I'm contemplating the purchase of a 1986 CUCV with 6.2L diesel. I'm trying to get up to speed on how diesel motors work and I'm hoping someone will take a minute to help me out. :D

I understand the basic idea, that the air alone is compressed and the fuel injected at the top of compression. As I understand it also, there is no throttle as in a gas motor, the intake manifold is wide open at all times. So what specifically happens when you press down on the gas pedal? You must be controlling the fuel, but I'm confused because I believe that the injector should always inject the same volume of fuel per stroke, or else the mixture would be too lean or too rich. So what is going on?

Another question, do you set timing on a diesel motor the same as in a gas motor? I mean, do you adjust the exact time of fuel injection relative to TDC? I assume you must.

Thanks for any insight, or possibly links.

Check out www.banksdiesel.com (http://www.banksdiesel.com/) under knowledge and tech tips links

The diesel engine does not have a butterfly in the intake as in a carburetor gasoline engine. The engine speed is controlled by the injection pump setting. And the fuel volume does vary with the control on the injection pump. The speed is very low at the low setting, but as the control shaft is opened up then more fuel is pumped and the engine speed increases. Diesel engine speed is controlled by the amount of fuel being pumped by the injection pump. The more fuel then the faster it will run. If you poured some diesel fuel in the intake then you can get into a runaway speed condition. And that can be real scary!!!!

The injection pump is set in relation to TDC, but it is not advanced as much as in a gasoline engine. Neither does it have a centrifigal or RPM advance as on a gasoline engine. A diesel engine with a mechanical injection pump is very simple. The new electronic injection pumps controlled by a computer are more complicated and also much more expensive. Your 1986 engine will have the mechanical DB-2 injection pump. The pump was made in standard and heavy duty configuration with the heavy duty be able to pump more fuel into the engine. When my standard failed then I replaced it with the heavy duty that gave me more torque and horse power to climb grades without down shifting. MPG fuel consumption didn't change much.

The heavy duty engine configuration (-J) with the heavy duty injection pump did not have an EGR or the butterfly in the exhaust manifold. I removed both to convert my engine to the J engine configuration versus the standard C.

Thanks a bunch for the info. I think I'm starting to get the picture. I'm still a little confused by the idea of controlling RPM with fuel. The injector pump controls the amount of fuel per cylinder, per firing, right? So if it increased it, wouldn't it just run more rich? The air would be about the same per firing, or maybe leaner if a little bit of vacuum is being pulled at high RPM - I think. So it seems like increasing or decreasing fuel is mostly modifying mixture.

The truck I'm looking at is a surplus military CUCV. I wonder if it is already the heavy duty configuration you're talking about.

Cougar was sorta right, but even a mechanical injection pump does have both a Speed and Load Advance, but it is much less than a gasoline, max at about 10*, because diesel fuel combusts so much faster than gasoline does.

There are several major differences in gasoline engine operation and a diesel. Your right in thinking that a diesel will run lean without a butterfly valve on the intake, it does, it needs a full charge of air in order to compress it to high enough temps to ignite the fuel when it is injected, no spark plugs, just the heat created by compressing the air will ignite the fuel, which is also why diesels run higher compression ratios (18-21:1) than gassers (7-8.5:1). This system also requires much higher fuel pressures to operate, diesel doesn't evaporate like gas, it has to be atomized by the injector, which has an opening pressure of about 1800psi, compared to what, 15lbs in an MPI system?