New member here. Been lurking on this site for a while, but I have finally reached a point where I need to ask a few questions of the knowledge base. I have been having a similar problem with my van and I am struggling to diagnose. I bought my 88 4wd, manual cargo with 240k a couple months back. Since purchasing it the car has driven without issue other than a handful of times where it had a harder time starting than usual. Recently I decided to redo the cooling system as I knew the radiator to be old and it seemed to be warmer than I wanted. I pulled out the radiator, had it recored, and replaced all the coolant hoses as well as the water pump and fan clutch. Right before the coolant system job the van started fine, but upon completion the engine has not been able to start.

The engine cranks fine but does not even get close to starting. I have begun the diagnosis and have checked the following

-good spark
-~40 psi of fuel pressure at injection manifold both by shorting test connector and also when cranking
-visual inspection of distributor cap for wear
-12V at ECU pins No. 10 and No. 20 (fuel injector supplies)
-Check engine code reads 5-1. I have cleared the code by removing fuse/disconnecting battery but immediately comes back on even before attempting to start. Could a mis-calibrated TPS cause a no-start?

My first thoughts obviously jumped to the idea that I forgot some connector/vacuum tube etc. that was removed during the cooling system restoration, but after quite a bit of searching and diagnosis time I am becoming less convinced. Would greatly appreciate any insight, thanks in advance.