Actually Marlin is right on, as well.
A universal EGR will come with different size orificed "washers" to adjust the metered amount of exhaust flow to the air fuel mixture.
So modifying a washer with a small hole will do the same thing. Just be sure that, if you have to smog your vehicle, you use as large a hole as your drivability performance will allow.
What size hole did you drill Marlin? do you remember? or was this just experimentation?
I believe he checked that, but are you trying to say that the air/fuel mixture is too rich and that by leaving a small orafice for air to flow this will lean it out?
In fact, the opposite is true.
With too large an orifice the mixture is lean because exhaust gas is known as being "inert" or not able to burn which lowers combustion temps thus reducing NOX emissions. so by lowering combustion temps the engine also runs cooler as well. All of a sudden blocking one of these off doesn't sound so great does it?
Nonetheless, By running a smaller orifice it reduces the amount of exhaust gas only enough to stop performance problems but not hamper it from an emissions stand point.
fordh8r got it right. Great answer.
It sure sounds like a EGR problem to me.
Did you in fact unplug the vacume hose at the EGR valve and then test drive the truck?
Our '85 one ton efi 2wd shop truck stumbles just like you have said and goes completely away when the egr hose is removed and plugged.
In the past, to overcome this problem, I have removed the valve and installed a washer with a smaller hole to restrict the exhaust flow.
Also have seen resticted egr ports on the efi mainfold.
Just my two cents....
Marlin
Thanks, Marlin! Really, for everything!
