1993 Ford F150 4.9L I6 . Dual tanks. Engine cranks, won't start. Good fire to plugs. With KOEO, fuel pump runs constantly, causing failure to start due to flooding. Tried to retrieve trouble codes but PCM will not display - voltage across test terminals remains 12.5v after trying to start self test. Swapped relays, thinking ?maybe stuck relay. No good. R&R fuel pressure regulator. No good. R&R PCM with one from NAPA for $65 thinking that was why I could not retrieve codes. Still no good. Still won't give me codes. Pumps still run and flood KOEO. I am OUT of ideas and would apprec your help! Tim
DOes the check engine light come on with the key on?
WHat is the fuel pressure at currently?
CE light does not come on in the cab - that's why I was using a voltmeter at the EEC pigtail. Suspect it's burned out. I don't have a fuel pressure, but smell raw fuel in the exhaust. Select either tank and pumps pour it on with KOEO. Pulled the Fuel Pump relay and truck ran for 15-20 sec (real choppy) on accumulated fuel.
It sounds to me like the computer is not coming on. The computer is supposed to turn the check engine light on when the key is turned to the on position.
This would also make sense that you do not have communication with the computer.
TO verify this, we should check the reference voltages under the hood to the tps sensor and maybe even the egr sensor.
With the key on, we should have some sort of reference voltage to most of the sensors under the hood.
Start with the tps sensor.
I'll check TSP and EGR tonite and reply. Computer on this thing along side the steering column? Thanks and talk to you a little later.
I will be waiting!
If no reference voltage to any of the sensors, check all computer fuses, powers and grounds!
KOEO, TPS VRef 4.8v, TPSig closed = 4.0v, open = .33v. Getting 12v to the EGR valve position sens.
WHat is fuel pressure at when you turn the key on?
DO you have fuel trigger?
don't have instrument to measure fuel pressure. I've been pulling the FP relay for KOEO diagnostics so it won't run nonstop. Not familiar with a fuel trigger. Both FPs are working like crazy - what in the control circuit would keep them from shutting off appropriately?
Well there are a few things. Let me get you a wiring diagram.
We just have to figure out which signal is staying on. Here is some info about the fuel pump relay.
OPERATION When the ignition switch is turned ON, the Electronic Engine Control (EEC) power relay is energized, providing power to the fuel pump relay for 1 to 2 seconds through the Powertrain Control Module (PCM) and an Inertia Fuel Shutoff (IFS) switch.
Fuel pump power is provided through the fuel pump relay contacts, if the PCM does not receive an ignition signal within approximately one second after the ignition switch is turned to the "ON" position. A timer circuit in the PCM will open the ground circuit to the fuel pump relay, causing the fuel pump relay contacts to OPEN. This action stops the power supply to the fuel pump.
When the ignition switch is turned to the "START" position, the PCM closes the ground circuit to the fuel pump relay, resuming operation of the fuel pump.
After the ignition switch is returned to the "ON" position, power to the fuel pump is supplied through the fuel pump relay.
The PCM monitors engine speed and opens the fuel pump relay ground circuit if the engine speed drops below 120 rpm.
I'm going to see if there is juice to the CE light with key on to see if the ECC wakes up. If the ECC is out, would power bypass both EEC and PCM and goes straight thru relay? Where is the Engine Control Computer located on this thing?
UNDERHOOD VIEW Left side of safety wall.
Check Eng lite was out. Comes on now w key on. Tried to read codes again. After placing the correct diagnostic jumper wire at the ECC pigtail, fuel pump ran nonstop (didn't matter whether front or rear selected - raw gas smell everywhere but no leaks) and CE lite burned steady with KOEO - no code info. Am i at a point where i need to take this to my shop? Tim
Well I can definitely walk you through this. You might need some diagnostic tools
I would like to check fuel trigger, as well as fuel pressure. In addition, I would like to find out why the fuel pump continues to run.
DO you need the procedure for pulling codes? wOuld that help you?
The reason I ask if you need the procedure to pull codes is because my references may be different that yours. This might help you out. Remember, I am just trying to help you.If you are confident that you are pulling codes correctly and still no luck, we can move on to other things like fuel pressure and fuel trigger. I can also assist you in the wiring issue that is causing the fuel pump or pumps to continue running. We are going to need to test the light blue with orange stripe wire going into the fuel pump relay. We need to see if we are getting a ground on this wire from the computer causing this relay to stay on.