2003 F150 Crank but no start....intermittent
#31
#32
One more question: As I've mentioned previously, I do not hear the pump run the 3 sec every time I turn key on.....only about 50% of the time. At first, I thought this was symptom of a bad pump, but now I'm thinking PCM may not be getting power every time. I'm 99% sure PCM relay is good. So maybe an open between PCM relay and PCM? Going to re-seat that connector now....
#34
Yep, done that. Plus, it starts every 20th time or so when the pump decides to prime at key on and the PCM seems to power up. Most of the time, i'm not getting any fuel inj pulses or spark per noid lights and spark tester.
#35
There is a possibility the ignition switch is faulty.
A check of voltage to the PCM should be done to verify the power is getting through to the PCM,.
For the pump to run with key...On... the PCM has to power up because a 'timer circuit' in the PCM operates the fuel pump relay connecting separate fused power source to the fuel pump through the crash sensor.
Being a timer circuit it only hold up for a few seconds until at cranking, the timer is re-operated again full time as long as the crank sensor is supplying the PCM with rotation signal pulses that are needed by all the other functions even misfire timing..
All this is done for safety. In event of an accident, the system design prevents the fuel pump from supplying a fire.
By the crash sensor opening the circuit, the engine stops and \ or fuses blow or wiring gets cut.
A check of voltage to the PCM should be done to verify the power is getting through to the PCM,.
For the pump to run with key...On... the PCM has to power up because a 'timer circuit' in the PCM operates the fuel pump relay connecting separate fused power source to the fuel pump through the crash sensor.
Being a timer circuit it only hold up for a few seconds until at cranking, the timer is re-operated again full time as long as the crank sensor is supplying the PCM with rotation signal pulses that are needed by all the other functions even misfire timing..
All this is done for safety. In event of an accident, the system design prevents the fuel pump from supplying a fire.
By the crash sensor opening the circuit, the engine stops and \ or fuses blow or wiring gets cut.
#36
#37
Interesting.....sometimes when it would randomly start, I had switched to N, then back to P. Not sure if that allowed it to start or if it was just a random start but worth looking at.
#38
Been away on travel and just got back to remove the ignition switch. I found instructions for a continuity check online and found some interesting results. I'm hoping that someone can help me interpret this. With switch in the "run" position, it said to check continuity between the following 5 sets of pins:
B1 and I2: I had no continuity
B2 and A2: yes
B3 and A3: yes
B4 and A4: yes
B5 and I1: yes
In the "lock" position and the "off" position, says there should be continuity between P1 and P2.....I did not get continuity between P1 and P2.
In the "start" position, there were another 5 pin combinations to check.....all 5 checked ok.
Can the "no continuity" between B1 and I2 be causing my failure to start? What about lack of continuity between P1 and P2 in "off" and "lock"?
It was a bit of a pain to get to the switch, but hoping I have found something here....new ignition switch would be an easy fix.
B1 and I2: I had no continuity
B2 and A2: yes
B3 and A3: yes
B4 and A4: yes
B5 and I1: yes
In the "lock" position and the "off" position, says there should be continuity between P1 and P2.....I did not get continuity between P1 and P2.
In the "start" position, there were another 5 pin combinations to check.....all 5 checked ok.
Can the "no continuity" between B1 and I2 be causing my failure to start? What about lack of continuity between P1 and P2 in "off" and "lock"?
It was a bit of a pain to get to the switch, but hoping I have found something here....new ignition switch would be an easy fix.
#39
Join Date: Oct 2002
Location: St. Louis (Out in the woods)
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B1 and I2: I had no continuity
Can the "no continuity" between B1 and I2 be causing my failure to start?
In the "lock" position and the "off" position, says there should be continuity between P1 and P2.....I did not get continuity between P1 and P2.
Your source of information is incorrect. The correct information is attached.
The circuit of interest that runs the PCM/Fuel pump control circuitry is the B5/I1 circuit. It's function is easily checked by looking for power at CJB F30 when the switch is in the RUN or START position.
Last edited by projectSHO89; 01-14-2019 at 07:33 AM.
#40
Thanks for the attached....I realized my mistake late last night when I looked at the connector harness and saw there were no leads running to P1, P2, or I2. I'll check for power at F30.
#41
#42
#43
Good suggestion. It really seems like the pump may be failing.....it does not run every time the key is turned on, very intermittent. But test with noid lights showed I'm not getting injector pulses and test with spark tester showed no spark. When this condition first started about 6 mos. ago, it would crank/no start....then would start on the 2nd or 3rd attempt. That has gotten progressively worse to where truck is stuck in garage with one start in the last 25 or so attempts.
#45
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Location: St. Louis (Out in the woods)
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Have you verified if you even have power at the COPS and injectors when it fails?
How about at the inertia switch during the 2-3 second pump priming interval.
Before messing with a pressure gauge or a scan tool, do the basic circuit checks.
How about at the inertia switch during the 2-3 second pump priming interval.
Before messing with a pressure gauge or a scan tool, do the basic circuit checks.
Last edited by projectSHO89; 01-24-2019 at 09:35 PM.