory reman when i got. condition of any unknown...

 

Sold on compression ignition, are ya? So am I. I started off with an '83 ranger diesel.

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