<!-- from fixya rte -->E 250 ford van 5.7 misfire problem - Cars & Trucks

Craig, Check the attached links,instruction and guides, Good luck
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1987 ford 250 economize van 5 8 liter4v engine firing order diagram Google...
Wants to start but wont Ford Truck Enthusiasts Forums

1987 ford 5 8 liter 4v engine firing order diagram Google Search

misfires are also from faulty injectors and low fuel pressures. from what you state I would be looking at those areas for the problem.

there should be a decal under the hood somewhere that shows the belt routing.

Did you resolve the other codes? p0300 random multiple misfire, p0305 misfire cyl #5, p0307 misfire cyl #7? You could have bad ignition coils or a vacuum leak. Check your coils and check for vacuum leaks at the intake manifold check vacuum hoses. Hope this helps!

front to back is one thur six . 1-5-3-6-2-4

truthfully , wear and tear. rubber gaskets can not last forever, they are exposed to extreme conditions (weather) and naturally occur over time.
the leak can be premature if there's been a history of abuse, or neglect.
over filling the oil and even faulty parts causing the oil pressure to get too high can cause this.

on the inside of the frame rail just below the drivers seat under the van

PO135 = Upstream Heated Oxygen Sensor Heater (HTR 11) circuit (Bank #1)

P1131 = Lack of upstream Heated Oxygen Sensor (HO2S 11) switch, sensor indicates lean (Bank #1)

P0305 = Cylinder #5 Misfire detected

It looks like you have two separate issues happening. Bank 1 would be the left side of the engine if you were standing in front of the truck looking at the engine. The "upstream" oxygen sensor will be on the exhaust pipe coming from the bank one side of the truck IN FRONT of the catalytic converter. From the codes, it appears that the upstream sensor has gone bad, but the oxygen sensor behind the catalytic converter, or "down stream" is fine.

The misfire on cylinder 5 on the right side of the engine, 2nd one from the front, could be something as simple as a fouled spark plug or a coil malfunction.

To identify if it is a bad coil, swap the #5 cylinder coil with another coil, and see if the misfire follows the relocated coil.

#1 plug is the 1st plug on passenger side by firewall