OK Guys before I go spending money on a computer I'm looking for other ideas.

This truck started and then quit. About 3 minutes later it started again and I drove it for about a mile with several hiccups until it just plain quit.

I could not hear the fuel charge pump so I started there. The relay works fine when bench tested but not when plugged in as the trigger wire only delivers 5.15 volts. (yes I tested it using it's own harness ground) The EEC relay beside it gets a fulls 12.6. So I jumpered the fuel pump circut and off the pumps go. Both tanks and the in line frame rail pump all make noise. Fuel rail pressure test of 55psi and holds there after pumps are off.

Does not start.

I figured I'd check the ignition. Hook up the timing light and put it on the damper pulley while cranking and there was my red paint mark on the scale. So I have appear to have ignition and it appears that it did not jump time either.

Does not start. Confused....

Then I noticed that the fuel pressure had not dropped at all still at 55psi. The pump relay is still unplugged and the jumper removed. I'm beginning to suspect the injectors are not being told to fire. I should have lost fuel pressure while cranking , Right? So I cranked it over and gave it a shot of ether and it fired. Couldn't keep it running but it fired. So I tried it with a squirt bottle of gas, ala gas down the carburetor. Same thing fires but couldn't keep it running. I still have 55psi in the fuel rail.

Now after that I looked at the wiring and did not see any obvious problems. I pulled the plug off the computer to check for corrosion. Nothing.

After all this I figure maybe I should have tried to pull codes before I did all of this. Never thought about it because it did not have a check engine light. I thought it was a bad fuel pump to start with.

I jumper the self test wire in the test harness to the single input wire like I had many times in the past. This thing will not go into self test mode. The check engine light just stays on solid. I never use a volt meter on this truck and never have as the engine light has always flashed the codes anyway.

Now I'm thinking I have a bad computer. If anyone has any suggestions on something else to check or where the best place is to buy a computer I'm all ears.

JeffD11N

 

The fuel pump relay has two ways to activate it.
The EEC grounds the Tan/Light Green wire which energizes the relay.
12 volts from the Yellow wire passes thru the closed relay contact
and passes 12 volts to the Brown wire that goes to the tank
selector valve. 12 volts then goes to the fuel pumps.

Grounding the Tan/Light Green wire at the Test connector does the
same thing.

Which color wire are you saying has 5.15 volts on it?

When the EEC relay closes, 12 volts is applied to a Red wire at
the Primary coil of the Fuel Pump Relay. The same Red wire also powers the Canister
Purge solenoid, EGR valve solenoid, Thermactor air bypass solenoid,
Thermactor diverter valve solenoid, IAC, the 6 fuel injectors and also
powers the EEC.

 

Idk if you have checked this yet, but power to the injectors would be a good check. Also the computer batch fires injectors on these engines, 3 at a time, so if you have access to a noid light or the appropriate test light, you can pull and injector connector and see if you get blinking light while cranking.

 

I have 5.15 volts at the red wire for the coil on the fuel pump relay. I will check the output of the EEC relay to see what is there. It seemed as if that was not enough voltage to energize the coil for the pump. Direct battery voltage made the thing snap right to attention on the bench.

I did not know the correct test for checking power to the injectors. Now I do. Plain old 12 v test light should work right?

I will reread and double check all the things you guys tell me a let you guys know what I find.

I will not have time to work on the old girl till at least midnight Friday or Saturday morning.

 

Here are two diagrams which should help locate your problem.

Page 35 shows the EEC relay and Fuel pump relay.

A Brown colored fusible link at the starter solenoid turns into a Yellow wire at the ECC Power relay. That's 12 volts and hot all the time.

When you turn the ignition On, 12 volts passes thru the relay and
cnanges to a Red wire. The Red wire goes to a splice as shown on the second
diagram. As you can see it provides 12 volts for a bunch of stuff.

One of the Red wires loops back to the first page show as Blue and goes to the Fuel Pump
relay which you say measures 5 volts. Two wires also loop back and go to the EEC on the
first diagarm. A fourth Red wire also loops back to the first diagram and powers the EGR solenoid.

So if the Yellow wire at the EEC Power relay measures 12 volts with the ignition Off and then only 5 volts when the ignition is On something is loading down the 12 volts or the Fusible link is corroded and falling apart.

Unplugging items will help point you in the right direction.

 

F150,

I have not had time to go through the wiring diagram as it is now 11:30pm. I did have a minute to do the fuel injector test that jdan said to do.

I took the connector off of #5 injector. Key on and fuel pump relay unplugged. I had a dim light on both wires. So I put the voltmeter to it. 5.19v from both wires. I then went back to the test light and cranked the engine. Both wire stay steady dim light no pulsation. To late to be tracing wires. I'm guessing a short in the harness or a wacked computer is still lurking.

I have printed your diagram and will do some more work this weekend.

JeffD11N

 

PS do you happen to know just where in the harness this big splice is? I'm guessing It would be fastest to start at that point and eliminate each circuit from there.

 

Connector C178 as shown in the first diagram is a Black 8 pin connector.
Second diagram shows the location of C178 in View A

Two of the wires on the C178 are Red. One Red wire goes to the fuel injectors the other Red wire goes to the Splice S271.

Or you can find S271 by tracing the Red wires from the 3 solenoids
attached to the valve cover on the back of the engine on the driver side.
( EGR, TAB and TAD solenoids). Each of the solenoids has a Red wire going to them. So you can trace the Red wires which should lead you to Splice S271.

 

jdan - F150,

It's running...Whoopie!

Anyway, F150 with all your diagrams, what a help that was. When you know who goes where it makes it so much easier. I started unplugging stuff and I had 5.19v at all the solenoids. Had it at C179 as well. So I figured Just unhook it from the computer and pull it up where you can get at it. As soon as I rolled the harness over there it was. The red wire coming from the EEC relay was corroded right in half. Cut out the bad wire crimped in a splice, hooked it all back up and it started right up.

Don't know where the 5v was coming from as this wire was completely in two and I had the EEC relay unplugged as well.

Now I had a little strange problem with wire colorings. My wire 37 on the EEC relay is Black with a Yellow not Yellow and 20 is Yellow with Black not Light Blue. Then 361 is Blue from the relay to the Fusable link capsule and red after that on into the harness. Any ideas on what that's all about? I bought it new so this is all factory.

Since you guys helped me so much with this one I have one more I have never been able to fix. When you start this truck cold it will fast idle just fine. Then after a couple of minutes it acts like it tries to lean down too fast and starts hunting untill it stalls. When you start it hot it will rev up come down to crub idle not catch itself and either stall right away or hunt a couple of times and then stall. If you start it and catch the throttle at 1500rpm for 10 seconds and then let it idle it's fine. It only does this stuff when you start it. Never any other time.

Any Guesses?

 

It sounds like the IAC is malfunctioning due to carbon buildup or age..also sounds like TPS and or dirty, sludged, or worn throttle body blades or shaft.

If you ever remove the TB, clean it carefully and use only a MAF cleaner. Most trucks built after '91 have a sludge tolerate coating that can be removed with solvent if not careful. After careful cleaning, hold TB up to light and see if you can see light pass the blades. This can cause high rpm and stalling as it has become an unmetered intake leak.

 

Timbersteel,

I have replaced the IAC, cleaned the throttle body with the Ford cleaner, checked every sensor for ohms, checked wiring, Replaced TP sensor, replaced manifold gasket and check for vacuum leaks. I haven['t found a single thing. Now I did not look around the butterflies that I can remember. I do remember trying to wobble the shaft and it is still tight. Someone told me a long time ago that there are non-serviceable o-rings in the ends of the shaft. Do you know? Wonder it they might be shot?

One other question. Why does this thing only do this after start up? I would think a vacuum leak would do it all the time. After it runs 5 minutes it never does it again untill you shut it of for 5 minutes or so and start it again.