try replacing the map sensor,when it goes bad it doesn't throw a code at times ,will make it run rich if bad

 

So I checked the Fuel pressure, and it's sitting at between 35 and 40psi. I still haven't checked the return line to see if it has a blockage, but with the pressure looking normal I can't imagine that being the problem. My next thought is maybe a flat cam. It seemed to start running crappy all of the sudden, but maybe the cam was on the verge of going. My vacume is sitting pretty low ( around 15-18 ) I might pull the valve covers off and have a look-see.

 

It's not a fuel problem then. Is the wiring harness and computer from the same vehicle? I believe the '86 EFI harness is a bit unique so you may have some things connected to the wrong pins on the computer if it's not also an '86 5.0 computer.

 

It is the original computer, I changed it out with another computer just to test it (i believe it was from an 89 though), and it didn't make a difference at all. So I changed it back. I have gone through the entire engine wiring harness and fixed any damaged or bare wires. I haven't gone through the chassis wiring yet, or the wiring to the transmission. that's next.

 

I had this happen to me once, never was able to fix the issue. I gutted the EFI and put a Carb on it (85 Bronco).

I am going to need follow this thread, right now I am working on the same situation with a friends truck but we want to figure it out and fix it. I'll post what we have done to troubleshoot it, but at the moment we are rebuilding the tranny.

 

Lets go back to the EFI system, exactly what codes does it throw?

 

EGR out of range, Map out of range, O2 out of range, TPS out of range, Idle too low, knock sensor failure. Basically everything. I don't have the codes with me at the moment. when I do I will post them literally.

 

Well it's very unlikely all the sensors are bad so you probably have a wiring problem, the sensors are fed a reference voltage from the EEC via a common wire so that would be the first thing I'd check. Time to break out the wiring diagrams, maybe put a request out to see if anybody has them for the '86 truck.

 

Haynes Manual has the wiring schematic. Don't have a scanner or i'd post it.

http://www.fordfuelinjection.com/files/EFI_harness2.gif

Pin number 26 is the Voltage Reference from the EEC (5 Volts)

 

Best bet Dura Spark & an Edelbrock preformer RPM & Holley 600 Carb.

I just happen to have an extra set if you need them.

 

Anybody hear what the problem turned out to be for this. I have the exact same problem. Am about to let son put carb on though would rather keep fuel injection for better economy.

 

I know it's been almost 5 years since I started this thread but I finally dove back into this pickup the other day and finally fixed the problem. It was the dual tank fuel reserviour on the frame rail. I replaced it with a single tank res and now it runs like a champ. Of course I also had to drain and flush the fuel system and replace the tubing for the rear tank pump as well since it's sat for 5 years. Thought I would finally give this issue some closure.

Zac