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Discussion Starter #1 (Edited)
I've got a 425 C-model that I have recently replaced the fuel pump with one off of a b-model due to a cam issue.
We used the nozzles that came out of the b.

I don't think the truck is running right, clatters a little, and sounds as if it has a misfire, and has a slightly rough idle when it gets hot.
With that said the it pulls very well and has good response. Black smoke quite a bit more than it did with the c-model pump but was told to expect that. I'm just concerned it's not fueling right.
Pyro runs around 900* (pré-turbo) at its hottest.
I know the nozzles are 3421's.

My question is are 3421's the nozzles I need or should I be using 3423's?
OR-3587's are what was in it before we swapped the pumps.
Not sure compression ratio but
the cylinder packs are OR-3782

Are there any other concerns with this set up?

It is a 24* pump and was timed with a meter.

Motor is serial#3ZJ05756
Pump is off serial#7FB27285

Thanks
 

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Junior Member
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168 Posts
It being a 3zj it most likley has 15.2 or 15.6:1 compression and the 3423's should match up better than the 3421's and run a bit cleaner. As far as the miss fire goes is it an off idle stumble that goes away or is it stuttering under a hard strain? What was the initial timing set to at 1000rpms and what degree is it at at 2000-2100rpms and what rpm does it start advancing? Also does the truck have a boost guage? If so how many psi is it making?
 

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Junior Member
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I see now you say it has a rough idle..id bet you have a nozzle that isnt right or a weak barrel and plunger....crack each injector line individually at idle and see if you can find the cylinder thats weak....also i didnt mention that the 3421's are for the 14.5:1 7fb bowl and the spray angle is different than that of the 3423 and has a bit less flow. The 3423 is what the 4mg's and 5kj's used with 15.2:1/15.6:1.
 

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Junior Member
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Discussion Starter #4 (Edited)
Thanks for the reply Cat Attack.
Just ordered a set of 3423's.
at idle, what I'm calling a "misfire" sounds kind of like an old gas carbureted motor through the exhaust if that makes any sense. Or maybe like a faint air compressor type noise through the exhaust.
Going down the road it Sounds good through the lower gears but the last few gears from 1300-1650 ,when the boost is up, you get a popping noise in the exhaust. Just doesn't sound right, although it Runs good and pulls good and It is not sluggish at all.
Everyone says I'm hearing things and it sounds like it should but I've driven the truck everyday for the last 12 yrs and I can tell it's different.

Just some more info
Has about 85,000 on complete inframe that had to be pullled back down about 24,000 miles ago because counterbores weren't cut The first time. (This was also the very first time that counterbores had ever been cut on this block.) New rod and main bearings were put in at that time as a precaution.
7FB pump was put on about 15,000 miles ago.
 

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Junior Member
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I see now you say it has a rough idle..id bet you have a nozzle that isnt right or a weak barrel and plunger....crack each injector line individually at idle and see if you can find the cylinder thats weak....also i didnt mention that the 3421's are for the 14.5:1 7fb bowl and the spray angle is different than that of the 3423 and has a bit less flow. The 3423 is what the 4mg's and 5kj's used with 15.2:1/15.6:1.
My money is on the B&P or bad nozzle. Your not crazy. I had the same sound in the exhaust under a hard pull at about 1600 and nobody could hear it put me.... Lapped and replaced pumps same day I replaced new junk reman Cat injectors with new -not reman. I highly discourage using Cat reman injectors. I had 3 that were junk and 1 suspect at under 50k miles. No matter what you use, I would have them checked for pop and pattern so you know for fact what you have.
 
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