Hello: I hope one of you guys can help me with this problem. I have a '86 F-150 that I bought new and now only use to plow out my drive. It crapped out in the middle of last winter, in the middle of a snow storm, and in the middle of my drive. I had to move it by squirting starting fluid in the air intake as my wife drove it off the drive. Now I am trying to get it running again.
I figured it was a fuel problem. I pulled the rear tank out and the tank pump was not running. I ran new wires and got that running. I traced the flow at each hose connection until I got to the high pressure pump. No flow out of that pump. I pulled the pump out, got it running and tied it into the rewiring. Checking it again, I have fuel all the way to the engine. I removed the little black cap on the left side of the injector manifold and gas shoots out when I move the toggle switch to activate the pumps but the engine will still not fire unless I shoot starting fluid down the intake.
This is about as far as this old carpenter's engine knowledge goes. I would appreciate any help on this because if I can't get it running before snow I will have to get another truck.
Hi Jimmy, Here are a few things that might help with your fuel problem. Since the engine will not fire-up unless you inject starter fluid then we can assume one or both of two things. 1. your fuel is NOT being pumped into the intake when you turn the key OR it is being pumped in but the ignition system is not igniting it.
Your pump appears to work but does it work from the iginition key when you crank the engine? It can get cranky if the ground side gets too oxidized. Your pump has two wires coming out. One is hot and the other is ground. It may have a pigtail to ground or run with the chassis wiring to some other ground point. You can test it by using a DVM or even an old VOM (volt-ohm-meter). If you don't have one, WalMart and other stores sell them. A cheap $15 one will do just fine. You probably do not have a OEM wiring diagram for your 86 truck.
What you need to do is to
UNHOOK the positive lead from the battery.
Find the harness wires that break out to the pump. There should be two.
Staying as far from the pump itself as you can, strip off some insulation from each of the two wires. Seal up good later when testing is finished.
Set you digital volt meter to OHMs or resistance on the lowest scale.
attach the black meter lead to a rust free area on the chassis frame near the pump.
Touch the red lead to either pump wire and notice the meter reading. If it reads "ZERO" or close to it, you are on the ground side of the pump.
Now touch the other pump wire and it should read many ohms higher than zero. Depending on the pump, it's age and other factors the exact reading can vary. It will not be above 100 ohms. It should be lower than that.
Now clip the red lead of the meter back on the ground wire side of the pump. The meter should again be reading zero ohms. Take a hammer and lightly tap around the pump and the harness while watching the meter. It should stay rock solid. If the reading jumps around, you probably have a faulty ground connection. That's the easy part. The hard part is to find exactly where the problem is.
Your pump is hot switched - meaning that the ground stays connected even when the engine is turned off. If you do have a ground fault condition one solution is to splce in a new ground wire and run it to the frame where you can drill a hole and bolt the new wire down. Just be real sure that you do not splice in to the hot side or you'll be blowing fuses every time you turn the key on.
Once the ground side is verified as being good... the hot side comes next for testing. a) reconnect the battery b) switch your digital meter to VOLTS DC c) don't forget to do "b"... it must NOT be on OHMS. d) ask your wife to help by sitting behind the wheel working the key when you signal her. e) Set the meter to DC Volts on a low scale (15 volt) f) hook the red meter lead to the wire on the hot side of the pump. The black meter lead to frame ground. g) Pull the center feed wire from the distributor cap being careful to not bend it much. We don't want the high voltage going to the spark plugs for this test. h) Get positioned so that you can read the meter. i) Ask your wife to turn the key on and be ready to turn it back off at your command. j) when she turns it on, you should be reading a positive DC voltage on the hot lead to the pump. k) use the hammer to lightly tap around the pump and it's harness wiring. The voltage reading MUST remain rock solid steady when you tap around. If it jumps around at all... you have discovered a problem that requires fixing. k) If the voltage is low - say under 6 volts... you have hit upon why the engine will not start from the key switch but will start from direct fuel injection at the intake.
The DC voltage at that point in the harness should be at or near the operating voltage of the engine. This is not always the same as the battery voltage for several reasons such as "voltage drop", resistance aging in connectors, alternator diode creep (reverse resistance drops over time) and swich oxidation to name a few.
So if your hot lead at the pump jumps around or is low - it must be corrected. The hard part is isolating where the problem is. Based on the age of the truck, it could be almost anything in the wiring chain from the ignition switch to relays, to connectors and possible even a connector that came loose but not pulled completely apart.
You can tract it down by using you meter and a long jumper wire from the hot side of the pump. Hold the long jumper wire in your hand (don't touch it to ground!!!) Now have your wife turn on the key - and measure the voltage on the jumper then measure the voltage on the connector that is in the harness to the pump. They should be the same. If both are low or jumpy, the problem is farther up the chain. At some point you will find the voltage is much higher or more steady than the jumper wire. That's the bad location... replace the connector or switch or relay or ?
If your pumping circuit tests out Ok, then you can assume the pump is fine and is pumping correctly during start up. The next consideration is quanity of fuel delivered. You can measure the line pressure but that's not too easy. So I would suggest the following
-- Remove and replace the inline fuel filter with a new one.. don't try to clean the old one.
-- you said that your truck is hardly used. You may have organic residue from fuel decay. Blow out your lines from the tank to the engine. I've seen this problem where direct injection starts the engine but pumping does not. Use WD-40 in a bulk spayer to get some serious cleaning in the lines. Pressure it in.
-- your fuel tank will for sure have some rusting inside. You said it was cleaned.. hope you had it coated inside also. Water sinks in gas.
If none of that helps then try this. Instead of squirting in starer fluid... squirt in some regular gas. Does it start then? If so, then your ignition system is Ok.
Gasoline will not burn. In fact it will put out a flame. The thing that burns from gasoline is the fumes it gives off. That's why an empty gas can is FAR more dangerous than a full one. The fumes are explosive. In order for your engine to start, the gas must be vaporized and the more the better. Whereas starting fluid is much more reactive and will burn more easily. So if your pump is Ok and it still wont start on gas but will start on starting fluid, then check to be sure you have plenty of fuel pressure at the intake and also a free flow of needed air. For example if you had nearly no air and just pure gas, the engine would flood and not start.
My gut feel is that you do not have an air flow problem but I'd not rule it out.
Rick: Thank you for responding to my request for help with the injectors. Both the pump in the tank and the pump in the frame web were not working because they were not getting power. I tied to trace the wires but gave up and wired the
2 pumps directly from the battery with a SPST toggle switch on the hot leg. When I throw the switch both pumps go on and the gas is delivered to the engine's injectors. I know this because I took the little black plastic cap off the left front injector manifold and gas shot out so gas is being delivered to the injectors but it seems to stop there. Is there a control box or something that tells the injectors to shoot in the damn gas or some such thing?
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