3406 C low boost

[JasonG]

Posting here for someone else.

"I just purchased this truck about 4 weeks ago i have a 3406 c 3zj43112 arg # 6I1733 15-17 manifold psi is all i can build up. I have replaced fuel lines from primary filter to transfer pump to second filter and then to pump. also replaced transfer pump got 40 pounds fuel psi.
checked the air to air it will hold 17 psi for around 5 minutes no leaks i sprayed the air charger with soapy water no bubbles. replaced 4 air boots no leaks. had a cat man rebuild my timing advance and inspect my governor housing. at around 1230 rpms it starts building he set at 16 degrees. the truck smokes pretty good from a start but you have to stay in it to reach 70 mph also has what i call trashy smoke coming out of stack pryo stays around 81/2 water temp does try to climb slightly. when it starts out it seems to do ok until the boost hits 15-17 then thats the end of the story. i have checked the diaphragm and replaced it it was fine , my nozzles are suppose be 2or5169 i just found out this engine could have 16:4 or 15:2 compression pistons not sure what i have yet truck runs smooth just does not have that clack you normally here with one with a little fuel to it. i also took around out of each screw no change. had a spare turbo changed it no difference the turbo on it is a 7w9568 it should have been a or6689 from what i was told it is fine i have a 6nz turbo to install but going to have to make a few modifications to install. "

 

[rzucker]

What is the HP rating and does the truck have acceptable performance? I've seen 400 HP B's that only ran 20-22Lbs of boost under a full load and that was normal for them. Also, is he trying to run 1900-2000 rpms? I've seen 425 HP B's that would not boost until they got lugged down to 15-1600 to get some manifold heat going. Don't know if that was right or wrong... but it was 5 identical trucks. And what is the water temp. Some of those were happier powerwise at 195 than they were at 180. Just some thoughts. It may be more operating conditions than an engine issue.

Oh... check the boost gauge for accuracy and the tubing for holes, seen that one too.

 

[Truck Shop]

That pressure is low should have at least 70 psi, check the filter housing and primer pump. Did he check pressure at filter housing? That is a early C model with a 3ZJ#.

Truck Shop

 

[rzucker]

Whoops... Didn't catch the fuel pressure. My bad.

 

[Truck Shop]

Whoops... Didn't catch the fuel pressure. My bad.

Well the manual says minimum of 10 psi at low idle and full load at approximately 35 psi. And for some that's all they will do at full load. But what I have found is several that I had worked on
years ago would run anywhere from 50 to 70 at full load. And those engines ran better than any others. The fuel flows through the primer pump, if the check valve partially rolled it will cut the fuel back.
If it turns over completely it can shut fuel off. I know this because I've had it happen right after priming the system.

Personally I wouldn't go swapping turbos around because each turbo is matched to engine parameters. The only way you know what it's doing is on the dyno. But what has me puzzled is a C model with
a 3ZJ#. 3ZJ's were the last of the mechanical's, 3KC were I thought the first C models starting in 1993. Or so I thought, learn something new/old everyday.

Truck Shop

 

[rzucker]

I've had so many bad Cat primers right out of the box that I have considered trying to design one that works and do that as a retirement project. Or even add a good electric gear pump ala ISX Cummins style... Could be a Million dollar idea.

 

[JasonG]

Now that would be cool RZ.

Partial reply

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It is a 425 hp 2000rpm
i have had b models before that would run circles around this c model cat even my 350 mack I owned would
It's just dont have that crack you normally hear with a little adjustments
If it would be up boost to 30 it would be right the
water temp tries to reach 205 while the pyro never gets to 9
you have to keep your foot in it plus it has trashy smoke it is brown smoke though
no blow by runs smooth
it's crazy i beginning to wonder if they might have put some b model or different nozzles in the guy i bought it from new nothing about the engine
***************

I'll let you know if the filter head does it.

 

[Longhood]

20 to 22 boost is stock 425 3ZJ boost, many were set up 10 percent at the dealer new, at least here. I don't think the timing is advanced enough, a C should only smoke light grey for 30 second or so on fire up,
C denotes the wide bearing crank shaft, but SIS often refers to the early ones as B, only to say C on the next page.
the timing pin hole can get in the wrong place if the flywheel has gotten swapped during a clutch job, I can't remember the specifics
Mechanicals also have to have the correct fuel filters, many times the numbers get crossed up to the same as electronics, but these filters are Too restrictive