Check for vacuum leaks?

Vacuum leaks would be the yellow hoses from intake manifold to the intake correct iv been trying to find a Manual to look it up but I can’t find a serial number on mine it’s rubbed off the top of the electric box

Vacuum leaks can occur anywhere in the lower intake manifold, the gaskets between the lower and the upper plenum, and between the upper plenum and throttle body. Or any vacuum hose/line.

There are smoke machines that can be used to test for leaks, or, the other option is a propane cylinder with the valve open but the flame not ignited, aimed around all the gaskets and joints of the intake system, looking for any location where the idle speed increases when exposed to propane. You can look up a more detailed procedure.

Your serial number likely falls in this range:


https://cimg2.ibsrv.net/gimg/www.off...398b9471b9.jpg

Ok I replaced the intake manifold gasket the guy I got it from did not do it correctly and it was leaking water but the motor was running fine after I did that and iv fired it up 6 or 7 times it was after I seen it was getting hot cuz of thermostat and I replaced stat and impeller is when it started acting like this and that’s what confused me on where to even start

Could be leaking from intake gaskets even if it's not leaking water... also lower injector o-rings can be a source of vacuum leaks.

Keep in mind, these aluminum intakes will corrode over the years, especially if used in salt, and the sealing surfaces might not be so good anymore.

1 fuel tank or 2? Check your fuel tank vents and anti siphon valves. Im pretty sure fuel psi should be 35 psi or more

Ok I’ll look into that and see what I can find

Has 1 big tank that feeds both motors and that was my next check was anti syphon and from what I read it says fuel pressure suppose to be 35 but was not sure on for my motor I guess if both pump motors are acting that way maybe it is anti syphon or something to affect both

DieselBoy,

I've personally twice witnessed a tank check valve that was corroded/clogged to the point where adequate FP would be observed at idle but would restrict flow to the point the engine would lean out even before WOT. If you haven't changed yours, assume they need changed. They are cheap. The fact that you get increasing FP readings with each subsequent key-on, makes me suspect the check valve is at least part of the issue, or an issue unto its own.

Thanks. Brad.