Suspect Fuel Pump Question
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Suspect Fuel Pump Question
I have an 86 F 350 with the 4180 motorcraft / holley carb in it. Initially the vehicle was stumbling a little at idle and being the person I am I could not live with that. none the less I decided to put a rebuild kit in it (Walker) and reinstalled it. The truck still stumbles at idle. I put a tack on it and it floats between 800 and 1000rpm Also, after it warms up pretty good I end up with a loss of power above 65 mph or with a really hard acceleration up hill (again after it warms up) It acts like no fuel is getting to the motor. I confirmed my needles were not sticking and that the floats are set correctly. I initially thought it might be the EGR so I unhooked it to make sure but same thing. I HATE this carb due to all the emissions BS but the kit should have resolved this. Changed the in carb filter as well as added an inline filter. Only happens when the truck is warmed up pretty good and around 65mph. I"m thinking a fuel pump. Out of gear I can rev it up to my hearts content with no problems or hesitation. any ideas????
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From: sunny fla sometimes windy
The rev in neutral and bog in drive is a big time symptom of water in the fuel!!
If because of gas prices and having a huge tank you never fill it up, All that empty space is condensing water out of the air and after a while it builds up to the point
of causing problems. 2 bottles of heet and 2 of Iso heet on whatever is in there
now 3/4,1/2,1/4 tank and run it until 1/8 or so. Refill with fresh fuel and some
marvel mystery oil and another of iso heet and you should be good to go.
Try to have the tank filled above a half tank most of the time if you can and if you
park it for an extended time some sta bil and a full tank. It stinks you did the carb
rebuild but I guarantee just doing the gas line dryer will fix your issue don't do
anything else but the double dose of heets and that truck will be running like new!!
If because of gas prices and having a huge tank you never fill it up, All that empty space is condensing water out of the air and after a while it builds up to the point
of causing problems. 2 bottles of heet and 2 of Iso heet on whatever is in there
now 3/4,1/2,1/4 tank and run it until 1/8 or so. Refill with fresh fuel and some
marvel mystery oil and another of iso heet and you should be good to go.
Try to have the tank filled above a half tank most of the time if you can and if you
park it for an extended time some sta bil and a full tank. It stinks you did the carb
rebuild but I guarantee just doing the gas line dryer will fix your issue don't do
anything else but the double dose of heets and that truck will be running like new!!
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It is a 460 Carbureated engine with Dual Tanks. Based on my research the system has a low pressure fuel pump in each tank and a hi pressure pump on the rail of the driver side. I pulled the high pressure pump off the truck and was going to replace it since the fuel would be starving at a high rate of pressure vs a low pressure rate.
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From: Virginia
I have never heard that before. The first generation fuel injected engines had the low pressure pumps in the tanks, and the high pressure pump on the frame, since that system runs at about 40psi. Your carbed system only runs about 4 to 6 psi. If you took a pump off the frame rail, I have a funny feeling that is a pump someone added in. You should have the low pressure pumps in the tanks that run up to the carb, and your carb should have a tee fitting at the carb inlet, with a return line. You should have a fuel pump relay that drives the fuel pump, and this relay is powered by the starter solenoid during cranking, and then it's power by a oil pressure switch on the engine after the engine is running.
Some of the 460's had this system, and some had the old mech pump on the engine. The electrical pump system usually runs into problems eventually, seeing all the questions we get about it all the time. So you may find it rigged up by a previous owner to get the truck running.
Some of the 460's had this system, and some had the old mech pump on the engine. The electrical pump system usually runs into problems eventually, seeing all the questions we get about it all the time. So you may find it rigged up by a previous owner to get the truck running.
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From: Virginia
See if you can buy a replacment pump for it. If you have trouble, and they keep giving you something different, then you will know something is fishy. Also make sure what you took off is not the motorized switching valve. Your truck should have this valve that switches the fuel lines from one tank to the other. It also switches the sending unit wires. The pump power is switched at the dash switch.
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From: Niceville, FL.
Sounds like your carburetor may have a bad power valve (sometimes called economizer valve). Be sure to replace with the correct one for your particular carburetor to get best performance. Carburetor number (ex. E5TE-9510-AB) and Holley list number (ex. 50006) are stamped on the carburetor airhorn. Franklin2 is correct in identifying the powered switching valve on the frame rail. So far as I know only FI motors use a high pressure pump.
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Franklin2 was right. It was the tank switching valve. I recently like last weekend put a rebuild kit on the carb which included the power valve as part of the kit so It's not that. I'm going to check and see if maybe their is a leak in the back of one of the heads where the smog pump piping used to be (I did plug those but you never know). Other than that I really am at a loss. Damn shame to cuz it's a very clean truck but if I can't get it to be reliable I'm going to have to dump it.
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Found an inline filter kind of hidden so I removed that and put in an adhock one since it's a california truck and the filter was difficult to locate. Truck did not bog once after that so it's quite possible that was the problem. I drove it quite a bit afterwards. Now I need to figure out how to get it to idle smoother.
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The Plugs are new (redid the heads) but The Rotor, Cap and Wires are not. The condition of the Cap and Rotor was not suspect nor were the plug wires but I could put a timing light on each plug wire and see if I get a miss. Great analysis Franklin.
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