Where were those underhood relays? I know there are the three on the driver side by the brake booster, is it one of those? I couldn't ever find a good diagram confirming where all the relays were haha

 

On my '93 they are in a black box on the driver's side just behind the battery.

 

I found a good piece of 3/16 scrap metal that I can use to make a blockoff plate for the EGR. I'm gonna throw it on to see if it helps or not. I did take off the EGR and examine it, it looks like this EGR has 2 parts to it, the main valve and then a weird black plastic part connected via two hoses (idk how any of that works lol). The main valve actuates with vacuum applied, BUT on the backside of the main EGR piece there is a LOT of buildup and crud in there so I'm thinking that may end up being the culprit if that stuff is keeping it stuck open and essentially causing an uncontrolled vacuum leak.

I finally found my multimeter too so I'm gonna test the MAP as well. If neither of these do the trick/lead me to a solution I may just go ahead and do the fuel pressure regulator as that's the only other thing I can think of that would cause it to run so poorly in open loop but fine in closed loop. and assuming I get this truck running 100% I plan on taking it on a road trip soon so I may as well go the extra mile with maintenance.

 

Mine look like the relays in the top of picture, there's 3 (maybe 4..?) and they're just bolted to the side lol

 

The plastic part between two hoses should have the wiring harness plugged into it. That is the valve that opens and closes to let the exhaust gas in or keep it out. According to the late Ralph P, who drove a late 80's dak a lot of miles for his work, the EGR does make a difference in MPG.
When I clean mine I set it so it sits bottom up and fill it with carb cleaner and just let it soak a while, an hour or more. Then I pour it out and spray it out. Here's a link to RA picture of it as it looks new. https://www.rockauto.com/en/catalog/...egr+valve,4968
You can also scroll up to look at what the relays look like. They have to be somewhere. Your engine bay is different than later model that have the relay box where your wiper washer bottle is.
Just found this diagram Looks like your ASD relay is the second from right starting closest to the wiper washer bottle. Scroll through it there are several pictures and KenF describes for the poster what is in the picture he posted. https://static.cargurus.com/images/s...-1600x1200.gif

 

Interesting, long term I'll def try and keep it then. I'll prob try and block it off to diagnose at least and then depending on my findings I may just go ahead and order a new one since this one looks like it's the original from 1989 haha

and I'll swap the AC relay for the ASD later as well and see if that fixes it, I know those two are the same relay style and my AC doesn't work right now anyways

 

Make sure your AC doesn't work because the relay is bad.

 

haha that is a good point! but there is no freon in it, it looks like it hasn't worked since the 90's at least. It hasn't even been converted to r134a yet... that's the next project to tackle once I get it running like a top

 

Alright well the relays didn't make a difference, I swapped them with each other, tested them with a separate jumper, and then had some extra ones I "collected" from junkyards over the years and no difference was made. I did inspect the ECU plug and saw a tiny bit of corrosion, I cleaned that off and again it didn't really make a difference. From frantically googling the last week I think it's either the fuel pressure reg, EGR acting whacky when warm, or potentially the MAP acting whacky (it read fine when I tested it). The auto parts store down the road has both the FPR and EGR so I'll prob swap both of those for peace of mind, and if none of those pan out I may swap the MAP just to say I have replaced everything on the truck and then maybe take it to a "real shop" for diag lol please pray for me

 

One thing about replacing parts on an old vehicle. Even if it doesn't solve your problem, the part you replaced was probably gonna go bad soon anyway. So consider it preventative maintenance. The parts you are replacing wont break the bank.