Hey everyone, I’m completely new to actually posting a thread but I’ve read a bunch.

I’ve had my 1986 F-150 5.0 EFI AOD for roughly two years. We’ve put a rebuild 5.0 in it but everything that dresses it is original, we’ve also put a brand new AOD in it as well.

The Issues: In park the truck surges/hunts once truck gets to operating temp. It does this until it almost completely bogs out, then the idle shoots up and gets back to hunting. When I put the truck in reverse while warm, it will intermittently bog down and sometimes shut off completely. When switching to neutral idle shoots up higher than normal. When putting it into drive, it occasionally shuts off but aside from that it’ll idle just fine. While driving the truck, it runs beautifully aside from shifting to 3rd gear. It has a hard time shifting unless I take my foot almost completely off the gas. It does not have this issue when flooring it. It also jerks back around 55mph or when going uphill and I have to give it more gas to stay consistent. Finally, it downshifts kinda hard to 1st gear and bogs the engine down sometimes shutting off. I ran a “key on engine off” test and it brought up code 31 (EVP circuit below minimum voltage) & 84 (EGR vent fault).

I’ve replaced: Iac Valve, Egr valve, Egr switch, cleaned egr vent tube, Tps, Map sensor, Throttle cable… I’m sure there’s more but I can’t think of anymore right now.

Any help would be much appreciated, thank you!

 

Do you need to have the truck tested for emissions ? That will give the smart guys a hint of what you need to keep.

Where did the new parts come from and did you buy the cheapest parts ?

Lot's of junk parts out there now days.

This site will be referenced,
https://www.garysgaragemahal.com/1986-evtm.html

 

The truck doesn’t require an emission testing, I think the worse emissions the better here in Tennessee😂.

I’m still in High-school so I did try to stay on the cheaper side with parts (It’s bad I know), but I also tried to avoid cheapest. I think a lot of what i got was Dorman and a couple duralast. I typically get duralast when that’s the only brand that I can find at the part stores.

 

personally I would avoid dura-junk as we in the repair field calls it, many times those parts dont last long or they are already failed out of the box. Some times you can have luck with the parts but its something we tend not to mess with. Dorman isnt bad they are one of the big names in the aftermarket along with Cardone.

On the jerking and bogging and all that, have you checked fuel pressure? That sounds like a classic case of low fuel pressure or extremely aeriated fuel which can be caused by a weak or bad in tank lift pump.

 

I just had this exact problem when I swapped in a 86 fuel injected v6 into my 84 Bronco II. It has the same computer system as yours, only two less cylinders.

What I found, it was my neutral switch circuit. These old fuel injection systems did not have a speed sensor, so they used switches on the clutch pedal, the shifter and in your case the shifter since you have a automatic. Mine was undriveable, and was truly a "bucking bronco".

What I found that straightened mine out, I shorted the pin 30 wire to the signal ground wire. Instantly changed the whole engine into something I could drive. Since I was doing a swap, I had the harness opened up and had the wires right there. Since you have a factory setup, I would find the correct wires and see if you can short them together. I will see if I can find them on a wiring diagram for your truck.

 

Here is the computer diagram showing pin 30. It says the rest of this circuit is on page 30.

 

Here is the neutral safety diagram.

 

I keep studying the diagrams for your truck,, and I admit it is a little confusing. I am supposing when you are not in park or neutral, pin 30 floats up with no connection to the distributor or the starter relay. When it neutral or park, the switch closes, and unless you are cranking, pin 30 gets somewhat of a ground through the starter relay coil and or the distributor.

I would find connector C321. It should be over there on the driver's side inner fender. Look for the pink/white wire that comes from pin 30.

 

I’ll have to look into the fuel pressure because that’s something I’ve yet to explore.

I’ll also have to look into the Pin 30 situation. IF the truck shuts off when going into drive/reverse, I can fire it right back up and it’ll do completely fine. The whole issue is intermittent, it acts completely normal sometimes.

 

Would aerated fuel still be a potential issue if the truck runs rich? If you stand behind it, you smell straight gasoline.

 

Are we talking about just the smell of gasoline or are we talking about smell of gasoline and your eyes burn?

If just the smell of raw fuel is being smelled that is to be expected if you dont have converters or if your converters are burned out. If your eyes water then it is running excessively rich and yes a bad fuel pressure regulator could cause a rich condition. If the vacuum modulator or the regulator is busted it will suck raw fuel into the intake and make it run rich, if the regulator failed and is not regulating pressure it could have excessive pressure which results in a rich condition. It could even be a stuck fuel injector that is hung open just spraying fuel into the engine, this one isnt that likely cause it would try to hydrolock your engine on cranking.

 

Definitely not that bad. I don’t have any cats on the truck, just a Y pipe into a muffler ending with dual tips. I’m in a highschool diesel program that allows me to start trade school while in highschool, I’m gonna talk to my diesel instructor tomorrow about fuel pressure testing and all that jazz. I should be able to come back with updates within the next week. Thank you guys

 

yep without cats you will have a fuel smell in the exhaust its to be expected especially if you have a carb. If you have EFI it will still be there but be less than if you had a carb.

 

Update: We did the fuel pressure test just a few minutes ago. With just key on, it was running 31psi. With engine on it ran a consistent 26 even when put under a slight load. We unplugged the vacuum from the fuel pressure regulator and it allowed the fuel pressure to get up to 35 but this did not fix the hunting/surging. Now we’re even more lost

 

Pin 30.......pin 30...... pin 30.......