1. hello guys I visit this site when I need help and you guys have ALWAYS helped me out. As long as I truck I will be a member. Ive searched the forum for help and found some useful info. what I have is this.. A 1991 pete 379 with a B model. The truck has unknown milage on the engine. It runs good and has good oil pressure, no excessive blow-by, has a newer head (its rusted and the block,intake, and jakes are not) This is what I know. My problem is according to the boost gauge it wont get over 15 psi and feels like a 370 detroit in the power dept. just falls on its face once 15 psi is reached. sitting still the engine revs very quick(fastest cat i’ve ever revved) when pulling off it has lots of black smoke just weak as hell. So far I made a devise to check the charge cooler for leaks and its good, however by doing this i did find that 3 of the 4 boots leak when i charge the system to 10 psi. I have 4 new boots and 8 good clamps on the way.

    tomorrow i will be replacing fuel filters. I would like information on how to check and advance the timing, check diaphram in AFR, check adjust the fuel/rack screws in the pump, check fuel pressure. When i am sure the pressure side is leak free and i have fresh fuel filters i want to get a good bit more out of the 425. this is my second B model and I KNOW this thing will do way more. my last one would run with 550’s after the pump was turned up by a friend. thanks for any help.


  2. Two thijngs, whern you put the new boots and clamps on torque the clamps to 90 inch LBS. Anthting less the clamp will leak and anything more will cause the clamp to break prematurely. The other question I have is how do you know the ATAAC is not leaking. I used to pressureize them to a minimum of 30 PSI and look and listen for oleaks and then see if the system leaked down without leaking at the clamps. To check the AFR ratio, without disassembling it you can take the line and fitting off and see if there is oil onside. If so the AFR Ratio diaphragm is blown and will cause your symptoms. This can be replaced with little effort if you know what you are doing, otherwise have a “CAT” man remove, replace diaphragm and reinstall the AFR. They cannot be repaired on the engine. One other problem, maybe the timing advance is slipping internally causing the timing to not advance properly. This should be chacked by someone who knows to to check, repair and retime the engine.


  3. Fuel line maybe collapsed coming from tank reverse line from tank to injector pump


  4. Having lots of black smoke and high idle is usually a good indicator that you have a leak. Replace the boots you have coming and time the motor. Then see where your at, it could be a bunch of things but timing the motor costs nothing but your personal time and is a good starting point. Let us know how you make out.


  5. I’d say this guy got it figured out years ago…


  6. You want to check the CAC you pressurize it to 35 lbs, start by putting the plug in the right side and pressurizing the system, check the intake manifold, the boots, also the boost guage, and the AFC cover. Plug it at the left side and test the CAC put in 35 lbs air in the right side and read it on the left side.
    You want a ball valve to shut the air off and time it for 15 seconds, it should not lose 4 lbs air or you need a new one.
    The AFC you disconnect it from the intake manifold and AFC put on an adapter, #4 hose, and 10 lbs air if it leaks the diaphragm is junk.
    The fuel preasure you need about 30 lbs at full load and be sure the return line is open.
    The timing advance you should get a surge after starting about 2 seconds later it should change. If not you need to get it repaired. I set the timing 1/2 hole advanced, if you have never done it get it set and ask if you can watch.
    The timing it should have a slight rattle to it.
    JUst a thought!


  7. Haha your probably right. I didn’t even see the date. My bad.


  8. whats the AFC ?


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