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Discussion Starter #1
Hey All, I have a 3406b (sn 4mg15186) that I recently bought and rebuilt. everything on the truck is stock and has all been gone through. With the only exception that it has or3421 nozzles in it now. It has stock manifold and turbo but my exhaust temps climb way too fast and way too high. I barely give it any throttle and it goes to 1100+. I’m afraid to drive it. My belief is that the fuel screws have been backed out too far by the previous owner bc It’s always had more than normal black smoke but didn’t have the heat issue until I put the bigger nozzles in it. I know I should probably just back the fuel off until I get it right but thought someone here might have a more logical answer.
 

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Junior Member
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ck your air to air system for leaks, That will cause a sudden increase in both. As to the different nozzles I am not familiar with 3000 series but if they are real big u may have it pinned down. Could be your timing is off? What kind of boost are you seeing? Where is your pyro probe located? I have 580 marine nozzles in my 3zj C model . The screws were backed out to like 10% over spec when I put them in. My power went up a gob and smokes a little more. I dont think I want the screws out any farther for fear of heat.
 

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Discussion Starter #3
My pyro probe is after the turbo. The nozzles are the factory nozzles for a 425 hp. I’m not sure how much the screws have been turned out but I know they were messed with by someone before I got the truck. I haven’t changed the timing but I’ve checked it and I believe it’s right. I feel like I’ve gained 100 hp from this but I didn’t gain any boost and my temps sky rocketed which tells me something isn’t right
 

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Discussion Starter #7
I’ve adjusted the timing, advancing, retarding, and back to on the money, and no change. I’ve screwed the fuel back down 2 full turns and no change. My CAC was leaking a little so I’ve got one ordered, hoping that’s what it is and I can get back to work.
 

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Discussion Starter #8
Replaced the CAC and no change whatsoever, still heating up too quick. It’s going to 1050 degrees bobtailing from 0-60mph
 

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Ol Dirt Contractor
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Sounds like classic over-fueling combined with lack of air flow. Did you test boost pressure going directly into the head?

Sometimes a plugged intercooler will cause these symptoms. Or mechanics leave plastic caps or rags in the intake. Cam timing could be set wrong.. Might be a bad mismatch on the injector nozzles.. Don't know where to start..
 

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Sounds like a rag or something in the wrong place:whs I am thinking it is something really wrong if it gets that hot bobtail.... Your boost sounds about right. You might want to double check your pyro and probe. I never had one flake out and read hot but I can see how it could be possible. BTW, if you have recently changed the probe could it by some accident be the wrong probe. some of the probes and guages do not interchange. It depends on what the max on the pyro is. Some were 15 some 1800 iirc and if you use the wrong one you absolutely can have a overly hot reading. I remember reading that in Isspro bulletin somewhere. Pyrometers are actually pretty sensative instruments reading an electrical current generated in the probe by converting heat energy to electrical signal.
 

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Discussion Starter #12
Sorry it’s been so long, the cause was that the fuel was turned up too high previously and with the bigger nozzles it made it that much worse
 

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The other guy
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Sorry it’s been so long, the cause was that the fuel was turned up too high previously and with the bigger nozzles it made it that much worse
Unless structeral failure or bowl quench is reached in fuel delivery, which for a DITA mechanical Cat is around 2200HP unmodified for flow, there is no such thing as too much fuel. It's timing. The original nozzle number, 0R3424, is really only used in early PEEC engines. Converting a PEEC to mechanical it is easy to miss something on, plus timing needs compensated for a different rise rate in the advance and a slower valve cam. 19* @ 1000rpm with the start screw at 1260rpm and no stop screw. Also your replacement nozzle is a 3423 not a 3421. 3421's are for 14.5 piston bowls and 3423's are for 15.2's. Most likely the advance spool is'nt coming up so you're not getting actual advance. That's the only way you can move timing all around and have no change. If the advance is working right there's kinda no way you didn't get real close one of the times.
 
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