86' engine running rough, occasional no start.

[FrankinFox]

Hello, this is my first post and I've been trying to find info on my problem and can't find an answer that fits. So I'm gunna try to explain the best I can.

I bought an 83' GT with what I was told is an 86' engine (carb). Ran fine for a while then started to give me trouble. It started to miss when I was driving at a constant low rpm. Not long after it died completely and had trouble starting. When It did start it would die under load until it wouldn't start at all. Wasn't getting fuel to carb. So I replaced the fuel pump(electric inline) and she started right up but didn't last long. Little while down the road ( month or two) started giving me the same problem, so I assumed lines or pickup this time, dropped tank and checked, no problems looked like everything was fairly new.

It died again yesterday, no fuel to carb. but I was late for work so I left of on side of road and 7 hours later I come back and it starts right up. Now it's running like **** missing and running rough until I give it gas. Checked plugs and looks like they are possibly dry fouled. I can't figure out what is going on. Why fuel wouldn't be delivering or pump not pumping. I checked pumps ground and it was frayed so I redid that. Haven't checked volts to pump yet. I know that could cause less fuel but not none at all right?

I dont know much about these engines but I'm trying hoping I can learn a thing or two from yall. Tell me if you need specifics.

[FrankinFox]

Sorry for such ****ty info, drove it to get some new autolite 2545 plugs, on way home stopped for gas and after starting again and driving less than a mile, it suddenly died. Went to the fuel pump and it's running but not pumping. When I jiggled it a little the thing started pumping and making a little more noise. Got in and it started right up. Drove fine another 5-10 miles then I shut it off for a few. When I got back in it started but died suddenly again less than a mile. Same things thing not pumping but running. This time the jiggle didn't work I had to blow into tank to create back pressure through the line. Hooked back to pump real quick and the pump started pumping and making more noise again. Started up again. It's a brand new fuel pump btw. I have No idea why it would do this. Also the Pump felt fairly hot.

[grabbergreen84]

You probably need to rewire the fuel pump circuit, or at least find the bad connection and fix it. It sounds like a bad connection. Is there a relay?
Somebody probably added the pump and wiring, because I don't think very many (if any) '83s came with electric fuel pumps from the factory.

[FrankinFox]

Original is a mechanical pump.

There is a relay, none of the connections near pump "seem" bad could be under hood. What's the best way to check, Voltmeter?

[grabbergreen84]

Actually, after rereading your OP, it's probably the pump configuration. I think that the Mustangs which did use an inline pump also had another pump inside the tank.

Fuel pumps push a lot better than they pull. It might be having trouble pulling fuel up from the tank. If it's near the exhaust, it might be vapor-locking?

A testing the voltage at the pump would be good idea.

Do you have a pressure regulator at the carb?

[FrankinFox]

Stock pump was in tank, a metal pick up line was added and an external inline pump. It does have a pressure regulator, I haven't tested fuel pressure because I know it drops to 0. The pump seems to need primed when it acts up. Should be self priming. Also I noticed that when I unhook from tank side a little gas comes out but then the flow stops. Shouldn't it gush gas from tank line?

[84StangSVT]

Does your in tank pump setup look like this? This is a stock 84 in tank pump that I have for a FI car. As stated, originally your car would have had a mechanical fuel pump and it sounds like someone changed it over to electric when they put the 86 motor in for what ever reason.

Do you have just the single in tank pump or do you also have the external electric pump on the frame rail in front of the tank.

Attachment 88053

[FrankinFox]

My pickup is an aftermarket pickup, just a metal tube that has no pump.

[mustangxtreme]

Where is the electric pump mounted? They work best as close to the tank as possible since they are designed to push fuel not suck fuel.

[FrankinFox]

Its at the back of the tank, low as possible and pretty much close as possible.

[grabbergreen84]

Is your tank vented? Does pressure build up in it?

[FrankinFox]

When I blow into the line my tank pops like it is blowing up. Just happened again this time putting the back pressure didn't work. I'm so confused. Pump just isn't pumping it's running, I don't think there is any blockage. My lines have bled clean gas. This odd issue is giving me a headache. I can't reliably go anywhere.

[grabbergreen84]

Try leaving your gas filler cap off, and running it.

[FrankinFox]

So here I am again, died on me. I'm narrowing it down a little. So let's start at the tank, took line and made sure gas was flowing well out of tank with no pump. Then hooked flowing line to pump while the pump was on. The pump started to pump but weak barely any compared to the flow of fuel. It was increasing when I moved it to a different angle. Hooked to line to carb no pumping. It's like once there is any back pressure from carb it won't pump. Tried with gas cap off and it didn't work either.

6 hours later she starts right up

[84StangSVT]

Could it be possible that this needs a return line/pressure regulator/bypass back to the tank in the fuel system? I'm wondering if/when the floats close in the carb that it is not dead heading and causing the fuel to either vaporize or cause the pump to cavitate and lose prime. Since these pumps do a better job of pushing than pulling, I would think you would need a continuous flow running through them as I know if it is a centrifugal style pump, they vaporize liquid quickly if they deadhead.

Just a thought.

Sorry for such ****ty info, drove it to get some new autolite 2545 plugs, on way home stopped for gas and after starting again and driving less than a mile, it suddenly died. Went to the fuel pump and it's running but not pumping. When I jiggled it a little the thing started pumping and making a little more noise. Got in and it started right up. Drove fine another 5-10 miles then I shut it off for a few. When I got back in it started but died suddenly again less than a mile. Same things thing not pumping but running. This time the jiggle didn't work I had to blow into tank to create back pressure through the line. Hooked back to pump real quick and the pump started pumping and making more noise again. Started up again. It's a brand new fuel pump btw. I have No idea why it would do this. Also the Pump felt fairly hot.

Actually, after going back and reading this post of yours, I'm almost certain that my diagnosis above is spot on. This is a classic sign of when a centrifugal pump deadheads....growls, quits pumping and gets hot as hell due to the lack of fluid movement through it and the liquid vaporizing. If you don't have a return line, install one....if you do have one, check to ensure that it is not blocked.

[FrankinFox]

Thanks for the quick reply, how Would I put a return in? When I dropped tank the second port(?) on the pickup has a line hooked to it that just loops back with a T fitting that has one open end. And it's a single line from pump to carb. Don't know how I would put return in.

[84StangSVT]

Without seeing a picture of what you are talking about I will try my best to explain and hopefully it is correct. On the sending unit, I would think there should be 2 ports on it....1 supplies the fuel to the pump and the other would be used for the return. You would want to add/have a carburetor specific bypass regulator (5-7 psi) installed near the carburetor and the line coming off of the bypass regulator going back to the return port on the tank. What this will do is supply all of the fuel you will need to the carb at the proper pressure and the unneeded fuel will bypass the carb, head back to the tank and prevent the fuel from vaporizing.

Here is a basic diagram on a return setup

Attachment 88369

Here is a bypass regulator
http://www.summitracing.com/parts/qf...FQczaQodKmgDZg

When doing this, make sure that everything you use is fuel injection rated hoses, lines and fittings as the fuel system before the regulator will be "high" pressure.

[84StangSVT]

I just thought of a dumb question, but have you changed the fuel filter lately and would it by chance be a high flow filter? If not, I would try that before putting a return system on. Also, do you know what brand and model # the pump is? Knowing that might help a little too.

[FrankinFox]

I've bought a new filter, tried running without even. It's a Napa universal pump for carb. Heres a couple pics of what I have.

i could probably cut 4-6" off line to tank but I don't think that's the problem. gas pours out fine.

[84StangSVT]

Here's what the first pic looks like to me.....I assume the hose off the bottom runs to the carb and if so, the carb should be fed off of the side that has no hose as the bottom port is for the return to the fuel tank. Am I looking at that correctly?

When you say universal pump for carb, are you talking about the actual fuel pump? If so do you know the specs on it?

[FrankinFox]

The bottom(top in pic) line is from tank the one going to right is to carb. Goes in one side bottom out the next side at the top. I don't have specs right this second. i mean universal inline pump for any carborated system.

[84StangSVT]

The bottom of that regulator (top of the pic) should be the return line. The other two ports are the intake and outlet of the regulator. I believe this is your problem as the fuel system is piped wrong and if you get this fixed, this issue will disappear.

[FrankinFox]

I would say that's the issue but if the pump isn't hooked to carb it should pump fuel, regardless of a return line. There is no pumping so gas doesn't even hit the regulator. I can undo the "bottom" line from regulator and no gas comes out. ​

[84StangSVT]

How far is your fuel pump away from the tank? I can't really tell where it is located from the pic but it looks like it is in the trunk/hatch area. These work best when mounted within 12" of the tank and either vertical or a 45 degree angle with the intake being lower than the discharge and also lower than the carb. Every part of this system should head uphill and not ever go back downhill after the pump as It helps keep fuel in the pump and allows any vapor to rise towards the motor.

[FrankinFox]

So I redid the line to be as short as possible and In front of tank. Damn thing still died. Even bypassed inertia switch just to be sure. I'm at a loss!