I have an 86 F-150 4x2 with an EFI 302 and AOD trans, duel fuel tanks that is just giving me fits and I'm at my wits end with this thing. I'm hoping some of you can help or give me a little advice. First off it's very hard to start, it fires off then dies, start it again it fires and dies again. It will run for less then a minute and dies again. Once I am able to get it running the idle is very erratic, it almost dies and then revs up and continues to do this. Now I've put a lot of work into this truck, I've replaced both fuel pumps in the tanks, the boaster pump is wired directly into the fuse box. The fuel filter is new, I've replaced the timing chain, air idle control valve, coolant temp sensor, O2 sensor, throttle position sensor, made sure the ignition timing is set properly, and checked the codes which there are none only an All Clear code of 11. I drove it Saturday to put gas in it and put 10 gallons in the rear tank, and it seemed to run okay and not quite as much erratic idle. When I got home I went in the house to do a few things and came back out and find gas dripping out of the truck bed, and upon opening the fuel door to the front tank I find out that the fuel is leaking past the gas cap and running down the bed onto the ground. I remove the gas cap and the gas is right at the top of the filler neck. I go back and remove the cap from the rear tank and the gas in the filler neck of the front tank starts to go down. So what on earth is going on with this? Is it possibly a bad shuttle valve? And also the vapor line to the charcoal canister has gas in it and has filled up the vapor canister with gas. Any help would sincerely be appreciated as I'm really just about done with this thing!

 

Yes, if the switching valve goes bad, one fuel pump can transfer fuel to the other tank.

Once the engine is warmed up, does it run ok? If so, I would suspect intake plenum gaskets that might need to be changed. I would also make a block off gasket for the EGR valve and block it off. If it runs better, the EGR is leaking and you need a new one.

 

Can you fiddle with the EGR valve from the outside? The vacuum diaphragm thing? If there's an exposed lever connected to the diaphragm, try grabbing a hold of it and moving it in & out, the mechanism may be sticking.

I've heard of some people having luck removing & cleaning the things.

The selector valve is supposed to flip both the source and return lines, sometimes this doesn't work entirely correctly and the returning fuel all goes to one tank.

 

Parts stores have splice kits for the fuel lines and return lines. I've used those to bypass the valve and run on one tank because it was moving fuel from one tank to the other. We even removed the rear tank after bypassing the valve.

 

Thanks Gentlemen for all your input, I appreciate it. I've checked the EGR several times, I put vacuum to it with a hand pump and it responded accordingly. I have removed the EGR to check for leakage and found none, I checked it by turning it upside down and filling the pintle and seat up with carb cleaner and watched to see if anything leaked out and none did so I don't think the EGR valve is the problem. I've also done the upper end gaskets so the plenum to the manifold is new. I've repeatedly checked for vacuum leaks and haven't found any. I've put a vacuum gauge on it and it is within range, I've checked the fuel pressure and it to is within range. I've done all these tests and have come up with nothing and that's what's so frustrating about it. It did at one time run fairly well with little change in idle speed but now it's doing the surge at idle. I just don't know what else to do.

 

There is no vacuum being applied to the EGR valve at idle, correct?

 

They do have a vacuum regulator that can cause this.

 

What pump are you calling the "booster pump"? It has a lo-pressure pump in each tank and a hi-pressure pump on the frame rail.

 

Yes, there is a system of VCVs (Vacuum Control Valves) that can provide vacuum to the EGR when they shouldn't be if, say, the vacuum lines are hooked up wrong, or there's a problem with one or more of those valves.

The EGR should operate only with a warmed-up engine and at cruising speeds.

 

Now that I don't know and I'll have to check. Seems like I did it before but it never hurts to do it again, that is checking to see if there is vacuum at the ERG at idle. The booster pump I was referring to is the one on the frame rail. I also saw something on this site about the TPS and I'll have to check that too as some dummy (that would be me!) messed with the idle stop screw to keep it from dying, I think perhaps I screwed up (no pun intended) by messing with it. Thanks for all the help guys! So what do all those solenoids by the battery actually do and how can you tell if one is bad?